Patent ID: 8437037

Claim:
A computer-implemented screening system for converting an image representation for a region comprising a continuous tone value for a given separation channel into a screened image representation value for the given separation channel for printed reproduction of images on a digital printing system, said screening system being capable of rendering more than two density levels at a device pixel level, said screening system comprising a processor, and a first, a second, and a third separation screen and using precalculated rectangular screening tiles that define a spatially repetitive screening operation according to geometric clustered dot screen definitions for first, second and third separation screens, said first, second and third separation screens being configured so they have different screen angles and each having rulings with at least two of the screen rulings being different by a finite amount and with at least one vector sum of two frequency components of one pair of screens being equal to at least one frequency component of the other screen or to a multiple or submultiple of said at least one frequency component of the other screen, in which at least one of said three separation screens is simple rational, at least one of said three separation screens having target positions for centers of clustered dots, so that all the target positions for the centers of clustered dots for that separation screen have an identical relative position with respect to a device grid of addressable pixel positions, wherein said three screens have an angular relation between them which is equivalent by a rotation of the entire screening system to the angular relation of a system of three screens with screen angles at 15 degrees+delta 1 , 45 degrees+delta 2 , 75 degrees+delta 3 , with delta 1 , delta 2 , delta 3 when expressed in degrees satisfying the following relationships: |delta1|<1 degree, |delta2|<1 degree, |delta3|<1 degree, wherein the screening operation for each of said three separation screens is arranged to convert an image representation for a region comprising a continuous tone value for a given separation channel into a screened image representation value for the given separation channel with a specific density value out of the available more than two density values for each addressable pixel position to be rendered.