US-20260127724-A1 - APPARATUS AND METHOD FOR DYNAMIC RANGE TRANSFORMING OF IMAGES

US20260127724A1US 20260127724 A1US20260127724 A1US 20260127724A1US-20260127724-A1

Abstract

An image processing apparatus comprises a receiver ( 201 ) for receiving an image signal which comprises at least an encoded image and a target display reference. The target display reference is indicative of a dynamic range of a target display for which the encoded image is encoded. A dynamic range processor ( 203 ) generates an output image by applying a dynamic range transform to the encoded image in response to the target display reference. An output ( 205 ) then outputs an output image signal comprising the output image, e.g. to a suitable display. The dynamic range transform may furthermore be performed in response to a display dynamic range indication received from a display. The invention may be used to generate an improved High Dynamic Range (HIDR) image from e.g. a Low Dynamic Range (LDR) image, or vice versa.

Inventors

Charles Leonardus Cornelius Maria Knibbeler
Renatus Josephus Van Der Vleuten
Wiebe De Haan

Assignees

KONINKLIJKE PHILIPS N.V.

Dates

Publication Date: 20260507
Application Date: 20260106
Priority Date: 20110927

Claims (20)

1 . An image processing apparatus comprising: a receiver circuit, wherein the receiver circuit is arranged to receive an image signal, wherein the image signal comprises at least an encoded image, a dynamic range transform control data and a target display reference, wherein the target display reference specifies a dynamic range of a target display, wherein the target display is a display for which the encoded image is optimized, wherein the target display reference comprises a white point luminance of the target display, wherein the dynamic range transform control data comprises different dynamic range transform parameters for different output maximum luminance levels; a dynamic range processor circuit, wherein the dynamic range processor is arranged to generate an output image by applying a dynamic range transform to the encoded image, wherein the dynamic range transform is based on the white point luminance, a reference white point luminance and the dynamic range transform control data; and an output circuit, wherein in the output circuit is arranged to output the output image.
2 . The image processing apparatus of claim 1 , wherein the dynamic range transform control data comprises different tone mapping parameters, and wherein the dynamic range processor circuit is arranged to determine tone mapping parameters for the dynamic range transform based on the different tone mapping parameters and a maximum luminance of the output image.
3 . The image processing apparatus of claim 1 , wherein the dynamic range transform control data comprises parameters which specify a luminance mapping function.
4 . The image processing apparatus of claim 1 , wherein the dynamic range transform control data comprises different parameters which specify different luminance mapping functions for different maximum luminance levels of different end-user displays for viewing the output image.
5 . The image processing apparatus of claim 1 , wherein the target display reference comprises an Electro Optical Transfer Function indication of the target display.
6 . An encoding apparatus comprising: a receiver circuit, wherein the receiver circuit is arranged to receive an input image; a generator circuit, wherein the generator circuit is arranged to generate an image signal, wherein the image signal comprises the input image, a dynamic range transform control data and a target display reference, wherein the target display reference specifies a dynamic range of a target display, wherein the target display is a display for which the input image is optimized, wherein the target display reference comprises a white point luminance of the target display, wherein the dynamic range transform control data comprises different dynamic range transform parameters for different output maximum luminance levels; and a transmitter circuit, wherein the transmitter circuit is arranged to transmit the image signal.
7 . The encoding apparatus of claim 6 , wherein the dynamic range transform control data comprises different tone mapping parameters for different output maximum luminance levels.
8 . The encoding apparatus of claim 6 , wherein the dynamic range transform control data comprises parameters which specify a luminance mapping function.
9 . The encoding apparatus of claim 6 , wherein the dynamic range transform control data comprises different parameters which specify different luminance mapping functions for different maximum luminance levels of different end-user displays for viewing the input image.
10 . The encoding apparatus of claim 6 , wherein the target display reference comprises an Electro Optical Transfer Function indication of the target display.
11 . An image processing method comprising: receiving an image signal, wherein the image signal comprises at least an encoded image, a dynamic range transform control data and a target display reference, wherein the target display reference specifies a dynamic range of a target display, wherein the target display is a display for which the encoded image is optimized, wherein the target display reference comprises a white point luminance of the target display, wherein the dynamic range transform control data comprises different dynamic range transform parameters for different output maximum luminance levels; generating an output image by applying a dynamic range transform to the encoded image, wherein the dynamic range transform is based on the white point luminance, a reference white point luminance, and the dynamic range transform control data; and outputting an output image.
12 . The method of claim 11 , wherein the dynamic range transform control data comprises different tone mapping parameters for different output maximum luminance levels, and wherein the method further comprises determining tone mapping parameters for the dynamic range transform based on at least one of the different tone mapping parameters and a maximum luminance for the output image.
13 . The method of claim 11 , wherein the dynamic range transform control data comprises parameters which specify a luminance mapping function.
14 . The method of claim 11 , wherein the dynamic range transform control data comprises different parameters which specify different luminance mapping functions for different maximum luminance levels of different end-user displays.
15 . The method of claim 11 , wherein the target display reference comprises an Electro Optical Transfer Function indication of the target display.
16 . A non-transitory computer-readable medium storing a computer program, wherein the computer program when executed on a processor performs the method as claimed in claim 11 .
17 . A method of transmitting an image signal, the method comprising: receiving an input image; generating an image signal, wherein the image signal comprises the input image, a dynamic range transform control data and a target display reference, wherein the target display reference specifies a dynamic range of a target display, wherein the target display is a display for which the encoded image is optimized, wherein the target display reference comprises a white point luminance of the target display, wherein dynamic range transform control data comprises different dynamic range transform parameters for different output maximum luminance levels; and transmitting the image signal.
18 . The method of claim 17 , further comprising: determining different dynamic range transform parameters for different output maximum luminance levels; and writing the different dynamic range transform parameters in the dynamic range transform control data.
19 . The method of claim 17 , wherein the dynamic range transform control data comprises parameters which specify a luminance mapping function.
20 . The method of claim 17 , wherein the dynamic range transform control data comprises different parameters which specify different luminance mapping functions for different maximum luminance levels of different end-user displays.

Description

CROSS-REFERENCE TO PRIOR APPLICATIONS This application is a continuation of US patent application No. U.S. Ser. No. 19/290,499, filed on Aug. 5, 2025, which is a continuation of US patent No. U.S. Pat. No. 12,406,345, filed on Nov. 4, 2024, which is a continuation of US patent No. U.S. Pat. No. 12,229,928, filed on Feb. 8, 2019, which is a continuation of US patent No. U.S. Pat. No. 11,640,656, filed on Mar. 24, 2014, which is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/IB2012/054984, filed on Sep. 20, 2012, which claims the benefit of US Patent Application No. US 61/588,731, filed on Jan. 20, 2012, EP Patent Application No. EP 12160557.0, filed on Mar. 21, 2012 and EP Patent Application No. EP 11182922.2, filed on Sep. 27, 2011. These applications are hereby incorporated by reference herein. FIELD OF THE INVENTION The invention relates to dynamic range transforms for images, and in particular, but not exclusively to image processing to generate High Dynamic Range images from Low Dynamic Range images or to generate Low Dynamic Range images from High Dynamic Range images. BACKGROUND OF THE INVENTION Digital encoding of various source signals has become increasingly important over the last decades as digital signal representation and communication increasingly has replaced analogue representation and communication. Continuous research and development is ongoing in how to improve the quality that can be obtained from encoded images and video sequences while at the same time keeping the data rate to acceptable levels. An important factor for perceived image quality is the dynamic range that can be reproduced when an image is displayed. Conventionally, the dynamic range of reproduced images has tended to be substantially reduced in relation to normal vision. Indeed, luminance levels encountered in the real world span a dynamic range as large as 14 orders of magnitude, varying from a moonless night to staring directly into the sun. Instantaneous luminance dynamic range and the corresponding human visual system response can fall between 10.000:1 and 100.000:1 on sunny days or at night (bright reflections versus dark shadow regions). Traditionally, dynamic range of displays has been confined to about 2-3 orders of magnitude, and also sensors had a limited range, e.g. <10.000:1 depending on noise acceptability. Consequently, it has traditionally been possible to store and transmit images in 8-bit gamma-encoded formats without introducing perceptually noticeable artifacts on traditional rendering devices. However, in an effort to record more precise and livelier imagery, novel High Dynamic Range (HDR) image sensors that are capable of recording dynamic ranges of more than 6 orders of magnitude have been developed. Moreover, most special effects, computer graphics enhancement and other post-production work are already routinely conducted at higher bit depths and with higher dynamic ranges. Furthermore, the contrast and peak luminance of state-of-the-art display systems continues to increase. Recently, new prototype displays have been presented with a peak luminance as high as 3000 Cd/m2 and contrast ratios of 5-6 orders of magnitude (display native, the viewing environment will also affect the finally rendered contrast ratio, which may for daytime television viewing even drop below 50:1). It is expected that future displays will be able to provide even higher dynamic ranges and specifically higher peak luminances and contrast ratios. When traditionally encoded 8-bit signals are displayed on such displays, annoying quantization and clipping artifacts may appear. Moreover, traditional video formats offer insufficient headroom and accuracy to convey the rich information contained in new HDR imagery. As a result, there is a growing need for new approaches that allow a consumer to fully benefit from the capabilities of state-of-the-art (and future) sensors and display systems. Preferably, representations of such additional information are backwards-compatible such that legacy equipment can still receive ordinary video streams, while new HDR-enabled devices can take full advantage of the additional information conveyed by the new format. Thus, it is desirable that encoded video data not only represents HDR images but also allows encoding of the corresponding traditional Low Dynamic Range (LDR) images that can be displayed on conventional equipment. In order to successfully introduce HDR systems and to fully exploit the promise of HDR, it is important that the approach taken provides both backwards compatibility and allows optimization or at least adaptation to HDR displays. However, this inherently involves a conflict between optimization for HDR and optimization for traditional LDR. For example, typically image content, such as video clips, will be processed in the studio (color grading & tone mapping) for optimal appearance on a specific display. Traditionally, such optim