Existing photorealistic relightable hand models require extensive
identity-specific observations in different views, poses, and illuminations,
and face challenges in generalizing to natural illuminations and novel
identities. To bridge this gap, we present URHand, the first universal
relightable hand model that generalizes across viewpoints, poses,
illuminations, and identities. Our model allows few-shot personalization using
images captured with a mobile phone, and is ready to be photorealistically
rendered under novel illuminations. To simplify the personalization process
while retaining photorealism, we build a powerful universal relightable prior
based on neural relighting from multi-view images of hands captured in a light
stage with hundreds of identities. The key challenge is scaling the
cross-identity training while maintaining personalized fidelity and sharp
details without compromising generalization under natural illuminations. To
this end, we propose a spatially varying linear lighting model as the neural
renderer that takes physics-inspired shading as input feature. By removing
non-linear activations and bias, our specifically designed lighting model
explicitly keeps the linearity of light transport. This enables single-stage
training from light-stage data while generalizing to real-time rendering under
arbitrary continuous illuminations across diverse identities. In addition, we
introduce the joint learning of a physically based model and our neural
relighting model, which further improves fidelity and generalization. Extensive
experiments show that our approach achieves superior performance over existing
methods in terms of both quality and generalizability. We also demonstrate
quick personalization of URHand from a short phone scan of an unseen identity.

URHand 是第一个可以推广到不同视角、姿势、光照和身份的通用光真手部模型，通过使用手机捕捉的图像进行少样本个性化，能够在新型光照条件下实现光真渲染。通过建立基于神经光真技术和数百个身份的多视图手部图像的强大通用光真先验模型，进一步通过神经渲染器的线性光照模型来缩放身份跨越训练，并在自然光照下实现个性化的细节，以及在多样化身份下进行连续光照的实时渲染。通过物理模型和神经光真模型的联合学习，我们的方法在质量和推广性方面均取得了优秀的性能，还展示了使用手机扫描未知身份快速个性化 URHand 的能力。

URHand：通用可重新照明手部

URHand: Universal Relightable Hands

We introduce a neural relighting algorithm for captured indoors scenes, that
allows interactive free-viewpoint navigation. Our method allows illumination to
be changed synthetically, while coherently rendering cast shadows and complex
glossy materials. We start with multiple images of the scene and a 3D mesh
obtained by multi-view stereo (MVS) reconstruction. We assume that lighting is
well-explained as the sum of a view-independent diffuse component and a
view-dependent glossy term concentrated around the mirror reflection direction.
We design a convolutional network around input feature maps that facilitate
learning of an implicit representation of scene materials and illumination,
enabling both relighting and free-viewpoint navigation. We generate these input
maps by exploiting the best elements of both image-based and physically-based
rendering. We sample the input views to estimate diffuse scene irradiance, and
compute the new illumination caused by user-specified light sources using path
tracing. To facilitate the network's understanding of materials and synthesize
plausible glossy reflections, we reproject the views and compute mirror images.
We train the network on a synthetic dataset where each scene is also
reconstructed with MVS. We show results of our algorithm relighting real indoor
scenes and performing free-viewpoint navigation with complex and realistic
glossy reflections, which so far remained out of reach for view-synthesis
techniques.

利用卷积神经网络构建的光照算法，可以实时改变室内场景的光照，并保持了物体的阴影和光泽材质，从而实现自由视点浏览。