DiffusionLight: Light Probes for Free by Painting a Chrome Ball

We present a simple yet effective technique to estimate lighting in a single input image. Current techniques rely heavily on HDR panorama datasets to train neural networks to regress an input with limited field-of-view to a full environment map. However, these approaches often struggle with real-world, uncontrolled settings due to the limited diversity and size of their datasets. To address this problem, we leverage diffusion models trained on billions of standard images to render a chrome ball into the input image. Despite its simplicity, this task remains challenging: the diffusion models often insert incorrect or inconsistent objects and cannot readily generate images in HDR format. Our research uncovers a surprising relationship between the appearance of chrome balls and the initial diffusion noise map, which we utilize to consistently generate high-quality chrome balls. We further fine-tune an LDR difusion model (Stable Diffusion XL) with LoRA, enabling it to perform exposure bracketing for HDR light estimation. Our method produces convincing light estimates across diverse settings and demonstrates superior generalization to in-the-wild scenarios.

Talking Head(?) Anime from a Single Image 4: Improved Model and Its Distillation

We study the problem of creating a character model that can be controlled in real time from a single image of an anime character. A solution to this problem would greatly reduce the cost of creating avatars, computer games, and other interactive applications. Talking Head Anime 3 (THA3) is an open source project that attempts to directly address the problem. It takes as input (1) an image of an anime character's upper body and (2) a 45-dimensional pose vector and outputs a new image of the same character taking the specified pose. The range of possible movements is expressive enough for personal avatars and certain types of game characters. However, the system is too slow to generate animations in real time on common PCs, and its image quality can be improved. In this paper, we improve THA3 in two ways. First, we propose new architectures for constituent networks that rotate the character's head and body based on U-Nets with attention that are widely used in modern generative models. The new architectures consistently yield better image quality than the THA3 baseline. Nevertheless, they also make the whole system much slower: it takes up to 150 milliseconds to generate a frame. Second, we propose a technique to distill the system into a small network (less than 2 MB) that can generate 512x512 animation frames in real time (under 30 FPS) using consumer gaming GPUs while keeping the image quality close to that of the full system. This improvement makes the whole system practical for real-time applications.

Diffusion Sampling with Momentum for Mitigating Divergence Artifacts

Despite the remarkable success of diffusion models in image generation, slow sampling remains a persistent issue. To accelerate the sampling process, prior studies have reformulated diffusion sampling as an ODE/SDE and introduced higher-order numerical methods. However, these methods often produce divergence artifacts, especially with a low number of sampling steps, which limits the achievable acceleration. In this paper, we investigate the potential causes of these artifacts and suggest that the small stability regions of these methods could be the principal cause. To address this issue, we propose two novel techniques. The first technique involves the incorporation of Heavy Ball (HB) momentum, a well-known technique for improving optimization, into existing diffusion numerical methods to expand their stability regions. We also prove that the resulting methods have first-order convergence. The second technique, called Generalized Heavy Ball (GHVB), constructs a new high-order method that offers a variable trade-off between accuracy and artifact suppression. Experimental results show that our techniques are highly effective in reducing artifacts and improving image quality, surpassing state-of-the-art diffusion solvers on both pixel-based and latent-based diffusion models for low-step sampling. Our research provides novel insights into the design of numerical methods for future diffusion work.