HDR Video Decoder Luminance Mapping
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Solution Overview
Problem
Current video encoding technologies struggle to effectively render high dynamic range (HDR) images on various display types, particularly as existing HDR images appear too bright on standard dynamic range (SDR) displays, leading to loss of detail and mood in scenes with high contrast ratios.
Innovation Solution
A method and system for encoding HDR images that allows for dynamic range conversion, using reversible color transformation functions to adjust luminance while maintaining chromaticity, enabling HDR images to be decoded and rendered optimally on both HDR and SDR displays by transforming pixel luminances to fit the available dynamic range of the display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If HDR images are encoded with high peak brightness values, then the image quality and dynamic range are improved, but the images appear too bright on SDR displays causing loss of detail and mood
Solution Approach 1:
The patent applies dynamic tone mapping that adjusts the luminance transformation based on local image characteristics and display capabilities. The system dynamically selects between different transformation functions (F_ct) depending on the HDR scene content and target display type, enabling optimal rendering on both HDR and SDR displays without fixed static mapping
Solution Approach 2:
The patent changes the luminance parameter through reversible color transformation functions that map HDR luminance values to SDR luminance values. By modifying the luminance parameter while preserving chromaticity information, the system enables accurate rendering on SDR displays while maintaining the option to render on HDR displays with original luminance values
2Device complexity
If a single encoding is used for HDR video, then the encoding complexity is reduced, but the compatibility across different display types (HDR and SDR) is worsened
Solution Approach 1:
The patent creates a universal HDR encoding system that can be decoded and rendered on both HDR and SDR displays. By embedding reversible color transformation functions and metadata in the encoded stream, the system enables a single encoding to serve multiple display types, with the decoder adapting the rendering based on display capabilities
Solution Approach 2:
The patent introduces metadata and transformation functions as intermediaries between the HDR encoded content and the display device. These intermediaries carry the necessary information for the decoder to perform appropriate luminance mapping, enabling compatibility with SDR displays while preserving HDR rendering options
3Adaptability or versatility
If luminance transformation is applied to fit SDR display range, then the compatibility with SDR displays is improved, but the chromaticity accuracy may be degraded
Solution Approach 1:
The patent segments the color transformation process into separate luminance and chromaticity handling. By calculating a brightness index (J') that separates luminance information from chromaticity information, the system can transform luminance for SDR compatibility while preserving chromaticity accuracy through the reversible transformation functions
Data Source
AI summary
To have a much better usable pragmatic manner of HDR video encoding and decoding, the inventor invented a high dynamic range video decoder (500) arranged to receive an encoding (Im_COD) of a high dynamic range video and to decode and output a set of temporally successive images (Im_RHDR) comprising: An input (502) to receive three weight values (kRY, kGY, kBY); A video decoder (501) arranged to decode the encoding (Im_COD) into an intermediate image (Im_RLDR) being in a Y'CbCr color representation; A brightness index calculation unit (503) arranged to calculate for each pixel of the intermediate image (Im_RLDR) a brightness index (J') being defined as J'=Y'+MAX{kRY*(R'-Y'), kGY*(G'-Y'), kBY*(B'-Y')}; A brightness mapper (505) arranged to receive a specification of at least one one-dimensional function F_ct, and to apply it with the brightness index (J') as input, to obtain an output brightness index (J*); A multiplication factor calculation unit (506) arranged to calculate a multiplicative factor (g) being equal to the output brightness index (J*) divided by the brightness index (J'); Three multipliers (509, 510, 511) to multiply the respective color components (Y, Cr, Cb) of each pixel of the intermediate image (Im_RLDR) with the multiplicative factor (g), to obtain an output color (Y'H, Cb'H, Cr'H) for that pixel in the output dynamic range image (Im_RHDR) of the set of temporally successive images being currently decoded.