Structured Light 3D Face Recognition in Sunlight
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Solution Overview
Problem
Existing image recognition systems face challenges in capturing reliable 3D images of human faces in outdoor environments with varying distances, lighting conditions, and clutter, as they struggle to distinguish structured light patterns from intense sunlight.
Innovation Solution
A method using a coherent light source with a wavelength of 940 nanometres, projecting a pattern onto the subject, and capturing images with cameras at least 3 metres away, which allows for reliable 3D image formation and recognition even in bright sunlight, employing a laser or LED as the light source and a speckle pattern for enhanced discrimination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a coherent light source with wavelength of 940 nanometres is used to illuminate the subject, then the structured light pattern can be distinguished from sunlight interference, but the projected light becomes invisible to the subject and others
Solution Approach 1:
The patent applies the color changes principle by selecting a specific wavelength (940 nanometres) in the near-infrared spectrum for the coherent light source. This wavelength is invisible to the human eye but can be detected by the imaging sensor, allowing the structured light pattern to be distinguished from sunlight while remaining invisible to subjects and observers. The wavelength selection effectively changes the 'color' of illumination to a range that solves the visibility contradiction.
2Ease of operation
If the camera captures images at a distance of at least 3 metres from the human face, then the recognition system can operate at practical distances, but the intensity of sunlight interference increases
Solution Approach 1:
The patent applies parameter changes by selecting a specific wavelength parameter (940 nanometres) for the light source that is less affected by sunlight interference. This parameter change allows the system to operate at practical distances of 3 metres or more while maintaining the ability to distinguish the structured light pattern from environmental sunlight, effectively resolving the contradiction between operating distance and sunlight interference.
3Measurement precision
If a speckle pattern is projected onto the subject, then the 3D image capture accuracy is improved, but the pattern complexity increases
Solution Approach 1:
The patent applies the mechanical vibration principle by using a coherent light source to generate a speckle pattern, which is a random interference pattern characteristic of coherent light. This speckle pattern provides rich spatial frequency information that improves 3D image capture accuracy while the coherence of the light source naturally generates the pattern without requiring complex modulation mechanisms, thus balancing accuracy improvement with device complexity.
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
Enables accurate 3D image capture and recognition of human faces at distances of 3 to 5 metres in outdoor conditions, effectively overcoming the interference of sunlight and ensuring reliable image recognition.
Implementation Method 1
illumination means that comprises a coherent light source and transmits radiation at a wavelength of 940 nanometres
Implementation Method 2
said coherent light source comprises a laser
Implementation Method 3
capturing by camera means... an image of the human face illuminated by the illumination means
Data Source
Figure 1~2
AI summary
A subject (1) is illuminated by a light source (2) and observed by a pair of cameras (3). The outputs of the cameras (3) are input to an image processor (4), operated under the control of a controller (5), which also controls operation of the light source (2). The light source (2) transmits radiation in a frequency range that is limited substantially to a region of increased opacity in the atmospheric transmission spectrum. This may enable the illumination to be quite clearly discriminated, even at relatively great distances and in bright daylight.