Texture differences in a picture are difficult to analyse by digital techniques, but can be identified readily by optical spatial filtering. However, purely optical processors have several disadvantages. A low-cost system is described in which the output from an optical processor is digitized and processed by a microcomputer to produce a colour-coded image. This makes it possible to use the parallel processing capability of the optical processor for preliminary data reduction, while retaining the flexibility and interactive capability of a digital computer.