DETERMINING SURFACE ROUGHNESS

A measurement system (301) for determining surface roughness is shown. A coherent illumination device (303) illuminates the surface of, for example, a component (201) with coherent light. An imaging device (304) obtains an image of speckle caused by the scattering of the coherent light from the surface. A processing device (305) converts the image into a binary image according to a threshold, thereby classifying pixels below the threshold as background pixels and pixels above the threshold as foreground pixels. One or more regions of connected foreground pixels are then identified in the binary image, in which any two foreground pixels in a region are joined by a continuous path of foreground pixels. The total number of regions identified and the number of pixels in the largest region are then evaluated, each of which correlate with surface roughness. An indication of the surface roughness of the surface is then outputted.