Devices and methods for offset and similar printing systems

• US 5,793,500 A
• Filed: 01/21/1994
• Issued: 08/11/1998
• Est. Priority Date: 07/20/1989
• Status: Expired due to Term

• Current Assignee: Shira Computers Ltd.
• Original Assignee: Arnold Hoffman, Yoel Netz
• Inventors: Netz, Yoel, Hoffman, Arnold
• Primary Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US08/184,175
• Time in Patent Office: 1,663 Days
• Field of Search: 358/534-536, 358/429, 358/456-461, 358/298
• US Class Current: 358/3.2
• CPC Class Codes: G03F 5/22 combining several screens; Elimination of moiré
• CPC Class Codes: H04N 1/4058 with details for producing a halftone screen at an oblique angle H04N1/4056 takes precedence

Abstract

A method for producing a half-tone image faithfully representing a continuous-tone original includes a step of forming in the image a pattern of substantially continuous, substantially parallel lines at a frequency of between about 100 and 400 lines per inch, such that the width of the lines at a given point in the image varies in relation to the optical density of at least one color component at a corresponding point in the continuous-tone original. The method may be used for color separations with each separation produced by scanning at a different angle. The method may be implemented using photomechanical or electronic scanning techniques.

Claims

1. A method for producing a color image faithfully representing a continuous-tone color original comprising the steps of:

(a) producing a first half-tone image corresponding to a first color component of the continuous-tone color original, by forming in said first half-tone image a pattern of substantially continuous, substantially parallel lines at a frequency of between about 100 and 400 lines per inch, such that the width of said lines at a given point in the image varies in relation to the optical density of said first color component at a corresponding point in the continuous-tone original, said substantially parallel lines in said first half-tone image having a first line frequency, said substantially parallel lines in said first half-tone image defining a first direction;

(b) producing a second half-tone image corresponding to a second color component of the continuous-tone color original, by forming in said second half-tone image a pattern of substantially continuous, substantially parallel lines at a frequency of between about 100 and 400 lines per inch, such that the width of said lines at a given point in the image varies in relation to the optical density of said second color component at a corresponding point in the continuous-tone original, said substantially parallel lines in said second half-tone image having a second line frequency substantially equal to said first line frequency, said substantially parallel lines in said second half-tone image defining a second direction rotated from said first direction;

(c) producing a third half-tone image corresponding to a third color component of the continuous-tone color original, by forming in said third half-tone image a pattern of substantially continuous, substantially parallel lines at a frequency of between about 100 and 400 lines per inch, such that the width of said lines at a given point in the image varies in relation to the optical density of said third color component at a corresponding point in the continuous-tone original, said substantially parallel lines in said third half-tone image having a third line frequency substantially equal to said first line frequency, said substantially parallel lines in said third half-tone image defining a third direction rotated from both said first direction and said second direction; and

(d) combining said first, said second and said third half-tone images in registration.

2. A method according to claim 1, further comprising the step of producing a fourth half-tone image corresponding to a fourth color component of the continuous-tone color original, said step of forming said fourth half-tone image including forming in the image a pattern of substantially continuous, substantially parallel lines at a frequency of between about 100 and 400 lines per inch, such that the width of said lines at a given point in the image varies in relation to the optical density of said fourth color component at a corresponding point in the continuous-tone original, said substantially parallel lines in said fourth half-tone image having a fourth line frequency substantially equal to said first line frequency, said substantially parallel lines in said fourth half-tone image defining a fourth direction, rotated from each of said first direction, said second direction and said third direction.

3. A method according to claim 2, wherein each of said first direction, said second direction, said third direction and said fourth direction are rotated from all other said directions by substantially integer multiples of 30°

.

4. A method according to claim 1, wherein said step of forming in the image a pattern of substantially parallel lines is performed using a photomechanical screen.

5. A method according to claim 1, wherein said step of forming in the image a pattern of substantially parallel lines is performed using an electronic scanner.