Layered Codec for HDR Video Compatibility
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Solution Overview
Problem
Current video technologies struggle to efficiently compress and display high dynamic range (HDR) images, as they either lose detail in bright or dark areas when converting HDR to standard dynamic range (SDR) or require excessive bit depth, which is not compatible with existing SDR devices.
Innovation Solution
The implementation of a method for encoding video streams in a visual dynamic range (VDR) format, using 32 bits per pixel with 12 bits for luminance and 10 bits for each color channel, allowing for a dynamic range of 5 to 6 orders of magnitude, and employing tone mapping operators to reduce the dynamic range while preserving detail, using a layered codec that includes both SDR and VDR information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HDR video is converted to SDR for display on existing devices, then compatibility with existing SDR devices is improved, but detail in bright or dark areas is lost
Solution Approach 1:
The video stream is segmented into multiple layers: a base layer containing SDR video data for compatibility with existing devices, and enhancement layers containing HDR-specific data (transfer characteristics, tone mapping parameters) for devices capable of HDR display. This segmentation allows SDR devices to display the base layer without loss while HDR-capable devices can utilize the enhancement layers to recover and display full HDR detail.
Solution Approach 2:
Transfer characteristics and tone mapping parameters act as intermediaries between the HDR source content and the display device. These parameters encode the relationship between linear luminance values and display-referred values, enabling HDR content to be properly transformed for display on various devices while preserving the original HDR information in the bitstream.
2Measurement precision
If 32-bit per pixel format with 12 bits luminance and 10 bits color channels is used, then dynamic range and color gamut coverage is improved, but data size and processing complexity increases
Solution Approach 1:
The patent uses 32-bit per pixel format with 12 bits for luminance and 10 bits for each color channel, representing a parameter change from conventional 8-bit or 10-bit formats. This provides sufficient precision to cover the full HDR luminance range (5 to 6 orders of magnitude) and wide color gamut while maintaining manageable data sizes through efficient encoding and compression techniques.
Solution Approach 2:
The patent introduces a layered dimension to the video data structure, organizing HDR video information into base layers and enhancement layers. This dimensional organization separates compatibility-required data from HDR-enhancement data, allowing efficient processing where SDR devices process only the base layer while HDR devices process both layers, thereby reducing overall processing complexity.
3Adaptability or versatility
If tone mapping operators are used to reduce dynamic range, then compatibility with SDR displays is improved, but perception of original HDR quality deteriorates
Solution Approach 1:
The patent applies tone mapping operators during the encoding process rather than during display, performing the dynamic range transformation in advance. The encoded video stream contains both the tone-mapped SDR representation and the original HDR information with transfer characteristics. This preliminary action allows HDR-capable displays to reverse the tone mapping and restore the original HDR quality, while SDR displays correctly display the pre-tone-mapped content.
Solution Approach 2:
Instead of permanently compressing HDR to SDR, the patent inverts the approach by encoding HDR content with embedded transfer characteristics that enable reversible transformation. HDR-capable displays can invert the tone mapping process to recover the original luminance values, effectively undoing the compression and restoring full HDR quality, while SDR displays use the forward-transformed values.
Data Source
AI summary
A first image stream has a first dynamic range and a first color space. First and the second image streams are received in a layered codec. The second image stream has a second dynamic range, which is higher than the first dynamic range. The first image stream is in the codec's base layer; the second image stream is in its enhancement layer. The first image stream is encoded to obtain an encoded image stream, which is decoded to obtain a decoded image stream. The decoded image stream is converted from the first non-linear or linear color space to a second, different color space to obtain a color converted image stream. A higher dynamic range image representation of the color converted image stream is generated to obtain a transformed image stream. Inverse tone mapping parameters are generated based on the transformed image stream and the second image stream.