Detection of scratches on an image

• US 9,098,897 B2
• Filed: 03/29/2011
• Issued: 08/04/2015
• Est. Priority Date: 03/29/2011
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Kisilev, Pavel
• Primary Examiner(s): Lu, Tom Y
• Application Number:
  US14/008,546
• Publication Number:
  US 20140023244A1
• Time in Patent Office: 1,589 Days
• US Class Current: 1/1
• CPC Class Codes: G06T 7/001 using an image reference approach
• CPC Class Codes: H04N 1/00092 relating to the original or to the reproducing medium, e.g. imperfections or dirt detecting properties of a sheet H04N1/00681
• CPC Class Codes: H04N 1/4097 Removing errors due external factors, e.g. dust, scratches

Abstract

A method for detecting a scratch on a printed image is disclosed, which may include obtaining a digital representation of the printed image and a digital reference image. The method may also include summing values of pixels of pixel lines in at least one segment of the digital representation of the printed image along a suspected direction to obtain a projection signal of the digital representation of the printed image for that segment, and summing values of pixels in a corresponding at least one segment of the digital reference image in the suspected direction to obtain a projection signal of the reference image for the corresponding segment. The method may further include comparing the projection signals to detect dissimilarity indicative of a directional coherence in the suspected direction due to a scratch in the segment of the digital representation of the printed image. Non-transitory computer readable medium and system are also disclosed.

Claims

1. A method for detecting a scratch on a printed image, the method comprising:

obtaining, by a computing device, a digital representation of the printed image and a digital reference image;

summing, by the computing device, values of pixels of pixel lines in at least one segment of the digital representation of the printed image along a suspected direction to obtain a projection signal of the digital representation of the printed image for that segment, and summing values of pixels in a corresponding at least one segment of the digital reference image in the suspected direction to obtain a projection signal of the reference image for the corresponding segment; and

comparing, by the computing device, the projection signals to detect dissimilarity indicative of a directional coherence in the suspected direction due to a scratch in said at least one segment of the digital representation of the printed image.

2. The method of claim 1, wherein the step of comparing the projection signals includes calculating a similarity measure between the projection signals and declare an existence of a directional coherence in the suspected direction due to a scratch when the similarity measure is below a predetermined threshold.

3. The method of claim 1, comprising scanning, by the computing device, the printed image to obtain the digital representation of the printed image.

4. The method of claim 1, comprising, by the computing device, applying a preprocessing operation on the digital representation of the printed image and on the digital reference image.

5. The method of claim 4, wherein the preprocessing operation is selected from a group of preprocessing operations consisting of reducing noise, increasing contrast, transforming the pair of corresponding segments a different domain and employing an extremity filter.

6. The method of claim 1, wherein the digital reference image includes one grey level or a few grey levels.

7. The method of claim 1, wherein said at least one segment comprises a plurality of segments and wherein said corresponding at least one segment includes a plurality of corresponding segments, the method including performing the steps of summing and comparing on each segment of the plurality of segments and a corresponding segment of the corresponding plurality of segments to detect dissimilarity indicative of a directional coherence in the suspected direction due to a scratch for each segment of said plurality of segments.

8. The method of claim 1, wherein the pixel lines comprise separated pixel lines.

9. The method of claim 1, wherein the pixel lines comprise adjacent pixel lines.

10. A non-transitory computer readable medium having stored thereon instructions which when executed by a processor cause the processor to:

obtain a digital representation of the printed image and a digital reference image;

sum values of pixels of pixel lines in at least one segment of the digital representation of the printed image along a suspected direction to obtain a projection signal of the digital representation of the printed image for that segment, and sum values of pixels in a corresponding at least one segment of the digital reference image in the suspected direction to obtain a projection signal of the reference image for the corresponding segment;

compare the projection signals to detect dissimilarity indicative of a directional coherence in the suspected direction due to a scratch in said at least one segment of the digital representation of the printed image.

11. The non-transitory computer readable medium of claim 10, wherein the comparing the projection signals includes calculating a similarity measure between the projection signals and declare an existence of a directional coherence in the suspected direction due to a scratch when the similarity measure is below a predetermined threshold.

12. The non-transitory computer readable medium of claim 10, having instructions stored thereon which when executed by a processor cause the processor to scan the printed image to obtain the digital representation of the printed image.

13. The non-transitory computer readable medium of claim 10, having instructions stored thereon which when executed by a processor cause the processor to scan the printed image to apply a preprocessing operation on the digital representation of the printed image and on the digital reference image.

14. The non-transitory computer readable medium of claim 13, wherein the preprocessing operation is selected from a group of preprocessing operations consisting of reducing noise, increasing contrast, transforming the pair of corresponding segments a different domain and employing an extremity filter.

15. The non-transitory computer readable medium of claim 10, wherein said at least one segment comprises a plurality of segments and wherein said corresponding at least one segment includes a plurality of corresponding segments, the non-transitory computer readable medium having instructions stored thereon which when executed by a processor cause the processor to perform the steps of summing and comparing on each segment of the plurality of segments and a corresponding segment of the corresponding plurality of segments to detect dissimilarity indicative of a directional coherence in the suspected direction due to a scratch for each segment of said plurality of segments.

16. The non-transitory computer readable medium of claim 10, wherein the pixel lines comprise separated pixel lines.

17. The non-transitory computer readable medium of claim 10, wherein the pixel lines comprise adjacent pixel lines.

18. A system for detecting a scratch on a printed image, the system comprising:

a segmenter for dividing a digital representation of a printed image and a digital reference image into a plurality of corresponding segments;

a projector for summing values of pixels of pixel lines in at least one segment of the digital representation of the printed image along a suspected direction to obtain a projection signal of the digital representation of the printed image for that segment, and summing values of pixels in a corresponding at least one segment of the digital reference image in the suspected direction to obtain a projection signal of the reference image for the corresponding segment;

a comparator for comparing the projection signals to detect dissimilarity indicative of a directional coherence in the suspected direction due to a scratch in said at least one segment of the digital representation of the printed image.

19. The system of claim 18, further including a scanner for scanning the printed image to obtain the digital representation of the printed image.

20. The system of claim 18, incorporated in a printer.