Color image printing apparatus

• US 4,884,080 A
• Filed: 06/02/1987
• Issued: 11/28/1989
• Est. Priority Date: 01/31/1985
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Matsui, Toshikazu, Nagato, Hitoshi, Yamada, Kiyoshi, Hirahara, Shuzo, Higuchi, Kazuhiko, Ohno, Tadayoshi, Kanai, Tsutomu
• Primary Examiner(s): Shaw, Clifford C.
• Assistant Examiner(s): PRESTON, GERALD
• Application Number:
  US07/056,763
• Time in Patent Office: 910 Days
• Field of Search: 346/76 PH, 346/46, 358/75, 358/283, 358/296, 358/298, 400/120, 430/44, 430/293
• US Class Current: 346/46
• CPC Class Codes: G01D 15/10 Heated recording elements acting on heatsensitive layers
• CPC Class Codes: H04N 1/40087 Multi-toning, i.e. converting a continuous-tone signal for reproduction with more than two discrete brightnesses or optical densities, e.g. dots of grey and black inks on white paper
• CPC Class Codes: H04N 1/4058 with details for producing a halftone screen at an oblique angle H04N1/4056 takes precedence
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening

Abstract

A color image printing apparatus prints one pixel by superposing a predetermined dots of three colors within a 3×3 dot matrix in accordance with a density of the pixel. The positions of the printed dots within the dot matrix are stored as a dot pattern for each color. One dot pattern is used for each of a plurality of densities included in one density range. The printing energy for each of the dots included in the dot pattern is controlled in accordance with the density level of the pixel. The dot pattern is different for each color and three dot patterns are stored for each color and for each density range. These three dot patterns are repeatedly used for every three pixels which are continuous in the horizontal direction. These three dot patterns have two or three texture directions. The texture direction other than the vertical direction is different for each color.

Claims

1. A color image printing apparatus comprising:

dot printing means for printing dots of at least two colors on a printing medium; and

control means for controlling said dot printing means such that only a predetermined dot or dots in accordance with a density of each pixel in units of colors in a dot matrix corresponding to one pixel are printed,

wherein positions of printed dots in the dot matrix are determined such that angles of two texture directions of the printed dots which are generated upon printing of pixels arranged in a two-dimensional manner are different for each color.

2. An apparatus according to claim 1, in which said control means controls said dot printing means such that texture directions of printed dots of a single color are vertical and horizontal directions, and texture directions of printed dots of other colors are vertical and different oblique directions.

3. An apparatus according to claim 1, in which said control means prints each pixel by dots printed at different positions in the dot matrix in units of colors.

4. A thermal color image printing apparatus comprising:

dot printing means for printing dots of at least two colors on a printing medium;

means for moving one of said dot printing means and printing medium with respect to the other of said dot printing means and printing medium, to form a dot matrix on the printing medium;

table means for storing position data indicating a predetermined dot or dots in the dot matrix corresponding to a printing region of a single pixel and numerical data indicating an energy value which is applied to said dot printing means in order to print the dots, the position data being stored as a dot pattern, the dot pattern of each having two texture directions, one being a direction which is common to all the colors and along which one of said dot printing means and said printing medium is moved by said moving means and the other being an arbitrary direction which is different for each color; and

means, interlinked with said moving means, for reading out the position data and numerical data corresponding to each pixel of each color from said table means for each printing position of each pixel and for controlling said dot printing means.

5. An apparatus according to claim 4, in which said table means stores a set of dot patterns comprising a plurality of dot patterns in units of densities, each of said plurality of dot patterns being assigned to a plurality of pixels in a one-dimensional direction in accordance with its relative position in the set, the sets of dot patterns having texture directions.

6. An apparatus according to claim 5, in which said dot printing means forms dots of n colors (n is an integer of 2 or more), and

said table means causes an n×

n dot matrix to correspond to a printing region of a single pixel and forms a single set of dot patterns by n dot patterns.

7. An apparatus according to claim 6, in which said table means stores a single set of dot patterns for each of a plurality of densities.

8. An apparatus according to claim 6, in which said dot printing means forms dots of three colors, and the texture directions are a first direction which is common to all the colors and along which one of said dot printing means and said printing medium is moved by said moving means, and a direction inclined 18°

counterclockwise from a second direction which crosses the first direction and along which one of said dot printing means and said printing medium is moved by said moving means for a first color, the first and second directions for a second color, and the first direction and a direction inclined 18°

clockwise from the second direction for a third color.

9. An apparatus according to claim 6, in which said dot printing means forms dots of four colors, and the texture directions are a first direction which is common to all the colors and along which one of said dot printing means and said printing medium is moved by said moving means and a direction inclined 14°

counterclockwise from a second direction which crosses the direction which is common to all of the colors and along which one of said dot printing means and said printing medium is moved by said moving means for a first color, the first direction and directions inclined 63°

clockwise and counterclockwise from the first direction for a second color, the first direction and a direction inclined 14°

clockwise from the second direction for a third color and the first and second directions for a fourth color.