System for reproducing multi-level digital images on a bi-level printer of fixed dot size
US4654721A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 12, 1985 |
| Grant date | Mar 31, 1987 |
| Priority date | — |
| Expiry date | Apr 12, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N1/4055
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A system for producing improved halftone images from continuous tone input images, the pixels of which have been digitized as gray scale values, using a printer having the capability to print a set of output pel patterns producing a respective set of discrete gray scale values, is disclosed. Blocks of pel patterns with discrete gray scale values approximating the gray scale values of the input pixels are selected for printing, and the error in a first block due to the difference between the gray scale value associated with the block and the gray scale value of the corresponding input pixel, is determined. To diffuse this error it is distributed to at least two adjacent blocks using a random number generator to determine the distribution such that a random fraction of said error is distributed to one block and the remainder is distributed to the other block. This error diffusion process is carried through the adjacent blocks taking into account the error fraction already assigned. For edge enhancement the brightness gradient surrounding each input pixel is determined and a threshold value is set below which said gradient is classified as small and above which it is classified as lar…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.