Image processing apparatus and methods

• US 6,266,439 B1
• Filed: 09/06/1996
• Issued: 07/24/2001
• Est. Priority Date: 09/29/1995
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Pedersen, Claus Henrik, Pollard, Stephen Bernard
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): SHERALI, ISHRAT I
• Application Number:
  US08/714,839
• Time in Patent Office: 1,782 Days
• Field of Search: 382/176, 382/164, 382/171, 382/173, 382/170, 382/254, 358/1-15-, 358/300
• US Class Current: 382/164
• CPC Class Codes: H04N 1/56 Processing of colour picture signals H04N1/52 takes precedence

Abstract

An image processor receives color signals representing a color or black-and-white image, typically containing text and non-text areas. A sliding window or swath of the image is processed which progressively moves over the virtual image.

A spatial filter is applied to sharpen the image and it is then classified into text and non-text regions. The data from the text regions is subjected to a black text enhancement process in which the color signal from a single channel (here the green channel) is thresholded against two thresholds, T1, T2. The lower (darker) threshold T2 identifies pixels for being set to black, whereas the threshold T1 identifies “support” pixels used in component connectivity analysis. Having defined a connected component using both T1 and T2 pixels, the color statistics of the pixels making up the component are analyzed to determine whether the component should be rendered black. If so, the image data is enhanced by snapping the T2 pixels to black, and snapping a halo of pixels around the black text component to white.

Claims

1. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items; and

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image

wherein said analysing means compares the intensity of said colour signal in each pixel with a first threshold and classifies each pixel having an intensity below said first threshold as belonging to a potential text item.

2. An image processing apparatus according to claim 1, including means for storing data identifying each potential text item and the pixels belonging thereto.

3. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighboring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items; and

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image,

wherein said colour signals comprise red, blue and green colour signals, and said means for analysing analyses said green colour signal.

4. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items; and

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image,

wherein said colour signals comprise red, blue and green colour signals and said colour discriminating means monitors the red, green and blue intensities of each of the pixels making up each potential text item.

5. An image processing apparatus according to claim 4, wherein said colour discriminating means includes, for each colour signal, means for determining maximum, minimum and mean values of the intensity of the colour signal in the pixels making up a potential text item, and said colour discriminating means uses said maximum, minimum and mean values to discriminate a black text item.

6. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items; and

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image

wherein said means for enhancing sets each of the pixels within each discriminated black text item to black and said means for enhancing sets to black only those pixels where the intensity of said colour signal is below a second threshold, lower than said first threshold.

7. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items; and

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image,

wherein said means for enhancing sets each of the pixels within each discriminated black text item to black and said means for enhancing includes means for setting selected pixels adjacent said discriminated black text items to white or another suitable background colour.

8. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items;

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image;

(iv) means for classifying said image into potential test regions and non-text regions, said means for classifying including;

(a) means for monitoring the intensities of at least some of the colour signals at a plurality of pixels within a selected region of said image;

(b) means for monitoring said monitored intensities to determine intensity distribution data for the or each colour signal; and

(c) means responsive to said distribution data to classify said selected region as a text region or a non-text region, and

(v) means for supplying image data representing said potential text regions to said means for analysing,

wherein the intensity distribution data is compared with respective preset threshold data to classify said selected region and wherein said threshold data defines a black intensity maximum threshold and a white intensity minimum threshold, and said selected region is classified as a text region if the intensity distribution data for the or each of the said colour signals does not include a peak between said black intensity maximum threshold and said white intensity minimum threshold, and also meets at least one of the following conditions;

(i) it includes a peak above said white intensity minimum threshold and,

(ii) it includes a peak below said black intensity maximum threshold.

9. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items;

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image;

(iv) means for classifying said image into potential test regions and non-text regions, said means for classifying including;

(a) means for monitoring the intensities of at least some of the colour signals at a plurality of pixels within a selected region of said image;

(b) means for monitoring said monitored intensities to determine intensity distribution data for the or each colour signal; and

(c) means responsive to said distribution data to classify said selected region as a text region or a non-text region, and

(v) means for supplying image data representing said potential text regions to said means for analysing;

(vi) means for examining said intensity distribution data for each colour signal to identify peaks therein;

(vii) means responsive to said examining means to use said peaks to define potentially highly populated search spaces; and

,

(viii) means for monitoring the population in each of said search spaces thereby to classify said selected region as a text region or a non-text region.

10. An image processing apparatus for processing colour signals representing a colour or black-and-white image, to enhance the rendering of black text in a subsequent presentation of said image, said apparatus comprising:

(i) means for analysing at least one of said colour signals over said image or a part thereof to identify within said image or part thereof groups of neighbouring pixels, each of which defines a potential text item or part thereof;

(ii) colour discriminating means for monitoring at least some of the colour signals of pixels within and/or around each potential text item to discriminate black text items;

(iii) means for enhancing said discriminated black text items in a subsequent presentation of said image; and

,

(iv) means for storing a sliding window or swath of said image, wherein said means for analysing operates on data stored in said sliding window or swath.