Perceiving Systems, Computer Vision


2024


HOLD: Category-agnostic 3D Reconstruction of Interacting Hands and Objects from Video
HOLD: Category-agnostic 3D Reconstruction of Interacting Hands and Objects from Video

Fan, Z., Parelli, M., Kadoglou, M. E., Kocabas, M., Chen, X., Black, M. J., Hilliges, O.

Proceedings IEEE Conference on Computer Vision and Pattern Recognition (CVPR), June 2024 (conference)

Paper Project Code [BibTex]

2024

Paper Project Code [BibTex]


AMUSE: Emotional Speech-driven 3D Body Animation via Disentangled Latent Diffusion
AMUSE: Emotional Speech-driven 3D Body Animation via Disentangled Latent Diffusion

Chhatre, K., Daněček, R., Athanasiou, N., Becherini, G., Peters, C., Black, M. J., Bolkart, T.

Proceedings IEEE Conference on Computer Vision and Pattern Recognition (CVPR), June 2024 (conference) To be published

Abstract
Existing methods for synthesizing 3D human gestures from speech have shown promising results, but they do not explicitly model the impact of emotions on the generated gestures. Instead, these methods directly output animations from speech without control over the expressed emotion. To address this limitation, we present AMUSE, an emotional speech-driven body animation model based on latent diffusion. Our observation is that content (i.e., gestures related to speech rhythm and word utterances), emotion, and personal style are separable. To account for this, AMUSE maps the driving audio to three disentangled latent vectors: one for content, one for emotion, and one for personal style. A latent diffusion model, trained to generate gesture motion sequences, is then conditioned on these latent vectors. Once trained, AMUSE synthesizes 3D human gestures directly from speech with control over the expressed emotions and style by combining the content from the driving speech with the emotion and style of another speech sequence. Randomly sampling the noise of the diffusion model further generates variations of the gesture with the same emotional expressivity. Qualitative, quantitative, and perceptual evaluations demonstrate that AMUSE outputs realistic gesture sequences. Compared to the state of the art, the generated gestures are better synchronized with the speech content and better represent the emotion expressed by the input speech.

Project Paper Code link (url) [BibTex]

Project Paper Code link (url) [BibTex]


Ghost on the Shell: An Expressive Representation of General 3D Shapes
Ghost on the Shell: An Expressive Representation of General 3D Shapes

(Oral)

Liu, Z., Feng, Y., Xiu, Y., Liu, W., Paull, L., Black, M. J., Schölkopf, B.

In Proceedings of the Twelfth International Conference on Learning Representations, May 2024 (inproceedings) Accepted

Abstract
The creation of photorealistic virtual worlds requires the accurate modeling of 3D surface geometry for a wide range of objects. For this, meshes are appealing since they 1) enable fast physics-based rendering with realistic material and lighting, 2) support physical simulation, and 3) are memory-efficient for modern graphics pipelines. Recent work on reconstructing and statistically modeling 3D shape, however, has critiqued meshes as being topologically inflexible. To capture a wide range of object shapes, any 3D representation must be able to model solid, watertight, shapes as well as thin, open, surfaces. Recent work has focused on the former, and methods for reconstructing open surfaces do not support fast reconstruction with material and lighting or unconditional generative modelling. Inspired by the observation that open surfaces can be seen as islands floating on watertight surfaces, we parameterize open surfaces by defining a manifold signed distance field on watertight templates. With this parameterization, we further develop a grid-based and differentiable representation that parameterizes both watertight and non-watertight meshes of arbitrary topology. Our new representation, called Ghost-on-the-Shell (G-Shell), enables two important applications: differentiable rasterization-based reconstruction from multiview images and generative modelling of non-watertight meshes. We empirically demonstrate that G-Shell achieves state-of-the-art performance on non-watertight mesh reconstruction and generation tasks, while also performing effectively for watertight meshes.

Home Code Video Project [BibTex]

Home Code Video Project [BibTex]


Parameter-Efficient Orthogonal Finetuning via Butterfly Factorization
Parameter-Efficient Orthogonal Finetuning via Butterfly Factorization

Liu, W., Qiu, Z., Feng, Y., Xiu, Y., Xue, Y., Yu, L., Feng, H., Liu, Z., Heo, J., Peng, S., Wen, Y., Black, M. J., Weller, A., Schölkopf, B.

In Proceedings of the Twelfth International Conference on Learning Representations, May 2024 (inproceedings) Accepted

Abstract
Large foundation models are becoming ubiquitous, but training them from scratch is prohibitively expensive. Thus, efficiently adapting these powerful models to downstream tasks is increasingly important. In this paper, we study a principled finetuning paradigm -- Orthogonal Finetuning (OFT) -- for downstream task adaptation. Despite demonstrating good generalizability, OFT still uses a fairly large number of trainable parameters due to the high dimensionality of orthogonal matrices. To address this, we start by examining OFT from an information transmission perspective, and then identify a few key desiderata that enable better parameter-efficiency. Inspired by how the Cooley-Tukey fast Fourier transform algorithm enables efficient information transmission, we propose an efficient orthogonal parameterization using butterfly structures. We apply this parameterization to OFT, creating a novel parameter-efficient finetuning method, called Orthogonal Butterfly (BOFT). By subsuming OFT as a special case, BOFT introduces a generalized orthogonal finetuning framework. Finally, we conduct an extensive empirical study of adapting large vision transformers, large language models, and text-to-image diffusion models to various downstream tasks in vision and language.

Home Code HuggingFace project [BibTex]

Home Code HuggingFace project [BibTex]


TADA! Text to Animatable Digital Avatars
TADA! Text to Animatable Digital Avatars

Liao, T., Yi, H., Xiu, Y., Tang, J., Huang, Y., Thies, J., Black, M. J.

In International Conference on 3D Vision (3DV 2024), March 2024 (inproceedings) Accepted

Abstract
We introduce TADA, a simple-yet-effective approach that takes textual descriptions and produces expressive 3D avatars with high-quality geometry and lifelike textures, that can be animated and rendered with traditional graphics pipelines. Existing text-based character generation methods are limited in terms of geometry and texture quality, and cannot be realistically animated due to inconsistent align-007 ment between the geometry and the texture, particularly in the face region. To overcome these limitations, TADA leverages the synergy of a 2D diffusion model and an animatable parametric body model. Specifically, we derive an optimizable high-resolution body model from SMPL-X with 3D displacements and a texture map, and use hierarchical rendering with score distillation sampling (SDS) to create high-quality, detailed, holistic 3D avatars from text. To ensure alignment between the geometry and texture, we render normals and RGB images of the generated character and exploit their latent embeddings in the SDS training process. We further introduce various expression parameters to deform the generated character during training, ensuring that the semantics of our generated character remain consistent with the original SMPL-X model, resulting in an animatable character. Comprehensive evaluations demonstrate that TADA significantly surpasses existing approaches on both qualitative and quantitative measures. TADA enables creation of large-scale digital character assets that are ready for animation and rendering, while also being easily editable through natural language. The code will be public for research purposes.

Home Code Video [BibTex]

Home Code Video [BibTex]


POCO: {3D} Pose and Shape Estimation using Confidence
POCO: 3D Pose and Shape Estimation using Confidence

Dwivedi, S. K., Schmid, C., Yi, H., Black, M. J., Tzionas, D.

In International Conference on 3D Vision (3DV 2024), March 2024 (inproceedings)

Abstract
The regression of 3D Human Pose and Shape HPS from an image is becoming increasingly accurate. This makes the results useful for downstream tasks like human action recognition or 3D graphics. Yet, no regressor is perfect, and accuracy can be affected by ambiguous image evidence or by poses and appearance that are unseen during training. Most current HPS regressors, however, do not report the confidence of their outputs, meaning that downstream tasks cannot differentiate accurate estimates from inaccurate ones. To address this, we develop POCO, a novel framework for training HPS regressors to estimate not only a 3D human body, but also their confidence, in a single feed-forward pass. Specifically, POCO estimates both the 3D body pose and a per-sample variance. The key idea is to introduce a Dual Conditioning Strategy (DCS) for regressing uncertainty that is highly correlated to pose reconstruction quality. The POCO framework can be applied to any HPS regressor and here we evaluate it by modifying HMR, PARE, and CLIFF. In all cases, training the network to reason about uncertainty helps it learn to more accurately estimate 3D pose. While this was not our goal, the improvement is modest but consistent. Our main motivation is to provide uncertainty estimates for downstream tasks; we demonstrate this in two ways: (1) We use the confidence estimates to bootstrap HPS training. Given unlabelled image data, we take the confident estimates of a POCO-trained regressor as pseudo ground truth. Retraining with this automatically-curated data improves accuracy. (2) We exploit uncertainty in video pose estimation by automatically identifying uncertain frames (e.g. due to occlusion) and inpainting these from confident frames.

Paper SupMat link (url) [BibTex]

Paper SupMat link (url) [BibTex]


TECA: Text-Guided Generation and Editing of Compositional 3D Avatars
TECA: Text-Guided Generation and Editing of Compositional 3D Avatars

Zhang, H., Feng, Y., Kulits, P., Wen, Y., Thies, J., Black, M. J.

In International Conference on 3D Vision (3DV 2024), March 2024 (inproceedings) To be published

Abstract
Our goal is to create a realistic 3D facial avatar with hair and accessories using only a text description. While this challenge has attracted significant recent interest, existing methods either lack realism, produce unrealistic shapes, or do not support editing, such as modifications to the hairstyle. We argue that existing methods are limited because they employ a monolithic modeling approach, using a single representation for the head, face, hair, and accessories. Our observation is that the hair and face, for example, have very different structural qualities that benefit from different representations. Building on this insight, we generate avatars with a compositional model, in which the head, face, and upper body are represented with traditional 3D meshes, and the hair, clothing, and accessories with neural radiance fields (NeRF). The model-based mesh representation provides a strong geometric prior for the face region, improving realism while enabling editing of the person's appearance. By using NeRFs to represent the remaining components, our method is able to model and synthesize parts with complex geometry and appearance, such as curly hair and fluffy scarves. Our novel system synthesizes these high-quality compositional avatars from text descriptions. The experimental results demonstrate that our method, Text-guided generation and Editing of Compositional Avatars (TECA), produces avatars that are more realistic than those of recent methods while being editable because of their compositional nature. For example, our TECA enables the seamless transfer of compositional features like hairstyles, scarves, and other accessories between avatars. This capability supports applications such as virtual try-on.

arXiv project link (url) [BibTex]

arXiv project link (url) [BibTex]


TeCH: Text-guided Reconstruction of Lifelike Clothed Humans
TeCH: Text-guided Reconstruction of Lifelike Clothed Humans

Huang, Y., Yi, H., Xiu, Y., Liao, T., Tang, J., Cai, D., Thies, J.

In International Conference on 3D Vision (3DV 2024), March 2024 (inproceedings) Accepted

Abstract
Despite recent research advancements in reconstructing clothed humans from a single image, accurately restoring the "unseen regions" with high-level details remains an unsolved challenge that lacks attention. Existing methods often generate overly smooth back-side surfaces with a blurry texture. But how to effectively capture all visual attributes of an individual from a single image, which are sufficient to reconstruct unseen areas (e.g., the back view)? Motivated by the power of foundation models, TeCH reconstructs the 3D human by leveraging 1) descriptive text prompts (e.g., garments, colors, hairstyles) which are automatically generated via a garment parsing model and Visual Question Answering (VQA), 2) a personalized fine-tuned Text-to-Image diffusion model (T2I) which learns the "indescribable" appearance. To represent high-resolution 3D clothed humans at an affordable cost, we propose a hybrid 3D representation based on DMTet, which consists of an explicit body shape grid and an implicit distance field. Guided by the descriptive prompts + personalized T2I diffusion model, the geometry and texture of the 3D humans are optimized through multi-view Score Distillation Sampling (SDS) and reconstruction losses based on the original observation. TeCH produces high-fidelity 3D clothed humans with consistent & delicate texture, and detailed full-body geometry. Quantitative and qualitative experiments demonstrate that TeCH outperforms the state-of-the-art methods in terms of reconstruction accuracy and rendering quality.

Code Home Video arXiv [BibTex]

Code Home Video arXiv [BibTex]


{ArtiGrasp}: Physically Plausible Synthesis of Bi-Manual Dexterous Grasping and Articulation
ArtiGrasp: Physically Plausible Synthesis of Bi-Manual Dexterous Grasping and Articulation

Zhang, H., Christen, S., Fan, Z., Zheng, L., Hwangbo, J., Song, J., Hilliges, O.

In International Conference on 3D Vision (3DV 2024), March 2024 (inproceedings) Accepted

Abstract
We present ArtiGrasp, a novel method to synthesize bi-manual hand-object interactions that include grasping and articulation. This task is challenging due to the diversity of the global wrist motions and the precise finger control that are necessary to articulate objects. ArtiGrasp leverages reinforcement learning and physics simulations to train a policy that controls the global and local hand pose. Our framework unifies grasping and articulation within a single policy guided by a single hand pose reference. Moreover, to facilitate the training of the precise finger control required for articulation, we present a learning curriculum with increasing difficulty. It starts with single-hand manipulation of stationary objects and continues with multi-agent training including both hands and non-stationary objects. To evaluate our method, we introduce Dynamic Object Grasping and Articulation, a task that involves bringing an object into a target articulated pose. This task requires grasping, relocation, and articulation. We show our method's efficacy towards this task. We further demonstrate that our method can generate motions with noisy hand-object pose estimates from an off-the-shelf image-based regressor.

pdf project code [BibTex]

pdf project code [BibTex]


GRIP: Generating Interaction Poses Using Spatial Cues and Latent Consistency
GRIP: Generating Interaction Poses Using Spatial Cues and Latent Consistency

Taheri, O., Zhou, Y., Tzionas, D., Zhou, Y., Ceylan, D., Pirk, S., Black, M. J.

In International Conference on 3D Vision (3DV 2024), March 2024 (inproceedings)

Abstract
Hands are dexterous and highly versatile manipulators that are central to how humans interact with objects and their environment. Consequently, modeling realistic hand-object interactions, including the subtle motion of individual fingers, is critical for applications in computer graphics, computer vision, and mixed reality. Prior work on capturing and modeling humans interacting with objects in 3D focuses on the body and object motion, often ignoring hand pose. In contrast, we introduce GRIP, a learning-based method that takes, as input, the 3D motion of the body and the object, and synthesizes realistic motion for both hands before, during, and after object interaction. As a preliminary step before synthesizing the hand motion, we first use a network, ANet, to denoise the arm motion. Then, we leverage the spatio-temporal relationship between the body and the object to extract novel temporal interaction cues, and use them in a two-stage inference pipeline to generate the hand motion. In the first stage, we introduce a new approach to encourage motion temporal consistency in the latent space (LTC) and generate consistent interaction motions. In the second stage, GRIP generates refined hand poses to avoid hand-object penetrations. Given sequences of noisy body and object motion, GRIP “upgrades” them to include hand-object interaction. Quantitative experiments and perceptual studies demonstrate that GRIP outperforms baseline methods and generalizes to unseen objects and motions from different motion-capture datasets. Our models and code are available for research purposes.

Paper SupMat link (url) [BibTex]

Paper SupMat link (url) [BibTex]


Adversarial Likelihood Estimation With One-Way Flows
Adversarial Likelihood Estimation With One-Way Flows

Ben-Dov, O., Gupta, P. S., Abrevaya, V., Black, M. J., Ghosh, P.

In Proceedings of the IEEE/CVF Winter Conference on Applications of Computer Vision (WACV), pages: 3779-3788, January 2024 (inproceedings)

Abstract
Generative Adversarial Networks (GANs) can produce high-quality samples, but do not provide an estimate of the probability density around the samples. However, it has been noted that maximizing the log-likelihood within an energy-based setting can lead to an adversarial framework where the discriminator provides unnormalized density (often called energy). We further develop this perspective, incorporate importance sampling, and show that 1) Wasserstein GAN performs a biased estimate of the partition function, and we propose instead to use an unbiased estimator; and 2) when optimizing for likelihood, one must maximize generator entropy. This is hypothesized to provide a better mode coverage. Different from previous works, we explicitly compute the density of the generated samples. This is the key enabler to designing an unbiased estimator of the partition function and computation of the generator entropy term. The generator density is obtained via a new type of flow network, called one-way flow network, that is less constrained in terms of architecture, as it does not require a tractable inverse function. Our experimental results show that our method converges faster, produces comparable sample quality to GANs with similar architecture, successfully avoids over-fitting to commonly used datasets and produces smooth low-dimensional latent representations of the training data.

pdf arXiv [BibTex]

pdf arXiv [BibTex]


InterCap: Joint Markerless 3D Tracking of Humans and Objects in Interaction from Multi-view RGB-D Images
InterCap: Joint Markerless 3D Tracking of Humans and Objects in Interaction from Multi-view RGB-D Images

Huang, Y., Taheri, O., Black, M. J., Tzionas, D.

International Journal of Computer Vision (IJCV), 2024 (article)

Abstract
Humans constantly interact with objects to accomplish tasks. To understand such interactions, computers need to reconstruct these in 3D from images of whole bodies manipulating objects, e.g., for grasping, moving and using the latter. This involves key challenges, such as occlusion between the body and objects, motion blur, depth ambiguities, and the low image resolution of hands and graspable object parts. To make the problem tractable, the community has followed a divide-and-conquer approach, focusing either only on interacting hands, ignoring the body, or on interacting bodies, ignoring the hands. However, these are only parts of the problem. On the contrary, recent work focuses on the whole problem. The GRAB dataset addresses whole-body interaction with dexterous hands but captures motion via markers and lacks video, while the BEHAVE dataset captures video of body-object interaction but lacks hand detail. We address the limitations of prior work with InterCap, a novel method that reconstructs interacting whole-bodies and objects from multi-view RGB-D data, using the parametric whole-body SMPL-X model and known object meshes. To tackle the above challenges, InterCap uses two key observations: (i) Contact between the body and object can be used to improve the pose estimation of both. (ii) Consumer-level Azure Kinect cameras let us set up a simple and flexible multi-view RGB-D system for reducing occlusions, with spatially calibrated and temporally synchronized cameras. With our InterCap method we capture the InterCap dataset, which contains 10 subjects (5 males and 5 females) interacting with 10 daily objects of various sizes and affordances, including contact with the hands or feet. To this end, we introduce a new data-driven hand motion prior, as well as explore simple ways for automatic contact detection based on 2D and 3D cues. In total, InterCap has 223 RGB-D videos, resulting in 67,357 multi-view frames, each containing 6 RGB-D images, paired with pseudo ground-truth 3D body and object meshes. Our InterCap method and dataset fill an important gap in the literature and support many research directions. Data and code are available at https://intercap.is.tue.mpg.de.

Paper link (url) DOI [BibTex]


HMP: Hand Motion Priors for Pose and Shape Estimation from Video
HMP: Hand Motion Priors for Pose and Shape Estimation from Video

Duran, E., Kocabas, M., Choutas, V., Fan, Z., Black, M. J.

Proceedings of the IEEE/CVF Winter Conference on Applications of Computer Vision (WACV), 2024 (article)

webpage pdf code [BibTex]

webpage pdf code [BibTex]

2023


{FLARE}: Fast learning of Animatable and Relightable Mesh Avatars
FLARE: Fast learning of Animatable and Relightable Mesh Avatars

Bharadwaj, S., Zheng, Y., Hilliges, O., Black, M. J., Abrevaya, V. F.

ACM Transactions on Graphics, 42(6):204:1-204:15, December 2023 (article) Accepted

Abstract
Our goal is to efficiently learn personalized animatable 3D head avatars from videos that are geometrically accurate, realistic, relightable, and compatible with current rendering systems. While 3D meshes enable efficient processing and are highly portable, they lack realism in terms of shape and appearance. Neural representations, on the other hand, are realistic but lack compatibility and are slow to train and render. Our key insight is that it is possible to efficiently learn high-fidelity 3D mesh representations via differentiable rendering by exploiting highly-optimized methods from traditional computer graphics and approximating some of the components with neural networks. To that end, we introduce FLARE, a technique that enables the creation of animatable and relightable mesh avatars from a single monocular video. First, we learn a canonical geometry using a mesh representation, enabling efficient differentiable rasterization and straightforward animation via learned blendshapes and linear blend skinning weights. Second, we follow physically-based rendering and factor observed colors into intrinsic albedo, roughness, and a neural representation of the illumination, allowing the learned avatars to be relit in novel scenes. Since our input videos are captured on a single device with a narrow field of view, modeling the surrounding environment light is non-trivial. Based on the split-sum approximation for modeling specular reflections, we address this by approximating the pre-filtered environment map with a multi-layer perceptron (MLP) modulated by the surface roughness, eliminating the need to explicitly model the light. We demonstrate that our mesh-based avatar formulation, combined with learned deformation, material, and lighting MLPs, produces avatars with high-quality geometry and appearance, while also being efficient to train and render compared to existing approaches.

Paper Project Page Code DOI [BibTex]

2023

Paper Project Page Code DOI [BibTex]


Controlling Text-to-Image Diffusion by Orthogonal Finetuning
Controlling Text-to-Image Diffusion by Orthogonal Finetuning

Qiu*, Z., Liu*, W., Feng, H., Xue, Y., Feng, Y., Liu, Z., Zhang, D., Weller, A., Schölkopf, B.

Advances in Neural Information Processing Systems 36 (NeurIPS 2023), December 2023, *equal contribution (conference) Accepted

Abstract
Large text-to-image diffusion models have impressive capabilities in generating photorealistic images from text prompts. How to effectively guide or control these powerful models to perform different downstream tasks becomes an important open problem. To tackle this challenge, we introduce a principled finetuning method -- Orthogonal Finetuning (OFT), for adapting text-to-image diffusion models to downstream tasks. Unlike existing methods, OFT can provably preserve hyperspherical energy which characterizes the pairwise neuron relationship on the unit hypersphere. We find that this property is crucial for preserving the semantic generation ability of text-to-image diffusion models. To improve finetuning stability, we further propose Constrained Orthogonal Finetuning (COFT) which imposes an additional radius constraint to the hypersphere. Specifically, we consider two important finetuning text-to-image tasks: subject-driven generation where the goal is to generate subject-specific images given a few images of a subject and a text prompt, and controllable generation where the goal is to enable the model to take in additional control signals. We empirically show that our OFT framework outperforms existing methods in generation quality and convergence speed.

Home Code [BibTex]

Home Code [BibTex]


Emotional Speech-Driven Animation with Content-Emotion Disentanglement
Emotional Speech-Driven Animation with Content-Emotion Disentanglement

Daněček, R., Chhatre, K., Tripathi, S., Wen, Y., Black, M., Bolkart, T.

In ACM, December 2023 (inproceedings) Accepted

Abstract
To be widely adopted, 3D facial avatars must be animated easily, realistically, and directly from speech signals. While the best recent methods generate 3D animations that are synchronized with the input audio, they largely ignore the impact of emotions on facial expressions. Realistic facial animation requires lip-sync together with the natural expression of emotion. To that end, we propose EMOTE (Expressive Model Optimized for Talking with Emotion), which generates 3D talking-head avatars that maintain lip-sync from speech while enabling explicit control over the expression of emotion. To achieve this, we supervise EMOTE with decoupled losses for speech (i.e., lip-sync) and emotion. These losses are based on two key observations: (1) deformations of the face due to speech are spatially localized around the mouth and have high temporal frequency, whereas (2) facial expressions may deform the whole face and occur over longer intervals. Thus, we train EMOTE with a per-frame lip-reading loss to preserve the speech-dependent content, while supervising emotion at the sequence level. Furthermore, we employ a content-emotion exchange mechanism in order to supervise different emotions on the same audio, while maintaining the lip motion synchronized with the speech. To employ deep perceptual losses without getting undesirable artifacts, we devise a motion prior in the form of a temporal VAE. Due to the absence of high-quality aligned emotional 3D face datasets with speech, EMOTE is trained with 3D pseudo-ground-truth extracted from an emotional video dataset (i.e., MEAD). Extensive qualitative and perceptual evaluations demonstrate that EMOTE produces speech-driven facial animations with better lip-sync than state-of-the-art methods trained on the same data, while offering additional, high-quality emotional control.

arXiv link (url) DOI [BibTex]


From Skin to Skeleton: Towards Biomechanically Accurate {3D} Digital Humans
From Skin to Skeleton: Towards Biomechanically Accurate 3D Digital Humans

(Honorable Mention for Best Paper)

Keller, M., Werling, K., Shin, S., Delp, S., Pujades, S., Liu, C. K., Black, M. J.

ACM Transaction on Graphics (ToG), 42(6):253:1-253:15, December 2023 (article)

Abstract
Great progress has been made in estimating 3D human pose and shape from images and video by training neural networks to directly regress the parameters of parametric human models like SMPL. However, existing body models have simplified kinematic structures that do not correspond to the true joint locations and articulations in the human skeletal system, limiting their potential use in biomechanics. On the other hand, methods for estimating biomechanically accurate skeletal motion typically rely on complex motion capture systems and expensive optimization methods. What is needed is a parametric 3D human model with a biomechanically accurate skeletal structure that can be easily posed. To that end, we develop SKEL, which re-rigs the SMPL body model with a biomechanics skeleton. To enable this, we need training data of skeletons inside SMPL meshes in diverse poses. We build such a dataset by optimizing biomechanically accurate skeletons inside SMPL meshes from AMASS sequences. We then learn a regressor from SMPL mesh vertices to the optimized joint locations and bone rotations. Finally, we re-parametrize the SMPL mesh with the new kinematic parameters. The resulting SKEL model is animatable like SMPL but with fewer, and biomechanically-realistic, degrees of freedom. We show that SKEL has more biomechanically accurate joint locations than SMPL, and the bones fit inside the body surface better than previous methods. By fitting SKEL to SMPL meshes we are able to “upgrade" existing human pose and shape datasets to include biomechanical parameters. SKEL provides a new tool to enable biomechanics in the wild, while also providing vision and graphics researchers with a better constrained

Project Page Paper DOI [BibTex]

Project Page Paper DOI [BibTex]


Optimizing the 3D Plate Shape for Proximal Humerus Fractures
Optimizing the 3D Plate Shape for Proximal Humerus Fractures

Keller, M., Krall, M., Smith, J., Clement, H., Kerner, A. M., Gradischar, A., Schäfer, Ü., Black, M. J., Weinberg, A., Pujades, S.

International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI), pages: 487-496, Springer, October 2023 (conference)

Abstract
To treat bone fractures, implant manufacturers produce 2D anatomically contoured plates. Unfortunately, existing plates only fit a limited segment of the population and/or require manual bending during surgery. Patient-specific implants would provide major benefits such as reducing surgery time and improving treatment outcomes but they are still rare in clinical practice. In this work, we propose a patient-specific design for the long helical 2D PHILOS (Proximal Humeral Internal Locking System) plate, used to treat humerus shaft fractures. Our method automatically creates a custom plate from a CT scan of a patient's bone. We start by designing an optimal plate on a template bone and, with an anatomy-aware registration method, we transfer this optimal design to any bone. In addition, for an arbitrary bone, our method assesses if a given plate is fit for surgery by automatically positioning it on the bone. We use this process to generate a compact set of plate shapes capable of fitting the bones within a given population. This plate set can be pre-printed in advance and readily available, removing the fabrication time between the fracture occurrence and the surgery. Extensive experiments on ex-vivo arms and 3D-printed bones show that the generated plate shapes (personalized and plate-set) faithfully match the individual bone anatomy and are suitable for clinical practice.

Project page Code Paper Poster DOI [BibTex]

Project page Code Paper Poster DOI [BibTex]


{DECO}: Dense Estimation of 3D Human-Scene Contact in the Wild
DECO: Dense Estimation of 3D Human-Scene Contact in the Wild

Tripathi, S., Chatterjee, A., Passy, J., Yi, H., Tzionas, D., Black, M. J.

In Proc. International Conference on Computer Vision (ICCV), October 2023 (inproceedings) Accepted

Abstract
Understanding how humans use physical contact to interact with the world is key to enabling human-centric artificial intelligence. While inferring 3D contact is crucial for modeling realistic and physically-plausible human-object interactions, existing methods either focus on 2D, consider body joints rather than the surface, use coarse 3D body regions, or do not generalize to in-the-wild images. In contrast, we focus on inferring dense, 3D contact between the full body surface and objects in arbitrary images. To achieve this, we first collect DAMON, a new dataset containing dense vertex-level contact annotations paired with RGB images containing complex human-object and human-scene contact. Second, we train DECO, a novel 3D contact detector that uses both body-part-driven and scene-context-driven attention to estimate vertex-level contact on the SMPL body. DECO builds on the insight that human observers recognize contact by reasoning about the contacting body parts, their proximity to scene objects, and the surrounding scene context. We perform extensive evaluations of our detector on DAMON as well as on the RICH and BEHAVE datasets. We significantly outperform existing SOTA methods across all benchmarks. We also show qualitatively that DECO generalizes well to diverse and challenging real-world human interactions in natural images. The code, data, and models are available at https://deco.is.tue.mpg.de/login.php.

Project Video Poster Code Data link (url) DOI [BibTex]

Project Video Poster Code Data link (url) DOI [BibTex]


Generalizing Neural Human Fitting to Unseen Poses With Articulated {SE}(3) Equivariance
Generalizing Neural Human Fitting to Unseen Poses With Articulated SE(3) Equivariance

(Oral)

Feng, H., Kulits, P., Liu, S., Black, M. J., Abrevaya, V. F.

In Proc. International Conference on Computer Vision (ICCV), October 2023 (inproceedings) To be published

Abstract
We address the problem of fitting a parametric human body model (SMPL) to point cloud data. Optimization based methods require careful initialization and are prone to becoming trapped in local optima. Learning-based methods address this but do not generalize well when the input pose is far from those seen during training. For rigid point clouds, remarkable generalization has been achieved by leveraging SE(3)-equivariant networks, but these methods do not work on articulated objects. In this work we extend this idea to human bodies and propose ArtEq, a novel part-based SE(3)-equivariant neural architecture for SMPL model estimation from point clouds. Specifically, we learn a part detection network by leveraging local SO(3) invariance, and regress shape and pose using articulated SE(3) shape-invariant and pose-equivariant networks, all trained end-to-end. Our novel pose regression module leverages the permutation-equivariant property of self-attention layers to preserve rotational equivariance. Experimental results show that ArtEq generalizes to poses not seen during training, outperforming state-of-the-art methods by ~44%in terms of body reconstruction accuracy, without requiring an optimization refinement step. Furthermore, ArtEq is three orders of magnitude faster during inference than prior work and has 97.3% fewer parameters. The code and model are available for research purposes at https://arteq.is.tue.mpg.de.

arxiv project link (url) [BibTex]

arxiv project link (url) [BibTex]


D-IF: Uncertainty-aware Human Digitization via Implicit Distribution Field
D-IF: Uncertainty-aware Human Digitization via Implicit Distribution Field

Yang, X., Luo, Y., Xiu, Y., Wang, W., Xu, H., Fan, Z.

In Proc. International Conference on Computer Vision (ICCV), October 2023 (inproceedings) Accepted

Abstract
Realistic virtual humans play a crucial role in numerous industries, such as metaverse, intelligent healthcare, and self-driving simulation. But creating them on a large scale with high levels of realism remains a challenge. The utilization of deep implicit function sparks a new era of image-based 3D clothed human reconstruction, enabling pixel-aligned shape recovery with fine details. Subsequently, the vast majority of works locate the surface by regressing the deterministic implicit value for each point. However, should all points be treated equally regardless of their proximity to the surface? In this paper, we propose replacing the implicit value with an adaptive uncertainty distribution, to differentiate between points based on their distance to the surface. This simple "value to distribution" transition yields significant improvements on nearly all the baselines. Furthermore, qualitative results demonstrate that the models trained using our uncertainty distribution loss, can capture more intricate wrinkles, and realistic limbs.

Code Homepage link (url) [BibTex]

Code Homepage link (url) [BibTex]


{AG3D}: Learning to Generate {3D} Avatars from {2D} Image Collections
AG3D: Learning to Generate 3D Avatars from 2D Image Collections

Dong, Z., Chen, X., Yang, J., J.Black, M., Hilliges, O., Geiger, A.

In Proc. International Conference on Computer Vision (ICCV), October 2023 (inproceedings)

Abstract
While progress in 2D generative models of human appearance has been rapid, many applications require 3D avatars that can be animated and rendered. Unfortunately, most existing methods for learning generative models of 3D humans with diverse shape and appearance require 3D training data, which is limited and expensive to acquire. The key to progress is hence to learn generative models of 3D avatars from abundant unstructured 2D image collections. However, learning realistic and complete 3D appearance and geometry in this under-constrained setting remains challenging, especially in the presence of loose clothing such as dresses. In this paper, we propose a new adversarial generative model of realistic 3D people from 2D images. Our method captures shape and deformation of the body and loose clothing by adopting a holistic 3D generator and integrating an efficient and flexible articulation module. To improve realism, we train our model using multiple discriminators while also integrating geometric cues in the form of predicted 2D normal maps. We experimentally find that our method outperforms previous 3D- and articulation-aware methods in terms of geometry and appearance. We validate the effectiveness of our model and the importance of each component via systematic ablation studies.

project pdf code video [BibTex]

project pdf code video [BibTex]


{SINC}: Spatial Composition of {3D} Human Motions for Simultaneous Action Generation
SINC: Spatial Composition of 3D Human Motions for Simultaneous Action Generation

Athanasiou, N., Petrovich, M., Black, M. J., Varol, G.

In Proc. International Conference on Computer Vision (ICCV), pages: 9984-9995, October 2023 (inproceedings)

Abstract
Our goal is to synthesize 3D human motions given textual inputs describing multiple simultaneous actions, for example ‘waving hand’ while ‘walking’ at the same time. We refer to generating such simultaneous movements as performing ‘spatial compositions’. In contrast to ‘temporal compositions’ that seek to transition from one action to another in a sequence, spatial compositing requires understanding which body parts are involved with which action. Motivated by the observation that the correspondence between actions and body parts is encoded in powerful language models, we extract this knowledge by prompting GPT-3 with text such as “what parts of the body are moving when someone is doing the action ?”. Given this action-part mapping, we automatically create new training data by artificially combining body parts from multiple text-motion pairs together. We extend previous work on text-to-motions synthesis to train on spatial compositions, and introduce SINC (“SImultaneous actioN Compositions for 3D human motions”). We experimentally validate that our additional GPT-guided data helps to better learn compositionality compared to training only on existing real data of simultaneous actions, which is limited in quantity.

website code paper-arxiv video [BibTex]

website code paper-arxiv video [BibTex]


Pairwise Similarity Learning is SimPLE
Pairwise Similarity Learning is SimPLE

Wen, Y., Liu, W., Feng, Y., Raj, B., Singh, R., Weller, A., Black, M. J., Schölkopf, B.

In Proc. International Conference on Computer Vision (ICCV), October 2023 (inproceedings) Accepted

Abstract
In this paper, we focus on a general yet important learning problem, pairwise similarity learning (PSL). PSL subsumes a wide range of important applications, such as open-set face recognition, speaker verification, image retrieval and person re-identification. The goal of PSL is to learn a pairwise similarity function assigning a higher similarity score to positive pairs (i.e., a pair of samples with the same label) than to negative pairs (i.e., a pair of samples with different label). We start by identifying a key desideratum for PSL, and then discuss how existing methods can achieve this desideratum. We then propose a surprisingly simple proxy-free method, called SimPLE, which requires neither feature/proxy normalization nor angular margin and yet is able to generalize well in open-set recognition. We apply the proposed method to three challenging PSL tasks: open-set face recognition, image retrieval and speaker verification. Comprehensive experimental results on large-scale benchmarks show that our method performs significantly better than current state-of-the-art methods.

link (url) [BibTex]

link (url) [BibTex]


TMR: Text-to-Motion Retrieval Using Contrastive 3D Human Motion Synthesis
TMR: Text-to-Motion Retrieval Using Contrastive 3D Human Motion Synthesis

Petrovich, M., Black, M. J., Varol, G.

In Proc. International Conference on Computer Vision (ICCV), pages: 9488-9497, October 2023 (inproceedings)

Abstract
In this paper, we present TMR, a simple yet effective approach for text to 3D human motion retrieval. While previous work has only treated retrieval as a proxy evaluation metric, we tackle it as a standalone task. Our method extends the state-of-the-art text-to-motion synthesis model TEMOS, and incorporates a contrastive loss to better structure the cross-modal latent space. We show that maintaining the motion generation loss, along with the contrastive training, is crucial to obtain good performance. We introduce a benchmark for evaluation and provide an in-depth analysis by reporting results on several protocols. Our extensive experiments on the KIT-ML and HumanML3D datasets show that TMR outperforms the prior work by a significant margin, for example reducing the median rank from 54 to 19. Finally, we showcase the potential of our approach on moment retrieval. Our code and models are publicly available.

website code paper-arxiv video link (url) [BibTex]

website code paper-arxiv video link (url) [BibTex]


Synthetic Data-Based Detection of Zebras in Drone Imagery
Synthetic Data-Based Detection of Zebras in Drone Imagery

Bonetto, E., Ahmad, A.

2023 European Conference on Mobile Robots (ECMR), pages: 1-8, IEEE, September 2023 (conference)

Abstract
Nowadays, there is a wide availability of datasets that enable the training of common object detectors or human detectors. These come in the form of labelled real-world images and require either a significant amount of human effort, with a high probability of errors such as missing labels, or very constrained scenarios, e.g. VICON systems. On the other hand, uncommon scenarios, like aerial views, animals, like wild zebras, or difficult-to-obtain information, such as human shapes, are hardly available. To overcome this, synthetic data generation with realistic rendering technologies has recently gained traction and advanced research areas such as target tracking and human pose estimation. However, subjects such as wild animals are still usually not well represented in such datasets. In this work, we first show that a pre-trained YOLO detector can not identify zebras in real images recorded from aerial viewpoints. To solve this, we present an approach for training an animal detector using only synthetic data. We start by generating a novel synthetic zebra dataset using GRADE, a state-of-the-art framework for data generation. The dataset includes RGB, depth, skeletal joint locations, pose, shape and instance segmentations for each subject. We use this to train a YOLO detector from scratch. Through extensive evaluations of our model with real-world data from i) limited datasets available on the internet and ii) a new one collected and manually labelled by us, we show that we can detect zebras by using only synthetic data during training. The code, results, trained models, and both the generated and training data are provided as open-source at https://eliabntt.github.io/grade-rr.

Generation code Data and models pdf link (url) DOI [BibTex]

Generation code Data and models pdf link (url) DOI [BibTex]


Synthesizing Physical Character-scene Interactions
Synthesizing Physical Character-scene Interactions

Hassan, M., Guo, Y., Wang, T., Black, M., Fidler, S., Peng, X. B.

In SIGGRAPH Conf. Track, August 2023 (inproceedings)

Abstract
Movement is how people interact with and affect their environment. For realistic virtual character animation, it is necessary to realistically synthesize such interactions between virtual characters and their surroundings. Despite recent progress in character animation using machine learning, most systems focus on controlling an agent's movements in fairly simple and homogeneous environments, with limited interactions with other objects. Furthermore, many previous approaches that synthesize human-scene interaction require significant manual labeling of the training data. In contrast, we present a system that uses adversarial imitation learning and reinforcement learning to train physically-simulated characters that perform scene interaction tasks in a natural and life-like manner. Our method is able to learn natural scene interaction behaviors from large unstructured motion datasets, without manual annotation of the motion data. These scene interactions are learned using an adversarial discriminator that evaluates the realism of a motion within the context of a scene. The key novelty involves conditioning both the discriminator and the policy networks on scene context. We demonstrate the effectiveness of our approach through three challenging scene interaction tasks: carrying, sitting, and lying down, which require coordination of a character's movements in relation to objects in the environment. Our policies learn to seamlessly transition between different behaviors like idling, walking, and sitting. Using an efficient approach to randomize the training objects and their placements during training enables our method to generalize beyond the objects and scenarios in the training dataset, producing natural character-scene interactions despite wide variation in object shape and placement. The approach takes physics-based character motion generation a step closer to broad applicability.

pdf video [BibTex]

pdf video [BibTex]


{BARC}: Breed-Augmented Regression Using Classification for {3D} Dog Reconstruction from Images
BARC: Breed-Augmented Regression Using Classification for 3D Dog Reconstruction from Images

Rueegg, N., Zuffi, S., Schindler, K., Black, M. J.

Int. J. of Comp. Vis. (IJCV), 131(8):1964–1979, August 2023 (article)

Abstract
The goal of this work is to reconstruct 3D dogs from monocular images. We take a model-based approach, where we estimate the shape and pose parameters of a 3D articulated shape model for dogs. We consider dogs as they constitute a challenging problem, given they are highly articulated and come in a variety of shapes and appearances. Recent work has considered a similar task using the multi-animal SMAL model, with additional limb scale parameters, obtaining reconstructions that are limited in terms of realism. Like previous work, we observe that the original SMAL model is not expressive enough to represent dogs of many different breeds. Moreover, we make the hypothesis that the supervision signal used to train the network, that is 2D keypoints and silhouettes, is not sufficient to learn a regressor that can distinguish between the large variety of dog breeds. We therefore go beyond previous work in two important ways. First, we modify the SMAL shape space to be more appropriate for representing dog shape. Second, we formulate novel losses that exploit information about dog breeds. In particular, we exploit the fact that dogs of the same breed have similar body shapes. We formulate a novel breed similarity loss, consisting of two parts: One term is a triplet loss, that encourages the shape of dogs from the same breed to be more similar than dogs of different breeds. The second one is a breed classification loss. With our approach we obtain 3D dogs that, compared to previous work, are quantitatively better in terms of 2D reconstruction, and significantly better according to subjective and quantitative 3D evaluations. Our work shows that a-priori side information about similarity of shape and appearance, as provided by breed labels, can help to compensate for the lack of 3D training data. This concept may be applicable to other animal species or groups of species. We call our method BARC (Breed-Augmented Regression using Classification). Our code is publicly available for research purposes at https://barc.is.tue.mpg.de/.

On-line pdf DOI [BibTex]


{HOOD}: Hierarchical Graphs for Generalized Modelling of Clothing Dynamics
HOOD: Hierarchical Graphs for Generalized Modelling of Clothing Dynamics

Grigorev, A., Thomaszewski, B., Black, M. J., Hilliges, O.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 16965-16974, June 2023 (inproceedings)

Abstract
We propose a method that leverages graph neural networks, multi-level message passing, and unsupervised training to enable real-time prediction of realistic clothing dynamics. Whereas existing methods based on linear blend skinning must be trained for specific garments, our method is agnostic to body shape and applies to tight-fitting garments as well as loose, free-flowing clothing. Our method furthermore handles changes in topology (e.g., garments with buttons or zippers) and material properties at inference time. As one key contribution, we propose a hierarchical message-passing scheme that efficiently propagates stiff stretching modes while preserving local detail. We empirically show that our method outperforms strong baselines quantitatively and that its results are perceived as more realistic than state-of-the-art methods.

arXiv project pdf supp [BibTex]

arXiv project pdf supp [BibTex]


High-Fidelity Clothed Avatar Reconstruction from a Single Image
High-Fidelity Clothed Avatar Reconstruction from a Single Image

Liao, T., Zhang, X., Xiu, Y., Yi, H., Liu, X., Qi, G., Zhang, Y., Wang, X., Zhu, X., Lei, Z.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 8662-8672, June 2023 (inproceedings) Accepted

Abstract
This paper presents a framework for efficient 3D clothed avatar reconstruction. By combining the advantages of the high accuracy of optimization-based methods and the efficiency of learning-based methods, we propose a coarse-to-fine way to realize a high-fidelity clothed avatar reconstruction (CAR) from a single image. At the first stage, we use an implicit model to learn the general shape in the canonical space of a person in a learning-based way, and at the second stage, we refine the surface detail by estimating the non-rigid deformation in the posed space in an optimization way. A hyper-network is utilized to generate a good initialization so that the convergence of the optimization process is greatly accelerated. Extensive experiments on various datasets show that the proposed CAR successfully produces high-fidelity avatars for arbitrarily clothed humans in real scenes.

Code Paper Homepage Youtube link (url) [BibTex]

Code Paper Homepage Youtube link (url) [BibTex]


ECON: Explicit Clothed humans Optimized via Normal integration
ECON: Explicit Clothed humans Optimized via Normal integration

(Highlight Paper)

Xiu, Y., Yang, J., Cao, X., Tzionas, D., Black, M. J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 512-523, June 2023 (inproceedings) Accepted

Abstract
The combination of artist-curated scans, and deep implicit functions (IF), is enabling the creation of detailed, clothed, 3D humans from images. However, existing methods are far from perfect. IF-based methods recover free-form geometry but produce disembodied limbs or degenerate shapes for unseen poses or clothes. To increase robustness for these cases, existing work uses an explicit parametric body model to constrain surface reconstruction, but this limits the recovery of free-form surfaces such as loose clothing that deviates from the body. What we want is a method that combines the best properties of implicit and explicit methods. To this end, we make two key observations:(1) current networks are better at inferring detailed 2D maps than full-3D surfaces, and (2) a parametric model can be seen as a “canvas” for stitching together detailed surface patches. ECON infers high-fidelity 3D humans even in loose clothes and challenging poses, while having realistic faces and fingers. This goes beyond previous methods. Quantitative, evaluation of the CAPE and Renderpeople datasets shows that ECON is more accurate than the state of the art. Perceptual studies also show that ECON’s perceived realism is better by a large margin.

Page Paper Demo Code Video Colab link (url) DOI [BibTex]

Page Paper Demo Code Video Colab link (url) DOI [BibTex]


Instant Volumetric Head Avatars
Instant Volumetric Head Avatars

Zielonka, W., Bolkart, T., Thies, J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), June 2023 (inproceedings)

Abstract
We present Instant Volumetric Head Avatars (INSTA),a novel approach for reconstructing photo-realistic digital avatars instantaneously. INSTA models a dynamic neural radiance field based on neural graphics primitives embedded around a parametric face model. Our pipeline is trained on a single monocular RGB portrait video that observes the subject under different expressions and views. While state-of-the-art methods take up to several days to train an avatar, our method can reconstruct a digital avatar in less than 10 minutes on modern GPU hardware, which is orders of magnitude faster than previous solutions. In addition, it allows for the interactive rendering of novel poses and expressions. By leveraging the geometry prior of the underlying parametric face model, we demonstrate that INSTA extrapolates to unseen poses. In quantitative and qualitative studies on various subjects, INSTA outperforms state-of-the-art methods regarding rendering quality and training time.

pdf project video code face tracker code dataset [BibTex]

pdf project video code face tracker code dataset [BibTex]


{BEDLAM}: A Synthetic Dataset of Bodies Exhibiting Detailed Lifelike Animated Motion
BEDLAM: A Synthetic Dataset of Bodies Exhibiting Detailed Lifelike Animated Motion

(Highlight Paper)

Black, M. J., Patel, P., Tesch, J., Yang, J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 8726-8737, June 2023 (inproceedings)

Abstract
We show, for the first time, that neural networks trained only on synthetic data achieve state-of-the-art accuracy on the problem of 3D human pose and shape (HPS) estimation from real images. Previous synthetic datasets have been small, unrealistic, or lacked realistic clothing. Achieving sufficient realism is non-trivial and we show how to do this for full bodies in motion. Specifically, our BEDLAM dataset contains monocular RGB videos with ground-truth 3D bodies in SMPL-X format. It includes a diversity of body shapes, motions, skin tones, hair, and clothing. The clothing is realistically simulated on the moving bodies using commercial clothing physics simulation. We render varying numbers of people in realistic scenes with varied lighting and camera motions. We then train various HPS regressors using BEDLAM and achieve state-of-the-art accuracy on real-image benchmarks despite training with synthetic data. We use BEDLAM to gain insights into what model design choices are important for accuracy. With good synthetic training data, we find that a basic method like HMR approaches the accuracy of the current SOTA method (CLIFF). BEDLAM is useful for a variety of tasks and all images, ground truth bodies, 3D clothing, support code, and more are available for research purposes. Additionally, we provide detailed information about our synthetic data generation pipeline, enabling others to generate their own datasets. See the project page: https://bedlam.is.tue.mpg.de/.

pdf project CVF code [BibTex]

pdf project CVF code [BibTex]


{BITE}: Beyond Priors for Improved Three-{D} Dog Pose Estimation
BITE: Beyond Priors for Improved Three-D Dog Pose Estimation

Rüegg, N., Tripathi, S., Schindler, K., Black, M. J., Zuffi, S.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 8867-8876, June 2023 (inproceedings)

Abstract
We address the problem of inferring the 3D shape and pose of dogs from images. Given the lack of 3D training data, this problem is challenging, and the best methods lag behind those designed to estimate human shape and pose. To make progress, we attack the problem from multiple sides at once. First, we need a good 3D shape prior, like those available for humans. To that end, we learn a dog-specific 3D parametric model, called D-SMAL. Second, existing methods focus on dogs in standing poses because when they sit or lie down, their legs are self occluded and their bodies deform. Without access to a good pose prior or 3D data, we need an alternative approach. To that end, we exploit contact with the ground as a form of side information. We consider an existing large dataset of dog images and label any 3D contact of the dog with the ground. We exploit body-ground contact in estimating dog pose and find that it significantly improves results. Third, we develop a novel neural network architecture to infer and exploit this contact information. Fourth, to make progress, we have to be able to measure it. Current evaluation metrics are based on 2D features like keypoints and silhouettes, which do not directly correlate with 3D errors. To address this, we create a synthetic dataset containing rendered images of scanned 3D dogs. With these advances, our method recovers significantly better dog shape and pose than the state of the art, and we evaluate this improvement in 3D. Our code, model and test dataset are publicly available for research purposes at https://bite.is.tue.mpg.de.

pdf supp project [BibTex]

pdf supp project [BibTex]


{MIME}: Human-Aware {3D} Scene Generation
MIME: Human-Aware 3D Scene Generation

Yi, H., Huang, C. P., Tripathi, S., Hering, L., Thies, J., Black, M. J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 12965-12976, June 2023 (inproceedings) Accepted

Abstract
Generating realistic 3D worlds occupied by moving humans has many applications in games, architecture, and synthetic data creation. But generating such scenes is expensive and labor intensive. Recent work generates human poses and motions given a 3D scene. Here, we take the opposite approach and generate 3D indoor scenes given 3D human motion. Such motions can come from archival motion capture or from IMU sensors worn on the body, effectively turning human movement in a “scanner” of the 3D world. Intuitively, human movement indicates the free-space in a room and human contact indicates surfaces or objects that support activities such as sitting, lying or touching. We propose MIME (Mining Interaction and Movement to infer 3D Environments), which is a generative model of indoor scenes that produces furniture layouts that are consistent with the human movement. MIME uses an auto-regressive transformer architecture that takes the already generated objects in the scene as well as the human motion as input, and outputs the next plausible object. To train MIME, we build a dataset by populating the 3D FRONT scene dataset with 3D humans. Our experiments show that MIME produces more diverse and plausible 3D scenes than a recent generative scene method that does not know about human movement. Code and data will be available for research at https://mime.is.tue.mpg.de.

project arXiv paper [BibTex]

project arXiv paper [BibTex]


Learning from synthetic data generated with GRADE
Learning from synthetic data generated with GRADE

Bonetto, E., Xu, C., Ahmad, A.

In ICRA 2023 Pretraining for Robotics (PT4R) Workshop, June 2023 (inproceedings) Accepted

Abstract
Recently, synthetic data generation and realistic rendering has advanced tasks like target tracking and human pose estimation. Simulations for most robotics applications are obtained in (semi)static environments, with specific sensors and low visual fidelity. To solve this, we present a fully customizable framework for generating realistic animated dynamic environments (GRADE) for robotics research, first introduced in~\cite{GRADE}. GRADE supports full simulation control, ROS integration, realistic physics, while being in an engine that produces high visual fidelity images and ground truth data. We use GRADE to generate a dataset focused on indoor dynamic scenes with people and flying objects. Using this, we evaluate the performance of YOLO and Mask R-CNN on the tasks of segmenting and detecting people. Our results provide evidence that using data generated with GRADE can improve the model performance when used for a pre-training step. We also show that, even training using only synthetic data, can generalize well to real-world images in the same application domain such as the ones from the TUM-RGBD dataset. The code, results, trained models, and the generated data are provided as open-source at https://eliabntt.github.io/grade-rr.

Code Data and network models pdf link (url) [BibTex]

Code Data and network models pdf link (url) [BibTex]


{PointAvatar}: Deformable Point-Based Head Avatars From Videos
PointAvatar: Deformable Point-Based Head Avatars From Videos

Zheng, Y., Yifan, W., Wetzstein, G., Black, M. J., Hilliges, O.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 21057-21067, June 2023 (inproceedings)

Abstract
The ability to create realistic animatable and relightable head avatars from casual video sequences would open up wide ranging applications in communication and entertainment. Current methods either build on explicit 3D morphable meshes (3DMM) or exploit neural implicit representations. The former are limited by fixed topology, while the latter are non-trivial to deform and inefficient to render. Furthermore, existing approaches entangle lighting and albedo, limiting the ability to re-render the avatar in new environments. In contrast, we propose PointAvatar, a deformable point-based representation that disentangles the source color into intrinsic albedo and normal-dependent shading. We demonstrate that PointAvatar bridges the gap between existing mesh- and implicit representations, combining high-quality geometry and appearance with topological flexibility, ease of deformation and rendering efficiency. We show that our method is able to generate animatable 3D avatars using monocular videos from multiple sources including hand-held smartphones, laptop webcams and internet videos, achieving state-of-the-art quality in challenging cases where previous methods fail, e.g., thin hair strands, while being significantly more efficient in training than competing methods.

pdf project code video [BibTex]

pdf project code video [BibTex]


Generating Holistic {3D} Human Motion from Speech
Generating Holistic 3D Human Motion from Speech

Yi, H., Liang, H., Liu, Y., Cao, Q., Wen, Y., Bolkart, T., Tao, D., Black, M. J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 469-480, June 2023 (inproceedings) Accepted

Abstract
This work addresses the problem of generating 3D holistic body motions from human speech. Given a speech recording, we synthesize sequences of 3D body poses, hand gestures, and facial expressions that are realistic and diverse. To achieve this, we first build a high-quality dataset of 3D holistic body meshes with synchronous speech. We then define a novel speech-to-motion generation framework in which the face, body, and hands are modeled separately. The separated modeling stems from the fact that face articulation strongly correlates with human speech, while body poses and hand gestures are less correlated. Specifically, we employ an autoencoder for face motions, and a compositional vector-quantized variational autoencoder (VQ-VAE) for the body and hand motions. The compositional VQ-VAE is key to generating diverse results. Additionally, we propose a cross-conditional autoregressive model that generates body poses and hand gestures, leading to coherent and realistic motions. Extensive experiments and user studies demonstrate that our proposed approach achieves state-of-the-art performance both qualitatively and quantitatively. Our novel dataset and code are released for research purposes at https://talkshow.is.tue.mpg.de.

project SHOW code TalkSHOW code arXiv paper [BibTex]

project SHOW code TalkSHOW code arXiv paper [BibTex]


{TRACE}: {5D} Temporal Regression of Avatars With Dynamic Cameras in {3D} Environments
TRACE: 5D Temporal Regression of Avatars With Dynamic Cameras in 3D Environments

Sun, Y., Bao, Q., Liu, W., Mei, T., Black, M. J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 8856-8866, June 2023 (inproceedings)

Abstract
Although the estimation of 3D human pose and shape (HPS) is rapidly progressing, current methods still cannot reliably estimate moving humans in global coordinates, which is critical for many applications. This is particularly challenging when the camera is also moving, entangling human and camera motion. To address these issues, we adopt a novel 5D representation (space, time, and identity) that enables end-to-end reasoning about people in scenes. Our method, called TRACE, introduces several novel architectural components. Most importantly, it uses two new "maps" to reason about the 3D trajectory of people over time in camera, and world, coordinates. An additional memory unit enables persistent tracking of people even during long occlusions. TRACE is the first one-stage method to jointly recover and track 3D humans in global coordinates from dynamic cameras. By training it end-to-end, and using full image information, TRACE achieves state-of-the-art performance on tracking and HPS benchmarks. The code and dataset are released for research purposes.

pdf supp code video [BibTex]

pdf supp code video [BibTex]


Simulation of Dynamic Environments for SLAM
Simulation of Dynamic Environments for SLAM

Bonetto, E., Xu, C., Ahmad, A.

In ICRA 2023 Workshop on the Active Methods in Autonomous Navigation, June 2023 (inproceedings) Accepted

Abstract
Simulation engines are widely adopted in robotics. However, they lack either full simulation control, ROS integration, realistic physics, or photorealism. Recently, synthetic data generation and realistic rendering has advanced tasks like target tracking and human pose estimation. However, when focusing on vision applications, there is usually a lack of information like sensor measurements or time continuity. On the other hand, simulations for most robotics tasks are performed in (semi)static environments, with specific sensors and low visual fidelity. To solve this, we introduced in our previous work a fully customizable framework for generating realistic animated dynamic environments (GRADE) [1]. We use GRADE to generate an indoor dynamic environment dataset and then compare multiple SLAM algorithms on different sequences. By doing that, we show how current research over-relies on known benchmarks, failing to generalize. Our tests with refined YOLO and Mask R-CNN models provide further evidence that additional research in dynamic SLAM is necessary. The code, results, and generated data are provided as open-source at https://eliabntt.github.io/grade-rr .

Code Evaluation code Data pdf link (url) [BibTex]

Code Evaluation code Data pdf link (url) [BibTex]


Virtual Reality Exposure to a Healthy Weight Body Is a Promising Adjunct Treatment for Anorexia Nervosa
Virtual Reality Exposure to a Healthy Weight Body Is a Promising Adjunct Treatment for Anorexia Nervosa

Behrens, S. C., Tesch, J., Sun, P. J., Starke, S., Black, M. J., Schneider, H., Pruccoli, J., Zipfel, S., Giel, K. E.

Psychotherapy and Psychosomatics, 92(3):170-179, June 2023 (article)

Abstract
Introduction/Objective: Treatment results of anorexia nervosa (AN) are modest, with fear of weight gain being a strong predictor of treatment outcome and relapse. Here, we present a virtual reality (VR) setup for exposure to healthy weight and evaluate its potential as an adjunct treatment for AN. Methods: In two studies, we investigate VR experience and clinical effects of VR exposure to higher weight in 20 women with high weight concern or shape concern and in 20 women with AN. Results: In study 1, 90% of participants (18/20) reported symptoms of high arousal but verbalized low to medium levels of fear. Study 2 demonstrated that VR exposure to healthy weight induced high arousal in patients with AN and yielded a trend that four sessions of exposure improved fear of weight gain. Explorative analyses revealed three clusters of individual reactions to exposure, which need further exploration. Conclusions: VR exposure is a well-accepted and powerful tool for evoking fear of weight gain in patients with AN. We observed a statistical trend that repeated virtual exposure to healthy weight improved fear of weight gain with large effect sizes. Further studies are needed to determine the mechanisms and differential effects.

on-line DOI [BibTex]

on-line DOI [BibTex]


{ARCTIC}: A Dataset for Dexterous Bimanual Hand-Object Manipulation
ARCTIC: A Dataset for Dexterous Bimanual Hand-Object Manipulation

Fan, Z., Taheri, O., Tzionas, D., Kocabas, M., Kaufmann, M., Black, M. J., Hilliges, O.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 12943-12954, June 2023 (inproceedings) Accepted

Abstract
Humans intuitively understand that inanimate objects do not move by themselves, but that state changes are typically caused by human manipulation (e.g., the opening of a book). This is not yet the case for machines. In part this is because there exist no datasets with ground-truth 3D annotations for the study of physically consistent and synchronised motion of hands and articulated objects. To this end, we introduce ARCTIC -- a dataset of two hands that dexterously manipulate objects, containing 2.1M video frames paired with accurate 3D hand and object meshes and detailed, dynamic contact information. It contains bi-manual articulation of objects such as scissors or laptops, where hand poses and object states evolve jointly in time. We propose two novel articulated hand-object interaction tasks: (1) Consistent motion reconstruction: Given a monocular video, the goal is to reconstruct two hands and articulated objects in 3D, so that their motions are spatio-temporally consistent. (2) Interaction field estimation: Dense relative hand-object distances must be estimated from images. We introduce two baselines ArcticNet and InterField, respectively and evaluate them qualitatively and quantitatively on ARCTIC.

Project Page Code Paper arXiv Video link (url) DOI [BibTex]

Project Page Code Paper arXiv Video link (url) DOI [BibTex]


Reconstructing Signing Avatars from Video Using Linguistic Priors
Reconstructing Signing Avatars from Video Using Linguistic Priors

Forte, M., Kulits, P., Huang, C. P., Choutas, V., Tzionas, D., Kuchenbecker, K. J., Black, M. J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 12791-12801, June 2023 (inproceedings)

Abstract
Sign language (SL) is the primary method of communication for the 70 million Deaf people around the world. Video dictionaries of isolated signs are a core SL learning tool. Replacing these with 3D avatars can aid learning and enable AR/VR applications, improving access to technology and online media. However, little work has attempted to estimate expressive 3D avatars from SL video; occlusion, noise, and motion blur make this task difficult. We address this by introducing novel linguistic priors that are universally applicable to SL and provide constraints on 3D hand pose that help resolve ambiguities within isolated signs. Our method, SGNify, captures fine-grained hand pose, facial expression, and body movement fully automatically from in-the-wild monocular SL videos. We evaluate SGNify quantitatively by using a commercial motion-capture system to compute 3D avatars synchronized with monocular video. SGNify outperforms state-of-the-art 3D body-pose- and shape-estimation methods on SL videos. A perceptual study shows that SGNify's 3D reconstructions are significantly more comprehensible and natural than those of previous methods and are on par with the source videos. Code and data are available at sgnify.is.tue.mpg.de.

pdf arXiv project code DOI [BibTex]

pdf arXiv project code DOI [BibTex]


{3D} Human Pose Estimation via Intuitive Physics
3D Human Pose Estimation via Intuitive Physics

Tripathi, S., Müller, L., Huang, C. P., Taheri, O., Black, M., Tzionas, D.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR) , pages: 4713-4725, June 2023 (inproceedings) Accepted

Abstract
The estimation of 3D human body shape and pose from images has advanced rapidly. While the results are often well aligned with image features in the camera view, the 3D pose is often physically implausible; bodies lean, float, or penetrate the floor. This is because most methods ignore the fact that bodies are typically supported by the scene. To address this, some methods exploit physics engines to enforce physical plausibility. Such methods, however, are not differentiable, rely on unrealistic proxy bodies, and are difficult to integrate into existing optimization and learning frameworks. To account for this, we take a different approach that exploits novel intuitive-physics (IP) terms that can be inferred from a 3D SMPL body interacting with the scene. Specifically, we infer biomechanically relevant features such as the pressure heatmap of the body on the floor, the Center of Pressure (CoP) from the heatmap, and the SMPL body’s Center of Mass (CoM) projected on the floor. With these, we develop IPMAN, to estimate a 3D body from a color image in a “stable” configuration by encouraging plausible floor contact and overlapping CoP and CoM. Our IP terms are intuitive, easy to implement, fast to compute, and can be integrated into any SMPL-based optimization or regression method; we show examples of both. To evaluate our method, we present MoYo, a dataset with synchronized multi-view color images and 3D bodies with complex poses, body-floor contact, and ground-truth CoM and pressure. Evaluation on MoYo, RICH and Human3.6M show that our IP terms produce more plausible results than the state of the art; they improve accuracy for static poses, while not hurting dynamic ones.

Project Page Moyo Dataset link (url) DOI [BibTex]

Project Page Moyo Dataset link (url) DOI [BibTex]


Instant Multi-View Head Capture through Learnable Registration
Instant Multi-View Head Capture through Learnable Registration

Bolkart, T., Li, T., Black, M. J.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 768-779, June 2023 (inproceedings)

Abstract
Existing methods for capturing datasets of 3D heads in dense semantic correspondence are slow, and commonly address the problem in two separate steps; multi-view stereo (MVS) reconstruction followed by non-rigid registration. To simplify this process, we introduce TEMPEH (Towards Estimation of 3D Meshes from Performances of Expressive Heads) to directly infer 3D heads in dense correspondence from calibrated multi-view images. Registering datasets of 3D scans typically requires manual parameter tuning to find the right balance between accurately fitting the scans’ surfaces and being robust to scanning noise and outliers. Instead, we propose to jointly register a 3D head dataset while training TEMPEH. Specifically, during training we minimize a geometric loss commonly used for surface registration, effectively leveraging TEMPEH as a regularizer. Our multi-view head inference builds on a volumetric feature representation that samples and fuses features from each view using camera calibration information. To account for partial occlusions and a large capture volume that enables head movements, we use view- and surface-aware feature fusion, and a spatial transformer-based head localization module, respectively. We use raw MVS scans as supervision during training, but, once trained, TEMPEH directly predicts 3D heads in dense correspondence without requiring scans. Predicting one head takes about 0.3 seconds with a median reconstruction error of 0.26 mm, 64% lower than the current state-of-the-art. This enables the efficient capture of large datasets containing multiple people and diverse facial motions. Code, model, and data are publicly available at https://tempeh.is.tue.mpg.de.

project video paper sup. mat. poster [BibTex]

project video paper sup. mat. poster [BibTex]


SLOPER4D: A Scene-Aware Dataset for Global 4D Human Pose Estimation in Urban Environments
SLOPER4D: A Scene-Aware Dataset for Global 4D Human Pose Estimation in Urban Environments

Yudi, D., Yitai, L., Xiping, L., Chenglu, W., Lan, X., Hongwei, Y., Siqi, S., Yuexin, M., Cheng, W.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 682-692, CVF, June 2023 (inproceedings) Accepted

Abstract
We present SLOPER4D, a novel scene-aware dataset collected in large urban environments to facilitate the research of global human pose estimation (GHPE) with human-scene interaction in the wild. Employing a head-mounted device integrated with a LiDAR and camera, we record 12 human subjects’ activities over 10 diverse urban scenes from an egocentric view. Frame-wise annotations for 2D key points, 3D pose parameters, and global translations are provided, together with reconstructed scene point clouds. To obtain accurate 3D ground truth in such large dynamic scenes, we propose a joint optimization method to fit local SMPL meshes to the scene and fine-tune the camera calibration during dynamic motions frame by frame, resulting in plausible and scene-natural 3D human poses. Eventually, SLOPER4D consists of 15 sequences of human motions, each of which has a trajectory length of more than 200 meters (up to 1,300 meters) and covers an area of more than 200 square meters (up to 30,000 square meters), including more than 100K LiDAR frames, 300k video frames, and 500K IMU-based motion frames. With SLOPER4D, we provide a detailed and thorough analysis of two critical tasks, including camera-based 3D HPE and LiDAR-based 3D HPE in urban environments, and benchmark a new task, GHPE. The in-depth analysis demonstrates SLOPER4D poses significant challenges to existing methods and produces great research opportunities. The dataset and code are released https://github.com/climbingdaily/SLOPER4D.

project dataset codebase paper arXiv [BibTex]

project dataset codebase paper arXiv [BibTex]


Detecting Human-Object Contact in Images
Detecting Human-Object Contact in Images

Chen, Y., Dwivedi, S. K., Black, M. J., Tzionas, D.

In IEEE/CVF Conf. on Computer Vision and Pattern Recognition (CVPR), pages: 17100-17110, June 2023 (inproceedings) Accepted

Abstract
Humans constantly contact objects to move and perform tasks. Thus, detecting human-object contact is important for building human-centered artificial intelligence. However, there exists no robust method to detect contact between the body and the scene from an image, and there exists no dataset to learn such a detector. We fill this gap with HOT ("Human-Object conTact"), a new dataset of human-object contacts for images. To build HOT, we use two data sources: (1) We use the PROX dataset of 3D human meshes moving in 3D scenes, and automatically annotate 2D image areas for contact via 3D mesh proximity and projection. (2) We use the V-COCO, HAKE and Watch-n-Patch datasets, and ask trained annotators to draw polygons for the 2D image areas where contact takes place. We also annotate the involved body part of the human body. We use our HOT dataset to train a new contact detector, which takes a single color image as input, and outputs 2D contact heatmaps as well as the body-part labels that are in contact. This is a new and challenging task that extends current foot-ground or hand-object contact detectors to the full generality of the whole body. The detector uses a part-attention branch to guide contact estimation through the context of the surrounding body parts and scene. We evaluate our detector extensively, and quantitative results show that our model outperforms baselines, and that all components contribute to better performance. Results on images from an online repository show reasonable detections and generalizability.

Project Page Paper Code DOI [BibTex]

Project Page Paper Code DOI [BibTex]


MeshDiffusion: Score-based Generative 3D Mesh Modeling
MeshDiffusion: Score-based Generative 3D Mesh Modeling

(Notable-Top-25%)

Liu, Z., Feng, Y., Black, M. J., Nowrouzezahrai, D., Paull, L., Liu, W.

Proceedings of the Eleventh International Conference on Learning Representations (ICLR), May 2023 (conference)

Abstract
We consider the task of generating realistic 3D shapes, which is useful for a variety of applications such as automatic scene generation and physical simulation. Compared to other 3D representations like voxels and point clouds, meshes are more desirable in practice, because (1) they enable easy and arbitrary manipulation of shapes for relighting and simulation, and (2) they can fully leverage the power of modern graphics pipelines which are mostly optimized for meshes. Previous scalable methods for generating meshes typically rely on sub-optimal post-processing, and they tend to produce overly-smooth or noisy surfaces without fine-grained geometric details. To overcome these shortcomings, we take advantage of the graph structure of meshes and use a simple yet very effective generative modeling method to generate 3D meshes. Specifically, we represent meshes with deformable tetrahedral grids, and then train a diffusion model on this direct parametrization. We demonstrate the effectiveness of our model on multiple generative tasks.

Home Code link (url) [BibTex]

Home Code link (url) [BibTex]


{Fast-SNARF}: A Fast Deformer for Articulated Neural Fields
Fast-SNARF: A Fast Deformer for Articulated Neural Fields

Chen, X., Jiang, T., Song, J., Rietmann, M., Geiger, A., Black, M. J., Hilliges, O.

IEEE Transactions on Pattern Analysis and Machine Intelligence (PAMI), pages: 1-15, April 2023 (article)

Abstract
Neural fields have revolutionized the area of 3D reconstruction and novel view synthesis of rigid scenes. A key challenge in making such methods applicable to articulated objects, such as the human body, is to model the deformation of 3D locations between the rest pose (a canonical space) and the deformed space. We propose a new articulation module for neural fields, Fast-SNARF, which finds accurate correspondences between canonical space and posed space via iterative root finding. Fast-SNARF is a drop-in replacement in functionality to our previous work, SNARF, while significantly improving its computational efficiency. We contribute several algorithmic and implementation improvements over SNARF, yielding a speed-up of 150× . These improvements include voxel-based correspondence search, pre-computing the linear blend skinning function, and an efficient software implementation with CUDA kernels. Fast-SNARF enables efficient and simultaneous optimization of shape and skinning weights given deformed observations without correspondences (e.g. 3D meshes). Because learning of deformation maps is a crucial component in many 3D human avatar methods and since Fast-SNARF provides a computationally efficient solution, we believe that this work represents a significant step towards the practical creation of 3D virtual humans.

pdf publisher site code DOI [BibTex]

pdf publisher site code DOI [BibTex]


{SmartMocap}: Joint Estimation of Human and Camera Motion Using Uncalibrated {RGB} Cameras
SmartMocap: Joint Estimation of Human and Camera Motion Using Uncalibrated RGB Cameras

Saini, N., Huang, C. P., Black, M. J., Ahmad, A.

IEEE Robotics and Automation Letters, 8(6):3206-3213, 2023 (article)

Abstract
Markerless human motion capture (mocap) from multiple RGB cameras is a widely studied problem. Existing methods either need calibrated cameras or calibrate them relative to a static camera, which acts as the reference frame for the mocap system. The calibration step has to be done a priori for every capture session, which is a tedious process, and re-calibration is required whenever cameras are intentionally or accidentally moved. In this letter, we propose a mocap method which uses multiple static and moving extrinsically uncalibrated RGB cameras. The key components of our method are as follows. First, since the cameras and the subject can move freely, we select the ground plane as a common reference to represent both the body and the camera motions unlike existing methods which represent bodies in the camera coordinate system. Second, we learn a probability distribution of short human motion sequences (~1sec) relative to the ground plane and leverage it to disambiguate between the camera and human motion. Third, we use this distribution as a motion prior in a novel multi-stage optimization approach to fit the SMPL human body model and the camera poses to the human body keypoints on the images. Finally, we show that our method can work on a variety of datasets ranging from aerial cameras to smartphones. It also gives more accurate results compared to the state-of-the-art on the task of monocular human mocap with a static camera.

publisher site DOI [BibTex]