ENCODING, DECODING, AND REPRESENTING HIGH DYNAMIC RANGE IMAGES

• US 20160134873A1
• Filed: 01/18/2016
• Published: 05/12/2016
• Est. Priority Date: 04/15/2011
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: JIA, Wenhui, NINAN, Ajit, TEN, Arkady, WARD, Gregory John
• Granted Patent: US 9,654,781 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/136 Incoming video signal characteristics or properties
• CPC Class Codes: H04N 19/169 characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
• CPC Class Codes: H04N 19/182 the unit being a pixel
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/50 using predictive coding H04N19/61 takes precedence
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 23/85 for matrixing
• CPC Class Codes: H04N 9/67 for matrixing camera processing pipelines for matrixing of colour signals H04N23/85
• CPC Class Codes: H04N 9/77 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

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.

Claims

1. An apparatus comprising a bitstream stored on a non-transitory machine-readable media, wherein the bitstream is characterized by high dynamic range image data in a compressed format, wherein the compressed format comprises:

a compressed JPEG base image;

high dynamic range (HDR) reconstruction data, wherein the HDR reconstruction data comprise a quantized luma ratio image and one or more sets of quantized residual chroma values; and

a JPEG application marker separating the base image from the HDR reconstruction data.

2. The apparatus of claim 1, wherein the quantized luma ratio image comprises quantized log ratio pixel values and the compressed format further comprises a minimum log ratio pixel value and a maximum log ratio pixel value.

3. The apparatus of claim 1, wherein the compressed format further comprises a minimum residual chroma pixel value (Cb_min) and a maximum residual chroma pixel value (Cb_max).

4. The apparatus of claim 1, wherein the compressed base image comprises a compressed tone-mapped image generated from a high dynamic range image.

5. The apparatus of claim 1, wherein the apparatus further comprises a processor configured to execute instructions to:

parse the bitstream to extract the compressed JPEG base image and the HDR reconstruction data;

generate a decoded base image based on the compressed JPEG based image;

extract quantization parameters from the HDR reconstruction data;

generate a dequantized luma ratio image and one or more sets of dequantized residual chroma values based on the quantization parameters, the quantized luma ratio image, and the one or more sets of quantized residual chroma values;

linearize the dequantized luma ratio image to generate a linearized luma ratio image; and

generate 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.

6. The apparatus of claim 5 wherein to generate the output HDR image further comprises executing instructions with the processor to:

generate an intermediate image by adding the one or more sets of dequantized residual chroma values to the decoded base image; and

generate the output HDR image by multiplying the intermediate image with the linearized luma ratio image.

7. The apparatus of claim 5, wherein the quantization parameters comprise a minimum log ratio pixel value (lr_min) and a maximum log ratio pixel value (lr_max), and given a quantized log ratio pixel value (H), a corresponding unquantized log ratio luma value lr is determined as

8. The apparatus of claim 5, wherein the quantization parameters comprise a minimum residual chroma pixel value (Cb_min) and a maximum residual chroma pixel value (Cb_max), and given a quantized residual chroma pixel value (U), a corresponding intermediate residual chroma pixel value Cb is determined as

9. The apparatus of claim 5, wherein linearizing the dequantized luma ratio image comprises applying an inverse logarithm function to pixels of the dequantized luma ratio image.