Digital Camera Signal Processing for Purple False Color Suppression
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Solution Overview
Problem
Conventional digital cameras using CCD or CMOS image sensors face the issue of generating purple false color in high brightness regions due to unequal saturation levels, which is typically addressed by clipping red and blue saturation levels, resulting in reduced dynamic ranges.
Innovation Solution
A signal processing method that applies white balance correction to red, green, and blue color signals, comparing their levels and correcting the green signal level to match the lower of either the red or blue signal level when both are higher, thereby preventing purple false color without reducing the dynamic ranges of red and blue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If red and blue saturation levels are clipped at the green saturation level to suppress purple false color, then purple false color is suppressed, but dynamic ranges of red and blue are reduced
Solution Approach 1:
Instead of clipping the red and blue saturation levels at the green saturation level (conventional approach), the invention inverts the approach by raising the green saturation level to match the lower of the red or blue saturation levels. This inversion resolves the contradiction by preventing purple false color through a different mechanism that preserves the dynamic ranges of red and blue channels.
Solution Approach 2:
The invention changes the parameter being adjusted from the red/blue saturation levels (clipping approach) to the green saturation level (raising approach). By changing which parameter is modified and in what direction, the system achieves purple false color suppression while maintaining the dynamic ranges of red and blue channels.
2Stability of the object's composition
If green saturation level is made coincident with red and blue saturation levels, then saturation balance is improved, but purple false color is generated in high brightness region
Solution Approach 1:
The invention introduces dynamic adjustment based on signal levels. Instead of a static saturation balance, the system dynamically raises the green saturation level only when necessary (when both R and B levels are higher than G level), allowing the system to adapt to different imaging conditions and prevent purple false color while maintaining saturation balance.
Solution Approach 2:
The system incorporates feedback by comparing the signal levels of R, G, and B channels and adjusting the green saturation level accordingly. When the feedback indicates that both R and B levels are higher than G level, the system raises the green saturation level to prevent purple false color, creating a closed-loop control system.
3Measurement precision
If white balance correction is applied to equalize sensitivity ratios, then color accuracy is improved, but green saturation level becomes lower than red and blue saturation levels
Solution Approach 1:
The invention performs preliminary white balance correction to equalize sensitivity ratios, which is necessary for color accuracy. Then, as a subsequent preliminary action, it compares the saturation levels and raises the green saturation level if needed, preventing purple false color before it occurs in the final image output.
Data Source
AI summary
A signal processing method comprises: applying white balance correction to R (red), G (green), and B (blue) color signals output from a solid-state image pickup element so as to form white-balance corrected R, G, and B color signals; comparing levels of the white-balance corrected R, G, and B color signals with each other; correcting the level of the white-balance corrected G signal to coincide with a lower one of the levels of the white-balance corrected R and B color signals in the case where both of the levels of the white-balance corrected R and B signals are higher than the level of the white-balance corrected G signal when the G color signal is saturated; and outputting the white-balance corrected R, G, and B color signals as image signals.