APPARATUS AND METHODS FOR ENCODING, DECODING AND REPRESENTING HIGH DYNAMIC RANGE IMAGES

• US 20080310501A1
• Filed: 07/31/2007
• Published: 12/18/2008
• Est. Priority Date: 04/23/2004
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: BrightSide Technologies Inc (Dolby Laboratories Incorporated)
• Inventors: WARD, Gregory John, SIMMONS, Maryann
• Granted Patent: US 8,514,934 B2
• Time in Patent Office: Days
• US Class Current: 375/240.02
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/90 Dynamic range modification of images or parts thereof
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: G09G 5/10 Intensity circuits
• CPC Class Codes: H04N 1/3871 the composed originals being of different kinds, e.g. low- and high-resolution originals
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/182 the unit being a pixel
• CPC Class Codes: H04N 19/184 the unit being bits, e.g. of the compressed video stream
• 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 19/463 by compressing encoding parameters before transmission
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]

Abstract

A data structure defining a high dynamic range image comprises a tone map having a reduced dynamic range and HDR information. The high dynamic range image can be reconstructed from the tone map and the HDR information. The data structure can be backwards compatible with legacy hardware or software viewers. The data structure may comprise a JFIF file having the tone map encoded as a JPEG image with the HDR information in an application extension or comment field of the JFIF file, or a MPEG file having the tone map encoded as a MPEG image with the HDR information in a video or audio channel of the MPEG file. Apparatus and methods for encoding or decoding the data structure may apply pre- or post correction to compensate for lossy encoding of the high dynamic range information.

Claims

1. Apparatus for decoding high dynamic range image data, the apparatus comprising:

an input for receiving a data structure comprising a tone map portion and a high dynamic range (HDR) image portion;

a decoder for decoding the tone map portion to yield a first image;

a correction subsystem configured to downsample the first image to yield a downsampled image, determine a ratio between a pixel value in the first image and a corresponding pixel value in the downsampled image and apply a correction based upon the ratio to a corresponding pixel in image data represented by the HDR portion.

2. Apparatus according to claim 1 wherein the decoder comprises a JPEG decoder.

3. Apparatus according to claim 1 wherein the decoder comprises an MPEG decoder.

4. Apparatus according to claim 1 wherein:

the correction subsystem is configured to upsample the downsampled image to yield an upsampled image; and

,

wherein the correction subsystem is configured to determine the ratio between the pixel value in the first image and the corresponding pixel value in the downsampled image by a process comprising dividing the first image by the upsampled image.

5. Apparatus according to claim 4 wherein the correction subsystem is configured to apply the correction based upon the ratio by a process comprising computing a power of the ratio.

6. Apparatus according to claim 5 wherein the correction sub-system is configured to compute the σ

power of the ratio, where σ

is a ratio of the variance of the image data represented in the HDR portion to a variance of luminance values in the downsampled image.

7. A viewer capable of processing images for display, the viewer comprising:

a decoder for decoding tone map data to provide first image data;

means for downsampling the first image data to provide downsampled image data;

means for upsampling the downsampled image data to provide upsampled image data;

means for correcting ratio image data based on differences between the upsampled image data and the first image data to yield corrected ratio data;

means for multiplying the first image data by the corrected ratio image data to provide high dynamic range data;

a display for displaying the high dynamic range data.

8. A display comprising:

a data store containing a data structure representing a high dynamic range image having an initial dynamic range, the data structure comprising a tone map portion and a high dynamic range information portion,

the tone map portion containing tone map information representing the image, the tone map portion having a reduced dynamic range less than the initial dynamic range;

the high dynamic range information portion containing information describing ratios of values in the tone map portion to corresponding values of the high dynamic range image;

a processor configured to reconstruct a high dynamic range image from the data structure by decoding the tone map portion to yield first image data and modifying the first image data according to the information to yield image data representing the high dynamic range image; and

,

a display for displaying the high dynamic range image.