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Summary: 1
Spectral Gradient: A Surface Reflectance Measurement Invariant to
Geometry and Incident Illumination
Technical Report MS-CIS-99-02
Abstract
Although photometric data is a readily available dense source of information in intensity
images, it is not widely used in computer vision. A major drawback is its dependence on
viewpoint and incident illumination. A novel methodology is presented which extracts
reflectivity information of the various materials in the scene independent of incident light
and scene geometry. A scene is captured under three different narrow-band color filters
and the spectral derivatives of the scene are computed. The resulting spectral derivatives
form a spectral gradient at each pixel. This spectral gradient is a surface reflectance
descriptor which is invariant to scene geometry and incident illumination for smooth dif-
fuse surfaces. The invariant properties of the spectral gradients make them a particularly
appealing tool in many diverse areas of computer vision such as color constancy, tracking,
scene classification, material classification, stereo correspondence, even re-illumination of
a scene.
1 Introduction
The starting point of most computer vision techniques is the light intensity reflected from an imaged
scene. The reflected light is directly related to the geometry of the scene, the reflectance properties of the
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