CMOS Imaging Device Flicker Reduction via Signal Gain Correction
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Solution Overview
Problem
XY-address scanning-type imaging devices, such as CMOS imaging devices, face challenges in accurately detecting and reducing fluorescent flicker due to the sequential shifting of exposure timings across the image plane, leading to brightness and color variations that deteriorate image quality.
Innovation Solution
A signal processing method that corrects the level or gain of the video signal through analog-to-digital conversion and executes flicker detection and reduction after other processing steps like equalizing signal gains and reducing fixed pattern noise, ensuring accurate flicker detection and reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If exposure timing is sequentially shifted across the image plane in XY-address scanning-type imaging devices, then reading efficiency and productivity are improved, but brightness and color variations occur due to fluorescent flicker, deteriorating image quality
Solution Approach 1:
The image plane is divided into multiple scanning lines that are read out sequentially. Each line is exposed at a slightly different time, allowing the reading operation to proceed efficiently while the flicker correction process segments the correction by line, applying appropriate gain adjustments to each line based on its exposure timing relative to the fluorescent lamp cycle.
Solution Approach 2:
The patent applies gain correction as a parameter change to compensate for fluorescent flicker. By dynamically adjusting the gain of each scanning line based on its exposure timing, the system maintains image quality despite the sequential exposure approach. The correction gain is calculated to counteract the brightness variations caused by the fluorescent lamp's cyclic luminance changes.
2Productivity
If flicker detection and reduction processing is executed before signal gain equalization, then processing efficiency is improved, but detection accuracy deteriorates due to signal level variations
Solution Approach 1:
The patent performs signal gain equalization and black level correction as preliminary actions before executing flicker detection and reduction processing. This ensures that the signal levels are standardized and the black level is established, providing a consistent baseline for accurate flicker detection. The preliminary processing steps prepare the signal in an optimal state for subsequent flicker analysis.
Solution Approach 2:
The system uses feedback from the detected flicker pattern to dynamically adjust correction gains. The flicker detection process analyzes the sequential scanning line signals to identify the fluorescent lamp's cyclic variation pattern, and this detected information feeds back into the correction process to apply appropriate gain adjustments to each line, improving both accuracy and adaptability.
3Reliability
If exposure time is set to 1/100 seconds to match fluorescent lamp cycle, then flicker is completely prevented, but exposure flexibility is reduced
Solution Approach 1:
Instead of fixing the exposure time to 1/100 seconds, the patent maintains flexible exposure time settings and compensates for fluorescent flicker through post-exposure gain correction. The system detects the flicker pattern and applies dynamic gain adjustments to each scanning line based on its exposure timing, allowing the camera to use various exposure times while still eliminating flicker effects in the final image.
Solution Approach 2:
The patent introduces gain correction as an intermediary processing step between exposure and final image output. This intermediary process acts as a mediator that decouples the exposure timing from the flicker prevention requirement, allowing flexible exposure settings while still achieving flicker-free images through the intermediate gain adjustment stage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for effective detection and reduction of fluorescent flicker, improving image quality by stabilizing brightness and color across the image plane, even under fluorescent lamp illumination.
Implementation Method 1
an imaging target is imaged by an XY-address scanning-type imaging element (imager, image sensor) such as a CMOS (complementary metal oxide semiconductor) imaging element
Implementation Method 2
under illumination with a fluorescent lamp operated by a commercial AC power supply
Data Source
AI summary
The present invention is to allow an XY-address scanning-type imaging device such as a CMOS imaging device to detect a fluorescent flicker correctly and accurately and reduce a fluorescent flicker component surely and sufficiently. The RGB primary color signals arising from A/D conversion of the RGB primary color signals obtained from an imaging element are clamped. Subsequently, for the clamped RGB primary color signals, the following processes are executed: correction of the gains of reading-out channels; reduction of fixed pattern noise; correction of the data of defective pixels; noise reduction; lens shading correction; and gain adjustment for exposure adjustment. Thereafter, for the resultant signals, a flicker detection and reduction unit detects and reduces a flicker component. Furthermore, white balance adjustment is implemented for the RGB primary color signals for which the flicker has been reduced.