Linearization of defocus for projector optical alignment in structured light illumination systems

Jungwirth, Matthew E. L.; Rudd, E.

doi:10.1117/12.2567172

Cited by 1 publication

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“…Notice that the blue field is focused on the front step and the red is defocused on the back step. Other aspects: the thick black line is the optical axis, the DMD produces the SLI pattern and is tilted to meet the Scheimpflug condition, distance Z1 is the camera’s target-space working distance, and distance Z2 is the projector’s back working distance 10 …”

Section: Quad Target Methodsmentioning

confidence: 99%

Linearized projector alignment system for structured light illumination systems using the quad target method

2022

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Structured light illumination (SLI) systems can measure a target's two-dimensional height profile. High-quality imaging in SLI systems is typically dependent upon well-focused optical systems that can be difficult to achieve due to the nonlinear nature of defocus. We present the quad target method (QTM), a simple and fast alignment technique that linearizes defocus for SLI projectors. This linear response provides a clear zero crossing along the optical axis to minimize any focus ambiguity and maximize projector focus quality. QTM creates the linearization by sampling the field at two locations along the optical axis using a quad target, which is a diffuse target with two different heights in opposing quadrants. To maximize feedback speed, QTM can estimate the current focus position using only a single image by measuring the contrast of projected sinusoidal fringes on the quad target. QTM was tested using a commercial SLI system and compared with a published phase shifting reconstruction technique. The nonlinear defocus behavior was efficiently linearized as evidenced by focus estimation accuracies over a broad range of QTM variables.

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