Post-filter for improving halftone image sharpness
US5822469A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Oct 22, 1996 |
| Grant date | Oct 13, 1998 |
| Priority date | — |
| Expiry date | Oct 22, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG06T5/20
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A post-filtering method and apparatus for increasing the high-frequency and edge information of halftoned images is described. If a continuous-tone (contone) image is processed by a halftoning algorithm into a binary or multi-level image, some of the high frequency information is lost. However, some of the lost information can be restored by judiciously rearranging some of the halftone picture elements (pixels). Each horizontally adjacent pair of pixels in the contone image are compared with each other. If the difference between their luminance is greater than a threshold, then the corresponding pair of adjacent pixels in the halftone image are compared. If the difference between the halftone image pixels has the opposite sign of the differences between the contone image pixels (e.g., the image changes from dark to light, but the halftone pixels change from light to black), the two halftone pixels are exchanged with each other. The procedure is then repeated in the vertical direction. The procedure can be applied as a post filter to any halftoned image, and can substantially improve the image quality. The procedure works with binary, multiple gray level and color images. The proced…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.