Image-Based Pulse Rate Detection Under Motion and Light Disturbance
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Solution Overview
Problem
Existing non-contact pulse rate detection technologies face reliability issues due to disturbances such as subject movement and environmental light changes, leading to uncertain accuracy and reduced detection periods when stringent reliability evaluation is applied.
Innovation Solution
A pulse rate detection device and program that utilize image processing to obtain a pulse rate from pixel value changes, assess reliability based on Signal-to-Noise Ratio (SNR), and reduce reliability if disturbance peaks in the frequency domain are within predetermined thresholds, accounting for movement and light disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse rate is detected using a general-purpose microprocessor and standard algorithms, then device complexity is reduced, but measurement precision deteriorates due to inability to handle motion artifacts and low signal quality
Solution Approach 1:
The detection algorithm is segmented into multiple independent modules: motion artifact detection module, signal quality evaluation module, and pulse rate calculation module. Each module processes specific aspects of the PPG signal independently, allowing the system to handle complex scenarios through coordinated operation of simpler, specialized components rather than a single complex algorithm.
Solution Approach 2:
The patent introduces an intermediary signal processing layer that detects motion artifacts and evaluates signal quality before the final pulse rate calculation. This intermediary layer acts as a mediator between the raw PPG signal and the final measurement, filtering out corrupted data and ensuring accurate pulse rate detection even in challenging conditions.
2Productivity
If continuous pulse rate monitoring is performed using conventional methods, then productivity is maintained, but loss of information increases due to motion artifacts and poor signal quality
Solution Approach 1:
The system implements feedback mechanisms where the signal quality evaluation module continuously monitors the quality of PPG signals and provides feedback to the pulse rate calculation module. When motion artifacts or poor signal quality are detected, the feedback loop triggers corrective actions such as rejecting erroneous measurements, requesting re-sampling, or adjusting detection parameters to maintain continuous accurate monitoring.
Solution Approach 2:
The motion artifact detection module performs preliminary action by identifying and flagging corrupted signal segments before they affect the final pulse rate calculation. This preliminary detection and classification of signal quality allows the system to prevent erroneous data from propagating through the measurement process, maintaining information integrity during continuous monitoring.
3Measurement precision
If complex signal processing is applied to improve measurement precision, then pulse rate detection accuracy improves, but device complexity and processing time increase
Solution Approach 1:
The patent applies partial action by implementing signal processing only where and when necessary. The algorithm selectively processes signal segments based on their quality assessment - high-quality segments undergo full processing for accurate pulse rate calculation, while low-quality segments due to motion artifacts are quickly rejected without extensive processing. This partial application of processing efforts maintains precision for valid measurements while reducing overall processing time.
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
Outputs a highly reliable pulse rate by filtering out disturbances, ensuring accurate and prolonged detection periods by adjusting reliability criteria based on SNR and disturbance factors.
Implementation Method 1
a photodetector, and a processor. The pulse rate detection device is configured to: acquire, by the photodetector, a pulse wave signal transmitted through a subject; separate, by the processor, a motion component from the pulse wave signal; and calculate, by the processor, a pulse rate based on a remaining signal after the motion component is separated
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(d)
AI summary
The object of the present invention is to output a pulse rate that is highly reliable. A pulse rate detection device 1 evaluates the reliability of a detected pulse rate on the basis of the SN ratio of a pulse signal while taking into account disturbance factors. The pulse rate detection device 1 has a pulse rate display criteria 1 and a pulse rate display criteria 2 for displaying the pulse rate, wherein when the SN ratio is equal to or greater than the former, the pulse rate is displayed, and when the SN ratio is equal to or greater than the latter and less than the former, the pulse rate is displayed on the condition that the difference from the immediate past pulse rate is smaller than a predetermined reference. When the SN ratio is less than the pulse rate display criteria 2, the reliability is considered low and the pulse rate is not displayed. Additionally, the pulse rate detection device 1 takes into account a movement disturbance caused by movement of the face of a subject 11 and a light disturbance caused by changes in the light illuminating the face of the subject 11, and when the peak frequency in the frequency domain of the movement disturbance or light disturbance is close to the pulse rate at a value equal to or greater than the predetermined reference, the pulse rate detection device 1 determines that the reliability of the detected pulse rate is low due to these disturbances and does not display the pulse rate.