Method and apparatus for halftone rendering of a gray scale image using a blue noise mask

• US 5,111,310 A
• Filed: 12/04/1990
• Issued: 05/05/1992
• Est. Priority Date: 12/04/1990
• Status: Expired due to Term

• Current Assignee: Research Corporation Technologies Incorporated A Not-For-Profit Non-Stock Corporation of de
• Original Assignee: Research Corporation Technologies
• Inventors: Mitsa, Theophano, Parker, Kevin J.
• Primary Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US07/622,056
• Time in Patent Office: 518 Days
• Field of Search: 358/465, 358/456-458, 358/463, 358/464
• US Class Current: 358/3.19
• CPC Class Codes: G06T 3/4084 in the transform domain, e.g. fast Fourier transform [FFT] domain scaling
• CPC Class Codes: H04N 1/40075 Descreening, i.e. converting a halftone signal into a corresponding continuous-tone signal; Rescreening, i.e. combined descreening and halftoning
• CPC Class Codes: H04N 1/4051 producing a dispersed dots halftone pattern, the dots having substantially the same size different sizes H04N1/4057
• CPC Class Codes: H04N 1/4105 for halftone screened pictures

Abstract

A method of and system for rendering a halftone image of a gray scale image by utilizing a pixel-by-pixel comparison of the gray scale image against a blue noise mask is disclosed in which the gray scale image is scanned on a pixel-by-pixel basis and compared on a pixel-by-pixel basis to an array of corresponding data points contained in a blue noise mask stored in a PROM or computer memory in order to produce the desired halftoned image. Both digital and optically implemented halftone methods are disclosed.

Claims

1. A method for the halftoning of gray scale images by utilizing a pixel-by-pixel comparison of the image against a blue noise mask in which the blue noise mask is comprised of a random non-deterministic, non-white noise single valued function which is designed to produce visually pleasing dot profiles when thresholded at any level of said gray scale images.

2. The method of claim 1, wherein said blue noise mask is used to halftone a color image.

3. The method of claim 1, wherein said blue noise mask is used to halftone multibit displays.

4. The method of claim 1, wherein said blue noise mask is comprised of a continuous, single valued aperiodic blue noise function.

5. The method of claim 4, wherein said blue noise function is a random function and in which, when said blue noise mask is thresholded at any level, a dot profile with desirable blue noise characteristics is produced.

6. The method of claim 1, wherein said blue noise mask is formed by an at least one dimensional function having predetermined properties of a thresholded dot profile using transform domain filtering and error criteria.

7. The method of claim 6, wherein said blue noise mask is formed by an at least one dimensional function using spatial domain filtering and error criteria equivalent to said transform domain filtering and error criteria.

8. A method for constructing a blue noise mask using a blue noise power spectrum for use for the halftoning of gray scale images by utilizing a pixel-by-pixel comparison of said images against said blue noise mask in which said blue noise mask is constructed by incrementally building up dot profiles over increments in gray level and in which said dot profile at each level is constrained by the dot profile at the previous level and by requiring the matching of each dot profile to said blue noise power spectrum predetermined for that gray level.

9. The method of claim 8, wherein said blue noise power spectrum is modified by human visual response to produce an appropriately pleasing pattern.

10. A method for the halftoning of gray scale images by utilizing an optical blue noise mask in which said gray scale image is photographed through said blue noise mask and is printed onto high contrast film.

11. The method of claim 10, wherein said optical blue noise mask and said image are separately photographed onto said high contrast film such that a repeated exposure of said film occurs.

12. The method of claim 10, wherein said blue noise mask is formed using a film printer interfaced to a computer containing blue noise mask data.

13. A method of halftoning a gray scale image by utilizing a pixel-by-pixel comparison of said image against a blue noise mask array stored in a first memory, comprising the steps of:

a) scanning said gray scale image to be halftoned to create a gray scale image array on a pixel-by-pixel basis;

b) storing said gray scale image array in a second memory;

c) comparing, on a pixel-by-pixel basis, the value of each corresponding pixel in said blue noise mask array and said gray scale image array to produce a binary image array; and

d) converting said binary image array to the desired halftoned image.

14. The method of claim 13, wherein said gray scale image array created by said scanning step is fed directly to a computer for performing said comparing step.

15. The method of claim 13, wherein said image is a color image.