Patent ID: 8824013

Claim:
An image processing method implemented in a controller unit adapted to control a printer unit, the controller unit adapted to perform an error diffusion half-toning process for quantizing and error diffusing each pixel of an image, wherein the image includes a quantized printer image (O) including a set of ink drops (D C , D M , D Y , D c , D m ) of respective ink channels that are a real combination of drops of ink to be printed, the method comprising: determining for each pixel, by the controller unit, a set of dye quantities cyan, magenta, and yellow (C′, M′, Y′) of subtractive primary colours and a further colour input variable value (S) representing a measure of solvent quantity that should be ejected by the printer unit for each set of dye quantities, the further colour input variable value (S) being computed by calculating for each dye quantity of the set of dye quantities (C′, M′, Y′) a respective measure of solvent quantity (Sx), by limiting said respective measure of solvent quantity (Sx) to be less or equal to a maximum measure of solvent (Smax) for a certain paper and by obtaining as a final colour input variable value (S) the addition of the respective measures of the solvent quantities (S x ); providing, by the controller unit, the determined further colour input variable value (S) and the set of dye quantities (C′, M′, Y′) as a limited number of colour input variables (I) to the same error diffusion half-toning process; adding error output values (E) to said limited number of input variables in the error diffusion process to generate values of a limited number of modified input variables (Im); quantizing (QS), by the controller unit within said error diffusion half-toning process, said limited number of modified input variables (Im), said further colour (s index ) being used as an input for a look up table whereon on the basis of the values of the modified input variables (C′ m , M′ m ) a quantized printer image (O) including a set of ink drops (D C , D M , D Y , D c , D m ) of respective ink channels used in the actual printing device is obtained.