Encoding, decoding, and representing high dynamic range images

Patent metadata

Field	Value
Publication number	US-9819938-B2
Application number	US-201715482689-A
Country	US
Kind code	B2
Filing date	Apr 7, 2017
Priority date	Apr 15, 2011
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

Techniques are provided to encode and decode image data comprising a tone mapped (TM) image with HDR reconstruction data in the form of luminance ratios and color residual values. In an example embodiment, luminance ratio values and residual values in color channels of a color space are generated on an individual pixel basis based on a high dynamic range (HDR) image and a derivative tone-mapped (TM) image that comprises one or more color alterations that would not be recoverable from the TM image with a luminance ratio image. The TM image with HDR reconstruction data derived from the luminance ratio values and the color-channel residual values may be outputted in an image file to a downstream device, for example, for decoding, rendering, and/or storing. The image file may be decoded to generate a restored HDR image free of the color alterations.

First claim

The invention claimed is:

1. A processor non-transitory readable medium having stored thereon an image file structure for representing a high dynamic range image in a compressed format, the image file structure comprising:
a compressed tone-mapped image in a standard-based compression format; and
high dynamic range (HDR) reconstruction data, wherein the HDR reconstruction data comprise:
a quantized luma ratio image comprising log ratio pixel values;
luma de-quantization parameters for the quantized log ratio pixel values;
one or more sets of quantized residual chroma values; and
chroma de-quantization parameters for the one or more sets of quantized residual chroma values, wherein the compressed tone-mapped image is separated by the HDR reconstruction data using one or more application markers.

2. The processor non-transitory readable medium of claim 1 , wherein the log ratio pixel values represent the logarithm of dividing, on an individual pixel basis, luminance values of an HDR input image with luminance values of an uncompressed version of the compressed tone-mapped image.

3. The processor non-transitory readable medium of claim 1 , wherein the luma de-quantization parameters comprise a minimum log ratio pixel value and a maximum log ratio pixel value.

4. The processor non-transitory readable medium of claim 1 , wherein the chroma de-quantization parameters comprise
a minimum residual chroma pixel value (Cb min ) and a maximum residual chroma pixel value (Cb max ).

5. The processor non-transitory readable medium of claim 2 , wherein the compressed tone-mapped image comprises a compressed tone-mapped image generated from the HDR input image.

6. The method of claim 1 wherein the standard-based compression format is the JPEG format.

7. A method for decoding high-dynamic range images with a processor, the method comprising:
receiving a coded bitstream comprising a high-dynamic range image encoded according to the file structure in claim 1 ;
parsing the coded bitstream to extract the compressed tone-mapped image and the HDR reconstruction data;
generating a decoded base image based on the compressed tone-mapped image;
extracting the luma de-quantization parameters from the HDR reconstruction data;
extracting the quantized luma ratio image;
generating a dequantized luma ratio image based on the quantized luma ratio image and the luma de-quantization parameters;
extracting the chroma de-quantization parameters;
extracting the one or more sets of quantized residual chroma values;
generating one or more sets of dequantized residual chroma values based on the chroma de-quantization parameters and the one or more sets of quantized residual chroma values;
linearizing the dequantized luma ratio image to generate a linearized luma ratio image; and
generating an output HDR image based on the one or more sets of dequantized residual chroma values, the linearized luma ratio image, and the decoded base image.

8. The method of claim 7 wherein generating the output HDR image further comprises:
generating an intermediate image by adding the one or more sets of dequantized residual chroma values to the decoded base image; and
generating the output HDR image by multiplying the intermediate image with the linearized luma ratio image.

9. The method of claim 7 , wherein given a quantized log ratio pixel value H, a corresponding unquantized log ratio luma value lr is determined as

lr
=

H
⁡

(

lr
max

-

lr
min

255

)

+

lr
min

,

wherein lr min denotes a minimum log ratio pixel value luma de-quantization parameter and lr max denotes a maximum log ratio pixel value luma de-quantization parameter.

10. The method of claim 7 , wherein given a quantized residual chroma pixel value U, a corresponding intermediate residual chroma pixel value Cb is determined as

Cb
=

U
⁡

(

Cb
max

-

Cb
min

255

)

+

Cb
min

,

wherein Cb min denotes a minimum residual chroma pixel value chroma de-quantization parameter and Cb max denotes a maximum residual chroma pixel value chroma de-quantization parameter.

11. The method of claim 7 , wherein linearizing the dequantized luma ratio image comprises applying an inverse logarithm function to pixels of the dequantized luma ratio image.

12. The method of claim 7 , further comprising applying a color space conversion and gamma decoding to the decoded base image to generate a gamma-decoded base image; and
generating the output HDR image based on the one or more sets of dequantized residual chroma values, the linearized luma ratio image, and the gamma-decoded base image.

13. The method of claim 12 , further comprising applying a color space conversion to the dequantized residual chroma values to generate color-transformed residual chroma values; and
generating the output HDR image based on the one or more sets of color-transformed residual chroma values, the linearized luma ratio image, and the gamma-decoded base image.

Assignees

• Dolby Laboratories Licensing Corp

Inventors

• Jia Wenhui
• Ninan Ajit
• Ten Arkady
• Ward Gregory John

Classifications

• H04N23/741

  by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors · CPC title

• H04N19/136

  Incoming video signal characteristics or properties · CPC title

• H04N19/124 Primary

  Quantisation · CPC title

• H04N9/77 Primary

  Circuits for processing the brightness signal and the chrominance signal relative to each other, e.g. adjusting the phase of the brightness signal relative to the colour signal, correcting differential gain or differential phase (circuits for matrixing H04N9/67) · CPC title

• H04N19/44

  Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder · CPC title