Image analysis – Image transformation or preprocessing – Measuring image properties
Reexamination Certificate
1998-12-14
2001-08-28
Couso, Yon J. (Department: 2623)
Image analysis
Image transformation or preprocessing
Measuring image properties
C382S275000
Reexamination Certificate
active
06282326
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image processing method and system which removes diagonally disposed artifacts such as lines on skew corrected images produced by scanning an original document, without loss of image information.
BACKGROUND OF THE INVENTION
Unexpected vertical black patterns or artifacts such as lines, dots, dashes, etc., have been a common image artifact in binary document images produced by production paper scanners. The vertical black patterns are not part of the original document image, however, the patterns are the result of pieces of dust or dirt blocking light between an illumination light source and the paper documents being scanned. For example, pieces of dust or dirt which come to rest on transparent image guides in an illumination path of the scanner will result in shaded lines upon the document moving through the scanner. When the document is electronically captured by a CCD device, the shaded lines will appear in the digital document image. The shaded vertical lines within a grey scale image will be indistinguishably treated as part of image content. After an adaptive thresholding is applied to the grey scale image, the shaded lines will show up as black lines in the binary image. A method which removes unwanted vertically disposed artifacts is described in the above-mentioned co-pending application Docket No. 78434.
When a paper document is scanned by a production scanner, the resulting digital image is often skewed. The causes of a skewed image are either that the document is not fed properly, or the application of uneven paper carrying forces in a scanning system while transporting a paper document. The skew of a document image produces an unpleasant effect on viewing an image, hence an image skew correction is becoming a desired feature in a document scanning system (see, for example, U.S. Ser. No. 09/006,565.
If the phenomenon of vertical line artifacts occur in a skew image or document
1
as shown in
FIG. 1A
, a vertical line artifact
3
will turn into a diagonal line artifact
5
in the skew corrected image or document
1
′ as shown in FIG.
1
B.
SUMMARY OF THE INVENTION
An object of the present invention is to provide for an artifact detection and removal system and method for skew corrected images. The method includes the steps of (1) applying an edge-based adaptive thresholding method twice with different contrast parameter settings to convert a skew corrected image such as a gray scale image into two binary images; (2) generating a bitmap of the difference from the two binary images; (3) projecting and accumulating black pixels in the two dimensional bitmap onto a straight line to form a projection profile; (4) detecting locations of local peaks (i.e., line locations) from the projection profile; (5) acquiring the equations of lines from the skew angle and the location values of the detected local peaks; (6) masking the black pixels whose coordinates are within a certain threshold distance along the equations of lines in the bitmap of the difference; and (7) reversing the pixels from a binary image based on the black pixels along the lines in the thresholded binary image.
The system and method of the present invention includes deskewing a captured document image such as a gray scale image; applying an edge-based adaptive thresholding technique with a normal contrast setting to extract every detail of image information; storing the resulting binary image, named as B
1
; applying the same edge-based adaptive thresholding technique with a low contrast setting which only extracts high contrast details of the image, named as B
2
; labelling the difference of B
1
and B
2
, and storing the map of the difference, named as D; projecting the black pixels in the two dimensional bitmap (D) onto a one dimensional straight line, where the direction of projection is determined by the document skew angle; accumulating the black pixels to form a projection profile; locating the lines by detecting the local peaks in the projection profile, where the detected lines are represented by a set of equations of lines; masking the black pixels whose coordinates are within a certain threshold distance along the equations of lines in the bitmap (D) and resulting in a bitmap of lines, named as V; reading the binary image (B
1
) and the map of the lines (V); and reversing the pixels in the binary image B
1
at the corresponding black pixel locations in V.
The present invention relates to an image processing method for processing skew corrected images which comprises the steps of: converting a captured skew corrected image into first and second binary images; generating a map indicative of a difference between the first and second binary images; projecting black pixels in the map onto a line to form a projection profile; and reversing pixels in the first binary images based on the projection profile.
The present invention further relates to an image processing method for processing skew corrected images which comprises the steps of: converting a captured skew corrected image into first and second binary images; comparing the first and second binary images and generating a map indicative of a difference between the first and second binary images; projecting black pixels in the map onto a line to form a projection profile, wherein a direction of projection of the line is based on an original skew angle of the captured image; detecting peaks in the projection profile which are above a specified threshold and generating a line based on the detected peaks, wherein the detected peaks correspond to artifacts on the captured image; masking black pixels in the map which are adjacent to the generated line; and reversing pixels in the first binary image based on the masked pixels.
The present invention further relates to an image processing method for processing a skewed captured image. The method comprises the steps of: deskewing the captured image; extracting image information from the captured image and storing a resulting image as a first binary image; extracting high contrast details from the captured image and storing a resulting image as a second binary image; comparing the first and second binary images and generating a map indicative of a difference between the first and second binary images; projecting black pixels in the map onto a line to form a projection profile, wherein a direction of projection of the line is based on a skew angle of the skewed captured image; detecting peaks in the projection profile which are above a specified threshold and generating a line based on the detected peaks, wherein the detected peaks correspond to artifacts on the captured image; masking black pixels in the map which are adjacent to the generated line; and reversing pixels in the first binary image based on the masked pixels.
The present invention further relates to an image capture assembly which comprises: an image capture section which captures an image; an image deskewing section which is adapted to correct a captured image that is skewed so as to provide for a captured skewed corrected image; a conversion section which converts the skewed corrected image into digital image information indicative of the skewed corrected captured image; and a processing section which receives the digital information and changes the skewed corrected captured image into first and second binary images, wherein the processing section generates a map indicative of a difference between the first and second binary images, projects black pixels in the map onto a line which is oriented based on a skew angle of the captured image to form a projection profile, and reverses pixels in said first binary image based on said projection profile.
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Jaramillo Daniel T.
Lee Yongchun
Rudak Peter
Couso Yon J.
Eastman Kodak Company
Nelson Adrian Blish
Novais David A.
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