Image Processing Circuit for HDR to SDR Tone Mapping
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Solution Overview
Problem
Conventional standard dynamic range (SDR) display devices degrade the quality of high dynamic range (HDR) images when displaying them due to differences in encoding and decoding functions, while HDR images are not accurately displayed on SDR devices due to mismatched decoding functions, leading to suboptimal image quality for both formats.
Innovation Solution
An image processing method and circuit that selects a gamma curve with minimal luminance error for SDR display devices to convert HDR images into SDR format without gamma transformation, using a roll-off processor to adaptively determine the roll-off inflection point and an image mapper to select the appropriate gamma curve and look-up table for accurate mapping, thereby minimizing image quality degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HDR images are displayed on conventional SDR display devices using standard gamma decoding, then the display device can show images, but image quality degradation occurs due to mismatched encoding and decoding functions
Solution Approach 1:
The patent introduces an image processing circuit as an intermediary component between the HDR image source and the SDR display device. This circuit performs tone mapping and gamma conversion to bridge the incompatibility between HDR encoding (SMPTE ST. 2084/PQ) and SDR decoding (Rec. 709 gamma 2.4), enabling HDR images to be displayed with improved quality on conventional SDR devices without requiring the display device itself to be HDR-capable
Solution Approach 2:
The patent changes the decoding parameters by implementing adaptive gamma curve selection and tone mapping algorithms in the image processing circuit. Instead of using the fixed gamma 2.4 decoding function, the system dynamically adjusts the decoding parameters based on the HDR image characteristics and display device capabilities, thereby resolving the contradiction between maintaining image quality and ensuring compatibility
2Reliability
If HDR display devices are designed to accurately display HDR images, then HDR image quality is improved, but SDR images are not accurately displayed due to the same decoding function mismatch
Solution Approach 1:
The patent implements dynamic decoding function selection in the image processing circuit. The circuit can adaptively switch between different decoding functions (HDR-oriented gamma curves or SDR-oriented gamma 2.4) based on the input image type. This dynamic capability allows a single display device to accurately display both HDR and SDR images by changing its decoding parameters in real-time, resolving the contradiction between HDR and SDR display accuracy
Solution Approach 2:
The system changes the decoding parameters dynamically based on the input image format. When an HDR image is detected, the image processing circuit applies HDR-appropriate tone mapping and gamma conversion parameters. When an SDR image is detected, it uses the standard gamma 2.4 decoding function, thereby maintaining manufacturing precision for both image types without requiring separate display devices
3Reliability
If gamma transformation is performed in high-cost data drive ICs to accurately display both SDR and HDR images, then image quality is improved, but the cost of the display device increases significantly
Solution Approach 1:
The patent extracts the gamma transformation and tone mapping functions from the data drive IC and relocates them to a separate, lower-cost image processing circuit. This extraction allows the use of simpler, more cost-effective data drive ICs while maintaining the capability to accurately display both SDR and HDR images through the external image processing circuit, thereby resolving the contradiction between image quality and manufacturing cost
Data Source
AI summary
An image processing method and circuit, and a display device using the same, for minimizing image quality degradation of a high dynamic range (HDR) image without gamma transformation of a data drive integrated circuit (IC) and displaying the image in a standard dynamic range (SDR) display device are disclosed. The image processing method includes selecting a gamma curve with a first image having an HDR and cumulative minimum luminance error among a plurality of gamma curves corresponding to a display device having a SDR, and converting the first image into a second image having an SDR according to the selected gamma curve.