1. A method for processing an image to increase sharpness of the image without changing hue characteristics, the method comprising: (a) performing a transformation process to transform an original image signal into CIE XYZ colorimetric channels; (b) forming a luminance channel Y; (c) applying a filter on the luminance channel Y to obtain a processed luminance channel Y″; (d) computing processed colorimetric channels X″ and Z″ based on the processed luminance channel Y″; and (e) performing an inverse transformation process to transform the processed colorimetric channels X″Y″Z″ into a processed image signal.