Luminance correction for color scanning using a measured and derived luminance value

Abstract

A color scanning technique that maintains a high image quality while permitting improved scanning speed and improved perceived resolution. A color pixel array and a luminance pixel array are generated representative of a target object. The pixel arrays are related in that one or more luminance pixels of the luminance pixel array cover each pixel of the color pixel array. A luminance value is sensed for each luminance pixel, and three primary color values are sensed for each color pixel. A measured luminance value is then associated with each respective color pixel wherein the measured luminance value is a function of the sensed luminance values for the one or more luminance pixels covering the respective color pixel. A derived luminance value is also calculated for each respective color pixel wherein the derived luminance value is a function of the three sensed primary color values for the respective color pixel. A luminance correction factor is then determined for each respective color pixel as a function of the color pixel's derived and measured luminance values. The luminance correction factor for each respective color pixel is applied to the sensed primary color values of the color pixel, or to a linear combination thereof, to determine luminance-corrected color values. In this way the overall pixel luminance implied by the aggregate measured color values will show a consistency with the directly measured luminances. The luminance-corrected color values together with the measured luminance values may then be subjected to further appropriate transformation to determine color coordinates for each luminance pixel and/or for each color pixel, which may then be used in further processing. A logarithmic method is used for efficient computation of correction factors and luminance-corrected color values.

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