Halftone apparatus that provides simultaneous, multiple lines per inch screens

• US 20080068659A1
• Filed: 09/06/2006
• Published: 03/20/2008
• Est. Priority Date: 05/16/2000
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: International Business Machines Corporation
• Inventors: Dittrich, Danielle, Qiao, Yue, Mitchell, Joan
• Granted Patent: US 8,004,721 B2
• Time in Patent Office: Days
• US Class Current: 358/3.01
• CPC Class Codes: H04N 1/405 Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels

Abstract

A halftone threshold matrix includes a plurality of submatrices, wherein a first group of the plurality of submatrices has a line screen frequency different from a second group of the plurality of submatrices. The halftone method and apparatus removes the restriction that at most one pel is turned on per basic cell for the next constant input level and allows the pels in some basic cells to be turned on much sooner that the corresponding positions in other basic cells. This creates a dominant low frequency line screen simultaneously with the higher frequency line screen of the other basic cells. The present invention also allows the basic cells inside the threshold matrix to have different shapes and sizes. Thus, the cells participating in the low frequency screen could be larger than the cells generating the higher frequency screen. for example, the low frequency screen'"'"'s pleasing patterns can distract the eye from noticing less pleasing patterns in the high frequency grid and vice versa.

Claims

1-20. -20. (canceled)

21. A halftone threshold matrix of a halftone screen used by an image processor for converting input gray-scale images into a dot pattern representing binary images, the halftone threshold matrix comprising a supercell divided into a plurality of subcells, the plurality of subcells comprising at least a first group of N×

M subcells having a a first line frequency and a separate and distinct second group of A×

B subcells having a second line frequency, wherein a size of the first and second group of subcells are not equal, and when the input gray-scale images undergoes binary image reproducing process to produce an output image and the produced image is output by an output device more than one pixel in a first subcell is turned on before a next pixel in a second cell is turned on.

22. The halftone threshold matrix of claim 21, wherein more than one pixel is capable of being turned on per subcell for a next constant input level.

23. The halftone threshold matrix of claim 21, wherein the line screen frequency of the first group is higher than the second group.

24. The halftone threshold matrix of claim 21, wherein the second group masks print imperfections.

25. The halftone threshold matrix of claim 24, wherein the print imperfections comprise paper texture imperfections.

26. The halftone threshold matrix of claim 24, wherein the print imperfections comprise banding.

27. The halftone threshold matrix of claim 21, wherein the first group provide greater detail and sharpness than the second group.

28. The halftone threshold matrix of claim 21, wherein the first group of subcells sets the lines per inch for the screen.

29. The halftone threshold matrix of claim 21, wherein the first group of subcells and the second group of subcells determine a number of shades provided by the matrix.

30. The halftone threshold matrix of claim 21, wherein each of the plurality of subcells comprises picture elements, wherein the second group of subcells are filled faster than the first group of subcells.

31. The halftone threshold matrix of claim 21, wherein first group of subcells have a shape different than the second group of subcells.