System and method for a multi-primary wide gamut color system
Inventors
Mandle, Gary B. • DeFilippis, James M.
Assignees
Publication Number
US-11694592-B2
Publication Date
2023-07-04
Expiration Date
2039-10-21
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Abstract
Systems and methods for a multi-primary color system for display. A multi-primary color system increases the number of primary colors available in a color system and color system equipment. Increasing the number of primary colors reduces metameric errors from viewer to viewer. One embodiment of the multi-primary color system includes Red, Green, Blue, Cyan, Yellow, and Magenta primaries. The systems of the present invention maintain compatibility with existing color systems and equipment and provide systems for backwards compatibility with older color systems.
Core Innovation
The invention relates to systems and methods for encoding and decoding image signals using a multi-primary color system, specifically involving an increased number of primary colors beyond traditional RGB. The system is configured to enhance color gamuts and reduce viewer metameric errors by utilizing at least four, and preferably six, primary colors; these typically include red, green, blue, cyan, magenta, and yellow. The core system processes image data, converts it into a colorimetric space (such as CIE xyY), and enables efficient transport, encoding, and display of this information, allowing for wide-gamut color reproduction.
A significant problem with prior art color systems is their reliance on three primaries (RGB), which leads to limits in displayable color range, introduces metameric errors due to observer variation, and creates complexities in achieving both wide color rendering and compatibility with legacy color processing infrastructure. Existing approaches either limit the support for additional color primaries to only display-side processing, or are not fully compatible with standard image signal acquisition, transport, or metadata systems.
The invention proposes a complete multiprimary color system wherein the image signal is processed through an encoder (possibly including hardware or software elements, and supporting features such as watermarking, look-up tables, and transfer functions), converted to xyY color space, and formatted for various standard transports (such as SDI, HDMI, Ethernet, or fiber). The data is then decoded to support output to one or more viewing devices, which may use multi-primary subpixels or traditional RGB, ensuring broad compatibility and improved color accuracy. A novel ½ gamma function is introduced as a data-efficient approach for converting the luminance (Y) channel to a display-appropriate luma (Y′).
Claims Coverage
There are three independent claims in the patent, each focusing on specific inventive features related to encoding and decoding image signals with colorimetric processing, watermarking, and gamma function use.
Encoding and decoding using xyY color space and ½ gamma function
The system includes an encoder/decoder pair that processes image data by converting it to xyY color space, which consists of two colorimetric coordinates (x and y) and a luminance (Y) value. A ½ gamma function is applied to the luminance to generate a luma (Y′), providing a data-efficient transform for transport and display. The encoder output is transmitted to a decoder, which processes the received data accordingly. The system covers all infrastructure: inputs, outputs, processors, and memory for both encoding and decoding stages.
Digital watermarking outside visible color gamut
The system integrates a watermark engine at the encoding stage and corresponding watermark detection and subtraction engines at the decoding stage. The watermarking process modifies the encoded data to embed a digital watermark that is outside the ITU-R BT.2020 color gamut, ensuring the watermark is invisible and undetectable on displays supporting the BT.2020 gamut. The decoder is structured to require the presence of this digital watermark in order to deliver decoded output, thereby providing a mechanism for content protection and authenticity.
Gamma function processing and removal in image signal workflows
The system utilizes a gamma function during encoding to process the luminance channel of the image signal (within xyY color space), converting it to a luma (Y′) that is optimized for transmission or storage. At the decoding end, a gamma-to-linear converter is employed to reverse this transformation and restore the linear luminance values before display or post-processing.
The independent claims encompass encoding and decoding systems that transform image data into xyY space with a ½ gamma function, integrate robust watermarking in the colorimetric domain, and manage gamma correction at both encoding and decoding stages—collectively providing an advanced workflow for multi-primary wide-gamut color systems.
Stated Advantages
Enables a wide color gamut and reduces metameric errors from viewer to viewer by increasing the number of primary colors beyond RGB.
Maintains compatibility with existing color systems and equipment, including backwards compatibility with older color systems.
Allows for efficient packaging, transport, and display of image data with more than three primaries using standard video and data interfaces (such as SDI, HDMI, Ethernet, fiber).
Utilizes a ½ gamma function for efficient, data-optimized transformation of luminance, facilitating easy conversion to and from linear values.
Supports advanced features such as digital watermarking in a way that is invisible and undetectable on standard wide-gamut displays.
Documented Applications
Image signal encoding and decoding for multi-primary color display systems, including those using six-color primaries (red, green, blue, cyan, magenta, yellow).
Integration with various display devices (including projectors, OLED monitors, LCD displays, quantum dot displays, direct emissive displays) capable of multi-primary color rendering.
Compatibility and mapping with standard video transport protocols and formats such as SDI, HDMI, Ethernet, fiber, SMPTE ST292, ST424, ST2082, ST2110, and CTA 861.
Incorporation in systems requiring digital watermarking of image data for security and content authentication purposes.
Use in workflows where image data must be converted between color spaces for hardware-agnostic or legacy-to-future display compatibility.
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