Generation of Stripe Patterns
Two major methods of stripe pattern generation have been established: Laser interference and projection.
The laser interference method works with two wide planar laser beam fronts. Their interference results in regular, equidistant line patterns. Different pattern sizes can be obtained by changing the angle between these beams. The method allows for the exact and easy generation of very fine patterns with unlimited depth of field. Disadvantages are high cost of implementation, difficulties providing the ideal beam geometry, and laser typical effects like speckle noise and the possible self interference with beam parts reflected from objects. Typically, there is no means of modulating individual stripes, such as with Gray codes.
The projection method uses non coherent light and basically works like a video projector. Patterns are generated by a display within the projector, typically a liquid crystal display (LCD) or liquid crystal on silicon (LCOS) display.
A proprietary projection method uses digital light processing (DLP; moving micro mirror) displays. DLP displays do not absorb light significantly and therefore allow very high light intensities. They also have an extremely linear gray value reproduction, as they are steered by pulse length modulation.
Principally, stripes generated by display projectors have small discontinuities due to the pixel boundaries in the displays. Sufficiently small boundaries however can practically be neglected as they are evened out by the slightest defocus.
A typical measuring assembly consists of one stripe projector and at least one camera. For many applications, two cameras on opposite sides of the projector have been established as useful.
Invisible (or imperceptible) structured light uses structured light without interfering with other computer vision tasks for which the projected pattern will be confusing. Example methods include the use of infrared light or of extremely high framerates alternating between two exact opposite patterns.
Read more about this topic: Structured-light 3D Scanner
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