Methods and apparatuses for encoding an HDR images, and methods and apparatuses for use of such encoded images
First Claim
1. A method of encoding a high dynamic range image (M_HDR), comprising the steps of:
- converting the high dynamic range image to an image of lower luminance dynamic range (LDR_o) by applying;
a) normalization of the high dynamic range image to a scale of the luma axis being [0,1] yielding a normalized high dynamic range image with normalized colors having normalized luminances (Yn_HDR),b) calculating a gamma function on the normalized luminances yielding gamma-converted luminances (xg),c) applying a first tone mapping yielding lumas (v) which is defined as v=log(1+(RHO−
1)*xg)/log(RHO), with RHO having a predetermined value, andd) applying an arbitrary monotonically increasing tone mapping function mapping the lumas to output lumas (Yn_LDR) of the lower dynamic range image (LDR_o); and
outputting in an image signal (S_im) a codification of the pixel colors of the lower luminance dynamic range image (LDR_o), andoutputting in the image signal (S_im) values encoding the function shapes of the above color conversions b to d as metadata, or values for their inverse functions, which metadata allows a receiver to reconstruct a reconstructed high dynamic range image (Rec_HDR) from the lower luminance dynamic range image (LDR_o), wherein RHO or a value being a function of RHO is outputted in the metadata.
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Abstract
Encoding a high dynamic range image (M_HDR), comprising: 1. converting the high dynamic range image to an image of lower luminance dynamic range (LDR_o) by applying the acts of: a) scaling the high dynamic range image to a predetermined scale of the luma axis such as [0,1], b) a sensitivity tone mapping which changes the brightnesses of pixel colors falling within at least a subrange comprising the darker colors in the high dynamic range image, c) a gamma function, and d) applying an arbitrary monotonically increasing function mapping the lumas resulting from performing the acts b and c to output lumas of the lower dynamic range image (LDR_o); and 2. outputting in an image signal (S_im) a codification of the pixel colors of the lower luminance dynamic range image (LDR_o), and 3. outputting in the image signal (S_im) values encoding the functional behavior of the above color conversions as metadata, or values for the inverse functions, which metadata allows to reconstruct a high dynamic range image (Rec_HDR) from the lower luminance dynamic range image (LDR_o).
14 Citations
9 Claims
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1. A method of encoding a high dynamic range image (M_HDR), comprising the steps of:
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converting the high dynamic range image to an image of lower luminance dynamic range (LDR_o) by applying; a) normalization of the high dynamic range image to a scale of the luma axis being [0,1] yielding a normalized high dynamic range image with normalized colors having normalized luminances (Yn_HDR), b) calculating a gamma function on the normalized luminances yielding gamma-converted luminances (xg), c) applying a first tone mapping yielding lumas (v) which is defined as v=log(1+(RHO−
1)*xg)/log(RHO), with RHO having a predetermined value, andd) applying an arbitrary monotonically increasing tone mapping function mapping the lumas to output lumas (Yn_LDR) of the lower dynamic range image (LDR_o); and outputting in an image signal (S_im) a codification of the pixel colors of the lower luminance dynamic range image (LDR_o), and outputting in the image signal (S_im) values encoding the function shapes of the above color conversions b to d as metadata, or values for their inverse functions, which metadata allows a receiver to reconstruct a reconstructed high dynamic range image (Rec_HDR) from the lower luminance dynamic range image (LDR_o), wherein RHO or a value being a function of RHO is outputted in the metadata. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An image encoder arranged to encode a high dynamic range image (M_HDR), comprising:
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a dynamic range conversion unit arranged to convert the high dynamic range image to an image of lower luminance dynamic range (LDR_o), the dynamic range conversion unit comprising; a) a normalizer arranged to normalize the high dynamic range image to a luma axis ranging over [0,1] and to output normalized luminances (Yn_HDR), b) a gamma conversion unit arranged to apply a gamma function to the normalized luminances and to output gamma-converted luminances (xg), c) a first tone mapping unit arranged to apply a first tone mapping which yields lumas (v) which is defined as v=log(1+(RHO−
1)*xg)/log(RHO), with RHO having a predetermined value,d) an arbitrary tone mapping unit arranged to apply an arbitrary monotonically increasing function which maps the lumas (v) to output lumas (Yn_LDR) of the lower dynamic range image (LDR_o); and
the image encoder further comprising;an image compressor arranged to apply a data reduction transformation to the colors of the lower dynamic range image (LDR_o) which colors are organized in component images, and which reduction transformation involves at least applying a DCT transform to blocks of adjacent color component values, yielding a compressed codification (LDR13 c) of the pixel colors of the lower luminance dynamic range mage; and a formatter arranged to output in an image signal (S_im) the compressed codification (LDR_c), and arranged to in addition output in the image signal (S_im) values encoding the function shape of the color conversions as metadata, or values for their inverse functions, which metadata allows a receiver to reconstruct a high dynamic range image (Rec_HDR) based upon the lower luminance dynamic range image (LDR_o), the values comprising RHO or a value being a function of RHO.
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8. An image decoder arranged to receive a high dynamic range image signal (S_im) and comprising:
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a deformatter arranged to obtain a compressed pixellized lower dynamic range image (LDR_c) and parameter data (P) out of the image signal (S_im); and a decompressor arranged to apply at least an inverse DCT transform to the compressed pixellized lower dynamic range image (LDR_c) to obtain a pixellized lower dynamic range image (LDR_t); and
a dynamic range conversion unit (153) arranged to transform the lower dynamic range image (LDR_t) into a reconstructed high dynamic range image (Rec_HDR), wherein the dynamic range conversion unit comprises;
a) an arbitrary tone mapping unit arranged to apply an arbitrary monotonically increasing tone mapping, the parameters which define it (P_CC) being received in the parameter data (P), b) a first tone mapping unit arranged to apply a mapping as defined by a function of the form;
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9. A method of decoding a high dynamic range image signal (S_im) comprising:
obtaining a compressed pixellized lower dynamic range image (LDR_c) and parameter data (P) out of the image signal (S_im);
decompressing the compressed pixellized lower dynamic range image (LDR_c) by applying at least an inverse DCT transform to the compressed pixellized lower dynamic range image (LDR_c) to obtain a pixellized lower dynamic range image (LDR_t); and
transforming the lower dynamic range image (LDR_t) into a reconstructed high dynamic range image (Rec_HDR), by;
a) applying an arbitrary monotonically increasing tone mapping, the parameters which define it (P_CC) being received in the parameter data (P), b)applying a mapping as defined by at least one received parameter (RHO) the mapping being defined by a function of the form;
Specification