Video contrast enhancer
First Claim
1. A contrast enhancer for enhancing contrast of a video signal representing luminance levels of pixels in a sequence of images constituting a moving picture, comprising:
- a block average processor for receiving said video signal, dividing each image in said sequence of images into a plurality of areas, associating with each area among said plurality of areas a set of pixels in said image, and calculating a mean luminance level of said set of pixels, thereby obtaining a plurality of mean luminance levels for each said image;
a selection memory for storing a selection signal, wherein each value of the selection signal corresponds to a mapping function from among a predetermined set of mapping functions;
a mapping function selector coupled to said block average processor and said selection memory, for adjusting the value of said selection signal responsive to the value of a previous selection signal corresponding to the mean luminance levels in a plurality of images in said sequence of images; and
a primary mapper coupled to said selection memory, for receiving said video signal and said selection signal, selecting the mapping function from among the predetermined set of mapping functions according to the value of said selection signal, and mapping the luminance levels represented by said video signal according to the mapping function thus selected.
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Accused Products
Abstract
A video contrast enhancer enhances luminance contrast by dividing each video frame or field into blocks, calculating a mean luminance level for each block, selecting mapping functions on the basis of these mean luminance levels over a series of frames or fields, and mapping the video luminance levels according to the selected mapping functions. Color-saturation contrast is enhanced by modifying the amplitude of the modulated chrominance signal by the histogram equalization method, preferably by making a single linear modification in each period of the chrominance signal, so that color phase is not affected. For video signals with non-picture bands, these enhancements are preferably restricted to the picture area. If a black offset is present, it is preferably removed.
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Citations
20 Claims
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1. A contrast enhancer for enhancing contrast of a video signal representing luminance levels of pixels in a sequence of images constituting a moving picture, comprising:
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a block average processor for receiving said video signal, dividing each image in said sequence of images into a plurality of areas, associating with each area among said plurality of areas a set of pixels in said image, and calculating a mean luminance level of said set of pixels, thereby obtaining a plurality of mean luminance levels for each said image; a selection memory for storing a selection signal, wherein each value of the selection signal corresponds to a mapping function from among a predetermined set of mapping functions; a mapping function selector coupled to said block average processor and said selection memory, for adjusting the value of said selection signal responsive to the value of a previous selection signal corresponding to the mean luminance levels in a plurality of images in said sequence of images; and a primary mapper coupled to said selection memory, for receiving said video signal and said selection signal, selecting the mapping function from among the predetermined set of mapping functions according to the value of said selection signal, and mapping the luminance levels represented by said video signal according to the mapping function thus selected. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of enhancing contrast of a video signal representing luminance levels of pixels in a sequence of images constituting a moving picture, comprising the steps of:
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dividing each image in said sequence of images into a plurality of areas; associating with each area among said plurality of areas a set of pixels in said image; calculating a mean luminance level of said set of pixels, thereby obtaining a plurality of mean luminance levels for each said image; storing a selection signal, wherein each value of the selection signal corresponds to a mapping function from among a predetermined set of mapping functions; adjusting the value of the selection signal responsive to the value of a previous selection signal corresponding to the mean luminance levels in a plurality of images in said sequence of images; selecting a mapping function from among the predetermined set of mapping functions according to the value of said selection signal; and mapping the luminance levels represented by said video signal according to the mapping function thus selected.
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Specification