Pulse Propagation Phase Measurement Using Opposite Rolling Shutter Scans
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Solution Overview
Problem
The resolution of pulse propagation across an area within a shutter scan duration is limited by the frame rate of cameras, particularly with rolling shutter cameras, where unknown phase changes occur during the shutter scan, hindering accurate measurement of phase changes.
Innovation Solution
An apparatus and method that capture two images of an area using different shutter scanning directions, convert these images into pulse-phase maps, and utilize a shutter-time difference map to correct pulse-phase difference maps, thereby obtaining maps of pulse-phase changes over the shutter scan duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rolling shutter camera is used to capture pulse propagation, then the device complexity is reduced and ease of operation is improved, but unknown phase changes occur within the shutter scan duration, degrading measurement precision
Solution Approach 1:
The patent divides the measurement process into two separate image captures with opposite shutter scanning directions. By segmenting the temporal measurement into two directional passes, the system can computationally eliminate the shutter scan duration effect, achieving high precision phase change measurement without being constrained by the shutter scan time of a single direction.
Solution Approach 2:
The patent employs opposite shutter scanning directions for the two image captures. By inverting the shutter scan direction between the first and second images, the systematic phase changes introduced by the rolling shutter are reversed, allowing their cancellation through subtraction to reveal the true pulse propagation phase changes.
2Measurement precision
If the frame rate of the camera is increased to improve temporal resolution of pulse propagation, then measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
Instead of changing the camera's frame rate parameter to achieve better temporal resolution, the patent changes the shutter scanning direction parameter between two captures. This parameter change approach allows high temporal resolution measurement of pulse propagation using standard frame rates, avoiding the need for high-speed or specialized cameras.
3Measurement precision
If two images are captured using different shutter scanning directions, then pulse-phase changes can be accurately detected, but the loss of time increases due to multiple captures
Solution Approach 1:
The patent utilizes the periodic nature of pulse propagation by capturing two images within a single pulse cycle or adjacent pulse cycles. By synchronizing the dual captures with the periodic pulse waveform and using opposite shutter directions, the system achieves accurate phase change measurement efficiently within the natural periodic timing of the physiological signal.
Data Source
AI summary
Examples of the disclosure relate to at least apparatus, methods, and computer programs, configured to control capture of two images of an area, across which a pulse propagates, using different shutter scanning directions. Either the images are converted into pulse-phase maps of the area and a pulse-phase difference map obtained which identifies differences between the pulse-phase maps of the area, or a colour difference map is obtained which identifies differences between the two images and the colour difference map is converted into a pulse-phase difference map. A shutter-time difference map is obtained which identifies differences between capture times of corresponding locations in the two images. Using the shutter-time difference map, the pulse-phase difference map is corrected to obtain a map of pulse-phase changes which have occurred over a duration of a shutter scan.