Halftone apparatus that provides simultaneous, multiple lines per inch screens

• US 8,004,721 B2
• Filed: 09/06/2006
• Issued: 08/23/2011
• Est. Priority Date: 05/16/2000
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Infoprint Solutions Company LLC (Ricoh Company Limited)
• Inventors: Dittrich, Danielle Kathryn, Qiao, Yue, Mitchell, Joan LaVerne
• Primary Examiner(s): Thompson; James A
• Application Number:
  US11/879,888
• Publication Number:
  US 20080068659A1
• Time in Patent Office: 1,812 Days
• Field of Search: 358/1.9, 358/2.1, 358/2.99, 358/3.01, 358/3.02, 358/3.06, 358/3.09, 358/3.1, 358/3.21, 358/3.26, 358/463, 382/176, 382/209
• US Class Current: 358/3.21
• 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. A printer system, comprising:

a memory for storing an image for rendering; and

a halftoning processor, coupled to the memory, for processing the image in the memory according to a halftone threshold matrix, the halftoning processor for converting input gray-scale images into a dot pattern representing binary images to render the image, wherein the halftone threshold matrix comprises a supercell comprising a plurality of submatrices, the plurality of submatrices comprising a first group of submatrices and a second group of submatrices, wherein each matrix in the first group of submatrices is formed using a jXk submatrix and each matrix in the second group of submatrices is formed using a nXm submatrix, wherein j, k, m and n are integers and wherein j, k, m and n are not all equal and form the supercell with more than one shape and size of submatrices, and wherein at least one submatrix is filled in faster than the other submatrices in the supercell by turning on a predetermined number of pels less than all of the pels in the at least one submatrix to increase input levels without alternating to the other submatrices to turn on pels until the predetermined number of pels have been turned on.

2. The printer system of claim 1, wherein more than one pel in the at least one submatrix is turned on without turning on subsequent pels for increasing levels by alternating submatrices until each of the submatrices have had a pel turned on in turn.

3. The printer system of claim 1, wherein the at least one submatrix being filled in faster than the other submatrices in the supercell provides a dominant low frequency line screen simultaneously while the other submatrices provide a higher frequency line screen.

4. The printer system of claim 1, wherein the second group of submatrices masks print imperfections.

5. The printer system of claim 4, wherein the print imperfections comprise paper texture imperfections.

6. The printer system of claim 4, wherein the print imperfections comprise banding.

7. The printer system of claim 1, wherein the first group of submatrices provide greater detail and sharpness than the second group of submatrices.

8. The printer system of claim 1, wherein the first group of submatrices sets the lines per inch for the screen.

9. The printer system of claim 1, wherein the line screen frequency of the first group of submatrices is higher than the second group of submatrices.

10. The printer system of claim 9, wherein the second group of submatrices are larger than the first group of submatrices.

11. The printer system of claim 10, wherein the second group of submatrices determine a number of shades provided by the supercell.

12. The printer system of claim 9, wherein the supercell formed using the first and second groups of submatrices providing different line screens eliminates perceptually undesirable patterns generated by horizontal and vertical repetition of pels being turned on.