Issue: Impact of the measuring conditions on optical shape
irregularity assessment, including illumination, object colour, viewing angle,
focusing, etc.
Comment: In case of 2D measurements, backlighting is used for higher precision and reliability. The color does not matter. The viewing angle should be as close as possible to orthogonal to the support surface. Since geometric correction is done, to a certain extent this angle is not critical. However, geometric correction cannot remove the effects of a non-orthogonal camera viewing an inner part of a hole, or other surface that should not be visible.
Currently, the rotation angle of the shape in the image is arbitrary. For higher precision and, mostly, speed, it is better to constrain the angle. Precise, well-focused camera yields contrast, correct image. This is strongly desired. De-focusing may be partially compensated for by enhancement and subpixel measurements. However, this should be avoided, as de-focusing is not linear, while enhancement and subpixel correction are usually linear.
The precision is influenced by non-flatness of the objects, so that the camera may see the inner surfaces near the edges. It is hard to estimate this influence, since it depends on how the objects lies on the surface: the bottom surface of the object may be non-flat or tilted. This is related to the viewing angle of the camera.