Pulsed Illumination Visibility Reduction in Biometric Imaging
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Solution Overview
Problem
Active illumination in biometric systems, such as iris and facial recognition, is often noticeable to users, causing discomfort and potentially triggering photosensitive epilepsy, due to the repetitive on/off cycle of pulsed lighting, which affects image quality and user experience.
Innovation Solution
A method utilizing two illumination modalities synchronized and asynchronous to frame acquisition, exploiting differences in human visual system persistence, spectral response, and perceived brightness to maximize image quality while minimizing perceived illumination, including pulsed and constant background lighting with varying wavelengths and intensities, and using photodiodes for feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulsed illumination is used to concentrate power during frame acquisition, then image quality is improved, but user perception of illumination increases causing discomfort and photosensitive epilepsy
Solution Approach 1:
The illumination is divided into two separate modalities: a first modality (pulsed illumination) optimized for image acquisition quality, and a second modality (background illumination) optimized for user comfort. Each modality operates with different characteristics - the first provides high-intensity pulsed light synchronized with frame acquisition, while the second provides lower-intensity continuous or asynchronously pulsed light that reduces user perception of flicker and discomfort.
Solution Approach 2:
The system changes multiple parameters of illumination including intensity, pulse duration, duty cycle, and synchronization timing. By adjusting these parameters independently for each modality, the system achieves high image quality during acquisition while maintaining user comfort during non-acquisition periods, thereby resolving the contradiction between image quality and user comfort.
2Illumination intensity
If high power LEDs are used to improve illumination intensity, then image quality is improved, but the LEDs become more noticeable to users
Solution Approach 1:
The illumination system is segmented into high-power LEDs for image acquisition and lower-power LEDs for background illumination. The high-power LEDs operate only during frame acquisition with synchronized pulsed illumination, while the lower-power LEDs provide continuous or asynchronous background light that masks the visibility of the high-power LEDs, thus maintaining both high illumination intensity and reduced user visibility.
Solution Approach 2:
The second modality of illumination acts as an intermediary that masks the visibility of the high-power first modality. By providing a background illumination level, the system reduces the contrast between the pulsed high-power illumination and the surrounding environment, making the high-power LEDs less noticeable to users while maintaining their effectiveness for image acquisition.
3Loss of energy
If pulsed illumination is synchronized to frame acquisition, then power efficiency is improved, but the repetitive on/off cycle is more noticeable to users
Solution Approach 1:
The illumination cycle is segmented into synchronized pulsed illumination for frame acquisition and asynchronous background illumination. The synchronized pulses maintain power efficiency by concentrating power only when needed for image capture, while the asynchronous background illumination fills in the gaps between pulses with lower-intensity light that is less perceptible to users, thereby reducing the visibility of the repetitive on/off cycle.
Solution Approach 2:
The system uses periodic pulsed illumination synchronized with frame acquisition rates (typically 30-60 Hz), which exploits the persistence of vision to reduce perceived flicker. By operating at frequencies above the critical flicker fusion threshold and combining with asynchronous background illumination, the system maintains power efficiency while minimizing user perception of the illumination cycle.
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 reduces user perception of illumination while maintaining high-quality image acquisition, minimizing discomfort and the risk of photosensitive epilepsy, by leveraging the temporal persistence and spectral sensitivity of the human eye, and the characteristics of imaging systems.
Implementation Method 1
sensing the actual output of the illumination source and adjusting the output of the illumination source in response to the sensed output
Data Source
AI summary
A method of providing active illumination during biometry that utilizes pulsed lighting synchronized to frame acquisition. Two distinct illumination modalities are provided: the first maximizes the quality of images captured by the imaging system, and the second minimizes the overall illumination perceived by the user in combination with the first. The two modalities are provided substantially simultaneously. The first modality always includes a set of pulses synchronized with frame acquisition. The second modality may be either a second set of pulses not synchronized with frame acquisition or constant background illumination. The two modalities may be generated by two separate sources of illumination or by the same single illumination source. Adding the second modality to the first reduces user discomfort and the chances of an epileptic response as compared to using the first modality alone. The two modalities may have different wavelengths, pulse durations, or intensities.