Abstract: A method of calibrating an incoherent optical fibre bundle to be used for image transmission, by determining the relative input to output position of each fibre in the bundle and processing the light output of the bundle accordingly. The calibration technique comprises, defining an address array capable of defining for the optical bundle the position of the ends of individual optical fibres in the bundle; transmitting a series of test images into one end of the optical fibre bundle, each test image illuminating a substantial proportion of the pixels and the combination of which selectively illuminate each pixel of the address array; analysing the output of the fibre bundle with reference to the transmitted images to produce a reference table of input to output for the fibres; and using the reference table to deconvolve an image transmitted along the fibre bundle. Calibrated incoherent optical fibres are of particular use for examining nuclear reactors, chemical vats and other harsh environments.