Method and system for contrast enhancement of digital video

A method for enhancing video picture contrast, comprising:

• determining an active window for a picture extracted from an input video signal;
• determining characteristics of a histogram calculated for luminance values of pixels in the active window of the picture;
• and
• mapping the luminance value of each pixel in the picture in accordance with a mapping function selected on the basis of determined characteristics of the histogram.

A method for enhancing video picture contrast, comprising:

• receiving an input video signal at a histogram data circuit, a black bar detector circuit, a scene change detector, and a picture mapping circuit;
• calculating a histogram for luminance values of pictures in an active window extracted from the picture in the histogram data circuit, the active window determined by including only pixels from the picture that do not form part of any black bars at the boundary of the picture as determined in the black bars detector circuit;
• determining characteristics of the histogram in a histogram analysis circuit;
• and
• mapping the luminance value of each pixel in the picture in a picture mapping circuit in accordance with a mapping function selected on the basis of determined characteristics from the histogram and generating therefrom an output video signal.

A method for enhancing video picture contrast, comprising:

• determining an active window for a picture extracted from an input video signal by including only pixels from the picture that did not form part of any black bars at the boundaries of the picture:
• calculating a histogram for luminance values of pixels in the active window of the picture,
• determining the characteristics of the histogram, including determining whether the picture is part of a smooth scene sequence, and if the picture is part of a smooth scene sequence, preventing the selection of a new mapping function, and further including the step of calculating the weighted difference between the value of each bin of the histogram and a corresponding value in the same bin of an earlier histogram relating to an earlier processed picture, and determining for the histogram a maximum number of M bins, where M is an integer, where each bin in the histogram is sequentially numbered n, according to the pattern n, n+1, n+2, and so on, where n is greater than or equal to zero, the sum of Q consecutive bins is determined by taking the sum of Q consecutive terms, starting from the term n=0 for all terms of n except for the terms of n greater than the term (M−n), and further including the steps of temporarily filtering the value of each bin of the histogram and determining the maximum sum of the calculated sum of Q consecutive bins, including determining the corresponding bin position for the maximum sum of each calculated sum of Q consecutive bins;
• and
• mapping the luminance value of each pixel in the picture in accordance with a selected mapping function based on the determined characteristics of the histogram, including the step of determining from the histogram whether the picture is low in contrast, and if the picture is determined to be low in contrast, determining whether a gray stretch mapping function is suitable for correcting the contrast, and where the picture is not low on contrast, determining whether the picture is over contrast.