An investigation of various computational techniques in optical fringe analysis
Fringe projection is an optical technique for three dimensional non-contact measurement of height distributions. A fringe pattern is projected onto an object's surface and, when viewed off-axis, it deforms to follow the shape of the object. The deformed fringe pattern is analysed to obtain its phase, information that is directly related to the height distribution of the surface by a proportionality constant. This thesis analyses some key problems in fringe projection analysis. Special attention is focused on the automatisation of the process with Fourier Fringe Analysis (FFA). Unwrapping, or elimination of 21t discontinuities in a phase map, is treated in detail. Two novel unwrapping techniques are proposed, analysed and demonstrated. A new method to reduce the number of wraps in the resulting phase distribution is developed. A number of problems related to FFA are discussed, and new techniques are presented for their resolution. In particular, a technique with better noise isolation is developed and a method to analyse non-fullfield images based on function mapping is suggested. The use of parallel computation in the context of fringe analysis is considered. The parallelisation of cellular automata in distributed memory machines is discussed and analysed. A comparison between occam 2 and HPF, two compilers based upon a very different philosophy, is given. A case study with implementations in occam 2 and high performance FORTRAN (HPF) is presented. The advantages and disadvantages of each solution are critically assessed.