Image processing device and control method for image processing device

Abstract

To provide an image processing device that detects color shift of a document image.SOLUTION: An image processing device includes an image processing unit and an image acquisition unit that acquires a document image generated from a document. The document image includes a first image, a second image, and a third image, each corresponding to one of three mutually different color components of the document. The first image, the second image, and the third image are sequentially generated by using a first sensor, a second sensor, and a third sensor, respectively, which are image sensors that read three mutually different color components arranged in accordance with a predetermined order relation along a conveying direction of the document. The image processing unit compares the first image, the second image, and the third image with one another and determines whether or not the document image includes color shift from the document on the basis of the comparison result.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to color shifts in scanned images generated by a scanner, and more particularly to color shifts in scanned images that occur in a scanner equipped with a document feeder (document transport unit). [Background technology]

[0002] In a scanner equipped with a document feeder, when scanning a document fed by the document feeder, the document feed speed may change due to document slippage during the scanning process, which may cause color shifts in the scanned image.

[0003] Regarding color shifts that occur in scanned images, Patent Document 1 describes a method of determining black edge pixels in a color image and performing color shift correction on pixels located within a predetermined color shift correction width in the sub-scanning direction from the determined black edge pixels. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-56888 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present disclosure is to provide an image forming apparatus that detects the occurrence of color misregistration in an original image. [Means for solving the problem]

[0006] The present disclosure provides an image processing device comprising an image processing unit and an image acquisition unit that acquires an original image generated from an original, wherein the original image consists of a first image, a second image, and a third image, each corresponding to one of three different color components of the original, and the first image, second image, and third image are generated in sequence using a first sensor, a second sensor, and a third sensor, which are image sensors that read the three different color components and are arranged according to a predetermined order along the transport direction of the original, and the image processing unit compares the first image, second image, and third image with each other, and determines whether or not there is color deviation in the original image from the original based on the result of the comparison.

[0007] The present disclosure also provides a control method for an image processing device, which includes acquiring an original image generated from an original, the original image consisting of a first image, a second image, and a third image, each of which corresponds to one of three different color components of the original, the first image, the second image, and the third image being generated in sequence using a first sensor, a second sensor, and a third sensor, which are image sensors that read the three different color components and are arranged in a predetermined order along the transport direction of the original, the first image, the second image, and the third image being compared with each other, and determining whether or not there is a color shift in the original image from the original based on the result of the comparison. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an image processing device that detects the occurrence of color shift in an original image. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an external perspective view of an MFP (Multi-Function Printer / Peripheral) according to a first embodiment of the present disclosure. [Figure 2]1 is a functional block diagram of an MFP according to a first embodiment of the present disclosure. [Figure 3] This figure explains the change in the positional relationship between the original and the sensor RGB when there is no change in the conveying speed and no color shift occurs, where Figure 3(A) shows the positional relationship between the original and the sensor RGB just before the start of capturing the black area, Figure 3(B) shows the positional relationship between the original and the sensor RGB at the time when the blue sensor captures the black area, Figure 3(C) shows the positional relationship between the original and the sensor RGB at the time when the green sensor captures the black area, and Figure 3(D) shows the positional relationship between the original and the sensor RGB at the time when the red sensor captures the black area. [Figure 4] This figure explains the change in the positional relationship between the original and the sensor RGB when the conveying speed changes and color shift occurs, where Figure 4(A) shows the positional relationship between the original and the sensor RGB just before the start of capturing the black area, Figure 4(B) shows the positional relationship between the original and the sensor RGB at the time when the blue sensor captures the black area, Figure 4(C) shows the positional relationship between the original and the sensor RGB at the time when the green sensor captures the black area, and Figure 4(D) shows the positional relationship between the original and the sensor RGB at the time when the red sensor captures the black area. [Figure 5] 4 is a flowchart for explaining the operation of the MFP according to the first embodiment of the present disclosure. [Figure 6] 6A and 6B are diagrams for explaining a method for detecting color shift areas, in which FIG. 6A is an original image of an original (business card), and FIG. 6B is a partially enlarged view of the area in the original image of FIG. 6A where color shift has occurred. [Figure 7] 6A and 6B are diagrams for explaining a method for detecting color shifts, and for explaining that color shifts are detected by comparing the red channel component and the blue channel component of the original image in FIG. 6B. [Figure 8] 10A and 10B are diagrams for explaining a method for identifying a range in which a fluctuation in the conveying speed occurs from an original image. [Figure 9]9 is a diagram for explaining a method for identifying the range in which the conveying speed has fluctuated from the document image, and is a partially enlarged view of the document image in FIG. 8. FIG. [Figure 10] 10 is a flowchart for explaining the operation of an MFP according to a second embodiment of the present disclosure. [Figure 11] 10 is a flowchart for explaining the operation of detecting color misregistration in an MFP according to a second embodiment of the present disclosure. [Figure 12] 12A and 12B are diagrams for explaining the occurrence of color shift in a three-line CCD and the occurrence of no color shift. Fig. 12A shows the correspondence between positions on a document (document position, Y coordinate value) and pixel values, Fig. 12B shows the lengths of the color sensor gaps between sensors LR and LG and between sensors LG and LB, Fig. 12C is a table showing the correspondence between document states and document positions read by each sensor, Fig. 12D is a table showing the correspondence between document positions when the document positions read by sensors LB, LG, and LR are combined by shifting them by the color sensor gaps, and Fig. 12E shows the pixel values ​​output by sensors LB, LG, and LR at the document positions in Fig. 12D and the color determined by the combination of these pixel values. [Figure 13] 13A and 13B are diagrams for explaining the occurrence of color shifts in scanned images generated using a three-line CCD, and for explaining the occurrence of color shifts. Fig. 13A shows the correspondence between positions on a document (document position, Y coordinate value) and pixel values, Fig. 13B shows the size of the gap between sensors LR and LG and between sensors LG and LB, Fig. 13C is a table showing the correspondence between the number of pixels (document feed status) corresponding to the distance the document will be transported until the next reading timing by sensors LB, LG, and LR and the document position currently being read by sensors LB, LG, and LR, Fig. 13D shows the document positions read by sensors LB, LG, and LR at each reading timing, and Fig. 13E shows the pixel values ​​at the document positions read by sensors LB, LG, and LR at each reading timing and the color determined by the combination of these pixel values. [Figure 14]14A and 14B are diagrams for explaining the occurrence of color shifts in scanned images generated using a three-line CCD, and for explaining other situations in which color shifts occur. Fig. 14A shows the correspondence between positions on a document (document position, Y coordinate value) and pixel values, Fig. 14B shows the size of the gap between sensors LR and LG and between sensors LG and LB, Fig. 14C is a table showing the correspondence between the number of pixels (document feed status) corresponding to the distance the document will be transported until the next reading timing by sensors LB, LG, and LR and the document position currently being read by sensors LB, LG, and LR, Fig. 14D shows the document positions read by sensors LB, LG, and LR at each reading timing, and Fig. 14E shows the pixel values ​​at the document positions read by sensors LB, LG, and LR at each reading timing and the color determined by the combination of these pixel values. [Figure 15] 10A and 10B are diagrams illustrating an example of a one-pixel document feed misalignment and a two-pixel document feed misalignment that occur in a scanned image generated using a three-line CCD. [Figure 16] FIG. 16A is a schematic diagram for explaining a document feed deviation of one pixel, and FIG. 16B is a schematic diagram for explaining a document feed deviation of two pixels. [Figure 17] 17A and 17B are diagrams for explaining a method for estimating the portion of a document where a three-line CCD repeatedly reads the same position on the document based on the color shift that occurs in the scanned image generated using the three-line CCD. FIG. 17A is a diagram for specifying the portion of the scanned image that contains the color shift, and FIG. 17B is a graph showing the correspondence between the pixel values ​​of each of the RGB colors and the Y coordinate value in the portion specified in FIG. 17A. [Figure 18]18A and 18B are diagrams illustrating a method for estimating the portion of a document where a three-line CCD repeatedly reads the same position on the document based on the color shift that occurs in a scanned image generated using the three-line CCD; FIG. 18A is a table showing the correspondence between the rise / fall, the color of the color shift, and the delay position of the R pixel; FIG. 18B is an excerpt from FIG. 13D and FIG. 13E, and is a table for explaining the case where the color shift is cyan; and FIG. 18C is a diagram for explaining the relationship between the delay positions of the R pixel, G pixel, and B pixel. [Figure 19] 10A and 10B are diagrams for explaining a mapping function for color misregistration correction; [Figure 20] FIG. 10 is a functional block diagram of an image processing device according to a third embodiment of the present disclosure. [Figure 21] 10 is a flowchart for explaining the operation of the MFP according to the fourth embodiment of the present disclosure. [Figure 22] FIG. 13 is a diagram for explaining a medium used when creating a color document in a modification of the fifth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] [1. First embodiment] For example, when an MFP (Multi-Function Printer / Peripheral) scans an original document to generate an original document image, an original document transport unit transports the original document, and an image input unit reads the original document to generate an original document image. At this time, the image input unit normally reads the original document, which moves at a constant linear speed. However, the transport speed of the original document may be slowed down due to, for example, the influence of glue adhering to the transport path of the original document transport unit. In such cases, color shifts may occur in the original document image, as will be described in detail later. In the first embodiment, this color shift is detected.

[0011] [1.1 Hardware configuration] FIG. 1 is an external perspective view of an MFP (Multi-Function Printer / Peripheral) 1 according to a first embodiment of the present disclosure. FIG. 2 is a functional block diagram of the MFP according to the first embodiment of the present disclosure. The MFP 1 is also called a multifunction peripheral, and typically has a copy function, an image scanner function, a facsimile function, and a printer function. The MFP 1 has a display unit 3, an operation unit 5, a document transport unit 7, an image input unit 9, an image forming unit 11, a communication unit 13, a connection unit 15, a control unit 17, and a storage unit 19.

[0012] The display unit 3 displays images and characters. For example, it is configured with a liquid crystal display (LCD), an organic electroluminescence (EL) panel, etc. The display unit 3 may be a standalone display device, or may further include an externally connected display device.

[0013] The operation unit 5 accepts operation inputs from a user. For example, the operation unit 5 is configured with hardware keys and / or software keys. The operation unit 5 also includes operation keys such as task keys for issuing instructions to execute tasks such as sending a fax or scanning an image, and a stop key for issuing an instruction to cancel an operation.

[0014] The document transport unit 7 includes a document setting table 7a and a transport mechanism 7b. The document setting table 7a is a table for setting paper on which an image to be read by the image input unit 9 is drawn, i.e., one or more documents. The transport mechanism 7b transports the document set on the document setting table 7a to the image input unit 9 and discharges the document with the image input by the image input unit 9. The document transport unit 7 includes a transport path for transporting the document, and transport rollers that rotate while in contact with the document to move the document along the transport path.

[0015] The image input unit 9 reads an image formed on the surface of a document and outputs it as image data (scanned image). The image input unit 9 is composed of a color scanner (image input device). The image input unit 9 has a reading surface on which the document is placed. The reading surface is made of a transparent plate-like material such as a glass plate. The image input unit 9 has a three-line image sensor 9a below the reading surface. The three-line image sensor 9a consists of three line image sensors LR, LG, and LB, which are a line image sensor that reads red, a line image sensor that reads green, and a line image sensor that reads blue, respectively. Hereinafter, the line image sensors that read red, green, and blue will also be referred to as sensors LR, LG, and LB, respectively. These sensors will also be collectively referred to as sensor RGB. The sensor RGB is made of a solid-state imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide-Semiconductor).

[0016] The sensors RGB are arranged along the direction in which the document transport unit 7 transports the document (document feed direction). That is, along the document feed direction, from rear to front in the document feed direction, the sensors LB, LG, and LR are arranged in this order. Therefore, when the document transport unit 7 transports the document, the leading edge of the document reaches the positions of the sensors LB, LG, and LR in that order. In other words, any point P on the document transported to the image input unit 9 first moves to a position directly facing the sensor LB and is read by the sensor LB. After the document is further transported, the point P moves to a position directly facing the sensor LG and is read by the sensor LG. After the document is further transported, the point P moves to a position directly facing the sensor LR and is read by the sensor LR. A gap of a predetermined length is provided between the B sensor and the G sensor. Similarly, a gap of the same length is provided between the G sensor and the R sensor.

[0017] The image forming unit 11 forms (prints) an image on a medium such as copy paper based on image data. The printing method of the image forming unit is arbitrary, and may be, for example, an inkjet printer, a laser printer, a thermal transfer printer, etc. The image forming unit may be a monochrome printer or a color printer.

[0018] The communication unit 13 is connected to a network. The communication unit 13 is configured with an interface that can be connected to, for example, a wired LAN (Local Area Network), a wireless LAN, or an LTE (Long Term Evolution) network. When the communication unit 13 is connected to a network, it is connected to other devices and an external network. Note that the communication unit 13 may be an interface that performs short-range wireless communication, such as NFC (Near Field Communication) or Bluetooth (registered trademark).

[0019] Connection unit 15 connects MFP 1 to other devices. For example, connection unit 15 is a USB interface to which a USB memory or the like is connected. Connection unit 15 may also be an interface other than a USB interface, such as HDMI (registered trademark).

[0020] Control unit 17 controls the entire MFP 1. Control unit 17 is configured with one or more control devices and control circuits, and is configured with, for example, a CPU (Central Processing Unit) which is a processor that executes various arithmetic processes, an SoC (System on a Chip), etc. Control unit 17 can realize each function by reading out and executing programs stored in storage unit 19. In particular, control unit 17 performs image processing on images input from image input unit 9, images acquired from other devices connected via connection unit 15, and images acquired from communication unit 13 and other devices connected via a communication line.

[0021] Storage unit 19 stores various programs and various data necessary for the operation of MFP 1. Storage unit 19 includes one or more recording devices capable of temporary storage, such as a dynamic random access memory (DRAM), and non-temporary recording devices, such as a solid state drive (SSD) configured with semiconductor memory or a hard disk drive (HDD) configured with a magnetic disk. For convenience of explanation, storage unit 19 is shown as a single unit, but it may also be configured as separate devices for each purpose, such as an area used for executing programs (main storage area), an area for saving programs and data (auxiliary storage area), an area used for caching, etc.

[0022] [1.2 Occurrence of color misalignment] Before explaining the operation of the MFP 1, we will explain the mechanism by which color shift occurs. When the document transport unit 7 is operating normally, the document is transported at a constant speed. Sensors LB, LG, and LR of the image input unit 9 capture images of the area of ​​the document that they are directly facing at each given timing, which is determined based on the assumption that the document is being transported at a constant speed, and output signals B, G, and R, respectively. By combining the signals B, G, and R thus obtained based on the timing of the imaging and the relative positions of sensors LB, LG, and LR, a pixel on the document image corresponding to any position on the document is obtained as a combination of signals B, G, and R.

[0023] However, there are cases where an abnormality occurs in the document transport unit 7, causing the transport of the document to stop for a very short time and delay the transport of the document. Such an abnormality occurs, for example, when the document transport unit 7 transports the document, because the document encounters temporary resistance, causing the transport rollers to slip for an instant.

[0024] This delay in document transport causes a shift in the timing at which sensors LB, LG, and LR acquire pixel values ​​from the document. When this happens, the combination of signals B, G, and R shifts from the intended combination. As a result, colors different from those in the document appear on the document image, causing color shifts.

[0025] The mechanism by which color misregistration occurs will be explained in more detail below. FIG. 3 is a diagram for explaining changes in the positional relationship between the original 123 and sensors RGB when there is no change in the conveying speed and no color misregistration occurs. As described above, sensors LB, LG, and LR are arranged in this order along the conveying direction T of the original 123, from rear to front in the conveying direction T. For simplicity of explanation, it is assumed that sensors LB, LG, and LR are arranged adjacent to each other with no gaps between them. The original 123 is two-tone or multi-tone monochrome and has a white area 123W and a black area 123B.

[0026] As the original 123 is transported along the transport direction T, sensors LB, LG, and LR read the original 123 line by line and output signals B, G, and R, respectively. The range of signals B, G, and R is 0 to 255, and the color of the read line is determined by the combination of the outputs of signals B, G, and R. For example, if the values ​​of signals B, G, and R are all 255, the color of that line is white, and if the values ​​of signals B, G, and R are all 0, the color of that line is black. The original 123 has a black area 123B and a white area 123W. A black-white boundary 125 indicates the position of the boundary between the black area 123B and the white area 123W. Sensors LB, LG, and LR first detect the white area 123W, and then the black area 123B.

[0027] 3A shows the positional relationship between the document 123 and sensors RGB immediately before the start of capturing the black area 123B. At this point, the black-white boundary 125 has not yet reached the position of sensor LB. Therefore, none of sensors LB, LG, and LR has read the black area 123B.

[0028] Figure 3(B) shows the positional relationship between the original 123 and sensors RGB at the timing when blue sensor LB captures black area 123B. Compared to Figure 3(A), in Figure 3(B) the original 123 has moved in the transport direction T, and black-white boundary 125 has reached the boundary between sensors LB and LG. At this timing, sensor LB reads black area 123B and outputs signal B with a value of 0.

[0029] 3C shows the positional relationship between the original 123 and the sensors RGB at the timing when the green sensor LG captures the black area 123B. In FIG. 3C, the original 123 has moved further in the conveying direction T than in FIG. 3B, and the black-white boundary 125 has reached the boundary between the sensors LG and LR. At this timing, the sensor LG reads the black area 123B and outputs a signal G with a value of 0.

[0030] 3(D) shows the positional relationship between the original 123 and the sensors RGB at the timing when the red sensor LR captures the black area 123B. In FIG. 3(D), the original 123 has moved further in the transport direction T than in FIG. 3(C), and the black-white boundary 125 has reached the end of the sensor LR (the end on the forward side in the transport direction T). At this time, the sensor LR reads the black area 123B and outputs a signal R with a value of 0.

[0031] 3(B), 3(C), and 3(D), the read result of the black area 123B is obtained by combining the signals B, G, and R output by the sensors LB, LG, and LR, respectively. In FIG. 3(B), 3(C), and 3(D), the signals B, G, and R are output as 0, so the color read by the image input unit 9 is black.

[0032] Next, a change in the positional relationship between the original and the sensor RGB when the conveying speed changes and color misalignment occurs will be described with reference to Fig. 4. The original 123 read in Fig. 4 is the same as the original 123 read in Fig. 3, and has a black area 123B and a white area 123W. Compared to Fig. 3, Fig. 4 differs in that a delay occurs in the conveyance of the original 123 while the sensor RGB is reading the original 123.

[0033] Figure 4(A) shows the positional relationship between the document and the sensor RGB just before the start of capturing the black area. Figure 4(B) shows the positional relationship between the document and the sensor RGB at the timing when the blue sensor captures the black area. Figures 4(A) and 4(B) are similar to Figures 3(A) and 3(B), respectively, so their explanations are omitted.

[0034] FIG. 4C shows the positional relationship between the document and sensors RGB at the time when green sensor LG captures black region 123B. In FIG. 3C, black-white boundary 125 reaches the boundary between sensors LG and LR. In contrast, in FIG. 4C, due to a delay in document transport, black-white boundary 125 does not reach the boundary between sensors LG and LR. Therefore, at this time, both the area including black-white boundary 125, i.e., white region 123W and black region 123B, are positioned directly opposite sensor LG. As a result, sensor LG outputs a value corresponding to the area ratio between white region 123W and black region 123B that it directly faces at this time. In FIG. 4C, sensor LG outputs signal G with a value of 170.

[0035] Figure 4(D) shows the positional relationship between the document and the sensor RGB at the timing when the red sensor captures the black area. In Figure 3(D), the black-white boundary 125 reaches the front edge of the sensor LR in the transport direction. In contrast, in Figure 4(D), due to a delay in document transport, the black-white boundary 125 does not reach the front edge of the sensor LR in the transport direction. Therefore, at this timing, both the area including the black-white boundary 125, i.e., the white area 123W and the black area 123B, are positioned directly facing the sensor LR. As a result, the sensor LR outputs a value corresponding to the area ratio between the white area 123W and the black area 123B that it directly faces at this timing. In Figure 4(D), the sensor LR outputs a signal R with a value of 200.

[0036] 4(B), 4(C), and 4(D), a yellow area is obtained as the reading result of the black area 123B due to the combination of signals B=0, G=170, and R=200 output by sensors LB, LG, and LR, respectively. In this way, the black area 123B on the original 123 appears as a yellow area in the original image due to color shift caused by the transport delay.

[0037] [1.3 MFP1 Operation] FIG. 5 is a flowchart for explaining the operation of the MFP 1 according to the first embodiment of the present disclosure. The control unit 17 reads the original document using the image input unit 9 while the original document is being conveyed using the original document conveying unit 7, and generates an original document image (step S1). Next, the control unit 17 detects color shift from the original document image (step S3). A method for detecting color shift will be described later. If there is color shift (step S5, Yes), the control unit 17 identifies the range of color shift (step S7). A method for identifying the range of color shift will be described later. Next, the control unit 17 displays a message on the display unit 3 (step S9) and outputs the original document image (step S11). If there is no color shift (step S3, No), the control unit 7 outputs the original document image without displaying a message (step S11).

[0038] The output destination of the original image may be the display unit 3, the memory unit 19, another device connected via the connection unit 15, or another device connected via the communication unit 13 and a communication line.

[0039] The message displayed on the display unit 3 is a message regarding color shift, and specifically includes the presence or absence of color shift, the position of the pixel in the original image where color shift has occurred, the color that appears in the original image due to color shift, the original color of the pixel where color shift has appeared, etc. For the color that appears in the original image due to color shift and the original color of the pixel where color shift has appeared, for example, a rectangular area filled with that color may be displayed as part of the message.

[0040] [1.3.1 Detecting color misalignment] The method for detecting color misalignment in step S3 will now be described. As described above, when the conveying speed changes, the outputs of sensors LB, LG, and LR are affected, and an original image containing color misalignment from the original is generated. The locations where color misalignment has occurred are detected from such an original image as follows.

[0041] 6A and 6B are diagrams for explaining a method for detecting color shift portions, in which Fig. 6A shows an original image 131 of an original (business card), and Fig. 6B is a partial enlarged view of an area 133 where color shift has occurred in the original image 131 of Fig. 6A. Area 133 includes color shift areas 135 and 137. Color shift areas 135 and 137 are black areas in the original, but in the original image 131, both have turned cyan due to color shift.

[0042] Here, for the following explanation, terms related to directions will be explained. The transport direction T is the direction in which the document is transported through the image input unit 9 by the document transport unit 7. The direction in which the document is transported is the forward transport direction, and the opposite direction is the backward transport direction. The sub-scanning direction is the direction in which the image input unit 9 reads the document. The forward and backward sub-scanning directions are opposite to the forward and backward transport direction. The main scanning direction is a direction perpendicular to the sub-scanning direction and the transport direction. When facing forward in the sub-scanning direction, the direction of the left hand is the forward main scanning direction, and the direction of the right hand is the backward main scanning direction. Figure 6 shows arrows indicating the forward transport direction, the sub-scanning direction (Y), and the main scanning direction (X). Similar arrows are also shown in Figures 7-9, 15, and 18.

[0043] FIG. 7 is a diagram illustrating a method for detecting a color shift portion. Image 133R is a portion of the red channel component of original image 131 that corresponds to region 133 in FIG. 5B. Image 133B is a portion of the blue channel component of original image 131 that corresponds to region 133 in FIG. 5B. By calculating the difference between image 133R and image 133B, it is possible to detect a portion where color shift has occurred. Note that the red channel component is an image consisting only of signal R among the signals R, G, and B that make up original image 131. Similarly, the green channel component is an image consisting only of signal G among the signals R, G, and B that make up original image 131, and the blue channel component is an image consisting only of signal B among the signals R, G, and B that make up original image 131.

[0044] In FIG. 7, there is a discrepancy between the values ​​of the red channel component 133R and the blue channel component 133B in the region between the two straight lines 135A and 135B. Therefore, by calculating the difference between the red channel component 133R and the blue channel component 133B, it is possible to detect the color shift of the color shift width 141. In this way, a portion where the difference between two of the three color channel components of the original image is not zero is detected as a color shift. While the difference between the red channel component 133R and the blue channel component 133B is used as an example here, color shift may also be detected based on the difference between the corresponding green channel component (not shown) and the red channel component 133R, or the difference between the corresponding green channel component (not shown) and the blue channel component 133B.

[0045] [1.3.2 Estimation of color misregistration range] The method for identifying the range of color misalignment in step S7 will now be described. Fig. 8 is a diagram for explaining a method for identifying the range in which a fluctuation in the transport speed has occurred from original document image 151. Fig. 9 is a diagram for explaining a method for identifying the range in which a fluctuation in the transport speed has occurred from original document image 151, and is an enlarged view of a portion (area 153) of original document image 151 in Fig. 8.

[0046] Assume that color misregistration areas 165a, 165b, 165c, 165d, and 165e are detected from original image 151 using the color misregistration detection method in step S3 described above, as shown in Fig. 9. At this time, control unit 17 determines a straight line (dotted line 161) that passes through the color misregistration area that is the foremost in the conveying direction in original image 151 and is perpendicular to the conveying direction. Control unit 17 also determines a straight line (dotted line 163) that passes through the color misregistration area that is the rearmost in the conveying direction in original image 151 and is perpendicular to the conveying direction. Control unit 17 determines an area 167 between dotted lines 161 and 163 as the area where color misregistration has occurred.

[0047] [1.4 Effects] As described above, according to the first embodiment, it is possible to detect that a color shift has occurred in an original image, and also to estimate the range in which a color shift has occurred in an original image.

[0048] [2. Second Embodiment] A second embodiment of the present disclosure will be described. In the first embodiment, color shift is detected based on the difference between color channel components of an original image, but in the second embodiment, changes in pixel values ​​in the transport direction of the original are compared between color channels, and color shift is detected based on the comparison results. In addition, while the first embodiment does not correct the detected color shift, the second embodiment does correct the detected color shift. Furthermore, in the second embodiment, color shift is corrected based on the detected color shift. The following mainly describes differences from the first embodiment. An MFP 1 is also used in the second embodiment. The configuration of the MFP 1 is the same as in the first embodiment, so description thereof will be omitted.

[0049] [2.1 MFP1 Operation] 10 is a flowchart for explaining the operation of the MFP according to the second embodiment of the present disclosure. The control unit 17 uses the document transport unit 7 to transport a document to the image input unit 9, and generates a document image from the document using the image input unit 9 (step S21). Next, the control unit 17 detects color shift according to a method described below (step S23). Next, the control unit 17 generates a document image in which the detected color shift is corrected to the color that would be obtained if no color shift occurred (step S25). Next, the control unit 17 detects distortion of the document image based on the document image after the color shift has been corrected (step S27). Next, the control unit 17 generates a document image in which the detected distortion has been corrected (step S29).

[0050] [2.1.1 Color misregistration detection (Step S23)] The color shift detection performed in step S23 will now be described with reference to a flowchart of FIG 11 for explaining the operation of color shift detection by the MFP 1 according to the second embodiment of the present disclosure.

[0051] The control unit 17 determines the rising point and the falling point in the sub-scanning direction for each color channel component (red channel component, green channel component, blue channel component) of the document image (step S31). Each color channel component may include multiple rising points or multiple falling points.

[0052] Next, the control unit 17 calculates the positional deviation in the sub-scanning direction between corresponding rising points / falling points among the color channel components (step S33). More specifically, a set of rising points consisting of corresponding rising points is calculated among the red, green, and blue channel components. A set of rising points consists of three rising points: a rising point of the red channel component, a rising point of the green channel component, and a rising point of the blue channel component. The positional deviation in the sub-scanning direction is calculated among these three rising points. If a color channel component includes multiple rising points, multiple sets of rising points are calculated, and for each set, the positional deviation in the sub-scanning direction between the rising points of the same set is calculated. The same process is performed for the falling points, and the positional deviation in the sub-scanning direction between the falling points of the same set is calculated.

[0053] Next, for pairs of rising / falling points that have a positional shift between them, the control unit 17 determines the type of rising / falling and the color of the color shift, and estimates the delay position of the pixel of the red channel component based on the determined type of rising / falling and the color of the color shift (step S35).

[0054] Next, the control unit 17 estimates the delay positions of the pixels of the green channel component and the pixels of the blue channel component based on the delay positions of the pixels of the red channel component estimated in step S35 and the color sensor gap (step S37).

[0055] Next, the control unit 17 generates a relationship table between the post-correction coordinate values ​​in the sub-scanning direction and the pre-correction coordinate values ​​(step S39).

[0056] [2.1.2 Color registration correction (Step S25)] The relationship table generated by the above-described color shift detection corresponds to a mapping function relating to color shift, and therefore, an original image in which color shift has been corrected is generated using the relationship table.

[0057] [2.1.3 Distortion detection and distortion correction (steps S27 and S29)] Based on the original image generated in step S25 and in which the color shift has been corrected, distortion is detected (step S27), and the detected distortion is corrected (step S29).

[0058] [2.2 Color shift occurrence with 3-line CCD] [2.2.1 3-line CCD output when no color shift occurs] 12 is a diagram for explaining the occurrence of color shift in a three-line CCD (sensors LR, LG, LB). For comparison with FIG. 13, which will be described later, a situation in which no color shift occurs will be explained in FIG. 12.

[0059] The sensors LR, LG, and LB are arranged in the order of sensors LB, LG, and LR from the front in the transport direction along the transport direction in which the document transport unit 7 transports the document. When the document is transported, the sensors LB, LG, and LR read one line of the document in this order. For this reason, the sensors LB, LG, and LR do not read one line at a time. The sensors LB, LG, and LR read one line of the document in this order.

[0060] Between sensors LR and LG, there is a gap corresponding to the number of lines indicated by color sensor gap 205. Between sensors LG and LB, there is also a gap corresponding to the number of lines indicated by color sensor gap 207. For simplicity, the original document is assumed to consist of only two colors, black and white. Lines are virtual rectangular areas obtained by dividing the original document in the main scanning direction (a direction perpendicular to the transport direction). Line numbers are numbers starting from 0 that are assigned to each line in the order in which the image input unit 9 reads the lines. Sensors LB, LG, and LR each start reading from original position 0 (line 0). Therefore, the image input unit 9 generates an original image based on the reading results of sensors LB, LG, and LR from original position 0 (line 0) onwards.

[0061] FIG. 12(A) shows the correspondence between positions on the document (document position, Y coordinate value) and pixel values. In the figure, sensors LR, LG, and LB indicate the initial reading position of the document. The document position indicates a line on the document, and the pixel value indicates the pixel value of that line. If the pixel value is 0, the line is black, and if the pixel value is 255, the line is white. When the document transport unit 7 transports the document by one line, the document position read by sensors LR, LG, and LB shifts one position to the right in the figure. Note that in FIG. 12(A), pixel values ​​from document positions -8 to 16 are stored, but this is for convenience of drawing, and it is assumed that pixel values ​​from document positions 17 to 24 are also stored in FIG. 12(A).

[0062] Fig. 12(B) shows the lengths of the color sensor gaps 205 and 207. Fig. 12(B) shows that the color sensor gaps 205 and 207 both have a length equivalent to four lines of the document.

[0063] Figure 12(C) is a table showing the correspondence between the document feed status and the position of each sensor. The document feed status is the number of lines corresponding to the distance the document feed unit 7 actually transported from the current reading position to the next reading position. The B sensor position indicates the document position currently being read by sensor LB. Similarly, the G sensor position and the R sensor position indicate the document positions currently being read by sensors LG and LR, respectively.

[0064] Incidentally, sensors LB, LG, and LR are arranged four lines apart in the conveyance direction. Therefore, the lines that sensors LB, LG, and LR simultaneously read from the document are not the same lines. Now, consider the timing at which sensors LB, LG, and LR read the same line L on the document. After sensor LB reads line L, sensor LG reads line L when document conveyance unit 7 has conveyed the document by four lines. Similarly, sensor LR reads line L when document conveyance unit 7 has conveyed the document by four lines after sensor LG reads line L.

[0065] For example, value 209 in Figure 12(C) indicates that sensor LB read line 0 of the document. Value 211 indicates that after document transport unit 7 transported the document four lines from that timing, sensor LG read line 0 of the document. Similarly, value 213 indicates that after document transport unit 7 transported the document four lines from the timing at which sensor LG read line 0 of the document, sensor LR read line 0 of the document. Naturally, as indicated by value 217, the lines simultaneously read by sensors LB, LG, and LR are different from one another.

[0066] FIG. 12(D) shows the correspondence relationship of the document positions when the document positions read by each RGB sensor are combined, shifted by the gap between the color sensors. The document position index represents the document position read by each RGB sensor at each timing. When the document is being transported normally (when the document is not temporarily stopped during transport), the document position index increases by 1. On the other hand, when the document is temporarily stopped during transport, the document position index value remains the same and does not increase. In this case, the document position index becomes the same as the document position index at the immediately preceding timing. For example, column 215 combines line 0 (value 209) read by sensor LB, the line number (value 211) of the line read by sensor LG at the timing when document transport unit 7 transports the document by four lines after sensor LB reads line 0, and the line number (value 213) of the line read by sensor LR at the timing when document transport unit 7 transports the document by another four lines after sensor LG reads line 0. Note that in Figure 12(D), document transport unit 7 transports the document at a constant transport speed, so the line numbers are consistent from start to finish.

[0067] FIG. 12(E) shows the pixel values ​​output by each RGB sensor at the document position in FIG. 12(D) and the color determined by the combination of these pixel values. Value 203 in FIG. 12(A) corresponds to value 219 in FIG. 12(E). Each column in FIG. 12(E) corresponds to each column in FIG. 12(D). For example, value 219 corresponds to the second column from the left in FIG. 12(D). That is, value 219 stores 255 as the output of sensor LB, which is the reading output by sensor LB at document position "1" read by sensor LB in the second column from the left in FIG. 12(D). Looking at the value in the "Appearance" column in FIG. 12(E), it is either W (white) or K (black), indicating that no color shift has occurred.

[0068] [2.2.2 3-line CCD output when color shift occurs 1] Fig. 13 is a diagram for explaining the occurrence of color shift in a scanned image generated using a three-line CCD. Unlike Fig. 12, Fig. 13 is a diagram for explaining the occurrence of color shift. The conditions such as the arrangement of sensors LR, LG, and LB and the document conveyance direction are the same as those in Fig. 12. Figs. 13(A), 23(B), 23(C), 23(D), and 23(E) correspond to Figs. 12(A), 22(B), 22(C), 22(D), and 22(E), respectively, and the corresponding table items are the same.

[0069] Color shifts occur due to index shifts. Under normal circumstances where transport is not temporarily stopped, the pixel position indexes for both RGB are the same. However, if transport is temporarily stopped, the pixel position indexes for RGB do not match. This situation is called "index shift." In Figure 13, index shifts occur in range 243.

[0070] 13(C), the document feed status value 231 is 0. This indicates that the document feed unit 7 did not feed the document after the sensors LG, LB, and LR output the value 233 and before outputting the next value 235. Because the document was not fed, the sensors LG, LB, and LR read the same line again as when they output the value 233, and as a result, the value 235 is the same as the value 231.

[0071] In the values ​​233 and 235, the line that sensor LR reads twice is line 4. For this reason, in FIG. 13(D), line 4 appears twice in a row in value 237, which indicates the document position read by sensor LR. Similarly, line 8 appears twice in a row in value 239, which indicates the document position read by sensor LG, and line 12 appears twice in a row in value 241, which indicates the document position read by sensor LB. Due to this effect, while the same line number would normally be stored in the same column as in FIG. 12(D), in FIG. 13(D), a certain line number (here, line number 6) is stored in two columns, as in value 245. This type of line number mismatch occurs in range 243. Note that the document positions read by sensors LB, LG, and LR are consistent before and after range 243.

[0072] If the reading positions of sensors LB, LG, and LR are incorrectly combined as shown in FIG. 13(D), the outputs of sensors LB, LG, and LR will be incorrectly combined, resulting in color shift as shown in FIG. 13(E).

[0073] For example, in Figure 13(D), there is a column 246 that stores the combination of line numbers 7, 7, and 6 as the reading positions of sensors LB, LG, and LR. In Figure 13(E), the column corresponding to column 246 stores the reading results of sensors LB, LG, and LR, respectively, as 255, 255, and 0. Because the output of sensor LR, i.e., the red channel, is zero, this combination results in cyan 247.

[0074] Similarly, column 248 in Figure 13(D) stores the combination of line numbers 12, 11, 11 as the reading positions of sensors LB, LG, and LR. In Figure 13(E), the column corresponding to column 248 stores 0, 255, 255 as the reading results of sensors LB, LG, and LR, respectively. This combination results in yellow 249.

[0075] [2.2.3 3-line CCD output when color shift occurs 2] Fig. 14 is a diagram for explaining the occurrence of color shift in a scanned image generated using a three-line CCD. Similar to Fig. 13, color shift occurs, but the occurrence is different between Fig. 14 and Fig. 13. The conditions, such as the arrangement of sensors LR, LG, and LB and the document conveyance direction, are the same as Figs. 12 and 13. Also, Figs. 14(A), 24(B), 24(C), 24(D), and 24(E) correspond to Figs. 12(A), 22(B), 22(C), 22(D), and 22(E), respectively, and the corresponding table items are the same.

[0076] Figures 14(A) and 24(B) are similar to Figures 12(A) and 22(B), respectively. In Figure 14(C), after sensors LB, LG, and LR read lines 17, 13, and 9 in order, as indicated by value 263, the document was not transported, as indicated by value 261. Therefore, sensors LB, LG, and LR output the same value as value 263, as indicated by value 265.

[0077] As shown by values ​​263 and 265, sensors LB, LG, and LB each read the same line on the document twice in succession. This results in repetition of values ​​such as values ​​267, 269, and 271 in FIG. 14(D). This repetition causes the document reading positions of sensors LB, LG, and LB to be incorrectly combined in range 273. For example, value 275 should originally be stored in the same column, but the reading position of sensor LR is shifted and stored in the later column.

[0078] 14(E), the value of document position 11 is used as the output of sensor LR, and as a result, 0, 0, 255 are combined as the read values ​​of sensors LB, LG, and LR, and the image input unit 9 outputs red. Note that, originally, the read values ​​0, 0, 0 of the outputs obtained by sensors LB, LG, and LR reading document position 12, respectively, were combined, and the image input unit 9 should output this line as black.

[0079] 14(E), the value of document position 17 is used as the output of sensor LB, and as a result, 255, 0, 0 are combined as the read values ​​of sensors LB, LG, and LR, and the image input unit 9 outputs blue. Note that, originally, the read values ​​of 0, 0, 0 of the outputs obtained by sensors LB, LG, and LR reading document position 16 were combined, and the image input unit 9 should output this line as black.

[0080] [2.3 Color shift with 3-line CCD] 15 is a diagram illustrating a one-pixel document feed misalignment and a two-pixel document feed misalignment that occurred in a scanned image generated using a three-line CCD. Region 293 in document image 291 is the region where a one-pixel document feed misalignment occurred. Color misalignment of one pixel width occurs at color misalignment locations 293a, 293b, 293c, 293d, 293e, 293f, and 293g. Region 295 in document image 291 is the region where a two-pixel document feed misalignment occurred. Color misalignment of two pixels width occurs at color misalignment locations 295a, 295b, 295c, 295d, 295e, 295f, 295g, 295h, and 295i.

[0081] FIG. 16 is a schematic diagram illustrating color misalignment of one pixel width and color misalignment of two pixels width. FIG. 16(A) is a schematic diagram illustrating a document feed misalignment of one pixel. In FIG. 16(A), a black area 301 where no color misalignment has occurred is followed adjacently by a cyan area 303 that has discolored due to color misalignment. The cyan area 303 has a length of one pixel in the conveying direction T. FIG. 16(B) is a schematic diagram illustrating a document feed misalignment of two pixels. In FIG. 16(B), a black area 305 where no color misalignment has occurred is followed adjacently by a cyan area 307 that has discolored due to color misalignment. The cyan area 307 has a length of two pixels in the conveying direction T.

[0082] [2.4 Estimation of the part where the same manuscript position is read] Figure 17 is a diagram for explaining a method for estimating the portion of a document where a three-line CCD repeatedly reads the same position on the document based on the color shift that occurs in the scanned image generated using the three-line CCD. Figure 17(A) is a diagram for specifying the portion of the scanned image that contains the color shift, and Figure 17(B) is a graph showing the correspondence between each RGB pixel value and the Y coordinate value in the portion specified in Figure 17(A).

[0083] The original image 321 has an area 323. An arrow 324 indicates the sub-scanning direction in FIG. 15, which is opposite to the conveying direction. The graph in FIG. 17(B) is a graph in which the direction of the arrow 324 (sub-scanning direction) is the positive direction on the horizontal axis and the pixel value (0 to 255) is the vertical axis. In FIG. 17(B), the outputs of the sensors LR, LG, and LB in the area 323 are plotted as curves corresponding to the red channel (R), green channel (G), and blue channel (B).

[0084] The curves for the red, green, and blue channels generally share a common feature of being downwardly convex, with the horizontal axis reaching a minimum value around 453-454, but the rise / fall points differ depending on the channel. On the left side of FIG. 17(B), the curves for the red, green, and blue channels generally share a common fall point 325. On the right side of FIG. 17(B), the curves for the green and blue channels both share a rise point 327, while the curve for the red channel has a separate rise point 329. As such, the portion where there is a discrepancy between the rise point 327 and the rise point 329 appears as a color shift in the original image.

[0085] As described above, the three sensors LB, LG, and LR are arranged along the transport direction so as to read the document in this order. Furthermore, there is a color sensor gap of four lines between sensors LG and LB, and between sensors LR and LG. In this case, the relationship shown in Figure 18(A) exists between the rising edge and the falling edge, the color that appears in the document image due to color shift, and the delay position of the R pixel.

[0086] FIG. 18(B) is an excerpt from FIGS. 13(D) and 13(E) and is a table illustrating the case where the color shift is cyan. Column 247 is the rising point of the blue channel and the green channel, and column 247 appears cyan (C). In this case, as can be seen from the fact that the same document position "4" is repeated twice in values ​​237a and 237b, a delay occurs in the red channel at value 237b. The distance 341 between value 237b and column 247 is 2 pixels. This corresponds to the description in the second row of FIG. 18(A), where the rising / falling edge is "rising," the color of the color shift is "cyan," and the delay position of the R pixel is "between 0 and 3 pixels."

[0087] Additionally, column 249 is the falling edge point of the blue channel, and column 249 appears yellow (Y). At this time, the distance 342 between value 237b where a delay occurred in the red channel and column 249 is 7 pixels. This corresponds to the description on the fourth line of FIG. 18(A), where the rising / falling edge is "falling edge," the color of the color shift is "yellow," and the delay position of the R pixel is "between 4 and 7 pixels."

[0088] In this way, the rising and falling points of the color shifts that occurred at different positions on the scanned image were identified, and the range of the corresponding delay positions of the R pixels is indicated by the bidirectional arrows 355a to 355e in FIG. 18(C). The ranges indicated by the bidirectional arrows 355a to 355e do not coincide. However, it is estimated that the delays of these R pixels are caused by the same delay in document transport. Therefore, the delay positions of the R pixels are identified by determining the common range of the bidirectional arrows 355a to 355e. The delay positions of the R pixels identified in this way are indicated by line 353R in FIG. 18(C).

[0089] As described above, there is a color sensor gap of four lines between sensors LG and LB, and between sensors LR and LG. Therefore, the delay position of the G pixel is shifted backward in the transport direction by four pixels from the delay position of the R pixel. Similarly, the delay position of the B pixel is shifted backward in the transport direction by four pixels from the delay position of the G pixel. For example, as shown in FIG. 18(C), if the delay position of the R pixel is identified as the position of line 353R, the delay positions of the G pixel and B pixel can be identified as lines 353G and 353B, respectively.

[0090] FIG. 19 is a diagram explaining the mapping function for color shift correction. As mentioned above, color shift in a 3-line CCD occurs when the document transport is temporarily stopped, causing each RGB sensor to read a position that is shifted from the position where it should have been read. If the correspondence between the pixel position of the scanned image where color shift has occurred and the original position where the sensor should have read it is known, it is possible to generate an image in which color shift has been corrected based on that information. The information showing this correspondence is the relationship table in FIG. 19.

[0091] In the portion where the document transport is temporarily stopped, the same position on the document is read, and the document undergoes a transformation that stretches it in the document transport direction. If this transformation is considered as a mapping, the relational table represents the mapping function of this transformation.

[0092] The terms used in Figure 19 are explained below. The post-correction coordinate value is the coordinate value of a pixel in an ideal document image without color shift. The pre-correction coordinate value is the coordinate value of a pixel in an image with color shift obtained immediately after scanning the document. The delay position information corresponds to the actual Y coordinate on the document (the original position read by the sensor) read at the pixel position corresponding to the pre-correction coordinate value. The numbers lined up along the top row of the delay position information are index values ​​for referencing the delay position information. The delay position information corresponds to the document position indexes in Figures 12(D), 13(D), and 14(D). As shown in the document position indexes in Figures 13(D) and 14(D) when color shift has occurred, the delay position information differs for each RGB sensor. Therefore, delay position information is created separately for each RGB sensor. In addition, the relationship table created from the delay position information is also created separately for each RGB sensor. Note that instead of creating delay position information and a relationship table separately for each sensor, it is also possible to create delay position information and a relationship table only for a specific color sensor (e.g., the R sensor). In this case, this delay position information and relationship table can also be used as delay position information and relationship tables for sensors of other colors (for example, G sensor and B sensor) by referring to the delay position information and relationship table shifted by the gap between the color sensors. The values ​​378 and 380 in Fig. 19 are delay positions identified by the procedure described above with reference to Fig. 18. The value 378 indicates a delay position where a document feed deviation of one pixel occurs. The value 380 indicates a delay position where a document feed deviation of two pixels occurs.

[0093] In step S37, the delay position information is created using the following procedure. The initial value of variable n for setting delay position information is set to 0. The table of pre-correction coordinate values ​​and the table of delay position information are referenced in order from the beginning, and n is increased by 1 each time until the delay position is reached, and set in the table of delay position information. Once the delay position is reached, n is not increased, and only the number of pixels where the document feed deviation occurred is set in the table of delay position information. The above procedure is repeated until the end of the table of pre-correction coordinate values.

[0094] In step S39, the relationship table is created using the following procedure. Processing is performed starting from the top of the corrected coordinate values. The corrected coordinate values ​​are searched for in the table of delayed position information, and the corresponding index value is determined. If there are multiple search results, the average value of the corresponding index values ​​is set as the value in the relationship table; if there is only one search result, the index value is set as is as the value in the relationship table. The above procedure is repeated until the end of the table of pre-corrected coordinate values.

[0095] Note that the length of the table of corrected coordinate values ​​and the relationship table is less than or equal to the length of the table of pre-corrected coordinate values. The length of the table of corrected coordinate values ​​and the relationship table is the same. The difference between the length of the table of corrected coordinate values ​​(or the length of the relationship table) and the length of the table of pre-corrected coordinate values ​​is the total number of delay pixels. In the case of Figure 19, this difference is three pixels, which is the sum of the one-pixel delay associated with the value 378 and the two-pixel delay associated with the value 380.

[0096] Next, in step S29, the relationship table is used to find the pre-correction coordinate values ​​from the post-correction coordinate values ​​using the following procedure: The coordinate value of the image after color shift correction is assumed to be (x, y). The value in the relationship table corresponding to the post-correction coordinate value y is obtained as y'. y' becomes the pre-correction coordinate value. The coordinate value (x, y') is used to reference the scanned image in which color shift has occurred. Because y' may not be an integer value, an image in which color shift has been corrected can be generated by performing an appropriate interpolation operation using pixel values ​​surrounding the reference position of the scanned image in which color shift has occurred. Note that a separate relationship table is created for each RGB sensor, so the value of y' above differs for RGB.

[0097] [2.5 Effects] According to the second embodiment, it is possible to correct color shift and distortion that occurs in an original image due to a delay in conveying the original.

[0098] 3. Third Embodiment The third embodiment will now be described. The first embodiment consists of only an MFP 1, which is equipped with a document transport unit 7 and an image input unit 9. In contrast, an image processing system 400 according to the third embodiment consists of an image processing device 1A and an image input device 1B, and the image processing device 1A does not have the document transport unit 7 or the image input unit 9.

[0099] Image processing device 1A is, for example, a personal computer such as a laptop computer or a desktop computer, a workstation, a tablet, etc. Image processing device 1A includes a display unit 3A, an operation unit 5A, a communication unit 13A, a connection unit 15A, a control unit 17A, and a storage unit 19A. Display unit 3A, operation unit 5A, communication unit 13A, connection unit 15A, control unit 17A, and storage unit 19A are similar to display unit 3, operation unit 5, communication unit 13, connection unit 15, control unit 17, and storage unit 19, respectively. Image processing device 1A is connected to image input device 1B via connections 15A and 15A.

[0100] Image input device 1B is, for example, a color scanner device. Image input device 1B performs an operation corresponding to step S1 in FIG. 5. In image input device 1B, control unit 17 uses document feed unit 7 to transport a document to image input unit 9. Next, control unit 17 reads the document using image input unit 9 to generate a document image. Next, control unit 17 uses connection unit 15 to transmit data of the document image to image processing device 1A.

[0101] In image processing device 1A, when connection unit 15A receives data of the original image, control unit 17A performs operations corresponding to step S3 and subsequent steps in FIG. 5 on the received data of the original image. The destination of the message in step S9 is display unit 3A. The destination of the original image in step S11 may be, for example, display unit 3A, memory unit 19A, another device connected via connection unit 15A (e.g., image input device 1B), or another device connected via communication unit 13A and a communication line.

[0102] According to the third embodiment, even for an original image generated by an image input device 1B that is incapable of detecting color shift in an original image, the image processing device 1A can detect color shift in the original image.

[0103] [4. Fourth Embodiment] This embodiment is a modification of the second embodiment. In the second embodiment, a monochrome image is used as the original image. In contrast, in the fourth embodiment, a color original is used as the original image. FIG. 21 is a flowchart for explaining the operation of the MFP according to the fourth embodiment of the present disclosure. The operation of the fourth embodiment differs from the operation of the second embodiment (the flowchart in FIG. 10) in that it includes steps S51 and S53. The control unit 17 transports a color document to the image input unit 9 using the document transport unit 7, and generates a document image from the color document using the image input unit 9 (step S21). Next, the control unit 17 performs region separation processing to detect black regions (regions consisting only of black, such as black text or solid black), the document background, and other regions from the document image (step S51). Next, the control unit 17 identifies black regions from each region separated in step S51 (step S53). Next, the control unit 17 detects color shifts in the identified black regions (step S23). The detection method is the same as that used for the document image in the second embodiment. Next, the control unit 17 generates a document image in which the detected color shifts are corrected to colors that would occur if no color shifts occurred (step S25). At this time, the control unit 17 corrects the color shifts in the document image at the Y coordinate where color shifts were detected in the black regions, assuming that color shifts occur not only in the black regions but across the entire width of the document image. The correction method is the same as that used for the document image in the second embodiment. Next, the control unit 17 detects distortion of the original image based on the original image after the color shift has been corrected (step S27), and then generates an original image in which the detected distortion has been corrected (step S29). According to this embodiment, it is possible to correct color misregistration in an original image generated by reading a color original.

[0104] [5. Fifth Embodiment] The fifth embodiment is a modification of the second embodiment. In the fourth embodiment, in order to handle color originals, area separation processing is performed on the original image and the boundary between black and white areas is identified, thereby detecting color shifts in the black areas of the original image, and based on this, color shifts in the entire original image are detected and corrected. In the fifth embodiment, a different method is used to handle color originals.

[0105] FIG. 22 is a diagram illustrating a medium 501 used when creating a color document in a modification of the fifth embodiment of the present disclosure. The medium 501 is a medium for drawing characters, images, etc. of a document, such as copy paper. The medium 501 has a document field 503 and black lines 505. The document field 503 is an area for drawing characters, images, etc. that will become the document. The black lines 505 are black lines formed outside the margin of the document field 503, regardless of the content of the document. The black lines 505 are formed at equal intervals in a direction perpendicular to the sub-scanning direction. It is preferable to form as many black lines 505 as possible, as long as the three-line image sensor 9a can distinguish each black line 505.

[0106] In the MFP1 of the second embodiment, when a medium 501 with a color original drawn in the original field 503 is read, the MFP1 can detect color shift of the black line 505. Based on this, the MFP1 can correct the color shift of the color original image.

[0107] [6. Modifications] The present disclosure is not limited to the above-described embodiments and variations, and various modifications are possible. In other words, embodiments obtained by combining appropriately modified technical means within the scope of the gist of the present disclosure are also included in the technical scope of the present disclosure.

[0108] In the second embodiment, referring to FIG. 18 , after estimating the delay position of the R pixel, the delay positions of the G pixel and the B pixel are estimated based on the gap between the color sensors. However, the R pixel is not necessarily the first pixel to be estimated. A table similar to that shown in FIG. 18A may be prepared for the delay of the G pixel, and after estimating the delay position of the G pixel, the delay positions of the B pixel and the R pixel may be estimated based on the gap between the color sensors. Similarly, a table similar to that shown in FIG. 18A may be prepared for the delay of the B pixel, and after estimating the delay position of the B pixel, the delay positions of the G pixel and the R pixel may be estimated based on the gap between the color sensors. Furthermore, instead of estimating the delay positions of pixels of two other colors based on the estimated delay position of a pixel of a specific color and the gap between the color sensors, a table similar to that shown in FIG. 18A may be prepared for each of the RGB colors, and the delay positions of the RGB pixels may be estimated based on the corresponding table.

[0109] In the third embodiment, image processing device 1A acquires data of the document image via connection unit 15A, but the method of acquiring the document image data is not limited to this. For example, document image data may be received from image input device 1B via communication unit 13A, a communication line, and communication unit 13. Alternatively, image input device 1B may store the document image data in an external storage device (e.g., a USB (Universal Serial Bus) memory) not shown connected to connection unit 15, and connect the external storage device to connection unit 15A of image processing device 1A to acquire the document image data.

[0110] The programs that run on each device in the embodiments are programs that control the CPU, etc. (programs that make a computer function) so as to realize the functions of the above-described embodiments. Information handled by these devices is temporarily stored in a temporary storage device (e.g., RAM) during processing, and then stored in various storage devices such as ROMs (Read Only Memories) and HDDs, and is read, modified, and written by the CPU as needed.

[0111] Here, the recording medium for storing the program may be any of semiconductor media (e.g., ROM, non-volatile memory card, etc.), optical recording media / magneto-optical recording media (e.g., DVD (Digital Versatile Disc), MO (Magneto Optical Disc), MD (Mini Disc), CD (Compact Disc), BD (Blu-ray (registered trademark) Disc), etc.), magnetic recording media (e.g., magnetic tape, flexible disk, etc.), etc. Furthermore, not only are the functions of the above-described embodiments realized by executing the loaded program, but the functions of the present disclosure may also be realized by processing in cooperation with an operating system or other application programs, etc., based on instructions from the program.

[0112] Furthermore, when distributing the program on the market, the program can be stored in a portable recording medium and distributed, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is also included in the present disclosure. [Explanation of symbols]

[0113] 1 MFP(Multi-Function Printer / Peripheral) 1A Image processing device 1B Image input device 3 Display section 5 Control section 7 Document transport section 9 Image input section 9a 3-line image sensor 11 Image forming unit 13 Communications Department 15 Connection 17 Control Unit 19 Memory section 123 manuscripts 123B Black area 123W white area 125 Black and White Border 131, 151, 173, 291, 321, 351 Original images 133, 153, 167, 293, 295, 323 (including color shift) areas 133B Blue channel component 133R Red channel component 135A, 135B straight line 135, 137, 165a, 165b, 165c, 165d, 165e, 293a-293g, 295a-295i Color misalignment areas 141 Color shift width 201B (for blue) CCD (Charge Coupled Device) 201G (for green) CCD 201R (for red) CCD 203, 209, 211, 213, 215, 217, 219, 231, 233, 235, 237, 239, 241, 245, 261, 263, 265, 267, 269, 271, 275, 371, 373, 375, 377, 379, 381 values 205, 207 Color sensor gap 243, 273 range Columns 246, 248, 277, 279 247 Cyan (C) 249 Yellow (Yellow, Y) 301, 305 Black area 303, 307 Cyan area 324 Arrow 325 (R, G and B) Falling Points 327 (G and B) Rising Point 329 (R) Rising Point 341, 342 distance 353B B pixel delay position 353G G pixel delay position 353R R pixel delay position 355a~355e Arrows 400 Image Input System 501 Medium 503 Manuscript column 505 Black Line LB Blue (B) line sensor LG Green (G) Line Sensor LR Red (R) line sensor

Claims

1. In the image processing device, an image processing unit and an image acquisition unit that acquires a document image generated from a document; the document image is made up of a first image, a second image, and a third image, each of which corresponds to one of three different color components of the document; the first image, the second image, and the third image are generated in order by using a first sensor, a second sensor, and a third sensor, which are image sensors that read three different color components and are arranged in a predetermined order along a transport direction of the document, respectively; The image processing unit comparing the first image, the second image, and the third image to one another; determining whether or not the original image has a color shift from the original based on the result of the comparison; Image processing device.

2. The image processing unit estimating a position where a color shift from the original occurs in the original image based on a change in pixel value of the original image in the conveying direction; estimating a pixel in the document image where a delay has occurred based on the estimated position; The image processing device according to claim 1 .

3. The image processing unit comparing rising edges and falling edges of changes in pixel values ​​of the first image, the second image, and the third image in the transport direction; Based on the result of the comparison, a position where a color shift from the original has occurred is estimated. The image processing device according to claim 2 .

4. determining a color appearing in the original image at a rising edge or a falling edge of a change in pixel value of the first image, the second image, and the third image; estimating a magnitude of pixel delay in any of the first image, the second image, and the third image based on the determined color; The image processing device according to claim 3 .

5. The image acquisition unit includes an image input unit, the image input unit includes a first sensor, a second sensor, and a third sensor, which are image sensors arranged in a predetermined order along a conveyance direction of the document and read three different color components; The image processing device according to claim 1 .

6. the image acquisition unit includes a connection unit for connecting the image processing device to another device, or a communication unit for connecting the image processing device to another device via a communication line; acquiring the document image from the other device via the connection unit or the communication unit; The image processing device according to claim 1 .

7. 1. A control method for an image processing device, comprising: an original image generated from an original is acquired, the original image being composed of a first image, a second image, and a third image, each of which corresponds to one of three different color components of the original, the first image, the second image, and the third image being generated in order by a first sensor, a second sensor, and a third sensor, which are image sensors that read the three different color components and are arranged in a predetermined order along a transport direction of the original; comparing the first image, the second image, and the third image to one another; determining whether or not the original image has a color shift from the original based on the result of the comparison; A method for controlling an image processing device.

Images