Distributed PWM halftoning unit and printer
US6191868A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 3, 1998 |
| Grant date | Feb 20, 2001 |
| Priority date | — |
| Expiry date | Sep 3, 2018 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N1/4058
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
In a halftoning unit of a laser printer and the like, a high speed, high density and high gradations halftoning is realized by multi-value implementation by clustered dot concentrated dither halftoning (known as a sub-matrix method) and PWM distributing gradation among the plurality of halftone dots with a small memory and circuit. For this purpose, the value of the difference between an input gradation value n.sub.i and a threshold value n.sub.c, .DELTA.n=n.sub.i -n.sub.c, is shortened within a range of 0 to .DELTA.h and the lower s bit of .DELTA.h is removed by a round-down or round-up process. Meanwhile, a threshold array is generated from an extended threshold pattern obtained by combining threshold patterns of 2.sup.s whose threshold interval is .DELTA.h, i.e. .DELTA.Ah.times.K, .DELTA.h.times.K+1, . . . , .DELTA..times.K+2.sup.(s-1). Thereby, a halftone dot dither process in which the PWM gradation increases distributively among the 2.sup.s dots may be realized with a small scale memory and circuit.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.