Brightness adjustment of images using digital scene analysis

An image processing method for processing a digital image signal representing an image, said image containing both luminance data and chrominance data, to optimally map the luminance data to a tonal reproduction capability of a destination application, said method comprising the steps of:

• acquiring the image signal and separating the luminance data from the image signal;
• storing said luminance data in an input buffer;
• reading and partitioning said luminance data from said input buffer into a plurality of image blocks of predetermined size;
• determining an average luminance block value for each said image block;
• combining preselected ones of said image blocks of said luminance data into sectors;
• 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;
• identifying an active sector as one where said difference exceeds said predetermined threshold value;
• 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;
• weighting and counting a number of active sectors corresponding to each said average luminance sector value;
• generating a histogram of said number of active sectors versus said average luminance sector values;
• selecting a tonal reproduction range corresponding to the tonal reproduction capability of the destination application;
• and
• 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.

A method for processing a digital input image and exporting the processed image to a downstream application having a given tonal reproduction range, said method comprising the steps of:

• partitioning the input image into sectors of predetermined size;
• determining for each said sector a luminance activity defined as a difference in luminance between at least two pixels within each said sector;
• generating an average luminance value for each said sector having said luminance activity greater than a predetermined threshold value;
• generating a count of sectors having each said average luminance value;
• mapping said average luminance values, having counts falling within a predetermined selection criterion, into the tonal reproduction range;
• and
• exporting the processed image to the downstream application in response to said mapped luminance values.

A system for processing a digital input image and exporting the processed image to a destination application having a given tonal reproduction range, said system comprising:

• means for partitioning the input image into sectors of predetermined size;
• means for determining for each said sector a luminance activity defined as a difference in luminance between at least two pixels within each said sector;
• means for generating an average luminance value for each said sector having said luminance activity greater than a predetermined threshold value;
• means for generating a count of sectors having each said average luminance value;
• means for mapping said average luminance values, having counts falling within a predetermined selection criterion, into the tonal reproduction range;
• and
• means for exporting the processed image on the destination application in response to said mapped luminance values.