Localized, adaptive video contrast enhancement using controlled histogram equalization

A method for processing a received video signal, said method comprising:

• deriving, from said received video signal of an image, a plurality of histograms corresponding to a plurality of luminance regions in said image;
• providing guard bands between said luminance regions;
• deriving a plurality of cumulative density functions (CDFs) from said plurality of histograms;
• and
• providing an output pixel of an output video signal by processing an input pixel based on one of said plurality of CDFs corresponding to a luminance region in which said input pixel falls.

Apparatus for processing a received video signal, said apparatus comprising:

• means for deriving a first histogram of said received video signal of an image wherein the first histogram comprises statistical information regarding luminance of pixels in the image;
• means for clamping said first histogram at a maximum value, and distributing points in said first histogram above said maximum value to other luminance values in said first histogram to derive a second histogram;
• means for deriving a cumulative density function (CDF) from said second histogram;
• and
• means for providing an output pixel of an output video signal by processing an input pixel and said cumulative density function.

Apparatus for processing a received video signal, said apparatus comprising:

• means for deriving a plurality of histograms from said received video signal of an image corresponding to a plurality of luminance regions in said image;
• means for providing guard bands between said luminance regions;
• means for deriving a plurality of cumulative density functions (CDFs) from said plurality of histograms;
• and
• processing means for providing an output pixel of an output video signal by processing an input pixel based on one of said plurality of CDFs corresponding to a luminance region in which said input pixel falls.

Apparatus for processing a received video signal, said apparatus comprising:

• circuitry that derives a first histogram of said received video signal of an image wherein the first histogram comprises statistical information regarding luminance of pixels in the image;
• circuitry that clamps said first histogram at a maximum value, and distributes points in said first histogram above said maximum value to other luminance values in said first histogram to derive a second histogram;
• and
• a processor that:
• derives a cumulative density function (CDF) from said second histogram, and
• provides an output pixel of an output video signal by processing an input pixel and said cumulative density function.

Apparatus for processing a received video signal, said apparatus comprising:

• circuitry that derives a plurality of histograms from said received video signal of an image corresponding to a plurality of luminance regions in said image, and provides guard bands between said luminance regions;
• and
• a processor that:
• derives a plurality of cumulative density functions (CDFs) from said plurality of histograms;
• and
• provides an output pixel of an output video signal by processing an input pixel based on one of said plurality of CDFs corresponding to a luminance region in which said input pixel falls.