Pixel Exposure Time Assignment for Digital Camera Shading Correction
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Solution Overview
Problem
Conventional digital camera systems face issues with shading due to reduced lens size, leading to vignetting and noise amplification in corner areas, which existing digital shading correction schemes cannot effectively address, especially when the signal-to-noise ratio is low.
Innovation Solution
A method and apparatus that vary exposure times for different pixel locations based on signal-to-noise ratio measurements, allowing for improved image quality by assigning longer exposure times to areas with lower signal-to-noise ratios and shorter times to areas with higher ratios, eliminating the need for software digital lens shading correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional digital shading correction schemes are used to brighten corners, then brightness uniformity is improved, but noise is amplified
Solution Approach 1:
The patent applies preliminary action by measuring the signal-to-noise ratio for each pixel location before the actual image capture. Based on these pre-measured ratios, exposure times are calculated and assigned to different pixel locations in advance. This allows the system to optimize exposure for each region without needing post-processing correction, thereby improving brightness uniformity while avoiding noise amplification that occurs with conventional digital shading correction.
Solution Approach 2:
The patent implements local quality by assigning different exposure times to different pixel locations based on their specific signal-to-noise ratio characteristics. Instead of using a uniform exposure time for the entire image sensor, the system tailors the exposure parameters to each local region, allowing corner pixels with lower signal-to-noise ratios to receive longer exposure times while center pixels with higher ratios receive shorter times. This localized optimization improves brightness uniformity without amplifying noise.
2Volume of moving object
If lens system size is reduced for compact cameras, then device size is reduced, but shading issues and vignetting are worsened
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the exposure time parameter for different pixel locations based on their signal-to-noise ratio measurements. This allows the system to compensate for the optical deficiencies introduced by the small lens system without changing the physical lens dimensions. By varying the exposure parameter across different regions of the sensor array, the system achieves improved shading uniformity while maintaining the compact camera design.
3Volume of moving object
If digital camera size is reduced, then portability is improved, but signal-to-noise ratio in corner areas deteriorates
Solution Approach 1:
The patent measures the signal-to-noise ratio for each pixel location in advance and uses these pre-calculated values to determine optimal exposure times. This preliminary measurement allows the system to compensate for the reduced signal-to-noise ratio in corner areas by assigning longer exposure times to those regions, thereby improving measurement precision without increasing camera size.
Solution Approach 2:
The system implements local quality by tailoring exposure parameters to each pixel location's specific signal-to-noise ratio characteristics. Corner pixels with lower signal-to-noise ratios receive longer exposure times, while center pixels with higher ratios receive shorter times. This localized parameter adjustment improves the overall signal-to-noise ratio across the image sensor without requiring a larger camera.
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 enhances image quality by improving brightness uniformity and reducing noise, resulting in better signal-to-noise ratios and color accuracy across the image, particularly in low-light conditions, without the drawbacks of conventional shading correction methods.
Implementation Method 1
A method for digital imaging is provided. The method includes determining a signal-to-noise ratio for each of a plurality of pixel locations in a pixel array
Data Source
AI summary
A method and digital imaging device, such as a digital camera module, is provided for digital imaging. The method includes the step of determining a signal-to-noise ratio associated with a first pixel location of a plurality of pixel locations and a signal-to-noise ratio associated with a second pixel location of the plurality of pixel locations, and the steps of assigning a first exposure time to the first pixel location in response to the signal-to-noise ratio associated with the first pixel location and assigning a second exposure time different from the first exposure time to the second pixel in response to the signal-to-noise ratio associated with the second pixel location. The method further includes the step of exposing the first pixel location for the first exposure time while exposing the second pixel location for the second exposure time to create a digital image.