Video Processing Gamma Correction for Dynamic Range and Gradation
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Solution Overview
Problem
Conventional video processing systems struggle to accurately reproduce the natural gradation, color, and sharpness of real subjects due to contrast compression in high-luminance regions, which limits the dynamic range and results in unnatural video displays.
Innovation Solution
A video processing apparatus with a control unit that sets a gamma characteristic for a second dynamic range larger than the first, using a referential gamma characteristic to perform gamma correction processing, maintaining the relationship between luminance input and output values across the entire luminance range, and a correction unit that applies this gamma characteristic to video signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If gamma correction processing including knee correction is performed to widen the input dynamic range, then the practical input dynamic range is secured, but the contrast in the high-luminance region is compressed resulting in unnatural gradation characteristics
Solution Approach 1:
The patent applies different gamma correction characteristics to different luminance regions. Specifically, it uses a first gamma correction characteristic for the low-luminance region and a second gamma correction characteristic for the high-luminance region, where the second characteristic has a smaller gamma value than the first. This local differentiation allows the system to maintain natural gradation in the high-luminance region while still expanding the overall input dynamic range, resolving the contradiction between widening dynamic range and preserving natural gradation characteristics.
2Quantity of substance
If the contrast in the high-luminance region is compressed to secure practical input dynamic range, then the input dynamic range is widened, but the luminance change in the high-luminance region is reduced compared to the real subject
Solution Approach 1:
The patent dynamically adjusts the gamma correction characteristic based on the luminance region being processed. By switching between a first gamma correction characteristic (for low-luminance regions) and a second gamma correction characteristic with a smaller gamma value (for high-luminance regions), the system adapts its correction behavior to the local luminance conditions. This dynamic adjustment ensures that luminance changes in the high-luminance region closely match the real subject while still achieving an expanded input dynamic range.
3Illumination intensity
If only display apparatus processing is performed to compensate compressed contrast, then the display apparatus can increase brightness, but the video signal does not include gradation information about the middle-luminance and high-luminance regions
Solution Approach 1:
The patent applies gamma correction processing at the imaging apparatus (camera) side before the video signal is transmitted to the display apparatus. By performing the gamma correction with the appropriate characteristics in advance at the imaging apparatus, the system preserves gradation information about middle-luminance and high-luminance regions in the video signal. This preliminary action ensures that when the display apparatus receives the signal, it already contains the necessary gradation information, allowing the display apparatus to simply adjust brightness without losing any gradation data.
Data Source
AI summary
A camera microcomputer sets a gamma characteristic that suits a luminance input value/output value relationship in the entire luminance region extending from lower luminance to higher luminance of a video signal to a luminance input value/output value relationship of a referential gamma characteristic, irrespective of input dynamic range. A gamma correction processing unit performs gamma correction processing on a captured video signal in such a way as to convert the input value into the output value based on the set gamma characteristic.