Skin Tone Detection Using Modulated Light and Synchronous Integration
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Solution Overview
Problem
Current methods for determining skin tone, such as reflectance spectroscopy, are prone to large tolerances due to ambient light and other environmental factors, leading to inaccurate skin type detection in IPL devices, which can result in inappropriate energy settings and potential skin damage or exclusion of users with darker skin tones.
Innovation Solution
A method and apparatus that intermittently emit light using a specific duty cycle and integrate sensor signals with a modulation reference signal to reduce ambient light interference, allowing for more reliable skin parameter determination, including skin tone, by calculating the number of cycles required for an integrated value to exceed a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reflectance spectroscopy is used to determine skin tone, then skin parameter detection can be performed, but measurement precision deteriorates due to ambient light interference and large tolerances
Solution Approach 1:
The patent applies periodic action by modulating the light source at a specific frequency (e.g., 1 kHz square wave) and using synchronous detection to measure skin reflectance. The light source is turned on and off periodically, and the detector synchronously samples the reflected light at the same frequency, allowing separation of the modulated signal from ambient light. This periodic modulation enables the system to distinguish between the intentional light source and ambient light, significantly improving measurement precision in the presence of environmental interference.
Solution Approach 2:
The patent implements feedback through synchronous detection where the detector output is fed back through a phase-sensitive detector that compares the signal phase with the modulation reference. The system continuously adjusts and refines the measurement by comparing the detected signal against the known modulation pattern, effectively filtering out ambient light components that are not synchronized with the modulation frequency. This feedback mechanism enhances measurement accuracy by selectively amplifying the modulated signal while rejecting unsynchronized ambient light.
2Measurement precision
If skin tone detection is performed with high sensitivity, then accurate skin parameter determination is achieved, but reliability worsens due to false readings from environmental factors
Solution Approach 1:
The system uses periodic modulation of the light source at a defined frequency and employs synchronous detection that samples only at these specific intervals. This periodic approach ensures that measurements are taken consistently at the same phase of the modulation cycle, eliminating variability introduced by ambient light fluctuations. The consistent periodic sampling improves reliability by ensuring that all measurements are made under identical temporal conditions, reducing false readings and enhancing detection consistency across different environmental conditions.
Solution Approach 2:
The patent converts the harmful effect of ambient light into a beneficial filtering mechanism by using synchronous detection. The system deliberately modulates the light source and then uses this modulation pattern as a reference to identify and reject ambient light components. By treating ambient light interference as a distinguishable signal characteristic rather than simply trying to eliminate it, the system improves reliability - the ambient light becomes identifiable and removable through phase-sensitive detection, allowing accurate skin parameter determination even in challenging lighting conditions.
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 significantly reduces the impact of ambient light and noise, enabling accurate skin parameter determination across a wider range of skin tones, improving safety and usability for IPL devices and other treatment applications.
Implementation Method 1
receiving a first sensor signal that is output by a first light sensor that is arranged to receive light emitted by a first light source after interaction of the emitted light with the skin
Implementation Method 2
One type of skin tone sensor that is currently used in IPL devices makes use of two light emitting diodes (LEDs) that operate at two distinct wavelengths
Implementation Method 3
Hair and the follicle (that are in their anagen phase of the growth cycle) absorbs this energy and goes into its resting phase
Data Source
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AI summary
According to an aspect, there is provided a method for determining a value of a skin parameter for skin of a subject. The method comprises receiving (510) a first sensor signal that is output by a first light sensor that is arranged to receive light emitted by a first light source after interaction of the emitted light with the skin. The first sensor signal is output while the first light source operates according to a first duty cycle to intermittently emit the light, and the emitted light has a first central wavelength. The method also comprises receiving (520) a first modulation reference signal that is related to the first duty cycle; integrating (530) a first function output signal, resulting from a function of the first sensor signal and the first modulation reference signal, to determine a first integrated value; determining (540) a first number of cycles of the emitted light that are required for the first integrated value to exceed a first threshold value; and determining (550) the value of the skin parameter based on the determined first number of cycles.