Pixel-By-Pixel Exposure Control For CMOS Dynamic Range
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Solution Overview
Problem
CMOS image sensing devices have a limited dynamic range, leading to saturation in bright areas and underexposure in dark areas, with existing solutions requiring non-standard sensors, increased memory, or multiple resets, which are costly and impractical.
Innovation Solution
Varying sensor exposure time on a pixel-by-pixel basis under digital camera processor control, allowing continuous illumination without reset, with non-destructive interrogation at intermediate times to adjust for saturation and extend dynamic range without additional memory or specialized sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single exposure time is used for all pixels, then the device complexity is low, but the dynamic range is limited causing saturation in bright areas and underexposure in dark areas
Solution Approach 1:
The image sensor array is divided into multiple regions (first region and second region) with different exposure times. The first region captures images at a first exposure time while the second region captures images at a second exposure time, allowing simultaneous capture of both bright and dark scene details without requiring complex per-pixel control
Solution Approach 2:
The patent introduces a spatial dimension to exposure time control by assigning different exposure times to different spatial regions of the sensor array. This regional segmentation approach transforms the problem from temporal multiplexing to spatial parallelism, capturing multiple exposure levels simultaneously
2Manufacturing precision
If multiple images are captured at different exposures, then the dynamic range is extended, but the productivity decreases due to multiple captures and processing
Solution Approach 1:
Multiple images captured at different exposure times are merged into a single composite image. The merging process combines the advantages of both short and long exposure images, preserving highlight details from the short exposure image and shadow details from the long exposure image, thereby extending the effective dynamic range while maintaining single-shot capture speed
Solution Approach 2:
The patent performs preliminary sorting and selection of pixel data before final image construction. By identifying which pixels are saturated or underexposed in each captured image and pre-selecting the appropriate data from different exposure images, the system efficiently combines multiple exposures without requiring complex post-processing of all pixel data
3Ease of manufacture
If standard CMOS sensors are used, then the ease of manufacture is high, but the dynamic range is limited compared to photographic film
Solution Approach 1:
The patent dynamically adjusts the exposure time for different regions of the sensor array based on the scene content. By controlling which regions capture images at different exposure times and dynamically merging the results, the system achieves film-like dynamic range using standard CMOS sensors without requiring specialized sensor design
Solution Approach 2:
The patent changes the exposure time parameter for different spatial regions of the sensor array. By varying the exposure time parameter across regions and subsequently merging the captured images, the system overcomes the inherent dynamic range limitations of standard CMOS sensors while maintaining their manufacturing advantages
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
Significantly expands the dynamic range of imaging systems, preserving details in highlights and shadows, reducing motion artifacts and maintaining image quality like photographic film, while being scalable and cost-effective.
Implementation Method 1
photons impinging on the diode will produce carriers which discharge its terminal voltage
Data Source
AI summary
An image capture system is presented where the dynamic range of photo imaging devices, such as a still or video camera, is increased by varying sensor exposure time on a pixel-by-pixel basis under digital camera processor control. The systems photo sensors are continuously illuminated without reset over the exposure interval. In addition to being interrogated at the end of the exposure interval, the pixels are also non-destructively interrogated at one or more intermediate times during the interval. At each interrogation, the image capture system determines individually whether the pixels have saturated and if not, the parameter value is recorded; if the pixel has saturated, the previously stored value from the preceding interval is maintained. To produce the final sensor value for the whole exposure interval, the data for pixels that reached the saturation level are adjusted to compensate for their shortened exposure.