JPH11219460A - Method for processing inclined image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inclined image processing method capable of quickly processing an image read out in an inclined state. SOLUTION: In the case of acquiring an image while successively scanning paper moneys carried, a minor length corresponding to the arrangement of non-transmissible pixel values is obtained in each scanning line together with its distribution (S1) and the maximum frequency value of the minor lengths is obtained from the above distribution (S2). After checking where an inclination angle can be correctly detected or not (S3), the inclination angle is detected from the minor length start coordinates of scanning lines on upper and lower ends having the maximum frequency value (S5). Then, a paper money area is calculated (S6), an excess inclination angle is checked (S7), and after checking the dispersions of inclination angles (S8), an inlination is corrected based on the inclination angle thus obtained (S9). Since the most frequent minor length is acquired by the search of minor lengths and an inclination angle is detected by coordinates having the most frequency length, the processing of an image can be executed simultaneously with its image pickup and a high speed processing can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt image processing method, and more particularly to a tilt image processing method for detecting a tilt angle of a tilted rectangular image from a scanned image and correcting the tilt image straight based on the tilt angle. About.

[0002]

2. Description of the Related Art In a device for discriminating banknotes, an image sensor arranged in the middle of a transport path reads a banknote image while transporting the banknote, and processes the read image to determine a denomination and authenticity. Judgment is being performed. Banknotes have various sizes depending on denominations, and especially foreign banknotes have various sizes. In order to discriminate such a bill, the width of the transport path for carrying the bill is made to match the width of the widest bill among the denominations to be discriminated.
For this reason, especially when a narrow banknote is conveyed, it is rarely conveyed always in a straight state, and it is conveyed in a bent state, that is, a skew state,
Also in the imaging by the image sensor, the image is read in a skewed state.

In order to discriminate bills, it is necessary to know the exact coordinates of a read bill image. However,
Since the image read in the skew state remains in the skew state and cannot be used as it is, skew correction for making the skew state straight as preprocessing is performed.

[0004] For example, in the technique described in Japanese Patent Application Laid-Open No. 8-212417, first, the outline of a bill, that is, the short and long sides of the bill are calculated from the read image data of the bill.
The side information is obtained, and the skew angle of the banknote is thereby obtained. After that, the skewed image is rotated by the amount of skew with the corner of the image as the origin, thereby obtaining a straight image.

[0005]

However, according to the technique disclosed in the above publication, after scanning the entire banknote to determine the skew state of the banknote, the contour information is extracted from the entire image and the four sides are extracted. And there is a problem that a relatively long processing time and memory resources are required. In addition, the origin when rotating based on the skew angle is determined from the beginning at one corner of the area consisting of four sides, but if the corner is broken or missing, the origin is the bill However, there is a problem that a part of the image may be discarded after rotation.

SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and an object of the present invention is to provide a tilted image processing method capable of processing an image read at a tilt at a high speed.

[0007]

In order to solve the above problem, the present invention provides a tilt image processing method for correcting the tilt of an image obtained by imaging a rectangular medium having a predetermined size. Following the movement, while acquiring the pixels of the scan line by scanning in a direction perpendicular to the movement direction, the starting coordinate value that first changes from the background pixel to the media pixel in the scan direction on the scan line and finally the media pixel to the background Obtaining an end coordinate value that changes to a pixel and sequentially obtaining the medium length on a scan line from the difference between the start coordinate and the end coordinate, and obtaining the most frequent medium length from the medium length of each scan line ,
The inclination angle of the medium image is calculated based on the start coordinates or the end coordinates of the medium length of the scan line located at a position apart in the most frequent medium length, and the rectangular medium is calculated based on the inclination angle. A tilt image processing method for correcting a tilt of an image is provided.

According to such an inclined image processing method, when an image is acquired by scanning a rectangular medium, the starting coordinate value and the last coordinate value which first change from a background pixel to a medium pixel on a scan line are obtained while scanning. By examining the end coordinate value at which the pixel changes from the medium pixel to the background pixel, the length of the medium on the scan line can be obtained simultaneously with image acquisition. This is because, in a type in which light transmitted through a medium is detected when scanning, a pixel value is significantly different between a light-transmitted pixel obtained without transmitting the medium and a non-light-transmitted pixel obtained through the medium. Therefore, both ends of the medium on the scan line, that is, the medium length can be obtained simultaneously with image acquisition. The medium length for each scan line obtained in this manner has almost the same value on a scan line that simultaneously crosses the two sides in the moving direction of the medium because the two sides are parallel to each other. By calculating, the inclination angles of the two sides with respect to the moving direction of the medium can be obtained. That is, a scan line at a position as far away as possible from the scan lines having the mode is selected, and the inclination angle is detected from the difference between the coordinate values of the start or end position of the medium length and the distance between the scan lines. Will be. Thus, since the detection of the tilt angle is performed simultaneously with the image capturing, high-speed processing can be performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, taking as an example a case where the present invention is applied to image reading for bill discrimination.

FIG. 1 is a diagram showing a schematic configuration of an image reading device of a bill validating device. In FIG. 1, an image reading device that scans in a direction perpendicular to the direction in which the banknote 1 is transported is provided. It is assumed that the bill 1 is transported by a bill transport unit (not shown), for example, in the longitudinal direction thereof. In the image reading device, the light emitting element 2 is disposed below the bill conveying path, and the light receiving element 3 is disposed above the self transport lens 3. Light emitting element 2
Is composed of, for example, a light emitting diode array in which light emitting diodes are arranged in a line.
(Charge coupled device) It is a line sensor.

The image of the bill 1 is read at a predetermined timing with respect to the bill 1 conveyed at a constant speed.
Is emitted, and the irradiated light is focused on the light receiving element 4 through the selfoc lens 3 on the opposite side. The light receiving element 4 detects light directly incident without passing through the banknote 1 as a light-transmitting pixel having a large pixel value, and detects light incident through the banknote 1 as a non-light-transmitting pixel having a small pixel value. To an image processing unit (not shown).

The image processing unit detects the skew direction of the banknote from the image obtained in this way and performs processing for correcting the skew image. The flow of the processing will be described.
FIG. 2 is a flowchart showing a schematic flow of the skew image processing. First, a short length corresponding to the length of the non-light-transmitting pixel value is obtained for each scan line from the pixel values obtained by the image reading device, and the distribution is obtained (Step S).
1). In order to improve the skew angle detection accuracy, the shortest mode in which the shortest length is distributed most is calculated from the shortest length distribution, that is, a highly reliable value excluding a portion where the bill is bent at the long side and a chipped portion is removed. (Step S2). Here, it is determined whether or not the total frequency of the shortest mode is equal to or greater than the set value (step S3). If the total frequency of the shortest mode is small, the long side of the banknote is abnormally short or both sides are not parallel, so the skew angle cannot be determined based on this, so this banknote is abnormal. A rejection process is performed to return it as being (step S4). If it is found that the skew angle can be correctly detected, the skew angle is detected (step S5). In the detection of the skew angle, a plurality of angle values are obtained and the skew angle is obtained by averaging a plurality of angle values in order to further improve the accuracy. Next, in order to determine the target of the skew correction, the bill area is calculated, and the coordinates of the four corners of the bill are obtained (step S6). Next, if the bill is skewed greatly, it may cause mis-discrimination. Therefore, it is determined whether the skew angle is within 10 °, for example (step S7), and the bill is skewed more than 10 °. If so, reject processing is performed. Next, it is determined whether the variance of the plurality of angle values for which the skew angle has been obtained is within the set range (step S8). If the variance is large, the obtained skew angle is not a reliable value, so that rejection processing is performed. Finally, skew correction is performed based on the skew angle thus obtained (step S9).

Hereinafter, the details of the above processing will be sequentially described.
First, image data of a bill will be described. FIG. 3 is a diagram illustrating the definition of terms of image data. The image data is represented by an xy coordinate system, and the direction opposite to the bill transport direction is the y-axis, and the direction perpendicular to the bill transport direction is the x-axis. The rectangular area shown in the skewed state is the bill area, the point of the bill area detected first by the scan line is the top point, the point detected last is the bottom point, and the y coordinate position of the long side where the scan line is detected first Is the leftmost point, the y coordinate position of the longitudinal side to be detected last is the rightmost point, the difference in the y-axis direction between the uppermost point and the lowermost point is the longitudinal length, the x-axis direction between the leftmost point and the rightmost point is the The difference is a short length, and the average inclination of the bill area is an average skew angle θ. Further, the short length, the long length, and the average skew angle θ are positive in the directions of the arrows shown respectively.

FIG. 4 is a diagram for explaining the calculation of the short hand length.
The image data of the banknote 1 is taken in from the top of the conveyed banknote, that is, from the top in the figure, and each scan line is scanned from left to right. In each scan line, first, the leftmost point and the rightmost point are obtained. Pixels obtained by scanning are significantly different between a translucent pixel value when input to the light receiving element 4 without passing through the bill and a non-transparent pixel value when passing through the bill. Therefore, the coordinate value where the non-light-transmitting pixel first appears on the scan line is set as the leftmost point, and the coordinate position where the non-light-transmitting pixel appears last is set as the rightmost point. It should be noted that some banknotes 1 have a clear hole 11 and become a non-translucent pixel by the hole 11, but since the last non-transparent pixel appearing on the scan line is determined, The right side of the banknote 1 is always required.

The short length is obtained by the following equation.

[0016]

## EQU2 ## Shortest length = rightmost point−leftmost point + 1 (2) The leftmost point, rightmost point, and shortest length of each scan line are stored in a table called a full scan line list. Further, the short-hand frequency distribution of the bills for each scan line is stored in a table called a short-hand frequency distribution entire list. Then, by using the entire short-span length frequency list, the short-span having the largest frequency, that is, the most frequent short-span, is calculated for short-spans having one or more pixels. As a result, the scan lines that cross the long sides on both sides (scan lines indicated by に in the figure), excluding the scan lines in which the chip 12 is present on the long sides, are the shortest hand lengths.

Next, the sum of the frequencies of the shortest hand length ± the number of allowable pixels (for example, = 2 pixels) is obtained. The sum of this frequency is
When either or both of the following two conditions are satisfied, the banknote is determined as a banknote for which the skew angle cannot be obtained, and the banknote is rejected. First condition: sum of frequencies ≦ longitudinal length before skew correction / 2 Second condition: sum of frequencies <threshold (for example, = 16 pixels) Next, the skew angle is detected, but the skew angle is detected. The target is
A scan line whose short side is within the range of the most frequent short side length ± the allowable number of pixels. This corresponds to removing a folded or chipped area of the bill, thereby increasing the calculation accuracy of the skew angle.

First, from the first scan line in the entire scan line list, all the scan lines whose short lengths are within the range of the most frequent short length ± the allowable number of pixels are extracted, and the leftmost point and the extracted scan lines are extracted in the extraction list. Is stored in a table called.

Next, a tilt angle value is obtained. Here, for example, three sets of two scan lines which are separated from the extraction list as far as possible are selected. For example, assuming that the number of extracted scan lines is N, the angle value p1 is obtained from the extracted scan line q = 0 and the extracted scan line r = N−1, and the extracted scan line q = 4 and the extracted scan line q The angle value p2 is obtained from r = N-10th, and the angle value p3 is obtained from the extracted scan line q = 9th and the extracted scanline r = N-5th.
The formula is as follows.

[0020]

P = S × (leftmost point of r−leftmost point of q) / (scanline of r−scanline of q) (3) where S is a coefficient. Note that these angle values p are expressed by the following equations.

[0021]

P = S × tan (θ) (4) The skew angle value T is obtained by averaging those angle values p. That is,

[0022]

T = (p1 + p2 + p3) / 3 (5) Next, in order to obtain the coordinates of the bill area to be corrected, the next four points in all scan lines, that is Search for the left, right, top, and bottom points. The leftmost point is the minimum value of the leftmost point of all scanline lists, the rightmost point is the maximum value of the rightmost point of all scanline lists, and the topmost point is that the shortest length of all scanline lists is 1 or more. Is the minimum value of the scan lines, and the lowest point is the maximum value of the scan lines in which the short length of the entire scan line list is 1 or more.

Next, the skew angle value T is calculated as the average skew angle θ ± 1.
It is checked whether it is within the range of 0 °, and if the skew angle value T is too large, it is rejected as an excessive skew angle.

In the following skew angle dispersion determination, it is determined whether or not all the previously obtained angle values p1 to p3 are within the range of ± 3.7 °, for example. Rejected as undefined.

Next, the skew feeding correction processing will be described. The skew correction processing includes detection of a processing image area, calculation of a skew origin, and coordinate conversion processing. FIG. 5 is a diagram illustrating detection of a processed image area. The effective image area read by the image reading device is indicated by a square, and the effective image area includes image data of a bill. The area where the banknote image data is present is located at the four corners (P
1, P2, P3, P4). P1 is
When scanning is performed in order from the top, first, the coordinates of the pixel position of the scan line including the short length, P2 is the coordinates of the pixel position of the scan line including the short length last, and P3 is the short length. Are the coordinates of the leftmost point of the scan line with the smallest x-coordinate value, and P4 is the coordinate of the rightmost point of the scan line with the largest x-coordinate value of the short side.
When the area where the banknote image data is present is detected in this way, next, the skew origin for correcting the skew of the area is calculated.

FIG. 6 is a diagram for explaining the calculation of the skew origin. The skew origin is the intersection (x1, y1) of a line parallel to the x-axis passing through the uppermost point of the bill and an extension of the left long side of the bill. I do. A specific example of the skew correction will be described below.

FIGS. 7A and 7B are diagrams for explaining the coordinate conversion process, wherein FIG. 7A shows a pixel area before skew correction, and FIG. 7B shows a pixel area after correction. Here, the image area before correction is, as shown in (A), a coordinate system before skew correction (x,
In y), it is assumed that the skew angle θ is 1/3 (= tan ⁻¹ θ) and the starting point coordinates are (x0, y0). This is represented by the coordinate system (z, w) after skew correction as shown in FIG.
The skew correction is performed by mapping to the area having the coordinates (0, 0) as the origin. Here, the skew correction is performed according to the following conversion equation.

[0028]

Z = x−x0−INT ((y−y0) tan θ) (6) (However, INT () is rounded down to the decimal point in parentheses) That is, the inclination angle θ is 1/3. Therefore, a pattern in which three short-side pixel columns are arranged and three pixels are arranged one above another should be repeated. Looking at the pixel unit,
First, in the case of a line starting from the origin (y = y0), the pixels on this line are all arranged in one line w = 0 in the z direction. The w coordinate value in this case is w
= Y-y0. Next, the next pixel is moved to the line above one line, and the three pixels at the head of the line are also arranged in the z direction next to the pixel on the same one line of w = 0. The coordinate value is w = y−y0 + 1
It is represented by Similarly, in the next line, the three pixels at the head of the line are w =
On the 0 line, they are arranged in the z direction. The w coordinate value in this case is expressed by w = y−y0 + 2.

Thus, a straightened image can be obtained after the coordinate transformation. However, after straightening, the long side and the short side opposite to the origin are disturbed in terms of pixels as shown in FIG. For this reason, the image is cut out again so as to eliminate these disturbances.

[0030]

As described above, according to the present invention, while scanning a rectangular medium, the most frequent medium length is obtained by searching for the medium length in the scanning direction, and the angle detection based on the coordinates having the most frequent medium length is performed. It was configured to do so. This allows
The angle detection can be performed simultaneously with the acquisition without waiting until the entire medium image is acquired, and the processing can be performed at high speed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an image reading device of a bill validator.

FIG. 2 is a flowchart illustrating a schematic flow of skew image processing.

FIG. 3 is a diagram illustrating definitions of terms of image data.

FIG. 4 is a diagram for explaining calculation of short length.

FIG. 5 is a diagram illustrating detection of a processed image area.

FIG. 6 is a diagram illustrating calculation of a skew origin.

FIGS. 7A and 7B are diagrams for explaining a coordinate conversion process, wherein FIG.
Shows a pixel area before skew correction, and (B) shows a pixel area after correction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Banknote 2 Light emitting element 3 Selfoc lens 4 Light receiving element

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tatsuya Furui 1-1-1, Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (9)

[Claims] 1. A tilt image processing method for correcting a tilt of an image obtained by imaging a rectangular medium having a predetermined size, wherein the scanning is performed by scanning in a direction perpendicular to a moving direction according to a relative movement of the rectangular medium. While obtaining the pixels of the line, the start coordinates and the end coordinates that first change from the background pixel to the medium pixel in the scan direction and the end coordinate value last change from the medium pixel to the background pixel on the scan line are obtained. The media length on the scan line is sequentially obtained from the difference from the end coordinates, and the most frequent media length is obtained from the media length of each scan line. Calculating a tilt angle of a medium image based on a start coordinate or an end coordinate of the medium length of a scan line; and calculating an image of the rectangular medium based on the tilt angle. You can correct the inclination image processing method characterized by. 2. The step of obtaining the most frequent medium length comprises:
2. The tilt image processing method according to claim 1, wherein a medium length in which a value of the medium length in the scanning direction is within a range of a predetermined allowable value is set as a most frequent medium length. 3. The step of calculating the tilt angle includes selecting a plurality of pairs of scan lines from a plurality of scan lines near the farthest position in the most frequent medium length;
Determine the tilt angle based on the start coordinates or end coordinates of the medium length in the plurality of pairs of scan lines,
2. The tilt image processing method according to claim 1, wherein an average of the plurality of tilt angles is used as the tilt angle of the medium image. 4. The method according to claim 1, further comprising the step of detecting that the frequency of the most frequent medium length is within a predetermined allowable range and judging that the medium is the rectangular medium having the predetermined size. Slant image processing method. 5. The tilt according to claim 1, further comprising a step of detecting that the calculated tilt angle is within a predetermined allowable range and determining that the rectangular medium is not excessively tilted. Image processing method. 6. The step of correcting the inclination of the image,
2. The tilt image processing method according to claim 1, wherein a processing image area is detected, a processing origin of the processing image area is calculated, and a rotation process is performed about the processing origin. 7. The step of detecting the processed image area includes the step of: detecting a coordinate point of the medium pixel on the scan line in which the medium pixel is first included, and the medium in a scan line including the medium length. A coordinate point of a medium pixel start position on a scan line in which a pixel start position is the leftmost, and a scan line in which an end position of the medium pixel is the rightmost in the scan lines including the most frequent medium length A correction target rectangular area including four coordinate points of an upper end of the medium pixel and a coordinate point of the medium pixel on the scan line that includes the medium pixel last is obtained. The tilt image processing method according to claim 6. 8. The step of calculating the processing origin of the processing image area includes the step of calculating a line on the scan line in which the medium pixel is first included and an extension line of a side on which the tilt angle of the medium image is obtained. 7. The tilt image processing method according to claim 6, wherein the intersection is a processing origin. 9. The step of performing the rotation process includes setting a start point of a correction target rectangular area of a pre-correction coordinate system (x, y) having the inclination angle of the medium image as θ and the processing origin as an origin as (x
0, y0), a conversion formula for converting the rectangular region to be corrected into a region having the origin at the coordinates (0, 0) of the corrected coordinate system (z, w): z = x−x0 −INT 7. The tilt image processing method according to claim 6, wherein mapping is performed in accordance with ((y-y0) tan [theta]) (1) (where INT () is rounded down to the decimal point in parentheses).