HDR Video Decoder Luminance Mapping SDR Compatibility
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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 need for standardized dynamic range and peak brightness, which restricts the ability to render scenes with both very bright and very dark regions accurately, especially when transitioning between different display types such as 100 nit SDR and 5000 nit HDR displays.
Innovation Solution
A method and system for encoding HDR images as SDR images, using reversible color transformation functions to ensure accurate reconstruction of HDR images on various display types, including a dynamic range optimizer and gain limiter to adjust luminance and maintain chromaticity, allowing for seamless conversion between different dynamic ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If HDR images are encoded using standardized dynamic range and peak brightness, then compatibility with existing displays is improved, but the ability to render scenes with both very bright and very dark regions accurately deteriorates
Solution Approach 1:
The patent divides the luminance range into multiple segments (dark tones, mid tones, bright tones) and applies different encoding strategies to each segment. The darkest tones are encoded with higher precision to preserve shadow detail, while brighter tones are handled separately to maintain contrast ratio. This segmentation allows the system to maintain both compatibility with standardized displays and accuracy in rendering extreme luminance values.
Solution Approach 2:
The patent introduces a new dimension to the encoding process by adding metadata that describes the original HDR luminance values and the transformation applied. This allows the encoded SDR image to carry information about its HDR origins, enabling accurate reconstruction on HDR displays while maintaining compatibility with SDR displays. The metadata layer adds a new dimension of information without compromising either display type.
2Measurement precision
If the dynamic range is extended to capture very bright and very dark regions, then the rendering accuracy is improved, but the complexity of encoding and decoding processes deteriorates
Solution Approach 1:
The patent uses a tone mapping function as an intermediary between the HDR source image and the SDR encoded image. This tone mapping function acts as a mediator that compresses the wide HDR luminance range into the narrower SDR range while preserving the essential visual information. The function is designed to be computationally efficient, balancing rendering accuracy with encoding complexity.
Solution Approach 2:
The patent changes the encoding parameters dynamically based on the content characteristics. Instead of using a fixed encoding scheme, the system adjusts parameters such as the tone mapping function and quantization levels according to the specific HDR image being encoded. This allows optimization of rendering accuracy for each image while controlling the overall complexity through adaptive rather than rigid processing.
3Adaptability or versatility
If tone mapping functions are applied to compress dynamic range, then compatibility with SDR displays is improved, but the loss of information in the process deteriorates
Solution Approach 1:
The patent applies preliminary actions by encoding the HDR image with metadata that preserves the original luminance information before the final SDR encoding is applied. This preliminary preservation of HDR information in the metadata allows for potential future use or reconstruction, while the main image data is optimized for SDR compatibility. The preliminary action of metadata encoding prevents information loss by maintaining the original HDR characteristics.
Solution Approach 2:
Instead of discarding HDR information during the compression process, the patent inverts the approach by preserving HDR information through metadata and using it to guide the SDR encoding process. The tone mapping function is designed to be invertible or reversible through the metadata, allowing the original HDR luminance values to be recovered if needed. This inversion of the typical compression approach minimizes information loss while maintaining SDR compatibility.
Data Source
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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 5 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 10 calculate a subset (502) of the darkest luminances of the HDR image, from corresponding darkest lumas (Y'_in) of the standard dynamic range image.