Intensity-Separated Local White Balance Correction for WDR Images
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Solution Overview
Problem
Existing digital camera image signal processors (ISPs) struggle to accurately correct for color casts in images captured under mixed lighting conditions using wide dynamic range (WDR) sensors, as global color specific gains fail to properly correct the entire image.
Innovation Solution
The implementation of intensity-separated local white balance correction, where local gain lookup tables (LUTs) are generated for each color channel based on local intensity measurements, allowing for pixel-specific gain adjustments in WDR images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If global color specific gains are applied to correct white balance, then correction is simple and fast, but correction accuracy deteriorates under mixed lighting conditions
Solution Approach 1:
The image is divided into multiple local regions, and separate gain values are computed for each region based on local color statistics. This segmentation allows each region to be corrected according to its specific lighting conditions, resolving the contradiction between simple global correction and accurate local correction under mixed lighting.
Solution Approach 2:
Different gain values are applied to different spatial locations within the image based on local color temperature analysis. The system computes local color statistics for each region and applies region-specific white balance corrections, enabling accurate correction of mixed lighting conditions while maintaining computational efficiency through localized processing.
2Measurement precision
If local gain values are computed for each region, then white balance correction accuracy improves under mixed lighting, but device complexity increases
Solution Approach 1:
The image is divided into multiple local regions, and separate gain values are computed for each region based on local color statistics. This segmentation allows each region to be corrected according to its specific lighting conditions, resolving the contradiction between simple global correction and accurate local correction under mixed lighting.
Solution Approach 2:
The system changes the gain parameters locally across different image regions based on detected color temperature variations. By computing local color statistics and adjusting gain values according to regional characteristics, the system achieves accurate white balance correction without requiring complex global processing algorithms.
3Measurement precision
If intensity separated local gain LUTs are generated and applied, then correction precision improves for WDR images, but computational complexity increases
Solution Approach 1:
Gain lookup tables (LUTs) are pre-computed and stored based on intensity-separated local color statistics. During image processing, the system simply queries these pre-computed LUTs using local intensity values to obtain appropriate gain values, avoiding the need for complex real-time calculations and significantly reducing computational complexity while maintaining high correction precision.
Solution Approach 2:
The system creates intensity-separated copies of gain tables for different luminance ranges. By generating separate LUTs for different intensity levels, the system can accurately correct both shadow and highlight regions independently, achieving high precision WDR white balance correction through table lookup rather than complex computation.
Data Source
AI summary
Local automatic white balance (AWB) of wide dynamic range (WDR) images is provided. Methods and systems include collecting, by an image signal processor (ISP), statistics for local AWB from at least one wide dynamic range (WDR) image received by the ISP; generating, by a processor, based on the statistics, local gain lookup tables (LUTs), one for each color channel represented in the WDR image(s), each local gain LUT providing a correlation between gain and intensity; and storing the local gain LUTs. Further processing includes, for each of multiple pixels of a WDR image to be output calculating an intensity value, accessing the local gain LUT for the color channel corresponding to that pixel using the calculated intensity value to identify a corresponding local gain value, and applying the local gain value to that pixel.