Method and apparatus for producing a contrast enhanced image

An apparatus for enhancing an input image to produce a contrast enhanced output image, the apparatus comprising:

• a filter operably configured to produce a contrast value for each pixel in the input image, said contrast value being proportional to an intensity gradient between each respective pixel and at least one pixel adjacent said respective pixel;
• a pixel selector operably configured to select pixels in said input image having respective contrast values that meet a first criterion thereby forming a selected plurality of pixels;
• a frequency distribution generator operably configured to produce a frequency distribution of intensity values of said selected plurality of pixels;
• an intensity range selector operably configured to select at least one range of intensity values in said frequency distribution that meet a second criterion, thereby producing a selected range of intensity values for enhancement;
• an output image generator operably configured to produce to produce a tone mapping function for mapping pixel intensity values in the input image to pixel intensity values in the output image and to produce the contrast enhanced output image by computing an output intensity value according to said tone mapping function for every pixel in the input image, wherein said producing comprises at least one of:
• selectively expanding the pixel intensity values of all of those pixels in the input image with pixel intensity values that fall within said selected range of intensity values;
• and
• selectively compressing the pixel intensity values of all of those pixels in the input image with pixel intensity values that fall outside said selected range of intensity values.

A non-transitory computer readable medium encoded with processor executable code for directing a processor circuit to execute a method for enhancing an input image to produce a contrast enhanced output image, the codes directing the processor circuit to:

• produce a contrast value for each pixel in the input image, said contrast value being proportional to an intensity gradient between each respective pixel and at least one pixel adjacent said respective pixel;
• select pixels in said input image having respective contrast values that meet a first criterion, thereby forming a selected plurality of pixels;
• produce a frequency distribution of intensity values of said selected plurality of pixels;
• select at least one range of intensity values in said frequency distribution that meet a second criterion, thereby producing a selected range of intensity values for enhancement;
• produce a tone mapping function for mapping pixel intensity values in the input image to pixel intensity values in the output image;
• produce the contrast enhanced output image by computing an output intensity value according to said tone mapping function for every pixel in the input image, wherein said producing comprises at least one of:
• selectively expanding the pixel intensity values of all of those pixels in the input image with pixel intensity values that fall within said selected range of intensity values;
• and
• selectively compressing the pixel intensity values of all of those pixels in the input image with pixel intensity values that fall outside said selected range of intensity values.

An apparatus for enhancing an input image to produce a contrast enhanced output image, the apparatus comprising:

• means for producing a contrast value for each pixel in the input image, said contrast value being proportional to an intensity gradient between each respective pixel and at least one pixel adjacent said respective pixel;
• means for selecting pixels in said input image having respective contrast values that meet a first criterion, thereby forming a selected plurality of pixels;
• means for producing a frequency distribution of intensity values of said selected plurality of pixels;
• means for selecting at least one range of intensity values in said frequency distribution that meet a second criterion, thereby producing a selected range of intensity values for enhancement;
• means for producing a tone mapping function for mapping pixel intensity values in the input image to pixel intensity values in the output image;
• means for producing the contrast enhanced output image computing an output intensity value according to said tone mapping function for every pixel in the input image, wherein said means for producing comprises, at least one of:
• means for selectively expanding the pixel intensity values of all of those pixels in the input image with pixel intensity values that fall within said selected range of intensity values;
• and
• means for selectively compressing the pixel intensity values of all of those pixels in the input image with pixel intensity values that fall outside said selected range of intensity values.