Pseudo halftone image expression method

• US 6,724,499 B1
• Filed: 08/30/1999
• Issued: 04/20/2004
• Est. Priority Date: 08/31/1998
• Status: Expired due to Term

• Current Assignee: Mutoh Industries Ltd. (Mutoh Holdings Company Limited)
• Original Assignee: Mutoh Industries Ltd. (Mutoh Holdings Company Limited)
• Inventors: Satoh, Takeshi
• Primary Examiner(s): Williams, Kimberly A.
• Assistant Examiner(s): VIDA, MELANIE M
• Application Number:
  US09/386,059
• Time in Patent Office: 1,695 Days
• Field of Search: 358/1.9, 358/3.01, 358/3.03, 358/3.06, 358/3.13, 358/3.16, 358/3.18, 358/3.19, 382/270, 382/271, 382/272, 382/273
• US Class Current: 358/1.9
• CPC Class Codes: G06K 15/02 using printers
• CPC Class Codes: G06K 2215/0045 Converting outline to bitmap
• CPC Class Codes: G06K 2215/0094 Colour printing

Abstract

There is provided a pseudo-halftone image expression method capable of processing vector data with an excellent image quality and small computational complexity. Gray levels of n×n/m are expressed by varying the number of formed dots within a matrix of n×n dots on an m-dot basis (where n denotes an integer of 8 or more and m denotes an integer of 4 or more). A dot formation rule corresponding to each gray level within a matrix is divided into at least two stages, form a low gray level to a high gray level. In a first stage, dots are arranged at random and in dispersion so as to separate a dot from each other. In a second stage, dots are extended in random directions in turn so as to prevent an island of successive dots from coupling with each other using the dots arranged at the first stage as a nucleus.

Claims

1. A pseudo-halftone image expression method of expressing way levels of n×

n/m by varying the number of formed dots within a matrix of n×

n dots on an m-dot basis (where n denotes an integer of 8 or more and m denotes any integer), comprising;

a first stage corresponding to each gray level within the matrix in a low gray range using a first dot formulation rule;

a second stage corresponding to each gray level within the matrix in a high gray range using a second dot formulation rule; and

a third stage subsequent to said second stage using a third dot formation rule corresponding to gray levels within the matrix;

wherein in the first stage, first dots are arranged at random and in dispersion so as to separate said first dots from each other by the first dot formulation rule;

wherein in the second stage, second dots are extended in directions in turn so as to prevent an island of successive dots from coupling with each other using said first dots arranged at said first stage as a nucleus by the second dot formulation rule; and

wherein in the third stage, third dots are arranged in the least dense area so that the third dots are not coupling the island formed at said second stage with each other, and the third dots are extended from a low gray level to a high gray level in turn using one of the third dots as a nucleus by the third dot formulation rule.

2. The pseudo-halftone image expression method of claim 1, wherein a position of said first dot to be arranged within said matrix at said first stage is determined by arranging a plurality of dots at random within said matrix, and repeating predetermined times a process of moving each dot so as to be separated from the nearest dot by a predetermined distance.

3. The pseudo-halftone image expression method of claim 1, wherein a position of said dot to be arranged within said matrix at said first stage is determined to the emptiest among dots already arranged.

4. The pseudo-halftone image expression method of claim 1, wherein said first stage is repeated until n×

n/16 dots are formed in the matrix.

5. The pseudo-halftone image expression method of claim 1, wherein a half dot formation pattern is stored in lower gray levels among the whole gray levels to be expressed, and another half dot formulation pattern is determined in higher gray levels as an inverted pattern of said dot formation pattern in said lower gray levels.