JP2009124674A - Image processing apparatus, image scanning apparatus, image processing method, and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of performing an image rotating process in a short period of time. <P>SOLUTION: Two integers "a" and "b", of which the ratio a/b is equal to a tangent value of a rotation angle, are inputted to perform a rotation process. Each time an x-coordinate (m) of a target pixel of a rotated image is changed by one pixel, "a" is added to a y-direction weight factor "kwy". When the y-direction weight factor "kwy" becomes more than or equal to "b", "b" is subtracted from the y-direction weight factor "kwy", and a y-coordinate of a corresponding target pixel of an original image is changed by one pixel. Each time a y-coordinate (n) of the target pixel is changed by one pixel, "a" is added to an x-direction weight factor "kwx". When the x-direction weight factor "kwx" becomes more than or equal to "b", "b" is subtracted from the x-direction weight factor "kwx", and an x-coordinate (i) of the corresponding target pixel of the original image is changed by one pixel. Four pixels including the corresponding target pixel are used to acquire a pixel value of the target pixel by two-dimensional interpolation by ratios acquired by dividing the x-direction weight factor "kwx" and the y-direction weight factor "kwy" respectively by "b". <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention mainly relates to an image processing apparatus that rotates image data.

  In an image scanner device, a copy device, a facsimile device, an optical character reader (OCR), or the like, when an original is read in a skewed state, a tilted image is obtained and reading quality is deteriorated. In order to avoid this, there has been proposed an image reading apparatus capable of electronically correcting skew by rotating image data.

It is generally known that such image rotation processing is performed using a rotation matrix. For example, in Non-Patent Document 1, when the coordinates of an arbitrary pixel of the original image are (x, y) and the coordinates of the corresponding pixel of the converted image are (x ^* , y ^* ), FIG. It is disclosed that the image is rotated using the equation shown in FIG. Further, Non-Patent Document 1 discloses that a gradation value (pixel value) of an intermediate pixel can be obtained by performing a two-dimensional interpolation process in the geometric correction process of the image including the rotation process. Has been.
Takeshi Yasui and Tomoharu Nagao, “Image Processing and Recognition”, First Edition, Shosodo Co., Ltd., October 2000, p.20-22

  However, since the method of Non-Patent Document 1 normally multiplies sinθ and cosθ, which are irrational numbers, for each pixel, the calculation cost becomes extremely high. Therefore, such an image rotation process significantly increases the processing time, and when applied to the skew correction of the image reading apparatus, it is not easy to realize high-speed reading. Therefore, an image processing apparatus capable of performing image rotation processing in a shorter time has been demanded.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to a first aspect of the present invention, there is provided an image processing apparatus having the following configuration, which obtains a rotated image by rotating a raster image that is an original image. That is, the image processing apparatus includes an integer parameter input unit, an original image corresponding position calculation unit, and a two-dimensional interpolation unit. The integer parameter input unit receives the first integer parameter and the second integer parameter such that the ratio value is equal to the tangent value of the rotation angle. The original image corresponding position calculation unit adds the first integer parameter to the y-direction weighting coefficient every time the x coordinate of the target pixel in the rotated image is changed by a predetermined number of pixels, and the y-direction weighting coefficient is the second weighting coefficient. When the number is greater than or equal to the integer parameter, the second integer parameter is subtracted from the y-direction weighting coefficient, and the y coordinate of the corresponding target pixel that is the pixel corresponding to the target pixel in the original image is changed by a predetermined pixel. Perform the process. In addition, the original image corresponding position calculation unit adds the first integer parameter to the x-direction weight coefficient every time the y-coordinate of the target pixel in the rotated image is changed by a predetermined pixel, and the x-direction weight coefficient is When the value is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the x-direction weight coefficient, and the x coordinate of the corresponding target pixel of the original image is changed by a predetermined number of pixels. The two-dimensional interpolation unit uses the corresponding pixel of interest in the original image and the corresponding pixel of interest as three pixels in which at least one of the x-coordinate and y-coordinate differs by a predetermined pixel. The pixel value of the pixel of interest in the rotated image is obtained by two-dimensional interpolation using the ratio obtained by dividing the coefficient by the second integer parameter and the ratio obtained by dividing the y-direction weight coefficient by the second integer parameter.

  With this configuration, it is possible to perform rotation processing with two-dimensional interpolation by frequently using integer arithmetic processing and integer comparison processing using two integer parameters and weighting factors. Accordingly, it is possible to reduce processing with a large calculation cost such as floating point arithmetic and to obtain a high-quality rotated image at high speed.

  In the image processing apparatus, it is preferable that the two-dimensional interpolation unit collectively performs division by the square of the second integer parameter in the calculation of the pixel value of the target pixel.

  With this configuration, division processing with a high calculation cost can be reduced, so that rotation processing can be performed at higher speed.

  In the image processing apparatus, the two-dimensional interpolation unit changes the second integer parameter to an integer power value of 2, and further divides the integer power value of 2 by the second integer parameter before the change. It is preferable to calculate the pixel value of the pixel of interest after multiplying the x-direction weighting coefficient and the y-direction weighting coefficient to approximate an integer value.

  With this configuration, the calculation cost of the division process can be significantly reduced, so that the speed of the rotation process can be further increased.

  According to a second aspect of the present invention, an image reading apparatus having the following configuration is provided. That is, from the image processing apparatus, the image reading unit that reads the image of the document to obtain image data, and the coordinates of two points in the image data, the ratio is equal to the tangent value of the tilt angle of the document. An inclination angle detection unit that obtains two inclination parameter integers. Then, the image reading apparatus provides the two inclination parameter integers to the image processing apparatus as the first integer parameter and the second integer parameter, and rotates the image data, thereby correcting the inclination of the document. It is configured to obtain data.

  With this configuration, image data with corrected inclination can be obtained in a short time, which is particularly suitable for high-speed reading.

  According to the third aspect of the present invention, the following image processing method is provided. That is, in this image processing method, based on the first integer parameter and the second integer parameter such that the value of the ratio is equal to the tangent value of the rotation angle, the raster image that is the original image is rotated to obtain the rotated image. An image processing method to obtain. This image processing method includes an original image corresponding position calculation step and a two-dimensional interpolation step. In the original image corresponding position calculation step, each time the x coordinate of the target pixel in the rotated image is changed by a predetermined number of pixels, the first integer parameter is added to the y direction weighting coefficient, and the y direction weighting coefficient is the second weighting coefficient. When the number is greater than or equal to the integer parameter, the second integer parameter is subtracted from the y-direction weighting coefficient, and the y coordinate of the corresponding target pixel that is the pixel corresponding to the target pixel in the original image is changed by a predetermined pixel. Perform the process. Further, in the original image corresponding position calculation step, each time the y coordinate of the target pixel in the rotated image is changed by a predetermined number of pixels, the first integer parameter is added to the x direction weight coefficient, and the x direction weight coefficient is calculated. When the value is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the x-direction weight coefficient, and the x coordinate of the corresponding target pixel of the original image is changed by a predetermined number of pixels. In the two-dimensional interpolation step, the weight in the x direction is targeted for the corresponding pixel of interest in the original image and three pixels in which at least one of the x coordinate and the y coordinate differs from the corresponding pixel of interest by a predetermined pixel. The pixel value of the pixel of interest in the rotated image is obtained by two-dimensional interpolation using the ratio obtained by dividing the coefficient by the second integer parameter and the ratio obtained by dividing the y-direction weight coefficient by the second integer parameter.

  According to this method, it is possible to perform rotation processing with two-dimensional interpolation by making extensive use of integer arithmetic processing and integer comparison processing using two integer parameters and weighting factors. Accordingly, it is possible to reduce processing with a large calculation cost such as floating point arithmetic and to obtain a high-quality rotated image at high speed.

  According to the fourth aspect of the present invention, there is provided an image processing program for obtaining a rotated image by rotating a raster image that is an original image as follows. That is, this image processing program executes an integer parameter input step, an original image corresponding position calculation step, and a two-dimensional interpolation step. In the integer parameter input step, the first integer parameter and the second integer parameter are inputted so that the value of the ratio becomes equal to the tangent value of the rotation angle. In the original image corresponding position calculating step, every time the x coordinate of the target pixel in the rotated image is changed by a predetermined number of pixels, the first integer parameter is added to the y-direction weighting coefficient, and the y-direction weighting coefficient is When the number is greater than or equal to the integer parameter, the second integer parameter is subtracted from the y-direction weighting coefficient, and the y coordinate of the corresponding target pixel that is the pixel corresponding to the target pixel in the original image is changed by a predetermined pixel. Perform the process. Further, in the original image corresponding position calculating step, every time the y coordinate of the target pixel in the rotated image is changed by a predetermined number of pixels, the first integer parameter is added to the x direction weight coefficient, and the x direction weight coefficient is calculated. When the value is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the x-direction weight coefficient, and the x coordinate of the corresponding target pixel of the original image is changed by a predetermined number of pixels. In the two-dimensional interpolation step, the weight in the x direction is targeted for the corresponding pixel of interest in the original image and three pixels that differ from the corresponding pixel of interest by at least one of the x coordinate and the y coordinate by a predetermined pixel. The pixel value of the pixel of interest in the rotated image is obtained by two-dimensional interpolation using the ratio obtained by dividing the coefficient by the second integer parameter and the ratio obtained by dividing the y-direction weight coefficient by the second integer parameter.

  As a result, it is possible to perform rotation processing with two-dimensional interpolation by making extensive use of integer arithmetic processing and integer comparison processing using two integer parameters and weighting factors. Accordingly, it is possible to reduce processing with a large calculation cost such as floating point arithmetic and to obtain a high-quality rotated image at high speed.

  Next, embodiments of the invention will be described. FIG. 2 is a front sectional view showing the overall configuration of the image scanner device according to the embodiment of the present invention.

  As shown in FIG. 2, an image scanner device 101 as an image reading device includes an image reading unit 115 including an auto document feeder unit and a flat bed unit.

  This will be specifically described below. That is, the image scanner apparatus 101 includes an original table 103 on which a platen glass 102 on which a read original is placed is disposed, and an original table cover 104 for holding the read original in a pressed state on the platen glass. It is equipped with. Further, the image scanner device 101 is provided with an unillustrated operation panel for instructing the start of reading of a document. A pressing pad 121 for pressing the document downward is attached to the lower surface of the document table cover 104 so as to face the platen glass 102.

  The document table cover 104 is provided with an auto document feeder (automatic document feeder) 107. The auto document feeder 107 includes a document tray 111 provided above the document table cover 104 and a paper discharge tray 112 provided below the document tray 111.

  As shown in FIG. 2, a curved document transport path 113 that connects the document tray 111 and the paper discharge tray 112 is formed inside the document table cover 104. A pickup roller 51, a separation roller 52, a separation pad 53, a conveyance roller 55, and a paper discharge roller 58 are disposed in the document conveyance path 113.

  The pickup roller 51 feeds the read document on the document tray 111, and the separation roller 52 and the separation pad 53 are configured to separate the fed document one by one. The conveyance roller 55 conveys the separated document toward the document reading position P, and the paper discharge roller 58 is configured to discharge the read document to the paper discharge tray 112. A pressing member 122 is provided at the document reading position P so as to face the platen glass.

  With the above-described configuration, the read originals set on the original tray 111 are separated one by one and conveyed along the curved original conveyance path 113, passing through the original reading position P, and a scanner unit described later. After being read by the printer 21, it is discharged to the paper discharge tray 112.

  As shown in FIG. 2, a scanner unit 21 is provided in the document table 103. The scanner unit 21 includes a carriage that can move inside the document table 103.

  The carriage 30 includes a fluorescent lamp 22 as a light source, reflection mirrors 23, 23..., A condenser lens 27, and a charge coupled device (CCD) 28. The fluorescent lamp 22 irradiates the read original with light, and the reflected light from the read original is reflected by a plurality of reflecting mirrors 23, 23. To form an image. The CCD 28 converts the incident convergent light into an electrical signal and outputs it.

  In the present embodiment, the CCD 28 is a three-line color CCD. The CCD 28 is provided with a one-dimensional line sensor elongated in the main scanning direction (document width direction) for each color of red, green, and blue (RGB), and provided with a different color filter corresponding to each line sensor. It has become.

  A driving pulley 47 and a driven pulley 48 are rotatably supported in the document table 103. An endless drive belt 49 is stretched between the drive pulley 47 and the driven pulley 48, and the carriage 30 is fixed to an appropriate portion of the drive belt 49. With this configuration, the carriage 30 can be moved horizontally along the sub-scanning direction by driving the drive pulley 47 forward and backward with an electric motor (not shown).

  With this configuration, the auto document feeder 107 is driven in a state where the carriage 30 has been moved in advance to a position corresponding to the document reading position P. Then, the read original conveyed on the original conveyance path 113 is scanned at the original reading position P, and the reflected light irradiated from the fluorescent lamp 22 and reflected by the read original is introduced into the carriage 30, and the reflection mirrors 23, 23,. The light is guided to the CCD 28 through the condenser lens 27 to form an image. As a result, the CCD 28 can output an electrical signal corresponding to the read content.

  Further, when used as a flatbed scanner, the read original placed on the platen glass 102 is scanned while moving the carriage 30 along the platen glass 102 at a constant speed. The reflected light from the document is guided to the CCD 28 in the carriage 30 to form an image as described above.

  FIG. 3 is a block diagram of the image scanner device 101. As shown in FIG. 3, in addition to the scanner unit 21, the image scanner device 101 includes a CPU 41, a ROM 42, an image processing unit 43, an image memory 66, an inclination detecting unit 67, and an inclination correcting unit (image processing apparatus). 68, a code conversion unit 69, and an output control unit 70.

  The CPU 41 is provided as a control unit for controlling the scanner unit 21, the tilt detection unit 67, the tilt correction unit 68, the output control unit 70, and the like provided in the image scanner device 101. A program, data, and the like for this control are stored in a ROM 42 as a storage unit.

  The scanner unit 21 includes an analog front end (AFE) 63, and this AFE 63 is connected to the CCD 28. At the time of document reading, the RGB line sensors included in the CCD 28 scan the document content in the main scanning direction to read one line, and the signals of each line sensor are converted from analog signals to digital signals by the AFE 63. . By this main scanning, pixel data for one line is output from the AFE 63 as gradation values of RGB colors. By repeating the above processing while feeding the document or carriage 30 by a minute distance in the sub-scanning direction, the image data of the entire document can be obtained as a digital signal.

  The scanner unit 21 includes an image processing unit 65, and a digital signal of image data output from the AFE 63 is input to the image processing unit 65. The image processing unit 65 performs shading correction on pixel data input line by line for each main scan, and corrects reading unevenness caused by the optical system of the scanner unit 21. The image processing unit 65 corrects the pixel data to correct a color shift caused by the arrangement interval (line gap) of the RGB line sensors in the CCD 28.

  The image memory 66 is for accumulating images read by the scanner unit 21. The image data read by the scanner unit 21 is further subjected to known image processing (filter processing or the like) in the image processing unit 43, and then is input and stored in the image memory 66.

  The tilt detection unit 67 analyzes image data input from the scanner unit 21 to detect a document area, and automatically detects the tilt of the document (an angle to be rotated to correct the tilt) based on this. It is configured as follows.

  Specifically, the inclination detection unit 67 performs the following processing. That is, in this embodiment, a white sheet (a platen sheet) that is brighter than normal paper is pasted on the surface of the pressing pad 121 and the pressing member 122 (FIG. 2) arranged on the back side of the scanned document. It is attached. Therefore, in the image data read by the CCD 28, the brightness of the background portion around the document is high.

  By using this, the inclination detection unit 67 performs image processing for calculating the luminance (Y component) from the RGB components of the pixel data according to a known formula. If the luminance is equal to or higher than a predetermined value, the background pixel, If the value is below the value, binarization processing is performed as a document pixel.

  An example of a binarized image is shown in FIG. In FIG. 4, one finely divided cell corresponds to one pixel, a blank cell represents a background pixel, and a hatched cell represents a document pixel.

  In the example of FIG. 4, as a result of the document being conveyed by the auto document feeder unit in a skewed state and read by the scanner unit 21, a rectangular image slightly rotated clockwise from the normal direction is obtained as the document pixel area. ing.

  In the present embodiment, the inclination detection unit 67 detects two points (illustrated by black squares) located at the corners of the document pixel area by appropriate image recognition processing. Then, the x coordinate and y coordinate of the two detected points are obtained, respectively, and the difference between the x coordinate and the y coordinate of the two points is calculated and obtained. The difference between the y coordinates obtained here is dy, and the difference between the x coordinates is dx. In the example of FIG. 4, dy = 10 and dx = 50.

  Then, the inclination detection unit 67 divides the y-coordinate difference dy and the x-coordinate difference dx by the greatest common divisor, and sets the obtained results as inclination parameters a and b. In the example of FIG. 4, a = 1 and b = 5.

Here, when the inclination angle of the document is θ, the relationship θ = tan ⁻¹ (dy / dx) = tan ⁻¹ (a / b) is established. That is, the ratio value (a / b) between a and b coincides with the tangent value tanθ of the document inclination angle. However, the inclination detector 67 of this embodiment only stores the inclination parameters a and b in an appropriate memory, and does not calculate the inclination angle θ.

  Since the x coordinate and y coordinate of the two points are respectively represented by integers, the above-described y coordinate difference dy and x coordinate difference dx are also integers, and the slope parameters a and b are also integers. The obtained slope parameter integers a and b are used as integer parameters given to the slope correction unit 68 described later.

  The above-described detection processing (angle detection processing) of the inclination parameters a and b may be performed without converting the resolution of the original image (magnification), but the angle is determined using reduced image data obtained by reducing the original image. Detection may be performed. By using the reduced image data, the angle detection process can be shortened particularly when processing is performed by software.

  The tilt correction unit 68 shown in FIG. 3 rotates raster image data in the image memory 66 based on the tilt parameter integers a and b obtained by the tilt detection unit 67, and electronically skews the document. It is configured to correct. The inclination correction unit 68 includes an integer parameter input unit 71, an original image corresponding position calculation unit 72, and a two-dimensional interpolation unit 73.

  The parameter input unit 71 is configured to be able to acquire two gradient parameter integers as a first integer parameter a and a second integer parameter b. As described above, the ratio value (a / b) of the two integer parameters a and b is equal to the tangent value tanθ of the angle at which the image is to be rotated (original tilt angle).

  The original image corresponding position calculation unit 72 performs a predetermined calculation based on the position of the pixel of interest (m, n) in the rotated image, so that the original image corresponds to the pixel of interest corresponding to the pixel of interest (m, n). The position of a certain corresponding target pixel (i, j) is obtained. Further, the original image corresponding position calculation unit 72 performs a predetermined calculation based on the position of the target pixel, so that the x-direction weighting coefficient kwx and the y-direction weighting coefficient kwy used in the interpolation performed by the two-dimensional interpolation unit 73. Ask for.

  The two-dimensional interpolation unit 73 performs two-dimensional interpolation based on the corresponding target pixel (i, j) and the corresponding target pixel and three pixels that are different in at least one of the x coordinate and the y coordinate. Then, the pixel value Q (m, n) of the target pixel in the rotated image is obtained. In this two-dimensional interpolation, ratios (kwx / b, kwy / b) obtained by dividing the x-direction weighting coefficient kwx and the y-direction weighting coefficient kwy by an integer b are used. Details of the rotation processing by the inclination correction unit 68 will be described later.

  The code conversion unit 69 encodes the image data stored in the image memory 66 by performing a known compression process such as JPEG.

  The output control unit 70 transmits the encoded image data to a personal computer (not shown) as a host device connected to the image scanner device 101. Although the transmission method is arbitrary, for example, a method using a local area network (LAN), a method using a universal serial bus (USB), and the like are conceivable.

  In the present embodiment, the image processing unit 65, the inclination detection unit 67, the inclination correction unit 68, the code conversion unit 69, and the like are realized using hardware such as ASIC and FPGA, for example. An image processing program for performing image rotation processing by a method to be described later is written in the ASIC or the like, so that the rotation processing function of the tilt correction unit 68 is realized. However, the inclination correction unit 68 and the like may be realized by a combination of the CPU 41 and a program.

  Next, image rotation processing by the tilt correction unit 68 will be described with reference to the flowchart of FIG.

  When the flow of FIG. 5 is started, the inclination correction unit 68 first inputs two inclination parameter integers obtained by the inclination detection unit 67 as the first integer parameter a and the second integer parameter b (S101). The process of S101 corresponds to an integer parameter input step (integer parameter input step).

  Next, variable initialization processing is performed (S102). In this initialization process, the x coordinate m and the y coordinate n of the pixel of interest in the rotated image are reset to zero. Further, the x-direction offset value moff and the y-direction offset value noff used when calculating the position of the corresponding target pixel (the pixel of the original image corresponding to the target pixel) are also reset to zero. Furthermore, the x-direction weight coefficient kwx and the y-direction weight coefficient kwy used for two-dimensional interpolation are also reset to zero. Note that the variables m, n, moff, noff, kwx, and kwy are all integer variables.

  Next, the pixel value Q (m, n) of the target pixel (m, n) of the rotated image is calculated (S103). In this process, first, the position (i, j) of the corresponding target pixel of the original image is calculated. The x coordinate i of the corresponding target pixel is obtained by adding an offset value moff to the x coordinate m of the target pixel of the rotated image (i = m + moff). Similarly, the y coordinate j of the corresponding target pixel is obtained by adding the offset value noff to the y coordinate n of the target pixel of the rotated image (j = n + noff).

  Here, the offset value moff is decremented by 1 every time the target pixel of the rotated image moves (b / a) pixels in the y direction (S114). The offset value noff is incremented by 1 every time the target pixel of the rotated image moves by (b / a) pixels in the x direction (S107). The offset value addition / subtraction process will be described later.

  FIG. 6 shows the pixel of interest and the original image of the rotated image when the slope parameter integers a = 1 and b = 5 obtained in the example of FIG. 4 are input to the slope correction unit 68 as the first integer parameter and the second integer parameter. The correspondence with the target pixel of interest is shown.

  In FIG. 6, the target pixel when the first row and the first column of the rotated image are set as the target pixel and the corresponding target pixel of the original image are indicated by squares surrounded by double lines. As shown in the upper side of FIG. 6, the corresponding target pixel of the original image is shifted by one pixel in the y direction every time the target pixel of the rotated image moves five pixels (= b / a) in the x direction. In addition, the corresponding target pixel of the original image is shifted by one pixel in the x direction every time the target pixel of the rotated image moves five pixels in the y direction.

  Next, the pixel value Q (m, n) of the target pixel of the rotated image is acquired by two-dimensional linear interpolation. As shown in FIG. 7, the two-dimensional linear interpolation is performed in the y direction with the corresponding target pixel (i, j) of the original image, the pixel (i−1, j) adjacent to the corresponding target pixel in the x direction. This is performed for a total of four pixels, which are adjacent pixels (i, j + 1) and diagonally adjacent pixels (i-1, j + 1). Based on the pixel values P (i, j), P (i−1, j), P (i, j + 1), and P (i−1, j + 1) of the four pixels, the x-direction weighting coefficient kwx The pixel of interest of the rotated image is linearly interpolated by the ratio (kwx / b) divided by the second integer parameter b and the ratio (kwy / b) obtained by dividing the y-direction weight coefficient kwy by the second integer parameter b. A pixel value Q (m, n) of (m, n) is acquired.

  Here, the x-direction weight coefficient kwx is incremented by the first integer parameter a every time the target pixel of the rotated image moves one pixel in the y direction (S112 in FIG. 5). The y-direction weight coefficient kwy is incremented by the first integer parameter a every time the target pixel of the rotated image moves one pixel in the x direction (S105). The weighting coefficient addition process will be described later.

In S103 of FIG. 5, a calculation formula of the pixel value Q (m, n) of the target pixel described in the conceptual diagram of FIG. 7 is shown. This calculation formula is modified so that the division by the second integer parameter b appears outside the brackets [~]. As a result, division processing with a high calculation cost can be combined into one division by the square of the second integer parameter (b ² ), and the calculation processing can be speeded up.

  After the pixel value acquisition process (two-dimensional interpolation step, two-dimensional interpolation step) in S103 is completed, 1 is added to the x coordinate m of the target pixel (S104). This process corresponds to moving the target pixel (m, n) of the rotated image by one pixel in the x direction.

  Next, the first integer parameter a is added to the y-direction weight coefficient kwy (S105). Then, it is checked whether the y-direction weight coefficient kwy after the addition is equal to or larger than the second integer parameter b (S106). If it is greater than or equal to the second integer parameter b, 1 is added to the offset value noff in the y direction (S107), and the second integer parameter b is subtracted from the y direction weight coefficient kwy (S108). Thereafter, the process returns to S106.

  If the y-direction weight coefficient kwy is below the second integer parameter b, the process proceeds to S109, and the x coordinate m of the pixel of interest of the rotated image is set to the cosine value (cosθ ) Is less than the number multiplied. If the x-coordinate m is less than width × cos θ, the process returns to S103.

  With the above flow, the pixel value Q (m, n) is calculated while changing the x coordinate m of the pixel of interest (m, n) of the rotated image from 0 to (width × cos θ−1) one by one. Is repeated. Then, every time the x coordinate m changes by 1, the y-direction weighting coefficient kwy is added by a (S105). Therefore, in the two-dimensional interpolation in calculating the pixel value Q (m, n), the lower side of FIG. The weight in which the two pixel values P (i, j + 1) and P (i-1, j + 1) are reflected increases. The change ratio of the weight every time m changes by 1 matches the value obtained by dividing a by b. Further, when the y-direction weight coefficient kwy is equal to or greater than b, the y-direction offset value noff is incremented by 1. This means that the corresponding target pixel (i, j) of the original image is shifted by one pixel in the y direction.

  If it is determined in S109 that the x coordinate m of the pixel of interest is greater than width × cos θ, the x coordinate m, the y direction offset value not, and the y direction weight coefficient kwy are all reset to 0 (S110). Then, 1 is added to the y coordinate n of the target pixel (S111). This process corresponds to moving the target pixel (m, n) of the rotated image by one pixel in the y direction.

  Next, the first integer parameter a is added to the x-direction weight coefficient kwx (S112). Then, it is checked whether or not the added x-direction weight coefficient kwx is greater than or equal to the second integer parameter b (S113). If it is greater than or equal to the second integer parameter b, 1 is added to the offset value moff in the x direction (S114), and the second integer parameter b is subtracted from the x direction weighting factor kwx (S115). Thereafter, the process returns to S113.

  When the x-direction weight coefficient kwx is smaller than the second integer parameter b, the process proceeds to S116, and the y coordinate n of the target pixel of the rotated image is set to the cosine value of the document tilt angle (height). It is determined whether it is below the number multiplied by cos θ). When the y coordinate n is less than height × cos θ, the process returns to S103. If the y coordinate n is equal to or higher than height × cos θ, it means that the calculation of the pixel value of the pixel of interest has been completed, and the processing is terminated.

  Processing for calculating the pixel value Q (m, n) of the target pixel (m, n) of the rotated image while changing the y coordinate n from 0 to (height × cos θ−1) one by one by the above flow. Is repeated. Each time n changes by 1, the x-direction weighting coefficient kwx is added by a. Therefore, in the two-dimensional interpolation when calculating the pixel value Q (m, n), the two pixel values P ( i-1, j) and P (i-1, j + 1) are reflected more frequently. The change ratio of the weight every time n changes by 1 matches the value obtained by dividing a by b. Further, when the x-direction weight coefficient kwx is equal to or greater than b, 1 is subtracted from the x-direction offset value moff. This means that the corresponding target pixel (i, j) of the original image is shifted by one pixel in the x direction. 5 corresponds to the original image corresponding position calculation step (original image corresponding position calculation step).

As described above, the raster image of the original image as shown on the upper side of FIG. 8 can be rotated to obtain a rotated image as shown on the lower side. In the two-dimensional interpolation processing (S103) in the flow shown in FIG. 5, the calculation formulas [˜] can be realized by addition and multiplication of integers, and division is performed only once (only division by the integer b ² ). The pixel value Q (m, n) of the target pixel can be obtained. Further, the calculation of the weight coefficient (S105, S108, S112, S115) can be realized by integer addition / subtraction processing, and the determination as to whether or not the position of the corresponding target pixel should be offset (S106, S113) is a comparison processing between integers. Can be realized. Therefore, the calculation cost can be significantly reduced and the processing time can be shortened.

  5 and 8 show the case where the image is rotated counterclockwise, it is also possible to rotate the image clockwise. This process may be performed by changing -1 to +1 and changing +1 to -1 in the processes of S103, S107, and S114 in the flowchart of FIG.

  Further, in FIGS. 6 and 8, for the sake of simplicity, the description has been made with a small image of 18 pixels in the vertical direction and 18 pixels in the horizontal direction, but the rotation processing of the present embodiment can be applied to an image of an arbitrary size. Furthermore, although the example of the gray scale image is described in FIGS. 6 and 8, the rotation processing of the present embodiment can also be performed by rotating the color image by performing the same processing as described above for the gradations of the RGB colors. Applicable. When rotating a color image, it is preferable to generate a weighting factor common to the three components for each pixel and then sequentially perform interpolation for each color component. That is, it is preferable to switch the color component for each pixel. As a result, the processing for calculating the weighting coefficient can be made common among the color components, and the processing time can be shortened.

  As described above, the tilt correction unit 68 included in the image scanner device 101 of the present embodiment is configured to rotate a raster image that is an original image to obtain a rotated image. As shown in FIG. 3, the inclination correction unit 68 includes an integer parameter input unit 71, an original image corresponding position calculation unit 72, and a two-dimensional interpolation unit 73. The parameter input unit 71 receives the first integer parameter a and the second integer parameter b such that the ratio value (a / b) is equal to the tangent value tanθ of the rotation angle. The original image corresponding position calculation unit 72 adds the first integer parameter a to the y-direction weight coefficient kwy every time the x coordinate m of the pixel of interest (m, n) in the rotated image is changed by one pixel ( S104, S105). When the y-direction weight coefficient kwy becomes equal to or greater than the second integer parameter b, the original image corresponding position calculation unit 72 subtracts the second integer parameter b from the y-direction weight coefficient kwy (S108). Further, a process of changing the x coordinate i of the corresponding target pixel (i, j), which is a pixel at a position corresponding to the target pixel (m, n) in the original image, by one pixel (S107). The original image corresponding position calculation unit 72 adds the first integer parameter a to the x-direction weight coefficient kwx every time the y coordinate n of the pixel of interest (m, n) in the rotated image is changed by one pixel. (S111, S112). When the y-direction weight coefficient kwy becomes equal to or greater than the second integer parameter b, the original image corresponding position calculation unit 72 subtracts the second integer parameter b from the x-direction weight coefficient kwx (S115). ), A process of changing the y coordinate j of the corresponding target pixel (i, j) of the original image by one pixel is performed (S114). As shown in FIG. 7, the two-dimensional interpolation unit 73 differs from the corresponding target pixel (i, j) in the original image and the corresponding target pixel by at least one of the x coordinate and the y coordinate by one pixel. A ratio (kwx / b) obtained by dividing the x-direction weighting factor by a second integer parameter for three existing pixels (i−1, j), (i, j + 1), (i−1, j + 1), and The pixel value Q (m, n) of the pixel of interest in the rotated image is obtained by two-dimensional interpolation using the ratio (kwy / b) obtained by dividing the y-direction weighting factor by the second integer parameter.

  As a result, it is possible to perform rotation processing with two-dimensional interpolation by frequently using integer arithmetic processing and integer comparison processing using integer parameters a and b and weighting coefficients kwx and kwy. Accordingly, it is possible to reduce processing with a large calculation cost such as floating point arithmetic and to obtain a high-quality rotated image at high speed.

  In other words, in the case of the image scanner apparatus 101 of the present embodiment, the inclination angle (rotation angle) θ of the document is usually about several degrees, even when the document is read using either the auto document feeder unit or the flat bed unit. . In this case, there is almost no error (decrease in image quality) even if cos θ = 1. In this embodiment, paying attention to this point, the above processing can be performed to greatly simplify the calculation. As described above, when the inclination of the original is about several degrees, high accuracy can be maintained, and complicated processing as in the prior art can be avoided.

Further, the two-dimensional interpolation unit 73 collectively performs the division by the square (b ² ) of the second integer parameter in the calculation of the pixel value Q (m, n) of the target pixel (S103 in FIG. 5). ing.

  As a result, division processing with a high calculation cost can be reduced, so that rotation processing can be performed at higher speed.

  In the calculation process (S103) of the pixel value Q (m, n) of the target pixel, the second integer parameter b is multiplied by an appropriate ratio to obtain a value of an integer power of 2, and the x-direction weighting factors kwx and y It is also possible to multiply the direction weight coefficient kwy by the above ratio and approximate it to an integer value. For example, although a = 1 and b = 5 in the example of FIG. 4, it is conceivable to multiply the second integer parameter b by a ratio (16/5) and change the value to 16 which is the value of 2 4. . Then, it is preferable that the x-direction weight coefficient kwx and the y-direction weight coefficient kwy are multiplied by the ratio (16/5) to approximate an integer value, and the pixel value Q (m, n) is calculated. The result obtained by multiplying the weighting factors kwx and kwy by a ratio and rounding them to an integer value is calculated in advance for each of the original kwx (kwy) value 0, 1 case 2, 2 ... It may be stored in a lookup table or the like and acquired by referring to it.

  As a result, the calculation cost of the division process can be significantly reduced, so that the speed of the rotation process can be further increased.

  The image scanner apparatus 101 according to the present embodiment includes an image reading unit 115 and an inclination detection unit 67 as shown in FIG. The image reading unit 115 is configured to read an image of a document and obtain image data. The inclination detecting unit 67 obtains two inclination parameter integers a and b such that the ratio is equal to the tangent value tanθ of the original inclination angle from the coordinates of the two points in the image data. Then, the image scanner device 101 gives the two inclination parameter integers a and b to the inclination correction unit 68 as two integer parameters, and rotates the image data, whereby the image data in which the inclination of the document is corrected is obtained. Configured to get.

  This makes it possible to obtain image data whose inclination is corrected in a short time, which is particularly suitable for high-speed reading.

  Although the preferred embodiment of the present invention and the modifications thereof have been described above, the above configuration can be modified as follows, for example.

  When the tilt angle θ is smaller than 45 ° (when a / b is smaller than 1), the process can be changed to proceed to S109 without returning to S106 after the process of S108. Similarly, after the process of S115, it can change so that it may progress to S116, without returning to S113. As described above, the rotation process can be further speeded up. Since the image scanner apparatus 101 according to the present embodiment is not supposed to rotate the document at an angle of 45 ° or more as long as it is used normally, the above change is effective.

  The value added to the y-direction weighting coefficient kwy in the process of S105 and the value added to the x-direction weighting coefficient kwx in the process of S112 can be changed not to the parameter a itself but to a value according to the scaling factor. it can. Similarly, the value subtracted from the y-direction weighting coefficient kwy in the process of S108 and the value subtracted from the x-direction weighting coefficient kwx in the process of S115 are changed not to the parameter b itself but to a value according to the scaling factor. can do. Thereby, enlargement / reduction processing can be performed simultaneously with inclination correction. When the scaling factor is X, a / X may be added to the weighting coefficient in the processes of S105 and S112, and b / X may be subtracted from the weighting coefficient in the processes of S108 and S115. For example, when 50% reduction (X = 1/2) is performed, 2a is added instead of a in the processes of S105 and S112, and 2b is subtracted instead of b in the processes of S108 and S115.

  5 to 8 illustrate the rotation processing when the rotation center of the original image is (0, 0), the position of the rotation center can be changed as appropriate. In this case, the initial values of the offset values moff and noff in the initialization process (S102) in the flow of FIG. 5 and the reset value of noff in S110 may be appropriately set according to the position of the rotation center.

  The two-dimensional interpolation process can be changed to two-dimensional interpolation using, for example, a quadratic curve or a spline curve, instead of the linear interpolation described above.

  In the tilt angle detection processing, instead of detecting by extracting the document area as shown in FIG. 4, two tilt parameter integers a and b are obtained based on, for example, the arrangement of characters and the tilt of the figure described in the document. Can be changed as follows.

  The image rotation process described above can be performed not only for skew correction during document reading by the auto document feeder unit but also for tilt correction during document reading by the flat bed unit. The image rotation processing described above can be applied not only to the image scanner apparatus 101 but also to other image reading apparatuses such as a copying apparatus, a facsimile apparatus, a multifunction peripheral, and an optical character reading apparatus (OCR).

The figure which shows the conversion formula of the general coordinate in the case of rotating an image. 1 is a front sectional view showing an overall configuration of an image scanner device according to an embodiment of the present invention. FIG. 3 is a block diagram showing an electrical configuration of the image scanner device. Explanatory drawing which shows two inclination parameter integers a and b detected in an inclination detection part. The flowchart which shows the rotation process performed in an inclination correction | amendment part. Explanatory drawing which shows the outline | summary of a rotation process. The conceptual diagram which shows a two-dimensional interpolation process. The figure which shows an original image and its rotation result.

Explanation of symbols

67 Inclination Detection Unit 68 Inclination Correction Unit (Image Processing Device)
71 Parameter Input Unit 72 Original Image Corresponding Position Calculation Unit 73 Two-dimensional Interpolation Unit 101 Image Scanner Device (Image Reading Device)
115 Image reading unit

Claims (6)

In an image processing apparatus that obtains a rotated image by rotating a raster image that is an original image,
An integer parameter input unit for inputting a first integer parameter and a second integer parameter such that the value of the ratio is equal to the tangent value of the rotation angle;
Each time the x coordinate of the pixel of interest in the rotated image is changed by a predetermined number of pixels, the first integer parameter is added to the y-direction weight coefficient,
When the y-direction weighting coefficient is greater than or equal to the second integer parameter, the second integer parameter is subtracted from the y-direction weighting coefficient, and the corresponding attention is a pixel at a position corresponding to the attention pixel in the original image A process of changing the y coordinate of the pixel by a predetermined pixel is performed,
Each time the y coordinate of the target pixel in the rotated image is changed by a predetermined number of pixels, the first integer parameter is added to the x-direction weight coefficient,
When the x-direction weighting coefficient is equal to or larger than the second integer parameter, the second integer parameter is subtracted from the x-direction weighting coefficient, and the x coordinate of the corresponding target pixel of the original image is changed by a predetermined pixel. An original image corresponding position calculation unit for processing,
Targeting the corresponding target pixel in the original image and three pixels in which at least one of the x coordinate and the y coordinate differs from the corresponding target pixel by a predetermined pixel, the x-direction weighting coefficient is set as the second integer parameter. A two-dimensional interpolation unit that obtains a pixel value of the pixel of interest in the rotated image by performing two-dimensional interpolation by the ratio divided by x and the ratio obtained by dividing the y-direction weighting factor by the second integer parameter;
An image processing apparatus comprising: The image processing apparatus according to claim 1,
The image processing apparatus, wherein the two-dimensional interpolation unit collectively performs division by the square of the second integer parameter in the calculation of the pixel value of the target pixel. The image processing apparatus according to claim 1, wherein:
The two-dimensional interpolation unit changes the second integer parameter to a value of an integer power of 2, and further calculates a ratio obtained by dividing the value of the integer power of 2 by the second integer parameter before the change. An image processing apparatus that calculates the pixel value of the target pixel after multiplying the x-direction weighting coefficient and the y-direction weighting coefficient to approximate an integer value. The image processing apparatus according to any one of claims 1 to 3,
An image reading unit that reads an image of a document and obtains image data;
A tilt angle detector that obtains two tilt parameter integers such that the ratio thereof is equal to the tangent value of the tilt angle of the document from the coordinates of the two points in the image data;
With
Two pieces of the inclination parameter integer are given to the image processing apparatus as the first integer parameter and the second integer parameter, and the image data is rotated to obtain image data in which the inclination of the document is corrected. Image reading device. Based on the first integer parameter and the second integer parameter such that the value of the ratio becomes equal to the tangent value of the rotation angle, an image processing method for obtaining a rotated image by rotating a raster image that is an original image,
Each time the x coordinate of the pixel of interest in the rotated image is changed by a predetermined pixel, the first integer parameter is added to the y-direction weight coefficient,
When the y-direction weighting coefficient is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the y-direction weighting coefficient, and the corresponding attention is a pixel at a position corresponding to the attention pixel in the original image A process of changing the y coordinate of the pixel by a predetermined pixel is performed,
Each time the y coordinate of the pixel of interest in the rotated image is changed by a predetermined amount, the first integer parameter is added to the x-direction weight coefficient,
When the x-direction weighting coefficient is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the x-direction weighting coefficient, and the x coordinate of the corresponding target pixel of the original image is changed by a predetermined pixel. Original image corresponding position calculation step,
Targeting the corresponding target pixel in the original image and three pixels that differ from the corresponding target pixel by at least one of the x coordinate and the y coordinate by a predetermined pixel, the x-direction weighting coefficient is set as the second integer parameter. A two-dimensional interpolation step of obtaining a pixel value of the pixel of interest in the rotated image by performing two-dimensional interpolation by the ratio divided by x and the ratio obtained by dividing the y-direction weighting factor by the second integer parameter;
An image processing method comprising: In an image processing program that obtains a rotated image by rotating a raster image that is an original image,
An integer parameter input step for inputting the first integer parameter and the second integer parameter such that the value of the ratio becomes equal to the tangent value of the rotation angle;
Each time the x coordinate of the pixel of interest in the rotated image is changed by a predetermined pixel, the first integer parameter is added to the y-direction weight coefficient,
When the y-direction weighting coefficient is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the y-direction weighting coefficient, and the corresponding attention is a pixel at a position corresponding to the attention pixel in the original image A process of changing the y coordinate of the pixel by a predetermined pixel is performed,
Each time the y coordinate of the pixel of interest in the rotated image is changed by a predetermined amount, the first integer parameter is added to the x-direction weight coefficient,
When the x-direction weighting coefficient is equal to or greater than the second integer parameter, the second integer parameter is subtracted from the x-direction weighting coefficient, and the x coordinate of the corresponding target pixel of the original image is changed by a predetermined pixel. An original image corresponding position calculating step for performing processing;
Targeting the corresponding target pixel in the original image and three pixels that differ from the corresponding target pixel by at least one of the x coordinate and the y coordinate by a predetermined pixel, the x-direction weighting coefficient is set as the second integer parameter. A two-dimensional interpolation step for obtaining a pixel value of the pixel of interest in the rotated image by performing two-dimensional interpolation by the ratio divided by x and the ratio obtained by dividing the y-direction weighting factor by the second integer parameter;
An image processing program characterized by executing

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