Video Block Selection for PPG Signal Extraction
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Solution Overview
Problem
Conventional photoplethysmography (PPG) methods using smartphones for estimating physiological parameters, such as heart rate, often result in poor-quality signals due to flash-induced pixel saturation and varying skin tones, leading to inaccurate measurements and limited operational utility, especially with devices of low computational power.
Innovation Solution
Divide video frames into blocks to select the region with the highest peak signal-to-noise ratio (PSNR) for signal extraction, followed by signal enhancement using adaptive filters and interpolation techniques to improve signal quality and accuracy, allowing for accurate physiological parameter determination even on low-processing-capability devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If video frames are processed using conventional PPG methods, then the measurement process is simple, but the signal quality is poor due to flash-induced pixel saturation and varying skin tones
Solution Approach 1:
The video frame is divided into multiple blocks, and each block is evaluated individually to identify the optimal block for PPG signal extraction. This segmentation allows the system to avoid regions with flash-induced saturation and select regions with better signal quality, directly addressing the measurement precision issue while maintaining computational feasibility through systematic block-wise processing.
Solution Approach 2:
Different regions of the video frame are treated differently based on their local characteristics. The system calculates PSNR for each block and selects the block with the highest PSNR value, applying local quality assessment to identify the most suitable region for signal extraction. This approach accounts for varying skin tones and flash effects in different parts of the frame.
2Illumination intensity
If the flash brightness is increased to improve video quality, then the illumination is better, but pixel saturation occurs reducing signal quality
Solution Approach 1:
The system changes the evaluation parameter from simple intensity measurement to PSNR (Peak Signal-to-Noise Ratio) calculation. By using PSNR as the selection criterion, the system can identify blocks where the flash brightness provides adequate illumination without causing saturation, thus resolving the contradiction between illumination intensity and signal quality.
Solution Approach 2:
The system converts the harmful effect of flash-induced saturation into a useful selection criterion. By calculating PSNR for each block, the system identifies blocks where flash effects are minimized or optimally balanced, transforming the potential harm into a method for selecting the best signal source.
3Measurement precision
If signal enhancement techniques are applied to improve accuracy, then the physiological parameter estimation is more accurate, but the computational load increases on low-processing-capability devices
Solution Approach 1:
The system performs preliminary action by selecting the optimal block based on PSNR before extracting and processing the PPG signal. This pre-selection ensures that the subsequent signal enhancement operations are applied to the best possible input data, maximizing the effectiveness of computational resources and improving accuracy without requiring excessive processing power.
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 the quality of PPG signals, increasing the accuracy of physiological parameter estimation and enabling the use of low-processing-capability devices like smartphones for reliable heart rate measurement, while adjusting flash brightness based on skin tone further optimizes signal quality.
Implementation Method 1
smart phones equipped with a light source, such as a light emitting diode (LED) flash
Implementation Method 2
The PPG is a non-intrusive optical technique and involves use of light for measuring change in blood volume of the individual
Data Source
AI summary
A physiological parameter measurement device comprising a processor and a video processing module coupled to the processor to divide each of a plurality of frames of a video into a plurality of blocks, where the video is of a body part of a subject whose physiological parameter is to be determined. The video processing module further is to select a block having highest peak signal to noise ratio (PSNR) from amongst the plurality of blocks. Further, the video processing module is to extract a photoplethysmogram (PPG) signal from the video based on a block identifier associated with the block. The physiological parameter measurement device further comprises a signal enhancement module coupled to the processor, to process the PPG signal to obtain an enhanced PPG signal for determining a value of the physiological parameter for the subject.