Adaptive ratio images in HDR image representation
First Claim
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1. A method to code a high dynamic range (HDR) image with a processor, the method comprising:
- receiving an input image with a first dynamic range;
generating a tone-mapped image based on the input image, wherein the tone-mapped image has a dynamic range lower than the first dynamic range;
generating a ratio image (YR), the ratio image comprising luminance pixel values of the input image divided pixel by pixel by corresponding luminance pixel values in the tone-mapped image;
applying an invertible function (F) to the ratio image to generate a modified ratio image (F(YR));
generating a look-up table to represent the inverse of the invertible function (F−
1), wherein applying the look-up table (F−
1) to the modified ratio image generates an approximation of the ratio image; and
generating a coded HDR image based on the tone-mapped image and the modified ratio image, wherein the invertible function is selected so that when applying its inverse to the modified ratio image, the distance between the ratio image and the approximation of the ratio image is minimized according to a predetermined measure.
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Abstract
Image encoding and decoding are described. An input HDR image is coded using a coded tone-mapped image, a coded invertible function of a ratio image, and a look-up table representing the inverse of the invertible function, wherein the ratio image represents the pixel by pixel ratio of the luminance pixel values of the input image and the corresponding luminance values in the tone-mapped image. A method to generate the invertible function based on a cumulative histogram of the ratio image is presented.
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Citations
14 Claims
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1. A method to code a high dynamic range (HDR) image with a processor, the method comprising:
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receiving an input image with a first dynamic range; generating a tone-mapped image based on the input image, wherein the tone-mapped image has a dynamic range lower than the first dynamic range; generating a ratio image (YR), the ratio image comprising luminance pixel values of the input image divided pixel by pixel by corresponding luminance pixel values in the tone-mapped image; applying an invertible function (F) to the ratio image to generate a modified ratio image (F(YR)); generating a look-up table to represent the inverse of the invertible function (F−
1), wherein applying the look-up table (F−
1) to the modified ratio image generates an approximation of the ratio image; andgenerating a coded HDR image based on the tone-mapped image and the modified ratio image, wherein the invertible function is selected so that when applying its inverse to the modified ratio image, the distance between the ratio image and the approximation of the ratio image is minimized according to a predetermined measure. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification