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Brightness adjustment of images using digital scene analysis

  • US 5,724,456 A
  • Filed: 03/31/1995
  • Issued: 03/03/1998
  • Est. Priority Date: 03/31/1995
  • Status: Expired due to Term
First Claim
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1. A system for processing a digital image signal representing an image, said image containing both luminance data and chrominance data, to map the luminance data to a tonal reproduction capability of a destination application, said system comprising:

  • means for acquiring the image signal and separating the luminance data from the image signal;

    an input buffer for storing said luminance data;

    means for reading and partitioning said luminance data from said input buffer into a plurality of image blocks of predetermined size;

    means for determining an average luminance block value for each said image block;

    means for selectively combining preselected ones of said image blocks of said luminance data into sectors;

    means for determining a difference between a maximum said average luminance block value and a minimum said average luminance block value of each sector, and comparing said difference with a predetermined threshold value;

    means for identifying an active sector as one where said difference exceeds said predetermined threshold value;

    means for determining an average luminance sector value for each active sector as an average of the maximum and minimum average luminance block values of each sector;

    means for weighting and counting a number of active sectors corresponding to each said average luminance sector value;

    means for generating a histogram of said number of active sectors versus said average luminance sector values;

    means for selecting a tonal reproduction range corresponding to the tonal reproduction capability of the destination application; and

    means for mapping said average luminance sector values into said tonal reproduction range of said destination application and generating a digital output signal corresponding to said mapping.

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