Patent ID: 11915072
Assignee: AGFA OFFSET BV
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  B  H | IPC B  G  H

Claim 18:
19. A method of transforming a continuous-tone image to a halftone raster image for rendering a continuous-tone image, wherein said halftone raster image comprises a plurality of regularly tiled halftone dots wherein a distance between feed points (1003, 2003) between each neighboring halftone dots is from 50 μm to 400 μm,
wherein each of said halftone dots comprises:
(a) image pixels arranged as a first arc (200) or as a plurality of arcs which together represent a first spiral (100) and
(b) non-image pixels arranged as a second arc (201) or as a plurality of arcs which together represent a second spiral (101),
wherein the outer ends of the first spirals of neighbor halftone dots of said plurality of regularly tiled halftone dots are connected to represent a double spiral or triple spiral, and
wherein the first arc, the first spiral, the second arc, and the second spiral of each halftone dot each have a length and/or a thickness which is determined by local densities of the continuous-tone image,
the method comprising the step of transforming said continuous-tone image to said halftone raster image by means of a single threshold tile, whereby
in highlights and midtones of the halftone raster image, the number of image pixels grows by increasing the length and/or the thickness of the first arc or the first spiral; and
in shadows of the halftone raster image, the number of image pixels grows by decreasing the length and/or thickness of the second arc or the second spiral.