# PixHt-Lab: Pixel Height Based Light Effect Generation for Image Compositing

## TL;DR

PixHt-Lab introduces a novel system that uses pixel height mapping to reconstruct 3D geometry for improved lighting effects in image compositing, enhancing realism of shadows and reflections.

## Contribution

The paper presents a new approach leveraging explicit pixel height to reconstruct 3D geometry, enabling more realistic soft shadows and reflections in 2D image compositing.

## Key findings

- Significant improvement in soft shadow quality.
- Enhanced reflection rendering with varying glossiness.
- Quantitative and qualitative evaluation confirms effectiveness.

## Abstract

Lighting effects such as shadows or reflections are key in making synthetic images realistic and visually appealing. To generate such effects, traditional computer graphics uses a physically-based renderer along with 3D geometry. To compensate for the lack of geometry in 2D Image compositing, recent deep learning-based approaches introduced a pixel height representation to generate soft shadows and reflections. However, the lack of geometry limits the quality of the generated soft shadows and constrain reflections to pure specular ones. We introduce PixHt-Lab, a system leveraging an explicit mapping from pixel height representation to 3D space. Using this mapping, PixHt-Lab reconstructs both the cutout and background geometry and renders realistic, diverse, lighting effects for image compositing. Given a surface with physically-based materials, we can render reflections with varying glossiness. To generate more realistic soft shadows, we further propose to use 3D-aware buffer channels to guide a neural renderer. Both quantitative and qualitative evaluations demonstrate that PixHt-Lab significantly improves soft shadow generation.