Method and apparatus for generating halftone images by discrete one-to-one dither tile rotation
US5422742A · kind A · utility
Inventors
Key dates
| Filing date | Sep 8, 1993 |
| Grant date | Jun 6, 1995 |
| Priority date | — |
| Expiry date | Sep 8, 2013 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N1/4058
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
The invention relates to a method and apparatus for automatic high-speed generation of digital angled halftone screens, specially suited for obtaining screens approximating the irrational angles which are generally required by high-quality color reproduction. The method enables color separations to be generated which minimize Moire effects, interferences and artifacts by applying discrete one-to-one rotations to digital halftone screens of the required period in order to reach the final screen angle. Dither tiles incorporating assemblies of the basic screen element are rotated by one-to-one discrete rotation and transformed into a new type of dither array, the scanning dither array. The scanning dither array is composed both of dither thresholds and of displacement vectors, providing the means to scan the dither array at image generation time. Several different discrete one-to-one rotation variants are proposed: a small angle rotation technique valid for a subset of rational rotation angles, a rigid band technique and an improved band technique valid for all rational rotation angles and a technique based on discrete shearing transformations. The high-quality of the so rotated dithe…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.