Tone dependent error diffusion
US6563957B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | May 7, 1999 |
| Grant date | May 13, 2003 |
| Priority date | — |
| Expiry date | May 7, 2019 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N1/4052
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A tone dependent error diffusion halftoning system uses tone dependent thresholds and error weightings that are optimized by minimizing a model based cost function. An upper and lower threshold are used to compare with the modified pixel value. If the modified pixel value is greater than the upper threshold, a dot is printed, if less than the lower threshold, no dot is printed, and if between, a binary bitmap is used to determine whether a dot should be printed. For each midtone threshold level, a halftone image is generated by a direct binary search method and an error diffusion method. The magnitudes of the fast Fourier transforms, of the halftone images are compared using a visual cost function and the thresholds and error weightings are altered to minimize the cost function. For highlight and shadow tone levels, a filtered halftone image from an error diffusion system is compared to the continuous tone image after filtering the image via a human visual system model. Again by minimizing the cost function, the thresholds and error weightings are optimized.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.