JP2018097304A - Image forming apparatus and image detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a position of a transparent color image by visible light only.SOLUTION: An image forming apparatus comprises: an image forming unit for forming a transparent color image on a sheet using transparent toner (S21); an image reading unit for irradiating a sheet surface on which the transparent color image is formed with visible light to generate image data read from a direction vertical to the sheet surface according to the amount of reflected light received from the vertical direction (S22) and to generate image data read from a direction oblique to the sheet surface according to the amount of reflected light received from the oblique direction (S23); and a control unit for detecting a position of the transparent color image according to a level difference between pixel values of the image data read from the vertical direction and the image data read from the oblique direction by the image reading unit (S24).SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus and an image detection method.

  Some electrophotographic image forming apparatuses can form not only chromatic colors but also transparent images using transparent toner. For example, when a chromatic image having a white character region is formed with chromatic toner and a transparent character image is formed on the character region, the character can be given gloss, and the design is high. Printed materials can be provided.

  In the image forming apparatus, there is a case where the position of the image of each color, which is referred to as “registration shift”, may occur. A registration reference image, such as a registration mark, is formed on a sheet, and alignment is performed based on the position of the reference image detected by reading the sheet surface. A transparent color image is read by irradiating visible light. Detection is difficult with a normal image sensor. Therefore, a method has been proposed in which the position of a transparent color image on a document is detected according to the difference in image data read by irradiating infrared light together with visible light (see, for example, Patent Document 1). .

Japanese Patent No. 5312186

  However, in the above method, in order to detect the position of a transparent color image, not only visible light but also an infrared light source and an image sensor that can handle infrared light are required. As the cost increases, the device configuration increases.

  An object of the present invention is to detect the position of a transparent image using only visible light.

According to the invention of claim 1,
An image forming unit that forms an image of a transparent color on a sheet using transparent toner;
The surface of the paper on which the transparent color image is formed is irradiated with visible light, and image data read from the vertical direction is generated according to the amount of reflected light received from the vertical direction with respect to the paper surface. An image reading unit that generates image data read from the oblique direction according to the amount of reflected light received from the oblique direction,
A control unit for detecting a position of the transparent color image according to a level difference between pixel values of the image data read from the vertical direction and the image data read from the oblique direction by the image reading unit;
An image forming apparatus is provided.

According to invention of Claim 2,
The control unit changes the arrangement position of the image reading unit and changes the angle in the oblique direction with respect to the sheet surface to determine the arrangement position where the level difference from the image data read from the vertical direction is maximized. , Determine the reading position from the oblique direction,
The image forming apparatus according to claim 1, wherein the image reading unit performs reading at a reading position determined by the control unit when reading from the oblique direction.

According to invention of Claim 3,
The control unit tilts the sheet surface with respect to the sheet conveyance direction and moves the image reading unit in the sheet conveyance direction, or rotates the image reading unit, thereby causing an angle in an oblique direction with respect to the sheet surface. The image forming apparatus according to claim 2, wherein the arrangement position of the image reading unit is changed so as to be different from each other.

According to invention of Claim 4,
4. The image forming apparatus according to claim 2, wherein the image reading unit circulates the sheet every time the arrangement position of the image reading unit is changed, and repeatedly reads the same sheet surface. The

According to the invention of claim 5,
The image forming unit forms a chromatic color image using chromatic toner, forms the transparent color image on a part of the chromatic color image,
The control unit includes levels of pixel values of the chromatic image area and the image area where the transparent image overlaps the chromatic image in the image data read from the vertical direction and the oblique direction. The image forming apparatus according to claim 1, wherein the position of the transparent color image is detected according to the difference.

According to the invention of claim 6,
The image forming unit forms the transparent color image on a part of the base of the paper;
In the image data read from the vertical direction and the oblique direction, the control unit determines the level difference between the pixel values of the image area of the background of the paper and the image area where the transparent color image overlaps the background. In response, the position of the transparent color image is detected, and the image forming apparatus according to claim 1 is provided.

According to the invention of claim 7,
The image forming unit forms a chromatic image using chromatic toner, forms the transparent color image on a part of the chromatic image, and forms the transparent image on a part of the background of the paper. Forming a transparent image,
In the image data read from the vertical direction and the oblique direction, the control unit includes the chromatic image area, an image area where the transparent image overlaps the chromatic image, and a background of the paper. 5. The position of the transparent color image is detected according to a level difference between pixel values of an image area and an image area where the transparent color image overlaps the background. An image forming apparatus according to one item is provided.

According to the invention described in claim 8,
The image forming unit forms a chromatic image having a white area as the chromatic image, and forms the transparent color image at a position shifted by a certain distance from the position of the white area. An image forming apparatus according to claim 7 is provided.

According to the invention of claim 9,
The image forming unit forms a chromatic image having a white area as the chromatic image, and forms the transparent color image in a range larger than the white area by a certain distance. An image forming apparatus according to claim 7 is provided.

According to the invention of claim 10,
A step of forming a transparent color image on a sheet using a transparent toner by an image forming unit;
The step of irradiating visible light onto the paper surface on which the transparent color image is formed by the image reading unit, and generating image data read from the vertical direction according to the amount of reflected light received from the vertical direction with respect to the paper surface When,
The image reading unit irradiates visible light onto the paper surface on which the transparent image is formed, and generates image data read from the oblique direction according to the amount of reflected light received from the oblique direction with respect to the paper surface. Steps,
Detecting a position of the transparent color image by a control unit according to a level difference between pixel values of image data read from the vertical direction by the image reading unit and image data read from the oblique direction;
An image detection method is provided.

  According to the present invention, it is possible to detect the position of a transparent color image using only visible light.

1 is a front view illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of an image forming apparatus for each function. It is a front view showing an example of an image reading unit when reading a sheet surface from a vertical direction. FIG. 3 is a front view illustrating an example of an image reading unit when reading a sheet surface from an oblique direction. FIG. 10 is a front view illustrating another example of an image reading unit when reading a sheet surface from a vertical direction. FIG. 10 is a front view illustrating another example of an image reading unit when reading a sheet surface from an oblique direction. 6 is a flowchart illustrating a processing procedure when the image forming apparatus optimizes a reading position in an oblique direction. It is a top view which shows an example of the image of the transparent color formed on a part of chromatic color image. It is a top view which shows the other example of the image of the transparent color formed on a part of chromatic image. It is a top view showing an example of a chromatic image and a transparent image read from the vertical direction. It is a top view which shows the example of the image of the chromatic color read from the diagonal direction, and the image of a transparent color. It is a graph which shows the level of the pixel value of the image data which read the chromatic image and the transparent color image from the perpendicular direction. It is a graph which shows the level of the pixel value of the image data which read the chromatic image and the transparent color image from the diagonal direction. 5 is a flowchart illustrating a processing procedure when the image forming apparatus performs alignment of a transparent color image.

  Embodiments of an image forming apparatus and an image detection method of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing a schematic configuration of an image forming apparatus G according to an embodiment of the present invention.
As shown in FIG. 1, the image forming apparatus G includes an image forming unit 20 that forms an image on a sheet and an image reading unit 30 that reads the sheet surface.
The image forming apparatus G can perform image alignment, color matching, inspection, and the like by reading and analyzing the sheet surface on which the image is formed by the image forming unit 20 by the image reading unit 30.

FIG. 2 is a block diagram illustrating the main configuration of the image forming apparatus G for each function.
As shown in FIGS. 1 and 2, the image forming apparatus G includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, a communication unit 15, an image generation unit 16, an image reading unit 17, an image memory 18, An image processing unit 19, an image forming unit 20, and an image reading unit 30 are provided.

The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like, and controls each unit by reading and executing various programs from the storage unit 12.
For example, the control unit 11 causes the image processing unit 19 to perform image processing on the image data generated by the image generation unit 16 or the image reading unit 17 and held in the image memory 18, and based on the image data after the image processing. Then, the image forming unit 20 forms an image on the sheet.

  In addition, the control unit 11 causes the image reading unit 30 to read the sheet surface on which the image is formed by the image forming unit 20 and analyzes the obtained image data, thereby performing image alignment, inspection, and the like. Can do.

  The storage unit 12 stores a program that can be read by the control unit 11 and the like, a file that is used when the program is executed, and the like. As the storage unit 12, a large-capacity memory such as a hard disk can be used.

  The operation unit 13 generates an operation signal corresponding to a user operation and outputs the operation signal to the control unit 11. As the operation unit 13, a keypad, a touch panel configured integrally with the display unit 14, or the like can be used.

  The display unit 14 displays an operation screen and the like according to instructions from the control unit 11. As the display unit 14, an LCD (Liquid Crystal Display), an OELD (Organic Electro Luminescence Display), or the like can be used.

The communication unit 15 communicates with external devices on the network, such as a user terminal, a server, and other image forming apparatuses.
The communication unit 15 receives data (hereinafter referred to as PDL data) in which an instruction content for forming an image is described in a page description language (PDL) from a user terminal or the like via a network.

  The image generation unit 16 rasterizes the PDL data received by the communication unit 15 to generate bitmap format image data in which each pixel has a pixel value of each color of transparent color and chromatic color. The image generation unit 16 may generate image data having pixel values of four colors of C (cyan), M (magenta), Y (yellow), and K (black) as chromatic colors, or R (red ), G (green), and B (blue) image data having pixel values of three colors may be generated, and then C, M, Y, and K image data may be obtained by color conversion processing. The pixel value is a data value representing the density of the image. For example, an 8-bit data value represents the density of 0 to 255 gradations.

  The image reading unit 17 reads the paper set manually and generates bitmap-format image data in which each pixel has a pixel value of each chromatic color of R, G, and B. This image data may be converted into C, M, Y, and K color image data by the control unit 11 or a dedicated color conversion unit. As the image reading unit 17, a scanner or the like provided under the platen glass can be used, and an original can be automatically fed to the scanner with an automatic document reader (ADF).

  The image memory 18 is a buffer memory that temporarily holds the image data generated by the image generation unit 16. As the image memory 18, a DRAM (Dynamic RAM) or the like can be used.

The image processing unit 19 reads out image data from the image memory 18 and performs various image processing such as density correction processing, color correction processing, and halftone processing.
The density correction process is a process of converting each pixel value of the image data so that the density characteristic of the image to be formed becomes the target density characteristic. The color correction process is a process for converting the pixel value of each color of the image data so that the color of the image becomes a target color. The halftone process is a process for reproducing a pseudo multi-tone such as a screen process using an dither method and an error diffusion process.

The image forming unit 20 forms an image of four colors on a sheet according to the four color gradation values of C, M, Y, and K of each pixel of the image data output from the image processing unit 19. The image forming unit 20 can also form a transparent color image based on the transparent color image data.
As shown in FIG. 1, the image forming unit 20 includes five writing units 21T, 21Y, 21M, 21C and 21K, an intermediate transfer belt 22, a secondary transfer roller 23, a fixing device 24, a paper feed tray 25, and a reversing mechanism 26. It has. The writing units 21T, 21Y, 21M, 21C, and 21K are arranged in series along the belt surface of the intermediate transfer belt 22 that is wound and rotated by a plurality of rollers. The secondary transfer roller 23 and the fixing device 24 are arranged on a conveyance path of a sheet conveyed from a sheet feeding tray 25 that accommodates the sheet.

The writing unit 21T forms a transparent color image using a transparent toner, and the writing units 21Y, 21M, 21C, and 21K use C, M, Y, and K chromatic toners, respectively. An image of each chromatic color of K is formed. As the chromatic toner, a general toner containing a colorant in resin particles can be used, and as the transparent toner, a toner such as resin particles not containing a colorant can be used.
The writing units 21T, 21Y, 21M, 21C, and 21K have the same configuration except for the color of the toner to be used. The exposure unit 2a, the photoreceptor 2b, the developing unit 2c, the charging unit 2d, and the cleaning units 2e and 1 A next transfer roller 2f is provided.

  In each of the writing units 21T, 21Y, 21M, 21C, and 21K, the charging unit 2d applies a voltage to the photosensitive member 2b to charge it, and then the transparent color image data, C, M, Y, and K chromatic colors. A laser beam is irradiated in accordance with each pixel value of the image data to expose the photoreceptor 2b. Each toner (transparent toner or chromatic toner) is supplied by the developing unit 2c to develop the electrostatic latent image, and the obtained image on each photoreceptor 2b is transferred onto the intermediate transfer belt 22 by the primary transfer roller 2f. Transfer sequentially (primary transfer). In each of the writing units 21T, 21Y, 21M, 21C, and 21K, the toner remaining on the photoreceptor 2b after the transfer is removed by the cleaning unit 2e.

  Thereafter, the paper is fed by the paper feed tray 25, the image on the intermediate transfer belt 22 is transferred onto the paper (secondary transfer) by the secondary transfer roller 23, and then the paper is heated and pressed by the fixing device 24. To fix the image on the paper. Each image is superimposed on the sheet in the order of K, C, M, and Y transparent colors from the sheet surface side. When images are formed on both sides of a sheet, the sheet surface may be reversed by the reversing mechanism 26 and conveyed to the secondary transfer roller 23.

  The image reading unit 30 reads the sheet surface on which the image is formed by the image forming unit 20. The image reading unit 30 is a line sensor in which an image sensor such as a light source that irradiates visible light on a paper surface and a CCD that generates image data in accordance with the amount of reflected light is one-dimensionally arranged, and an area that is arranged in two dimensions A sensor or the like can be used.

  When detecting the position of the transparent color image, the image reading unit 30 reads the sheet surface from the vertical direction and the oblique direction.

3A and 3B show the image reading unit 30 when reading from the vertical direction and the oblique direction, respectively, from the paper width direction. The paper width direction is a direction orthogonal to the paper transport direction.
As shown in FIGS. 3A and 3B, a contact glass 32 is disposed between the image reading unit 30 and the sheet S, and an abutting roller 33 is disposed at a position facing the contact glass 32 and the sheet S. . In addition, a trapezoidal guide 34 is disposed immediately before the abutting roller 33 in the transport direction of the paper S.

  When the leading edge of the sheet S conveyed in the conveying direction comes into contact with the abutting roller 33, the sheet S enters between the abutting roller 33 and the contact glass 32 along the surface of the guide 34. Since the contact glass 32 is horizontal with respect to the conveyance direction, the sheet surface is also horizontal on the contact glass 32, but the surface of the end portion of the guide 34 is inclined with respect to the conveyance direction. The sheet surface is inclined with respect to the transport direction.

As shown in FIG. 3A, the image reading unit 30 is arranged on the contact glass 32 at a position where the paper surface is horizontal, and the reflected light is received and read from the vertical direction at an angle with respect to the paper surface of 90 degrees. It can be performed.
On the other hand, as shown in FIG. 3B, by moving the position of the image reading unit 30 to a position where the sheet surface is inclined with respect to the transport direction, the angle with respect to the sheet surface is θ (θ <90 degrees). Reading can be performed by receiving reflected light from the direction. In FIG. 3B, each reading position to which the image reading unit 30 can move is represented by n. The reading position n is a position obtained by dividing the range of 0 to N where the sheet surface is inclined into N equally, where n = 0 is the position where the sheet surface starts to be inclined and n = N is the position of the end of the guide 34.

The image reading unit 30 can circulate the paper S and repeatedly read the same paper surface. For example, after reading from the vertical direction, the sheet S can be circulated to read the same sheet surface from an oblique direction. It is also possible to circulate the sheet S every time the reading position n from the oblique direction is changed and read the same sheet surface at a different reading position n.
At the time of circulation, the image reading unit 30 conveys the sheet S that has passed the reading position of the image reading unit 30 in the direction opposite to the conveyance direction by a reversing roller or the like, passes under the guide 34, and immediately before the guide 34. Return to Thereafter, the sheet S may be guided and conveyed onto the guide 34 by a guide plate or the like.

As described above, instead of moving the image reading unit 30 in the paper transport direction by inclining the paper surface, the image reading unit 30 can be rotated to change the arrangement position thereof, so that the vertical direction and the diagonal direction are also changed. Can be read from.
4A and 4B show the image reading unit 30 that rotates and reads from the vertical direction and the oblique direction, respectively.
As shown in FIGS. 4A and 4B, the image reading unit 30 is configured to be rotatable about a rotation shaft 31 having the paper width direction as an axial direction.

As shown in FIG. 4A, by arranging the image reading unit 30 at a position where the rotation angle is 0 degrees, the reflected light is received and read from the vertical direction where the angle with respect to the sheet surface is 90 degrees. it can.
As shown in FIG. 4B, by arranging the image reading unit 30 at a position where the rotation angle is rotated more than 0 degrees, the reflected light is reflected from an oblique direction where the angle with the sheet surface is θ (θ <90 degrees). Reading can be performed by receiving light. By changing the rotation angle of the image reading unit 30, the angle θ in the oblique direction with respect to the sheet surface can be changed.

The image forming apparatus G can detect a positional deviation of a transparent color image and correct the transparent color image forming position so as to coincide with the position of the chromatic color image.
The position of the transparent color image can be detected by comparing the pixel value levels of the image data read by the image reading unit 30 from the vertical direction and the oblique direction with respect to the paper surface. At the time of reading from the oblique direction, the detection accuracy varies depending on the angle θ in the oblique direction. Therefore, the image forming apparatus G optimizes the reading position from the oblique direction in advance.

FIG. 5 shows a processing procedure when the image forming apparatus G optimizes the reading position in the oblique direction.
As shown in FIG. 5, in the image forming apparatus G, the image forming unit 20 forms a chromatic image on a sheet using chromatic toner, and transparent toner is superimposed on a part of the chromatic image. A transparent color image is formed by using it (step S1). The image reading unit 30 reads the sheet surface on which the chromatic image and the transparent image are formed from the vertical direction (step S2).

  By reading the sheet surface, it is possible to acquire pixel values of a chromatic image region and an image region where a transparent image is superimposed on the chromatic image. An image area where a transparent image overlaps a chromatic image has a large level difference in pixel values when read from the vertical and diagonal directions, and the position of the transparent image can be accurately detected by this level difference. Can do.

  Since the image area where the transparent image is superimposed on the lower surface of the paper also has a large level difference in pixel values when read from the vertical direction and the oblique direction, the image forming unit 20 applies transparent toner to a part of the background of the paper. It is also possible to form a transparent color image, and obtain the pixel value of the image area of the background of the paper and the image area where the transparent color image overlaps the background.

  It is also possible to detect the position of the transparent image based on the pixel value levels of both the image area where the transparent color image overlaps the chromatic color image and the image area where the transparent color image overlaps the paper ground. . In this case, the image forming unit 20 forms a chromatic image on the paper using the chromatic toner, and forms a transparent image using the transparent toner on a part of the chromatic image. A transparent color image may be formed on a part of the background of the paper.

Specifically, the image forming unit 20 forms a chromatic image having a white area as a chromatic color image, and forms a transparent image at a position shifted by a certain distance from the white area. be able to.
Since the white area is the background of the paper, by reading this paper surface, the chromatic image area, the image area where the transparent image is superimposed on the chromatic image, the image area of the paper background, and the background Each pixel value of an image area where transparent images overlap can be acquired. It should be noted that the pixel value can also be acquired using a non-image area such as a paper margin as a base image area.

FIG. 6A shows an example of a transparent color image formed at a position shifted from the chromatic color image.
As shown in FIG. 6A, a chromatic image 51 having a white area 52 is formed, and a transparent color image 53 having substantially the same size as the white area 52 is formed from the white area 52 in the main scanning direction x and the sub-scanning direction. By forming the images by shifting them by a predetermined distance dx and dy in the scanning direction y, respectively, it is possible to superimpose a transparent image 53 on a part of the chromatic image 51 and a part of the background of the paper.

The image forming unit 20 can also form a chromatic image having a white area as a chromatic image, and form a transparent image in a range larger than the white area by a certain distance.
Also in this case, the pixel values of the chromatic image area, the image area where the transparent image overlaps the chromatic image, and the image area where the transparent image overlaps the lower surface of the paper are acquired by reading the paper surface. be able to. Further, the pixel value of the non-image area such as the margin of the paper can be acquired as the pixel value of the image area of the paper background. A chromatic image may be formed on a part of the paper to provide an image area on the base of the paper.

FIG. 6B shows an example of a transparent color image formed in a range larger than the white area.
As shown in FIG. 6B, a chromatic image 51 having a white area 52 is formed, and the transparent color is increased in the main scanning direction x and the sub scanning direction y from the white area 52 by a certain distance dx and dy, respectively. By forming the image 53, the transparent image 53 can be superimposed on a part of the chromatic image 51 and a part of the background of the paper.

  After reading from the vertical direction, the control unit 11 determines the reading position n in the oblique direction of the image reading unit 30 to be the reading value n = 1 as an initial value (step S3), and moves to the determined reading position n. Drive control. Further, the control unit 11 circulates the sheet surface read from the vertical direction and conveys it again to the image reading unit 30. The image reading unit 30 moves to the reading position n in the oblique direction according to the drive control of the control unit 11, and reads the re-conveyed paper surface (step S4).

  The control unit 11 calculates the level difference between the pixel values of the image data read from the vertical direction and the image data read from the oblique direction by the image reading unit 30 (step S5).

In the vertical direction and the diagonal direction, the amount of reflected light when light is irradiated onto the transparent color image on the outermost surface is different, so the level of the pixel values of the ground and chromatic image areas where the transparent color image overlaps changes. come.
7A and 7B show examples of transparent images read from the vertical direction and the oblique direction, respectively. This transparent color image is formed on a chromatic image having a white area within a range that is a certain distance away from the white area.
As shown in FIGS. 7A and 7B, the amount of reflected light differs depending on whether the image is a chromatic color image and a background portion of the paper on which the transparent color image overlaps on the reading line. For example, in an image region where a transparent image is superimposed on a chromatic image, the gloss of the transparent image is greater and the amount of reflected light is greater when read from an oblique direction than in the vertical direction. Where the gloss is greatest, the brightness is high and appears white.

FIG. 8A and FIG. 8B show the levels of pixel values in each image region when chromatic and transparent images are read from the vertical direction and the oblique direction on the reading lines shown in the drawing, respectively. 8A and 8B, the larger the pixel value level, the higher the luminance.
As shown in FIG. 8A, in the image data read in the vertical direction, the pixel value level CCl of the image area 55 where the transparent color image overlaps the chromatic image is higher than the pixel value level C of the chromatic color image area 51. Is also low. On the other hand, the pixel value level B of the background image area 52 is almost the same as the pixel value level BCl of the image area 54 where the transparent color image is superimposed on the background.

  As illustrated in FIG. 8B, when read in an oblique direction, the pixel value level CCh of the image area 55 where the transparent image is superimposed on the chromatic image is higher than the pixel value level C of the chromatic image area 51. . The pixel value level BCh of the image area 54 where the transparent color image overlaps the lower ground is also higher than the pixel value level B of the background image area 52.

  When comparing the vertical direction and the diagonal direction, as shown in FIGS. 8A and 8B, the pixel value level C of the chromatic image area 51 and the pixel value level B of the image area 52 of the background of the paper are changed. rare. On the other hand, in the image area 55 in which the transparent image is superimposed on the chromatic image, the pixel value level CCh in the oblique direction is higher than the pixel value level CCl in the vertical direction. Similarly, in the image area 54 where the transparent color image overlaps the background, the pixel value level BCh in the oblique direction is higher than the pixel value level BCl in the vertical direction.

Note that it is preferable that the density of the chromatic image overlaid with the transparent image is a halftone density because the level difference tends to increase between the vertical direction and the diagonal direction.
Specifically, when the density near the intermediate value between the pixel value level CCl when read in the vertical direction and the pixel value level CCh when read in the diagonal direction is used as the halftone density, the vertical direction and the diagonal direction are used. The difference in level tends to increase.

  In addition, the color of the chromatic image on which the transparent image is superimposed, among C, M, Y, and K, C or M tends to have a large level difference between the vertical direction and the diagonal direction, and C is particularly preferable.

  In this way, the background image area 54 and the chromatic image area 55 where the transparent images overlap each other cause a level difference in pixel values between the vertical direction and the diagonal direction. It can be detected as an image area. Since the detection becomes easier and the detection accuracy increases as the level difference is larger, the angle θ with respect to the sheet surface is changed to search for the reading position n when the level difference with the vertical direction is maximized.

For the search, until the reading position n reaches the maximum value N (step S6: N), n is incremented by 1 (step S7), and the above-described processing procedure is repeated at each of the reading positions 1 to N. The level difference between 1 and N is calculated (steps S4 and S5).
When the level difference at each reading position 1 to N is calculated (step S6: Y), the control unit 11 reads when the level difference of the pixel value in the vertical direction becomes the maximum among the reading positions 1 to N. The position is determined as an oblique reading position n (step S8).

After optimizing the reading position in the oblique direction as described above, the image forming apparatus G corrects the positional deviation of the transparent color image.
FIG. 9 shows a processing procedure when the image forming apparatus G corrects the positional deviation of the transparent color image. This processing procedure is performed after alignment of C, M, Y, and K chromatic images. At the time of alignment of each chromatic color image, the control unit 11 uses the image data generated by reading the sheet surface on which the registration image such as a registration mark is formed in the vertical direction by the image reading unit 30 to perform the alignment image. Is detected. The control unit 11 forms an image so that the position of each chromatic color image matches the reference position in accordance with the amount of positional deviation from the reference position of the detected image (for example, a position at a fixed distance from the edge of the paper). Adjust the position.

  As shown in FIG. 9, in the image forming apparatus G, a reference pattern for detecting the position of a transparent color image is formed on a sheet by the image forming unit 20 (step S21). As the reference pattern, a chromatic image and a transparent image superimposed on a part of the chromatic image are formed in the same manner as in the case of optimization of the reading position, or a part of the background of the paper. A transparent color image can be formed. Moreover, as illustrated in FIGS. 6A and 6B, a pattern including a chromatic color, a background, and each image region in which a transparent color is superimposed thereon can be formed.

  The image reading unit 30 reads the sheet surface on which the reference pattern is formed from the vertical direction (step S22), and then circulates the sheet and reads the same sheet surface from the oblique direction (step S23). The oblique reading position at this time is a reading position determined from among the reading positions 1 to N by the above-described optimization.

  The control unit 11 detects the position of the transparent color image in accordance with the level difference between the pixel values of the image data read from the vertical direction by the image reading unit 30 and the image data read from the oblique direction. (Step S24).

The control unit 11 performs transparent processing according to the level difference between the pixel values of the chromatic image region in each image data read from the vertical direction and the oblique direction and the image region in which the transparent image overlaps the chromatic image. The position of the color image can be detected.
Specifically, the level difference between the pixel values of the chromatic image area in the image data read from the vertical direction and the image area in which the transparent image overlaps the chromatic image, the image data read from the oblique direction The level difference of each pixel value in the image area where the transparent image overlaps the chromatic image area and the chromatic image, and the transparent color on the chromatic image in each image data read from the vertical direction and the diagonal direction The position of the transparent color image can be detected in accordance with at least one level difference among the pixel value level differences in the image region where the images overlap.

Further, the control unit 11 performs transparent processing according to the level difference between the pixel values of the background image area of the paper in the image data read from the vertical direction and the oblique direction and the image area where the transparent color image overlaps the background. The position of the color image can be detected.
Specifically, the level difference between the pixel values of the background image area in the image data read from the vertical direction and the image area where the transparent color image overlaps the background, the background image area in the image data read from the oblique direction And the level difference of each pixel value of the image area where the transparent color image overlaps with the background, and the level difference of the pixel value of the image area where the transparent color image overlaps the background in each image data read from the vertical direction and the oblique direction The position of the transparent color image can be detected according to at least one of the level differences.

  If there is a chromatic image area in the image data, an image area in which a transparent image is superimposed on the chromatic image, an image area in the background of the paper, and an image area in which the transparent image is superimposed on the background, these The position of the transparent color image can be detected in accordance with the level difference between the pixel values of each image area.

For example, when the pixel values shown in FIGS. 8A and 8B are acquired, the control unit 11 is lower than the pixel value level C of the chromatic image area 51 in the vertical image data, and the pixel values in the diagonal image data. The position of the image region 53 having a pixel value higher than level C and having a level difference between vertical and diagonal image data of, for example, | CCl−CCh | / 2 or more may be detected as the position of the transparent color image. it can.
In addition, the control unit 11 has a level difference between the pixel value level B of the background image area 52 in the vertical image data that is equal to or less than the threshold value, and the pixel value level B of the background image area 52 in the oblique image data. The position of the image area 54 that is high and has a pixel value level that has a level difference between vertical and oblique image data of, for example, | BCl−BCh | / 2 or more can also be detected as the position of the transparent image.

  The control unit 11 subtracts the shift amounts dx and dy between the transparent color image and the chromatic color image from the positional shift amount from the reference position of the detected transparent color image (for example, a position at a fixed distance from the paper edge). A displacement amount of the transparent color image from the reference position is calculated. The control unit 11 adjusts the transparent image forming position in accordance with the calculated amount of displacement (step S25). The adjustment of the image forming position can be performed by image processing such as enlargement or reduction of transparent color image data, image position shift, and rotation. By this adjustment, the position of the transparent color image can be adjusted to the same reference position as that of the chromatic color image.

  As described above, the image forming apparatus G of the present embodiment uses the transparent toner to form a transparent color image on the paper, and the visible light is applied to the paper surface on which the transparent color image is formed. Irradiate and generate image data read from the vertical direction according to the amount of reflected light received from the vertical direction with respect to the paper surface, and read from the oblique direction according to the amount of reflected light received from the diagonal direction with respect to the paper surface An image reading unit 30 that generates image data, and a position of a transparent color image is detected according to a level difference between pixel values of image data read from the vertical direction and image data read from the oblique direction by the image reading unit 30 And a control unit 11.

  A general optical image sensor corresponding to visible light can detect the position of a transparent color image by changing the direction of receiving reflected light of irradiated visible light between vertical and oblique directions. Can be used for position detection. No special configuration such as an infrared light source or an infrared light image sensor is required for the detection of the position of a transparent color image, so that the position can be detected with a simple configuration, which increases the cost and apparatus. Can be avoided.

The above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
For example, not only the image forming apparatus but also a computer of an image processing apparatus such as a general-purpose PC can cause the program to be read and the processing procedure of the control unit 11 can be executed.
As a computer-readable medium for the program, a non-volatile memory such as a ROM and a flash memory, and a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing program data via a communication line.

G Image forming apparatus 11 Control unit 12 Storage unit 20 Image forming unit 30 Image reading unit

Claims (10)

An image forming unit that forms an image of a transparent color on a sheet using transparent toner;
The surface of the paper on which the transparent color image is formed is irradiated with visible light, and image data read from the vertical direction is generated according to the amount of reflected light received from the vertical direction with respect to the paper surface. An image reading unit that generates image data read from the oblique direction according to the amount of reflected light received from the oblique direction,
A control unit for detecting a position of the transparent color image according to a level difference between pixel values of the image data read from the vertical direction and the image data read from the oblique direction by the image reading unit;
An image forming apparatus comprising: The control unit changes the arrangement position of the image reading unit and changes the angle in the oblique direction with respect to the sheet surface to determine the arrangement position where the level difference from the image data read from the vertical direction is maximized. , Determine the reading position from the oblique direction,
The image forming apparatus according to claim 1, wherein the image reading unit performs reading at a reading position determined by the control unit when reading from the oblique direction.   The control unit tilts the sheet surface with respect to the sheet conveyance direction and moves the image reading unit in the sheet conveyance direction, or rotates the image reading unit, thereby causing an angle in an oblique direction with respect to the sheet surface. The image forming apparatus according to claim 2, wherein the arrangement position of the image reading unit is changed so as to be different from each other.   4. The image forming apparatus according to claim 2, wherein the image reading unit circulates the sheet each time the arrangement position of the image reading unit is changed, and repeatedly reads the same sheet surface. The image forming unit forms a chromatic color image using chromatic toner, forms the transparent color image on a part of the chromatic color image,
The control unit includes levels of pixel values of the chromatic image area and the image area where the transparent image overlaps the chromatic image in the image data read from the vertical direction and the oblique direction. The image forming apparatus according to claim 1, wherein the position of the transparent color image is detected according to the difference. The image forming unit forms the transparent color image on a part of the base of the paper;
In the image data read from the vertical direction and the oblique direction, the control unit determines the level difference between the pixel values of the image area of the background of the paper and the image area where the transparent color image overlaps the background. The image forming apparatus according to claim 1, wherein the position of the transparent color image is detected accordingly. The image forming unit forms a chromatic image using chromatic toner, forms the transparent color image on a part of the chromatic image, and forms the transparent image on a part of the background of the paper. Forming a transparent image,
In the image data read from the vertical direction and the oblique direction, the control unit includes the chromatic image area, an image area where the transparent image overlaps the chromatic image, and a background of the paper. 5. The position of the transparent color image is detected according to a level difference between pixel values of an image area and an image area where the transparent color image overlaps the background. The image forming apparatus according to one item.   The image forming unit forms a chromatic image having a white area as the chromatic image, and forms the transparent color image at a position shifted by a certain distance from the position of the white area. The image forming apparatus according to claim 7.   The image forming unit forms a chromatic image having a white area as the chromatic image, and forms the transparent color image in a range larger than the white area by a certain distance. The image forming apparatus according to claim 7. A step of forming a transparent color image on a sheet using a transparent toner by an image forming unit;
The step of irradiating visible light onto the paper surface on which the transparent color image is formed by the image reading unit, and generating image data read from the vertical direction according to the amount of reflected light received from the vertical direction with respect to the paper surface When,
The image reading unit irradiates visible light onto the paper surface on which the transparent image is formed, and generates image data read from the oblique direction according to the amount of reflected light received from the oblique direction with respect to the paper surface. Steps,
Detecting a position of the transparent color image by a control unit according to a level difference between pixel values of image data read from the vertical direction by the image reading unit and image data read from the oblique direction;
An image detection method comprising: