Patent ID: 7733535

Claim:
A method of operating a micro-processor to manipulate a contone image data to be halftoned with a dither matrix, the contone image data having colour level values for pixels in the image, the colour level values having a certain distribution within a predetermined range of discrete colour levels, the method comprising: deriving a secondary dither matrix from a predetermined primary dither matrix, the primary dither matrix having a range of threshold values and the secondary dither matrix has a compressed range of threshold values, the compressed range of threshold values being determined in accordance with the following algorithm: T new =L min +T old ·( L max −L min )/ L total where: L max is the maximum number of discrete colour levels if a predetermined top-most portion of the colour level values of the contone image data is disregarded; L min is the minimum number of discrete colour levels that contain a predetermined bottom-most number of the colour level values of the contone image data; L total is the total number of levels in the range of discrete colour levels; T new is the compressed threshold values in the secondary dither matrix; and, T old is the threshold value in the primary dither matrix; and, halftoning the contone image data with the secondary dither matrix.