Ambient Light Correction via Pulsed Illumination and Pixel Sorting
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Solution Overview
Problem
Existing non-contact skin imaging systems face challenges in accurately correcting for ambient light inconsistencies in uncontrolled environments, leading to noisy measurements due to the limitations of current techniques such as active illumination and flash photography, which can introduce unwanted noise, especially in low-light conditions.
Innovation Solution
A system and method utilizing pulsed illumination with a light source and an imaging unit that captures images at exposure times shorter than the wave period of the illumination, where the pulse frequency is not a multiple integral of the frame rate, and a control unit sorts and weights pixel values based on a least squares approximation of the probability density function to generate an ambient light-corrected image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the maximum-minimum technique is used to correct ambient light, then ambient light correction is achieved, but noise is amplified especially in low-light conditions
Solution Approach 1:
The patent applies preliminary action by capturing multiple candidate images before processing to establish a statistical baseline of pixel value distributions. This preliminary capture phase allows the system to pre-characterize the ambient light conditions and noise patterns, so that when ambient light correction is applied, the system can distinguish between actual signal variations and noise, thereby correcting ambient light without amplifying noise artifacts.
Solution Approach 2:
The patent introduces an intermediary statistical model (probability density function) that mediates between the raw pixel values and the final corrected image. Instead of directly applying maximum-minimum subtraction which amplifies noise, the system uses this intermediary statistical representation to smoothly estimate ambient light contributions, effectively filtering out noise while maintaining correction accuracy.
2Measurement precision
If pulsed illumination with rolling shutter is used, then ambient light can be separated from artificial light, but dark-bright horizontal bands appear in the image
Solution Approach 1:
The system performs preliminary action by capturing multiple candidate images at different phases of the pulsed illumination cycle before processing. This preliminary multi-phase capture allows the system to build a complete statistical model of the illumination pattern and its interaction with the rolling shutter, enabling subsequent processing to correctly separate ambient and artificial light without producing visual artifacts.
Solution Approach 2:
The patent applies feedback by using the statistical distribution information derived from multiple candidate images to guide the ambient light correction process. The system continuously refines its estimate of ambient light contributions based on the observed pixel value distributions, feeding this information back into the correction algorithm to eliminate the dark-bright band artifacts while maintaining accurate ambient light separation.
3Measurement precision
If multiple candidate images are captured for ambient light correction, then correction accuracy improves, but processing time increases
Solution Approach 1:
The patent applies preliminary action by capturing multiple candidate images in rapid succession before the actual measurement phase. This preliminary multi-image capture establishes a statistical baseline that can be processed efficiently using closed-form solutions, allowing the system to achieve high correction accuracy without requiring lengthy processing times during actual operation.
Solution Approach 2:
The system employs parameter changes by varying the number of candidate images captured based on the specific application requirements and ambient conditions. The statistical processing methods used allow efficient handling of variable numbers of input images, enabling the system to optimize the trade-off between correction accuracy and processing time by adjusting this parameter dynamically.
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 enables accurate ambient light correction at video rates, even for low-cost imaging units with timing jitter, without requiring phase determination of the pulsed illumination pattern, thus providing a stateless technique for improved image quality.
Implementation Method 1
a light source configured to provide pulsed illumination to a subject; wherein a pulse frequency of the illumination provided by the light source is not a multiple integral of a frame rate at which a plurality of images are captured
Implementation Method 2
an imaging unit configured to capture, while the subject is illuminated by the pulsed illumination from the light source, a plurality of images of the subject, wherein each of the plurality of images is captured at an exposure time shorter than the wave period of the pulsed illumination
Data Source
AI summary
There is provided a system (100) comprising a light source (110), an imaging unit (120) configured to capture a plurality of images of an subject, wherein each of the plurality of images is captured at an exposure time shorter than the wave period of the pulsed illumination, wherein the pulse frequency of the illumination is not a multiple integral of the frame rate at which the images are captured, and wherein a total time during which the plurality of images is captured is at least half of the wave period of the pulsed illumination, and a control unit (130) configured to: obtain a predetermined number n of candidate images, generate a sorted list of pixels by sorting respective pixels, apply a set of weights to the respective sorted list of pixels, and generate an estimated ambient light corrected image based on the plurality of weighted and sorted lists of pixels.