Measurement of physical dimensions of produced parts is one of the applications area of visual inspection. High accuracy measurements -typical mechanical tolerances are about 0.1% or 0.05%- without needing image sizes of 1024 or 4096 pixels implies subpixel accuracy interpolation techniques. An overview of some algorithms will be given in this paper first. One of the subpixel accuracy algorithms has been implemented efficiently on an image computer which has been designed in our laboratory. A general image processor is implemented as a set of two microprogrammable processors: the first is optimized for search operations and will locate the edge of interest, the second is optimized for arithmetic operations and will calculate the accurate edge positions. Both operations are relatively independent and can be pipelined to achieve a maximum performance. Since on-line inspection is considered, execution time is of main importance.
"Fast Measurement Of Physical Dimensions", Proc. SPIE 0804, Advances in Image Processing, (14 October 1987); doi: 10.1117/12.941324; https://doi.org/10.1117/12.941324