HDR Sensor Color Correction Matrix Calibration for Bit-Depth Mismatch
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Solution Overview
Problem
High dynamic range (HDR) image sensors capture data with a large dynamic range that exceeds the memory and hardware capabilities of image signal processing (ISP) pipelines, leading to potential color inaccuracies due to differences in bit depth resolution, and conventional color correction methods fail to account for non-linear compression curves, exacerbating color distortion.
Innovation Solution
A mechanism that adjusts the color correction matrix (CCM) by decomposing pixel brightness into luminance and color components, applying a non-linear compression curve to maintain color ratios, and calibrating the CCM using a target image with known RGB values to preserve color accuracy during dynamic range compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If HDR image sensors capture data with high bit-depth (e.g., 24-bit) to provide large dynamic illumination range, then the dynamic range and illumination range are improved, but color inaccuracies occur due to the difference in bit depth resolution between the sensor and the ISP pipeline
Solution Approach 1:
The patent applies parameter changes by modifying the CCM parameters (matrix coefficients) specifically for HDR bit-depths. Instead of using conventional CCM parameters designed for lower bit-depths, the system calculates and applies adjusted CCM parameters that account for the higher precision of HDR sensors. This parameter adjustment resolves the color accuracy issue caused by bit-depth mismatch between sensor and ISP pipeline.
2Device complexity
If conventional color correction methods are used without accounting for non-linear compression curves, then the processing is simpler, but color distortion is exacerbated
Solution Approach 1:
The patent applies preliminary action by pre-calculating the CCM parameters specifically for HDR bit-depths before actual image processing. The system performs the complex calculation of adjusted CCM parameters in advance, storing them for use during HDR image processing. This preliminary preparation eliminates the need for complex real-time calculations during compression, maintaining simplicity while ensuring color accuracy.
3Measurement precision
If piecewise linear approaches are used to maintain color accuracy during compression, then color precision is improved, but additional hardware and resources are required
Solution Approach 1:
The patent applies the copying principle by creating adjusted CCM parameters that replicate the color correction functionality needed for HDR processing. Instead of implementing complex piecewise linear hardware, the system copies the essential color correction function into pre-calculated parameter sets that can be applied through standard matrix operations, eliminating the need for additional specialized hardware.
Data Source
AI summary
Apparatuses, systems, and techniques to receive, at a processor associated with an image signal processing (ISP) pipeline, a target image captured using a sensor at a first bit-depth associated with the sensor, where the ISP pipeline is associated with a second bit-depth; apply one or more dynamic range compression operations to brightness values associated with the target image to obtain compressed brightness values; determine brightness gain values using the brightness values and the compressed brightness values; apply the brightness gain values to each color channel of respective pixels of the target image to obtain a compressed target image such that a color ratio of the compressed target image is preserved; and adjust a color correction matrix (CCM) associated with the ISP pipeline using the compressed target image.