A Digital Unsharp Masking algorithm is proposed for enhancing color image in color reproduction systems. The proposed Digital Unsharp Masking filter uses variable enhancement gain to adapt to edge and tone features of the image. By including edge and white/black color detection mechanisms, the new Digital Unsharp Masking algorithm is able to perform detail enhancement without increasing graininess. The tone detection enables the proposed Digital Unsharp Masking to control the sharpness of different tone regions, i.e., highlight, midtone, and shadow, in the scanned image separately. A luminance channel is used as an unsharp channel in the algorithm. The color shift problem faced by existing digital unsharp masking algorithm is eliminated.
"Novel digital unsharp masking algorithm for color images", Proc. SPIE 1771, Applications of Digital Image Processing XV, (12 January 1993); doi: 10.1117/12.139080; https://doi.org/10.1117/12.139080