Image forming apparatus and control method thereof

• US 8,189,914 B2
• Filed: 05/22/2008
• Issued: 05/29/2012
• Est. Priority Date: 10/09/2007
• Status: Active Grant

• Current Assignee: HP Printing Korea Co., Ltd. (HP Inc.)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Hong, Jin Kyung
• Primary Examiner(s): Do, Anh Hong
• Application Number:
  US12/125,258
• Publication Number:
  US 20090091801A1
• Time in Patent Office: 1,468 Days
• Field of Search: 382/172, 382/318, 382/162, 382/163, 382/305, 382/167, 348/370, 348/371, 348/224.1, 358/497, 358/463, 358/464, 358/1.15, 358/1.9, 358/1.14
• US Class Current: 382/172
• CPC Class Codes: H04N 1/4074 using histograms
• CPC Class Codes: H04N 1/4095 Correction of errors due to scanning a two-sided document, i.e. show-through correction

Abstract

An image forming apparatus and a control method thereof include an adaptive threshold, which can be adapted for every block dividing an entire scanned region of a document, is set. A brightness value of original brightness data of the document is disregarded, and is substituted by a brightness value of background color data corresponding to the block, by use of a brightness threshold and a color difference threshold set as the adaptive threshold based on difference between brightness of the blocks and difference between color differences of the blocks. Accordingly, there is no problem of back surface noise such that an undesired object of a back surface of the duplex-printed document appears on a scan image in scanning a front surface of the document.

Claims

1. An image forming apparatus, comprising:

an image scanning unit to scan a duplex-printed document and output scan data; and

an image processing device to compensate background color data of the scan data based on an adaptive threshold which can be adapted according to a scanned region of the document,

wherein the image processing device removes an object printed on a region except for the scanned region in scanning the document.

2. The image forming apparatus according to claim 1, wherein the image processing device compensates the background color data with respect to a plurality of blocks, into which an entire scanned region of the document is divided, by block units.

3. The image forming apparatus according to claim 2, wherein the image processing device comprises:

a color coordinate converting unit to convert the scan data into brightness/color difference data; and

a histogram analysis unit to analyze a histogram of the brightness/color difference data.

4. The image forming apparatus according to claim 3, wherein the image processing device further comprises:

an adaptive threshold setting unit to set the adaptive threshold for every block according to a frequency of a brightness value and a rate of change of the frequency in the brightness histogram analyzed by the histogram analysis unit; and

an adaptive threshold storage unit to store the adaptive threshold.

5. The image forming apparatus according to claim 4, wherein the adaptive threshold setting unit sets a brightness value at the time of setting the adaptive threshold to a brightness threshold, and sets a color difference threshold corresponding to the brightness threshold.

6. The image forming apparatus according to claim 4, wherein the adaptive threshold setting unit sets a brightness threshold and a color difference threshold corresponding to the brightness threshold, based on difference between brightness of the blocks and difference between color differences of the blocks.

7. The image forming apparatus according to claim 4, wherein the image processing device includes an image compensation unit,

and wherein when brightness data of the scan data of the document is larger than a brightness threshold and color difference data corresponding to the brightness data is smaller than a color difference threshold, the image compensation unit carries out compensating operation.

8. The image forming apparatus according to claim 7, wherein the image compensation unit carries out the compensating operation by substituting the brightness value of the brightness data by a higher brightness value of the background color.

9. The image forming apparatus according to claim 2, wherein the image processing device comprises:

an initial background value setting unit to set a minimum allowable brightness value and a maximum allowable color difference value to an initial background value by use of superior brightness data and superior color difference data of the scan data extracted from any one of the plurality of blocks.

10. The image forming apparatus according to claim 9, wherein the initial background value setting unit extracts the scan data from other blocks except for certain blocks of the plurality of blocks of the document.

11. The image forming apparatus according to claim 10, wherein the initial background value setting unit excludes an upper end block of the document.

12. The image forming apparatus according to claim 10, wherein the initial background value setting unit performs down sampling in extracting the scan data.

13. A method to control an image forming apparatus, the method comprising:

scanning a duplex-printed document;

setting a minimum allowable brightness value and a maximum allowable color difference value in scan data extracted from any one block with respect to a plurality of blocks, into which an entire scanned region of the document is divided;

converting the scan data into brightness/color difference data by block units, and analyzing a brightness or color difference histogram with respect to the brightness/color difference data;

setting an adaptive threshold which can be adapted for every block according to a frequency of a brightness value and a rate of change of the frequency in the brightness histogram; and

compensating background color data of the scan data by use of the adaptive threshold set by block units.

14. The method according to claim 13, wherein the setting the adaptive threshold comprises:

setting a brightness value at a time of setting the adaptive threshold to a brightness threshold; and

setting a color difference threshold corresponding to the brightness threshold.

15. The method according to claim 13, wherein the setting the adaptive threshold comprises:

setting a brightness threshold corresponding to the adaptive threshold and a color difference threshold corresponding to the brightness threshold, based on a difference between a brightness of the blocks and a difference between color differences of the blocks.

16. The method according to claim 13, wherein the compensating the scan data is achieved when brightness data of the scan data of the document is larger than a brightness threshold and color difference data corresponding to the brightness data is smaller than a color difference threshold.

17. The method according to claim 13, wherein the compensating the scan data includes substituting the brightness value of the brightness data by a higher brightness value of the background color.

18. A method to control an image forming apparatus, the method comprising:

scanning a duplex-printed document and a test patch printed with a verification pattern to verify whether back surface noise occurring in scanning the document is compensated;

analyzing a brightness histogram by block units, into which a scanned region of the duplex-printed document is divided;

compensating background color data of scan data of the document by use of an adaptive threshold set for every block according to a frequency of a brightness value and a rate of change of the frequency in the brightness histogram; and

printing the verification pattern of the patch by applying the adaptive threshold set for every block.

19. The method according to claim 18, wherein the verification pattern is printed such that a range of a printed region is changed according to the adaptive threshold.

20. An image forming apparatus, comprising:

an image scanning unit to scan a duplex-printed document and output scan data; and

an image processing device to receive scan data, to remove a portion of the scan data according to a pattern of another portion of the scan data, and to identify and remove back surface noise due at least to an unwanted object scanned,

wherein the removal of the back surface noise is accomplished through compensation of background color data.

21. The image forming apparatus of claim 20, wherein the unwanted object scanned is located on an opposite side of the duplex-printed document being scanned with respect to the image scanning unit.

22. The image forming apparatus of claim 20, wherein the background color data is compensated for by outputting the unwanted object with a same brightness as a background color.

23. The image forming apparatus of claim 20, wherein the image scanning unit scans the duplex-printed document having a first surface and a second surface opposite to the first surface to generate the scan data according to images of the first surface and the second surface of the document, such that the portion of the scan data corresponds to the image of the second surface and the another portion of the scan data corresponds to the image of the first surface.

24. The image forming apparatus of claim 20, wherein another portion of the scan data includes color data, and the color data is adjusted according to a removal of the portion of the scan data.

25. The image forming apparatus of claim 24, wherein the portion and the another portion have an area to overlap each other.

26. A method of removing an appearance of an unwanted scanned object of an image forming apparatus, the method comprising:

scanning a duplex-printed document;

outputting scan data;

identifying the back surface noise due at least to an unwanted scanned object; and

removing the identified back surface noise is accomplished through compensation of background color data.