US-12621501-B2 - Signal reshaping for high dynamic range signals

US12621501B2US 12621501 B2US12621501 B2US 12621501B2US-12621501-B2

Abstract

In a method to improve backwards compatibility when decoding high-dynamic range images coded in a wide color gamut (WCG) space which may not be compatible with legacy color spaces, hue and/or saturation values of images in an image database are computed for both a legacy color space (say, YCbCr-gamma) and a preferred WCG color space (say, IPT-PQ). Based on a cost function, a reshaped color space is computed so that the distance between the hue values in the legacy color space and rotated hue values in the preferred color space is minimized. HDR images are coded in the reshaped color space. Legacy devices can still decode standard dynamic range images assuming they are coded in the legacy color space, while updated devices can use color reshaping information to decode HDR images in the preferred color space at full dynamic range.

Inventors

Robin Atkins
Peng Yin
Taoran Lu
Jaclyn Anne Pytlarz

Assignees

DOLBY LABORATORIES LICENSING CORPORATION

Dates

Publication Date: 20260505
Application Date: 20241126

Claims (4)

1 . An apparatus to perform image color conversion with a processor, the apparatus comprising: an input to receive an input image in a linear RGB color space with normalized RGB values in [0, 1]; and a processor, wherein the processor: generates a first image in a first-LMS color space by applying a first color transformation to the input image; applies a non-linear function to each color component of the first image to generate color components of a second image in a second-LMS color space; and generates an output image in an IPT-PQ color space by applying a second color transformation matrix to the color components of the second image, wherein the second color transformation matrix is: ( 0.4 0.4 0.2 4.455 - 4.851 0.396 0.8056 0.3572 - 1.1628 ) .
2 . The apparatus of claim 1 , wherein the non-linear function comprises an inverse of an electro-optical transfer function.
3 . The apparatus of claim 2 , wherein the electro-optical transfer function is determined according to the SMPTE ST 2084 specification.
4 . The apparatus of claim 1 , wherein the non-linear function is based on the Hybrid Log-Gamma (HLG) function.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisional of U.S. patent application Ser. No. 18/899,400, filed on Sep. 27, 2024, which is a continuation of U.S. patent application Ser. No. 18/780,325, filed on Jul. 22, 2024, now U.S. Pat. No. 12,167,048, which is a continuation of U.S. patent application Ser. No. 18/678,794, filed on May 30, 2024, now U.S. Pat. No. 12,120,358, which is a continuation of U.S. patent application Ser. No. 18/630,786, filed on Apr. 9, 2024, now U.S. Pat. No. 12,120,357, which is a continuation of U.S. patent application Ser. No. 18/616,959, filed on Mar. 26, 2024, now U.S. Pat. No. 12,041,275, which is a continuation of U.S. patent application Ser. No. 18/405,874, filed on Jan. 5, 2024, Now U.S. Pat. No. 12,028,555, which is a continuation of U.S. patent application Ser. No. 18/385,724, filed on Oct. 31, 2023, now U.S. Pat. No. 11,910,025, which is a continuation of U.S. patent application Ser. No. 18/215,129, filed on Jun. 27, 2023, now U.S. Pat. No. 11,924,477, which is a continuation of U.S. patent application Ser. No. 17/992,603, filed on Nov. 22, 2022, now U.S. Pat. No. 11,785,263, which is a continuation of U.S. patent application Ser. No. 17/234,815, filed on Apr. 20, 2021, now U.S. Pat. No. 11,582,490, which is a divisional of U.S. patent application Ser. No. 16/532,924, filed on Aug. 6, 2019, now U.S. Pat. No. 11,025,961, which is a continuation of U.S. patent application Ser. No. 15/749,231, filed on Jan. 31, 2018, now U.S. Pat. No. 10,432,977, which is the national stage entry for PCT/US2016/045362, filed on Aug. 3, 2016, which claims the benefit of priority from U.S. Provisional Applications Ser. No. 62/302,073, filed on Mar. 1, 2016, U.S. Provisional Applications Ser. No. 62/300,012, filed on Feb. 25, 2016, U.S. Provisional Applications Ser. No. 62/278,362, filed on Jan. 13, 2016, U.S. Provisional Applications Ser. No. Ser. No. 62/202,980, filed on Aug. 10, 2015, and U.S. Provisional Applications Ser. No. 62/200,797 filed on Aug. 4, 2015, each of which is incorporated herein by reference in its entirety. TECHNOLOGY The present document relates generally to images. More particularly, an embodiment of the present invention relates to signal reshaping of images with high dynamic range to improve backwards compatibility. BACKGROUND As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human visual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest darks (blacks) to brightest whites (i.e., highlights). In this sense, DR relates to a ‘scene-referred’ intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably. As used herein, the term high dynamic range (HDR) relates to a DR breadth that spans the some 14-15 orders of magnitude of the human visual system (HVS). In practice, the DR over which a human may simultaneously perceive an extensive breadth in intensity range may be somewhat truncated, in relation to HDR. As used herein, the terms enhanced dynamic range (EDR) or visual dynamic range (VDR) may individually or interchangeably relate to the DR that is perceivable within a scene or image by a human visual system (HVS) that includes eye movements, allowing for some light adaptation changes across the scene or image. As used herein, EDR may relate to a DR that spans 5 to 6 orders of magnitude. Thus while perhaps somewhat narrower in relation to true scene referred HDR, EDR nonetheless represents a wide DR breadth and may also be referred to as HDR. In practice, images comprise one or more color components (e.g., luma Y and chroma Cb and Cr) wherein each color component is represented by a precision of n-bits per pixel (e.g., n=8). Using linear luminance coding, images where n≤8 (e.g., color 24-bit JPEG images) are considered images of standard dynamic range, while images where n>8 may be considered images of enhanced dynamic range. EDR and HDR images may also be stored and distributed using high-precision (e.g., 16-bit) floating-point formats, such as the OpenEXR file format developed by Industrial Light and Magic. Given a video stream, information about its coding parameters is typically embedded in the bit stream as metadata. As used herein, the term “metadata” relates to any auxiliary information that is transmitted as part of the coded bitstream and assists a decoder to render a decoded image. Such metadata may include, but are not limited to, color space or gamut information, reference display parameters, and auxiliary signal parameters, as those described herein. Most consumer desktop displays currently support luminance of