Digital halftoning with error diffusion
AssigneeLexmark International, Inc.
InventorsAllan Chiwan Cheung, Scott Michael Heydinger, Shaun Timothy Love
Life of this patent
Estimating the term…
Abstract
An error diffusion halftoning technique calculates only two error terms with one being divisible by two and the other being divisible by four. This is accomplished through using a modified Floyd and Steinberg type filter preferably having weights of 8-0-4-4 expressed in clockwise sequence from the origin. The direction of scanning is preferably reversed each scan line.
Claims16
An error diffusion method for halftoning a digital image formed of an array of scan lines of pixels, each pixel having a gray value, for forming an output image including:
- scanning each line of image pixels in a processing direction from one end of the scan line to the other;
- determining the gray value of each image pixel;
- and error diffusing each of the image pixels by using an error diffusion filter having weights of 8-0-4-4 expressed in clockwise sequence from the origin.
An error diffusion method for halftoning, a digital image formed of an array of scan lines of pixels, each pixel having a gray value, for forming an output image including:
- scanning each line of image pixels in a processing direction from one end of the scan line to the other;
- determining the gray value of each image pixel;
- and error diffusing each of the image pixels through using a three term, two-weight error diffusion filter having weights of 8-0-4-4.
An apparatus for halftoning a digital image formed of an array of scan lines of pixels in which each pixel has a gray value to form an output image through error diffusion including:
- scanning means for scanning each line of image pixels in a processing direction from one end of the scan line to the other;
- determining means for determining the initial gray value of each input pixel;
- correction means for changing the initial gray value for each of the input pixels in accordance with the error corrections at other pixels having predetermined locations relative to the input pixel so that a modified value is produced for the input pixel;
- said correction means including error diffusion means for applying one half of the magnitude of the error produced by the input pixel being scanned to one of
- (a) the next scanned image pixel and
- (b) the three consecutive image pixels in the next scan line beginning with the image pixel vertically aligned with the image pixel in the scan line being scanned that precedes the image pixel being error diffused and ending with the image pixel vertically aligned with the next image pixel to be scanned and applying one fourth of the magnitude of the error produced by the image pixel being error diffused to each of two of
- (a) the next scanned image pixel and
- (b) the three consecutive image pixels in the next scan line beginning with the image pixel vertically aligned with the image pixel in the scan line being scanned that precedes the image pixel being error diffused and ending with the image pixel vertically aligned with the next image pixel to be scanned;
- and ascertaining means for ascertaining if the modified value of the input pixel exceeds a threshold value.
Dependencies are inferred from the claim text.