Automatic image segmentation for color documents

• US 5,341,226 A
• Filed: 04/22/1993
• Issued: 08/23/1994
• Est. Priority Date: 04/22/1993
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Shiau, Jeng-Nan
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): NING, JOHN K
• Application Number:
  US08/051,146
• Time in Patent Office: 488 Days
• Field of Search: 358/453, 358/448, 358/463, 358/462, 358/456, 358/534, 358/515, 358/518, 358/520, 382/47, 382/56, 382/48, 382/9
• US Class Current: 358/518
• CPC Class Codes: H04N 1/56 Processing of colour picture signals H04N1/52 takes precedence

Abstract

Method and apparatus for processing color document images to determine the presence of particular image types in order to designate areas for optimal image processing thereof. A multi-separation image defined in terms of color density for each separation is converted to a luminance-chrominance definition, where one component of the image represents image intensity. An image segmentation process operates on the image intensity signal, the results of which are used to determine processing of the multi-separation image.

Claims

1. A method of processing a multi-separation document image in accordance with image types present therein, the steps comprising:

receiving from an image source a multi-separation document image, where each pixel in the image is represented by a triplet of color density image signals, and storing at least a portion thereof representing an area of the document image in a data buffer;

with a color space converter, converting each color triplet of image signals in the portion received from the data buffer to a luminance-chrominance signal description of the document image, where one component signal thereof represents intensity of the document image;

with an image segmentation circuit, receiving the intensity component of the document image from the color space converter and determining image types present in an area of the image therefrom;

with a multi-image type image processor also receiving the color density signal from the data buffer, processing the color density signals for the portion in accordance with the determined image type; and

directing color density signals processed in accordance with determined image type to an output data buffer.

2. The method as described in claim 1, wherein the color density image signals are represented in terms of red-green-blue space.

3. The method as described in claim 2, wherein the luminance-chrominance signal description is defined as YES space and the intensity representing signal of the document image is given as Y, where Y is a function of the color density signals given as

4. The method as described in claim 1 where the color density image signals are represented in terms of cyan-magenta-yellow space.

5. The method as described in claim 1 wherein the luminance-chrominance space is defined as YES space.

6. The method as defined in claim 1, wherein the image segmentation circuit includes an autocorrelator circuit, operating on intensity signals to determine the presence of high and low frequency halftones.

7. The method as defined in claim 1, wherein the image segmentation circuit includes a discriminator circuit, operating on intensity signals to determine the presence of line art or text, or continuous tones.

8. The method as defined in claim 1, wherein the image segmentation circuit distinguishes areas of the image including the image types high frequency halftone, low frequency halftones, line art or text and continuous tone.

9. In a color printing system including a source of color density image signals representing multi separation color document images, an image processing arrangement processing the color density image signals preparatory to output, and an image type segmentation circuit, controlling the image processing arrangement to process the image signals in accordance with the image type thereof, comprising:

an image storage buffer, suitable for receiving color density signals representing at least a portion of the multi separation color document image;

a color space converter, connected to the image storage buffer and receiving color density signals therefrom and converting multi separation color density image signals into a luminance-chrominance image signals, in which at least one component signal thereof represents overall image intensity;

said image type segmentation circuit receiving and operative on said image intensity signal, and producing a control signal responsive thereto indicating image type;

an image processing arrangement controller, responsive to the control signal generated at the image type segmentation circuit and controlling operation of said image processing arrangement;

said image storage buffer and said image processing arrangement connected for transfer of said color density signals to said image processing arrangement, for processing thereof under control of said image processing arrangement controller; and

an output device, connected to said image processing arrangement, for receiving processed color density signals, processed in accordance with image type.

10. The device as described in claim 9, wherein the color density image signals are represented in terms of red-green-blue space.

11. The device as described in claim 10, wherein the luminance-chrominance signal description is defined as YES space and the intensity representing signal of the document image is given as Y, where Y is a function of the color density signals given as

12. The device as described in claim 9 where the color density image signals are represented in terms of cyan-magenta-yellow space.

13. The device as described in claim 9 wherein the luminance-chrominance space is defined as YES space.

14. The device as defined in claim 9, wherein the image segmentation circuit includes an autocorrelator circuit, operating on intensity signals to determine the presence of high and low frequency halftones.

15. The device as defined in claim 9, wherein the image segmentation circuit includes a discriminator circuit, operating on intensity signals to determine the presence of line art or text, or continuous tones.

16. The device as defined in claim 9, wherein the image segmentation circuit distinguishes areas of the image including the image types high frequency halftone, low frequency halftones, line art or text and continuous tone.