Colour image edge detector based on quaternion convolution

A new type of edge-detecting filter is presented, based on a new type of image convolution in which colour images are convolved with a pair of quaternion-valued (hypercomplex) masks. When applied to a colour image, the new filter converts areas of smoothly-varying colour to shades of grey; and generates colours in regions where colour (but not intensity) edges occur in the image. The result may be easily thresholded for chromaticity to produce an edge image exhibiting colour only where the original image exhibited a sharp change of colour.