Method and system for processing a multi-colour image

A method for processing a digital multi-colour image for reproduction thereof on a colour image reproduction system capable of complementary forming separation images of coloured marking particles, said method comprising the steps of:

• generating from said digital multi-colour image a sequence of image signals of a selection of process colours, each image signal of said sequence being associated with a digital separation image of a process colour of said selection of process colours and specifying an image density value for each pixel of said digital separation image of said process colour;
• and
• converting said sequence of image signals into a sequence of corresponding printing signals, each printing signal of said sequence indicating for each pixel of the corresponding digital separation image whether an image dot of marking particles of the corresponding process colour is to be formed;
• wherein at least one image signal selected from a second and any following image signal of said sequence of image signals is converted by using a matrix-dither technique, into the corresponding printing signal, said matrix-dither technique being such that said corresponding printing signal is built up from a raster of a two-dimensional matrix structure including threshold values being arranged in a predetermined order by comparing the input density value of each pixel of the corresponding digital separation image with the corresponding threshold value, said predetermined order being such that with gradually increasing input density value a linear growth pattern is generated in a predetermined direction by alternately adding image dots to both sides.

A computer program product embodied on at least one computer readable medium, for processing a digital multi-colour image for reproduction thereof on a colour image reproduction system capable of complementary forming separation images of coloured marking particles, the computer program product comprising computer-executable instructions for:

• generating from said digital multi-colour image a sequence of image signals of a selection of process colours, each image signal of said sequence being associated with a digital separation image of a process colour of said selection of process colours and specifying an image density value for each pixel of said digital separation image of said process colour;
• and
• converting said sequence of image signals into a sequence of corresponding printing signals, each printing signal of said sequence indicating for each pixel of the corresponding digital separation image whether an image dot of marking particles of the corresponding process colour is to be formed;
• wherein at least one image signal selected from a second and any following image signal of said sequence of image signals is converted by using a matrix-dither technique, into the corresponding printing signal, said matrix-dither technique being such that said corresponding printing signal is built up from a raster of a two-dimensional matrix structure including threshold values being arranged in a predetermined order by comparing the input density value of each pixel of the corresponding digital separation image with the corresponding threshold value, said predetermined order being such that with gradually increasing input density value a linear growth pattern is generated in a predetermined direction by alternately adding image dots to both sides.