US 2003/0152285 A1Published application

Method of real-time recognition and compensation of deviations in the illumination in digital color images

OwnerIngo Feldmann, Peter Kauff +2inventors

InventorsIngo Feldmann, Peter Kauff, Oliver Schreer, Ralf Tanger

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Abstract

During post-processing of video data in a YUV color space it may be necessary, for instance for immersive video conferences, to separate a video object in the image foreground from the known image background. Hitherto, rapid, locally limited deviations in illumination in the actual image to be examined, in particular shadows and brightenings, could not be compensated. The inventive recognition and compensation method, however, can compensate in real time shadows and brightenings, even at great quantities of image data by directly utilizing different properties of the technically based YUV color space. Chrominance, color saturation and color intensity of an actual pixel (P1) are approximated directly from associated YUV values (α, a, b) which leads to the avoidance of time-consuming calculations. The recognition of rapid deviations in illumination carried out in the YUV color space is based upon the approximation of a chrominance difference by an angle difference (α1−α2) of the pixels (P1, P2) to be compared, preferably in a plane (U, V) of the YUV color space. This proceeds on the assumption that the chrominance of a pixel at the occurrence of shadows and brightenings remains constant in spite of varying color saturation and color intensity. The method in accordance with the invention may be supplemented by a rapid decision program including additional decision parameters which excludes complex calculations of angle operations and separation error, even at significant deviations in illumination.

Claims8

Dependent claims

A method of real-time recognition and compensation of deviations in the illumination of digital color image signals for separating video objects as an image foreground from a known static image background by a pixel-wise component and threshold value dependent color image signal comparison between an actual pixel and an associated constant reference pixel in the image background in a YUV color space with color components luminance Y and chrominance U, V transformed from a color space with color components chrominance, color saturation and color intensity,

characterized by recognition of locally limited and rapidly changing shadows or brightenings is carried out directly in the YUV color space and which is based upon determination and evaluation of an angular difference of pixel vectors to be compared between an actual pixel (P1 and a reference pixel approximating a chrominance difference under the assumption that because of the occurring shadows or brightenings which at a constant chrominance cause only the color intensity and color saturation to change, the components Y, U and V of the actual pixel decrease or increase linearly such that the actual pixel composed of the three components Y, U, V is positioned on a straight line between its initial value before occurrence of the deviation in illumination and the YUV coordinate leap, whereby the changing color saturation of the actual pixel is approximated by the distance thereof from the origin of a straight line intersecting the origin of the YUV color space, the changing color intensity of the actual pixel is approximated by the share of the luminance component and the constant chrominance of the actual pixel is approximated by the angle of the straight line in the YUV color space.

Dependencies are inferred from the claim text.