Texas Instruments Solution: DLP 3D Biometrics
DLP technology simplifies 3D measurement by using DMD (Digital Micromirror Device) as a spatial light regulator.
Design considerations
DLP technology simplifies 3D measurement by using DMD (Digital Micromirror Device) as a spatial light regulator. DMD achieves high-quality, fast and flexible thematic sequential lighting of the theme. Generally, solid-state (LED) lighting is used to provide monochromatic or multi-color, high-brightness lighting in the range visible to NIR wavelengths.
It is necessary to synchronize the camera with sufficient resolution, sensitivity, and capture frame rate to complete the 3D measurement cycle. The DMD controller provides a synchronized output to trigger the camera shutter to capture each pattern in sequence.
Block diagram
The resolution of the camera / camera lens should be comparable to the DMD resolution to achieve the best measurement quality for each dimension of x, y, and z (depth). The projection pattern and camera imaging area should be closely matched. This overlapping area is where the subject will be placed for measurement.
3D measurement depends on the principle of geometric triangulation. This requires a certain amount of baseline offset between the pattern transmission lens and the camera lens, both of which are aimed at the subject area. Safe positioning of transmission and camera optics should be provided to establish and maintain measurement calibration.
The selected measurement algorithm determines the type and number of patterns used. The style can be binary or "grayscale" (the two operations are slightly different). Mainly multi-scale (coarse to fine) image analysis. The measurement algorithm, the type and number of patterns used will affect the speed, resolution, and accuracy of the measurement.
The measurement algorithm is implemented in software and executed on a PC or embedded processor. The output of the measurement algorithm can have multiple types. One example is a color-coded z-depth map. The other is that points (a set of measurements) can be processed by a 3D visualization program, such as MeshLab.
A series of drawings is required for a complete measurement to occur within a limited period of time. During measurement, the subject must remain fixed (static) in order to avoid blurring, streaking, and measurement errors. A faster mode rate can achieve less motion artifacts and errors.
The speed and efficiency of the 3D measurement system depends on the illumination brightness and the ambient light level. Generally, brighter lighting allows faster measurements. LED lighting (and electrical drivers) need to fully consider power and thermal factors to achieve normal operation and reliability for the expected environmental conditions.
DMD is part of the chipset and must be used with other devices that make up a complete chip.
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