DLP® technology facilitates 3D measurement by utilizing a DMD (Digital Micromirror Device) as a spatial light modulator. The DMD achieves high quality, fast, and flexible sequential pattern illumination of the subject field. Typically, solid state (LED) illumination is used to provide monochrome or multi-color, high brightness illumination within the visible to NIR wavelength range.
A synchronized camera of sufficient resolution, sensitivity, and capture frame rate is required to complete the 3D measurement loop. The DMD controller provides a SYNC output to trigger the camera shutter for capturing each pattern in sequence.
The resolution of the camera/camera lens should be commensurate with the DMD resolution for best measurement quality in x, y, and z (depth) dimensions. Both the projected patterns and the camera imaging field should match very closely. This overlapping area is where the subject will be placed for measurement.
The 3D measurement depends on the principle of geometric triangulation. This requires a certain amount of baseline offset between the pattern projection lens and the camera lens, with both lenses aimed at the subject field. Provision should be made for securely locating the projection and camera optics so that measurement calibration can be established and maintained.
The chosen measurement algorithm determines the type and number of patterns used. Patterns may be binary or “gray scale”(the operation of the two is somewhat different). The essential principal is multi-scale (coarse to fine) image analysis. The measurement algorithm, and the type and number of patterns used will affect the speed, resolution, and accuracy of the measurements.
The measurement algorithm is implemented in software and executed on a PC or embedded processor. The output of the measurement algorithm can take several forms. One example is a color-coded z-depth map. Another is a point cloud (set of measurements) which can be processed by 3D visualization programs, such as MeshLab.
The sequence of patterns required for a full measurement take a finite period of time to occur. The subject must be held immobile (still) during the measurement time in order to avoid blurring, striping, and measurement errors. Faster pattern rates allow for fewer motion artifacts and errors.
The speed and effectiveness of the 3D measurement system depend on illumination brightness and ambient light levels. In general, brighter illumination allows for faster measurements. The LED illuminators (and electrical drivers) require sufficient consideration of power and thermal factors to allow for proper operation and reliability for the expected environmental conditions.
The DMD is part of a chipset, and must be utilized with the other devices which constitute the full chipset.
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