HDR Image Processing Luminance Gain Reference Point
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Solution Overview
Problem
High Dynamic Range (HDR) images are displayed as dark compared to Standard Dynamic Range (SDR) images when viewed in bright environments due to absolute value setting of output luminance, leading to a perceived decrease in brightness.
Innovation Solution
An image processing apparatus and method that adjusts luminance by setting a reference point and applying a gain function to the input/output transfer function of HDR images, ensuring the output luminance is within the display device's capabilities, thereby maintaining image brightness in bright environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If HDR image with absolute value setting is displayed on SDR television, then luminance accuracy is improved, but perceived brightness decreases
Solution Approach 1:
The patent changes the output luminance parameter dynamically based on the input signal value. By setting a reference point and applying different gain values (greater than 1 for signals below reference, less than 1 for signals above reference), the system transforms the absolute luminance values of HDR images into adjusted values that maintain both accuracy and perceived brightness on SDR displays
Solution Approach 2:
The patent introduces dynamic adjustment of the transfer function by setting a reference point P and applying a gain function that varies with the input signal value. This dynamic approach allows the system to adapt the luminance output based on the specific signal being displayed, rather than using a fixed transformation, thereby maintaining both luminance accuracy and perceived brightness
2Illumination intensity
If gain greater than 1 is applied to increase brightness, then perceived brightness is improved, but luminance accuracy deteriorates
Solution Approach 1:
The patent applies different gain values to different regions of the input signal range. By setting a reference point P, the system applies gain greater than 1 to signals below the reference (to improve brightness) and gain less than 1 to signals above the reference (to maintain accuracy). This local differentiation resolves the contradiction by applying brightness enhancement only where needed
3Adaptability or versatility
If HDR image luminance range (0-10000 nit) is mapped to SDR display range (0-500 nit), then display compatibility is improved, but image quality deteriorates
Solution Approach 1:
The patent uses a dynamic transfer function with a reference point and variable gain to map HDR luminance values to SDR display range. This dynamic mapping preserves more image quality information compared to fixed mapping methods, while ensuring full compatibility with SDR displays. The reference point approach allows flexible adaptation to different display capabilities
Data Source
AI summary
Provided is a device and a method in which an HDR image of which a setting luminance is higher than the highest allowable luminance of a display unit, can be displayed as a bright image in a bright audiovisual environment. An adjusted luminance for output is calculated by multiplying an output luminance calculated according to an input/output transfer function corresponding to an input HDR image, and a predetermined gain, together, and thus, a display image is generated. An image signal processing unit sets a reference point P to be in a position based on the highest allowable luminance of a display unit, and calculates the adjusted luminance for output by applying a gain function of setting a gain, based on the reference point P, to an input/output transfer function according to the input HDR image, and thus, generates the display image.