This paper investigates the visual appearance of real-world surfaces and the dependence of appearance on imaging conditions. It introduces a new texture representation called the Bidirectional Texture Function (BTF), which captures texture variations with illumination and viewing direction. The authors present two databases: a BTF database with over 14,000 images from 60 different samples, each observed with over 200 combinations of viewing and illumination directions, and a BRDF (Bidirectional Reflectance Distribution Function) database with reflectance measurements for the same samples. These databases are publicly available and have significant implications for computer graphics, particularly in 3-D texture algorithms and realistic rendering. The paper also discusses the measurement methods used to collect these databases, including a robotic manipulator and CCD camera setup, and addresses the challenges and sources of error in the measurement process. The BTF and BRDF databases provide a comprehensive resource for researchers to evaluate and develop new models and algorithms for texture and reflectance analysis.This paper investigates the visual appearance of real-world surfaces and the dependence of appearance on imaging conditions. It introduces a new texture representation called the Bidirectional Texture Function (BTF), which captures texture variations with illumination and viewing direction. The authors present two databases: a BTF database with over 14,000 images from 60 different samples, each observed with over 200 combinations of viewing and illumination directions, and a BRDF (Bidirectional Reflectance Distribution Function) database with reflectance measurements for the same samples. These databases are publicly available and have significant implications for computer graphics, particularly in 3-D texture algorithms and realistic rendering. The paper also discusses the measurement methods used to collect these databases, including a robotic manipulator and CCD camera setup, and addresses the challenges and sources of error in the measurement process. The BTF and BRDF databases provide a comprehensive resource for researchers to evaluate and develop new models and algorithms for texture and reflectance analysis.