Image processing with noise enhancing operators for moire reduction and/or random dot generation

• US 5,225,915 A
• Filed: 06/09/1989
• Issued: 07/06/1993
• Est. Priority Date: 06/09/1989
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Bhaskar, Ranjit, Ciccone, Theresa J.
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): Lee, Thomas D.
• Application Number:
  US07/364,396
• Time in Patent Office: 1,488 Days
• Field of Search: 358/447, 358/448, 358/454, 358/455, 358/456, 358/457, 358/458, 358/465, 358/466, 358/75, 358/80, 382/54
• US Class Current: 358/447
• 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 1/405 Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
• CPC Class Codes: H04N 1/409 Edge or detail enhancement; Noise or error suppression

Abstract

In an image processing device for processing image data representing an image, and including an image filtering arrangement, a filter function is applied to the image data that greatly amplifies or enhanced high frequency imge data, including noise inherent in the image. Such noise, which may be the granularity of the image, when enhanced, serves to mask the beating pattern of moire. One function which accomplishes adequate high frequency and noise filtering is a modified Laplacian function with a maximum modulation at a frequency of the noise or granularity of the image. Similarly, the special effect of a random screen image or mezzo tint is obtained when a continuous tone image is processed with the modified Laplacian filtering function, and subsequently thresholded in a thresholding arrangement.

Claims

1. A method of processing digital image data to alter the appearance thereof, including the steps:

(a) supplying image data, said image data including inherent random noise, and having an original periodic function, said image data having superimposed thereon an additional periodic function, said original and additional periodic functions having frequencies creating a moire pattern in said image data;

(b) applying a filter function to the image data supplied, said filter function having the characteristics of enhancing high frequency and noise of said image data, whereby enhancement of said random noise masks the moire pattern in said image data.

2. The image processing method defined in claim 1 wherein the filter function applied is a modified Laplacian function, having a maxima at a frequency optimizing noise enhancement.

3. An arrangement for processing digital image data to alter the appearance thereof, including:

means for supplying image data, said image data including inherent random noise, and having an original periodic function, said means for supplying image data, superimposing on said image data an additional periodic function, said original and additional periodic functions having frequencies creating a moire pattern in said image data;

means for applying a filter function to the image data supplied, said filter function having the characteristics of enhancing high frequency and noise of said image data, whereby, enhancement of said random noise masks the moire pattern in said image data.

4. The image processing arrangement defined in claim 3 wherein the filter function applied is a modified Laplacian function, having a maxima at a frequency optimizing noise enhancement.

5. An arrangement for processing digital image data to alter the appearance thereof with a simulated random screen effect, including:

means for supplying image data, said image data including inherent random noise;

means for applying a filter function to the image data supplied, said filter function having the characteristics of enhancing high frequency elements and noise of said image data; and

means for applying a threshold level to said image data.

6. The image processing arrangement defined in claim 5 wherein the filter function applied is a modified Laplacian function, having a maxima at a frequency optimizing noise enhancement.