Method for half tone phase matching at run boundaries

• US 6,798,920 B1
• Filed: 03/29/2000
• Issued: 09/28/2004
• Est. Priority Date: 03/29/2000
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Wells, Terry C., McElvain, Jon S., Rumph, David E.
• Primary Examiner(s): Poon, King Y.
• Application Number:
  US09/538,597
• Time in Patent Office: 1,644 Days
• Field of Search: 382/275, 382/245, 382/151, 382/167, 382/232, 382/294, 358/1--, 358/1-1-, 358/537, 358/401, 358/3.26, 358/3.27, 358/426.02, 358/3.2, 358/426.15, 358/426.16, 358/448, 358/452, 358/453, 358/3.11, 358/3.12, 358/3.1, 345/55, 345/621, 345/674, 345/788, 345/794, 345/33, 715/521, 715/526, 715/517, 715/540
• US Class Current: 382/275
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression

Abstract

A method for correcting a white line artifact between low and high frequency printed pixels. A printer may be able to print either a high or low frequency halftone pixels in some locations, but may be able to print only high frequency halftone pixels in other locations, the latter known as out of phase locations. If the image data is in run length encoded form, and the printer tries to print a low frequency pixel in an out of phase location, no pixel will be printed in that location and a white space results. The remedy is to test at the beginning and end of low frequency runs bordering high frequency runs. If the first (last) low frequency pixel of an original run is in an out of phase location, a one pixel run of the high frequency screen and of the low frequency color is added before (after) the original run, and the run length of the low frequency run is decreased by one pixel.

Claims

1. A method of correcting the white line artifact at the boundary between low and high frequency pixels of image data in run length encoded form comprising the steps of:

locating an original run length of low frequency data which has a boundary with high frequency data,

determining whether the first or last pixel of the original run is on the boundary and is in a location where the high and low frequency screens are out of phase,

if the location is an out of phase location,

a) decrease the low frequency run length by one,

b) create a one pixel run for a high frequency pixel at the low frequency color, and

c) insert the one pixel run in the image data before the original run if it is the first pixel of the original run that is out of phase, or after the original run if it is the last pixel that is out of phase.