The image then interferes with the reference grating to form Moire fringe contour patterns which appear as dark and light stripes, as demonstrated by Fig. 7 . Ambiguities arise in interrogating the fringe patterns. It is not possible to determine whether adjacent contours are higher or lower in depth. Resolve by moving one of the gratings and taking multiple Moire images. Reference grating can also be omitted and its effect can be simulated in software.
Methods are relatively computationally expensive.
Shape from Shading Methods Methods based on shape from shading employ photometric stereo techniques to produce depth measurements. Using a single camera, two or more images are taken of an object in a fixed position but under different lighting conditions. By studying the changes in brightness over a surface and employing constraints in the orientation of surfaces, certain depth information may be calculated. Methods only work well on objects with uniform surface texture. It is difficult to infer absolute depth, and only surface orientation is easily inferred.