HDR Video Decoder Luminance Mapping
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Solution Overview
Problem
Current video encoding technologies struggle to effectively handle high dynamic range (HDR) images, as they are limited by the standard dynamic range (SDR) philosophy, which cannot accurately represent the wide contrast ratios found in HDR scenes, leading to suboptimal rendering on both HDR and SDR displays.
Innovation Solution
A system that encodes HDR images as SDR images using reversible color transformation functions, allowing for the reconstruction of the original HDR image, while maintaining chromaticity and adjusting luminance to fit within the SDR dynamic range, enabling rendering on both HDR and SDR displays with optimal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HDR images are encoded using traditional SDR video coding technologies, then compatibility with existing SDR displays is maintained, but the ability to accurately represent wide contrast ratios and render HDR content is lost
Solution Approach 1:
The patent encodes HDR images by creating a copy of the HDR image in SDR format (SDR representative) while preserving the original HDR data. This allows the same encoded data to be displayed on both SDR and HDR displays, with the SDR display showing the converted image and the HDR display showing the original high dynamic range image, thus resolving the contradiction between compatibility and accuracy
Solution Approach 2:
The patent applies reversible color transformation functions that change the luminance parameters of the image while maintaining chromaticity. By adjusting the luminance range and applying tone mapping operations, the HDR image is converted to an SDR representative that fits within the SDR display range, enabling both formats to coexist in the same encoding
2Ease of operation
If the luminance range of HDR images is compressed to fit within SDR display range, then compatibility with SDR displays is achieved, but the dynamic range information is lost
Solution Approach 1:
The patent creates an SDR representative copy that preserves the essential visual information of the HDR image while adapting to SDR display limitations. The reversible color transformation functions ensure that the compressed luminance information can be accurately recovered when decoding, thus preventing information loss while maintaining SDR compatibility
Solution Approach 2:
The patent performs preliminary tone mapping and luminance compression during the encoding process to prepare the image for SDR display. By applying the reversible color transformation functions in advance, the system pre-processes the HDR image into a format that is ready for both SDR and HDR display, avoiding information loss during subsequent processing
3Device complexity
If traditional SDR encoding is used, then device complexity is kept low, but the ability to handle high contrast ratios and wide dynamic range is limited
Solution Approach 1:
The patent creates a universal encoding system that can handle both HDR and SDR content using the same video coding framework. By integrating reversible color transformation functions into the existing SDR encoder, the system gains multi-functionality to process HDR images while maintaining the simplicity of traditional SDR encoding infrastructure, thus resolving the contradiction between complexity and adaptability
Data Source
AI summary
To enable a high quality HDR video communication, which can work by sending corresponding LDR images potentially via established LDR video communication technologies, which works well in practical situations, applicant has invented a HDR video decoder (600, 1100) arranged to calculate a HDR image (Im_RHDR) based on applying to a received 100 nit standard dynamic range image (Im_RLDR) a set of luminance transformation functions, the functions comprising at least a coarse luminance mapping (FC), which is applied by a dynamic range optimizer (603), and a mapping of the darkest value (0) of an intermediate luma (Y′HPS), being output of the dynamic range optimizer, to a received black offset value (Bk_off) by a range stretcher (604), the video decoder comprising a gain limiter (611, 1105) arranged to apply an alternate luminance transformation function to calculate a subset (502) of the darkest luminances of the HDR image, from corresponding darkest lumas (Y′_in) of the standard dynamic range image.