We propose a colour to greyscale algorithmproviding colour separation as well as edge and texture enhancement. An image dependent grey-axis is computed based on the colour distribution in the image. An initial greyscale image is created by a point-wise operation where the grey value is the magnitude of the RGB coordinates re-mapped to the grey axis. The resulting greyscale image is enhanced by applying a novel correction mask. This mask, resembling an unsharp mask, is the sum of the difference between each of the colour components and a blurred version of the greyscale image. The resulting greyscale images are rich in detail without undesirable artifacts.
Ali Alsam, Øyvind Kolås, "Grey Colour Sharpening" in Proc. IS&T 14th Color and Imaging Conf., 2006, pp 263 - 267, https://doi.org/10.2352/CIC.2006.14.1.art00048