US 7,321,447 B2
System and method for processing a multi-colour image
Paul Kuiper, Eindhoven (Netherlands)
Assigned to Oce-Technologies B.V., Venlo (Netherlands)
Filed on Dec. 09, 2003, as Appl. No. 10/730,118.
Claims priority of application No. 02080674 (EP), filed on Dec. 10, 2002.
Prior Publication US 2004/0114168 A1, Jun. 17, 2004
Int. Cl. H04N 1/52 (2006.01); H04N 1/58 (2006.01); H04N 1/56 (2006.01); B41M 1/14 (2006.01)
U.S. Cl. 358—1.9  [358/535; 358/3.26; 358/540; 358/530; 347/15; 347/175; 347/176] 20 Claims
OG exemplary drawing
 
1. A method for image processing a digital multi-colour image, the method comprising the steps of:
generating from said digital multi-colour image, image signals for a selection of process colours, each image signal being associated with a digital separation image of a process colour of said selection of process colours and specifying for each pixel of said digital multi-colour image an image density value for the associated process colour; and
adding up, for each image part of said digital multi-colour image, the image density values of all said process colours of the pixels of the image part in order to determine for each said image part a total area coverage value (CT),
wherein, if the total area coverage value of an image part exceeds 100%, the method further comprises the following steps:
a) dividing image density values of pixels of the image part specified by the image signals, into first image density values associated with a first layer of image dots of marking particles and at least second image density values associated with a second and any following layer of image dots of marking particles such that the sum of said at least second image density values corresponds to an area coverage value equal to CT-100%, and
b) converting the image signals by using a matrix-dither technique into corresponding first printing signals and at least corresponding second printing signals, each printing signal indicating for each pixel of the image part whether an image dot of marking particles of the corresponding process colour is to be formed, said matrix-dither technique being such that each of the first printing signals is built up from a raster of a first two-dimensional matrix structure by thresholding said first image density values, while each of the second printing signals is built up from a raster of a second two-dimensional matrix structure different from said first two-dimensional matrix structure, by thresholding said second image density values.