Dynamic Clipping Control for CMOS Image Sensor Noise Correction
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Solution Overview
Problem
Current image capturing apparatuses, particularly CMOS sensors, face challenges in accurately correcting lateral stripe and band noise due to fluctuations in circuit output levels when capturing high luminance subjects, leading to blown-out highlights and non-proportional digital values, which hinder effective noise correction.
Innovation Solution
An image capturing apparatus with a pixel matrix, column output lines, a clip portion to clip signals at a predetermined level, and an A/D conversion portion, where the clipping signal level is adjusted based on the A/D conversion range's maximum value, enabling accurate correction of lateral smearing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clipping is performed at a fixed predetermined signal level, then the circuit structure is simple, but accurate correction of lateral smearing cannot be achieved when the A/D conversion range does not match the signal voltage level
Solution Approach 1:
The clipping signal level is made dynamically adjustable rather than fixed. The control unit changes the clipping signal level according to the maximum value of the A/D conversion portion's conversion range, allowing the system to adapt to different signal conditions and maintain proportionality between lateral smearing amount and digital signal values.
Solution Approach 2:
The clipping signal level parameter is changed based on the A/D conversion range. By adjusting this parameter to match the maximum conversion value, the system ensures that the clipping operation maintains accurate proportionality between the analog signal and its digital representation, enabling precise lateral smearing correction.
2Power
If analog gain is applied to the block where lateral smearing occurs, then signal amplification is achieved, but the digital value becomes non-proportional to the lateral smearing amount due to A/D conversion range limitations
Solution Approach 1:
The clipping operation is performed before A/D conversion to prevent signal levels from exceeding the conversion range. By clipping the analog signal at an appropriate level prior to conversion, the system maintains proportionality between the lateral smearing amount and the resulting digital value, even when analog gain is applied for signal amplification.
Solution Approach 2:
The clipping portion acts as an intermediary between the analog signal amplification stage and the A/D conversion stage. It mediates the signal level to ensure it within the appropriate range for accurate conversion, maintaining the proportional relationship between the lateral smearing amount and digital representation.
3Loss of information
If the A/D conversion range is smaller than the signal voltage level, then blown-out highlights occur and digital values are lost, but increasing the conversion range reduces measurement precision
Solution Approach 1:
Clipping is performed as a preliminary action before A/D conversion to prevent signal levels from exceeding the conversion range. This prevents blown-out highlights by ensuring that no signal portion exceeds the maximum conversion value, thereby retaining detail information that would otherwise be lost.
Solution Approach 2:
The clipping signal level parameter is adjusted to match the maximum value of the A/D conversion range. This dynamic parameter adjustment ensures optimal utilization of the conversion range without exceeding it, preventing information loss while maintaining measurement precision within the available range.
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 solution allows for precise correction of lateral stripe and band noise by ensuring proportional digital values and signal levels, preventing misalignment and enhancing image quality by matching the clipping level with the A/D conversion range, thereby improving the accuracy of noise correction.
Implementation Method 1
a pixel portion in which pixels that convert entered light into electric signals are arranged in a matrix
Data Source
AI summary
An image capturing apparatus including a pixel portion in which pixels that convert entered light into electric signals are arranged in a matrix, a column output line provided for each pixel column of the pixel portion, a clip portion configured to clip, at a predetermined signal level, signals respectively output from the pixels to the column output lines, an A/D conversion portion configured to A/D convert the signals clipped by the clip portion, and a control unit configured to change a signal level at which clipping is performed by the clip portion according to a maximum value of a conversion range of the A/D conversion portion.