JP2016092475A - Image processing system and image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing system and an image reader, which suppress deterioration of image quality.SOLUTION: An image processing section 20 mainly includes: an edge determination section 20b; a color determination section 20d; and a resolution conversion section 20e. The edge determination section 20b determines whether target pixels are equivalent to an edge part on an upstream in a sub-scanning direction, to an edge part on a downstream in the sub-scanning direction or a non-edge part with pixels of respective colors corresponding to reading operation for one line as targets. The color determination section 20d determines color shift directions of the target pixels and performs color/black determination for determining whether the target pixels are black or not in response to pixel values of the respective colors on the target pixels and a color/black determination condition for determining whether the target pixels are color or black. When the color determination section 20d determines that the target pixels are black, the resolution conversion section 20e corrects a sub-scanning direction width of an image, which is expressed by image data for one line, in response to a determination result by the edge determination section 20b and a determination result of color shift determination by the color determination section 20d.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image processing apparatus and an image reading apparatus.

  2. Description of the Related Art Conventionally, an image reading apparatus for reading an image on a document is known, and the image reading apparatus is mounted and used in, for example, an image forming apparatus. The image reading apparatus mainly includes a plurality of light sources corresponding to different colors, an image sensor shared by each color, and an image processing unit (image processing apparatus). The plurality of light sources are composed of, for example, three light sources including red (R), green (G), and blue (B).

  In this image reading apparatus, corresponding to the reading operation for one line, the RGB light sources are sequentially turned on and the reflected light from the original is sequentially read by the image sensor. An electrical signal (image signal) corresponding to the intensity of the reflected light is sequentially output from the image sensor for each color. When each color image signal is digitally converted, it is sequentially input to the image processing unit as image data. The image processing unit generates image data for one line by aggregating pixel values of RGB colors.

  For example, Patent Document 1 discloses an image reading apparatus that can suppress deterioration in image quality. According to this image reading apparatus, attention is paid to pixel values of each color of RGB which are pixel values for one line, and it is determined whether the pixel of interest is monochrome or color. This determination is performed by the pixels on the line before and after the target pixel. If the target pixel is color and the preceding and following pixels are determined to be monochrome, the target pixel is determined to be an abnormal monochrome pixel. Then, the pixel value of the target pixel is corrected to a desired monochrome pixel value. In the correction process, it is detected at which position during the lighting period of each RGB color the black and white of the document is switched, and the color and correction value to be corrected are determined according to the detection result.

JP 2013-131861 A

  According to the technique disclosed in Patent Document 1, although effective in suppressing color misregistration, the line width of the read image becomes thicker than that of the read image on the actually read document. There is a disadvantage that the position of the center of gravity of the image is shifted. For this reason, there is a problem that image quality is deteriorated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image processing apparatus and an image reading apparatus capable of suppressing deterioration in image quality.

  In order to solve such a problem, the first invention performs a lighting operation of sequentially turning on a plurality of light sources that emit light of different colors corresponding to a reading operation for one line and is relative to the sub-scanning direction. Provided is an image processing apparatus for inputting image data of each color obtained by sequentially reading light of each color that has acted on a moving read image by an image sensor and generating image data for one line. In this image processing apparatus, for each color pixel corresponding to a reading operation for one line, the target pixel corresponds to an upstream edge portion in the sub-scanning direction, or a downstream edge portion in the sub-scanning direction. An edge determination unit that determines whether the pixel corresponds to a non-edge portion, a color shift determination unit that determines the direction of color shift of the target pixel, a pixel value of each color related to the target pixel, and whether the target pixel is a color When the target pixel is determined to be black by the color black determination unit that determines whether the target pixel is black or not based on the color black determination condition that distinguishes whether the target pixel is black or not And a correction unit that corrects the sub-scanning direction width of the image represented by the image data for one line based on the determination result of the edge determination unit and the determination result of the color misregistration determination unit.

  Here, the first invention further includes a condition switching unit that switches the determination width determined as black by the color black determination unit by setting the color black determination condition based on the determination result of the edge determination unit. Is preferred.

  In the first aspect of the invention, the correction unit increases the resolution of the image data for one line in the sub-scanning direction, and in the sub-scanning direction according to the determination result of the edge determination unit and the determination result of the color shift determination unit. It is preferable to deviate the image to the upstream side or the downstream side in the sub-scanning direction.

  In the first invention, the correction unit determines that an upstream edge portion in the sub-scanning direction is determined, and color misregistration in a color direction caused by a light source with a fast lighting order among a plurality of light sources is determined. The image is biased downstream in the sub-scanning direction, while the downstream edge portion in the sub-scanning direction is determined, and color misregistration in the color direction caused by a light source with a slow lighting order among a plurality of light sources is determined. In such a case, it is preferable to deviate the image to the upstream side in the sub-scanning direction.

  Further, in the second invention, corresponding to the reading operation for one line, a plurality of light sources each having a different color are sequentially turned on to sequentially irradiate light of each color on a read image that is relatively moved in the sub-scanning direction. A light source unit, a sensor control unit that sequentially reads light of each color that has acted on the read image with an image sensor, and outputs image data of each color corresponding to a plurality of light sources, and inputs image data of each color, and an image for one line An image reading apparatus including an image processing unit that generates data is provided. Here, for each color pixel corresponding to the reading operation for one line, the image processing unit corresponds to the upstream edge portion in the sub-scanning direction or the downstream side in the sub-scanning direction. An edge determination unit that determines whether it corresponds to an edge portion or a non-edge portion, a color shift determination unit that determines the direction of color shift of the target pixel, a pixel value of each color related to the target pixel, and the target pixel Based on a color / black determination condition for distinguishing between color and black, a color / black determination unit that determines whether the target pixel is black or not, and the color / black determination unit determines that the target pixel is black A correction unit that corrects the sub-scanning direction width of the image represented by the image data for one line based on the determination result of the edge determination unit and the determination result of the color misregistration determination unit.

  According to the present invention, the line width tendency of the read image can be grasped by referring to the determination result of the edge determination unit and the determination result of the color misregistration determination unit. In addition, the sub-scanning direction width of the image represented by the image data for one line can be corrected. Thereby, it can suppress that the line width of an image expands or a gravity center position shifts | deviates. As a result, deterioration in image quality can be suppressed.

1 is an explanatory diagram schematically showing the configuration of an image forming apparatus according to a first embodiment; Block diagram showing the configuration of the image reading apparatus Explanatory drawing which shows lighting control of a light source unit Explanatory drawing showing the mechanism of color misregistration in the sub-scanning direction A flowchart showing a procedure of image processing according to the present embodiment. Explanatory drawing which shows typically the black-and-white determination conditions which concern on 1st Embodiment. Explanatory drawing which shows the concept of the resolution conversion process which concerns on 1st Embodiment. Explanatory drawing which shows the concept of the resolution conversion process which concerns on 2nd Embodiment.

(First embodiment)
FIG. 1 is an explanatory diagram schematically illustrating a configuration of an image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 according to the first embodiment is an electrophotographic image forming apparatus such as a copying machine, for example, and is arranged in full color by arranging a plurality of photoconductors facing one intermediate transfer belt in the vertical direction. This is a so-called tandem type color image forming apparatus. The image forming apparatus 1 mainly includes an image reading device 10, image forming units 30Y, 30M, 30C, and 30K, a fixing device 50, and a control unit 70.

  The image forming apparatus 1 includes an automatic document feeder ADF at the top thereof. The document D is placed on the document placing table 25 of the automatic document feeder ADF. The documents D are separated one by one, sent out to the document transport path, and transported by the transport drum 26. The first transport guide G1 and the document discharge roller 27 discharge the document D transported by the transport drum 26 to the document discharge tray 28.

  The image reading apparatus 10 reads the document D transported by the transport drum 26. The image reading apparatus 10 irradiates the original D with the light source unit 15 at the original reading position RP. When the reflected light reflected by the document D is guided by the plurality of mirrors 11, 12, and 13, it is imaged on the light receiving surface of the image sensor CCD by the imaging optical system 14. The image sensor CCD photoelectrically converts incident light and outputs a predetermined image signal. The image processing unit 20 inputs image data obtained by digitally converting an image signal, performs predetermined processing on the image data, and creates image data used for image formation. Details of the image reading apparatus 10 will be described later.

  The image forming units 30Y, 30M, 30C, and 30K are an image forming unit 30Y that forms a yellow (Y) image, an image forming unit 30M that forms a magenta (M) image, and an image that forms a cyan (C) image. The forming unit 30C corresponds to the image forming unit 30K that forms a black (K) image.

  The image forming unit 30Y includes a photosensitive drum 1Y and a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a drum cleaner 5Y arranged around the photosensitive drum 1Y. Similarly, the image forming units 30M, 30C, and 30K include photoconductor drums 1M, 1C, and 1K and charging units 2M, 2C, and 2K, optical writing units 3M, 3C, and 3K, and developing devices 4M, disposed around the photosensitive drums 1M, 1C, and 1K. 4C, 4K and drum cleaners 5M, 5C, 5K.

  The surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K are uniformly charged by the charging units 2Y, 2M, 2C, and 2K, and by scanning exposure by the optical writing units 3Y, 3M, 3C, and 3K, Latent images are formed on the photosensitive drums 1Y, 1M, 1C, and 1K. Further, the developing devices 4Y, 4M, 4C, and 4K develop the latent images on the photosensitive drums 1Y, 1M, 1C, and 1K by developing with toner. As a result, an image (toner image) of a predetermined color corresponding to any of yellow, magenta, cyan, and black is formed on the photosensitive drums 1Y, 1M, 1C, and 1K. Images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are sequentially transferred to predetermined positions on the intermediate transfer belt 6 by primary transfer rollers 7Y, 7M, 7C, and 7K.

  The image transferred onto the intermediate transfer belt 6 is transferred by a secondary transfer roller 9 onto a sheet P that is conveyed at a predetermined timing by a sheet conveying unit 40 described later. The secondary transfer roller 9 is disposed in pressure contact with the intermediate transfer belt 6 to form a nip (transfer nip), and transfers the image onto the paper P while conveying the paper P.

  The paper transport unit 40 transports the paper P along the transport path. The paper P is stored in the paper supply tray 41, and the paper P stored in the paper supply tray 41 is taken in by the paper supply unit 42 and sent out to the transport path. A plurality of transport means for transporting the paper P is provided in the transport path. Each conveying means is constituted by, for example, a pair of rollers pressed against each other, and at least one of the rollers is rotationally driven through an electric motor as a driving means.

  The fixing device 50 is a device that performs a fixing process for fixing the image on the paper P to which the image has been transferred. The fixing device 50 includes a pair of fixing members that form a nip (fixing nip) by being placed in pressure contact with each other, and a heating unit that heats the fixing member. For example, a pair of fixing rollers 51 and 52 can be used as the pair of fixing members. The individual fixing rollers 51 and 52 are configured to be rotatable, and at least one of the rollers (for example, the fixing roller 52) is rotationally driven through a driving motor (not shown) that is a driving unit. For example, a halogen lamp 53 can be used as the heating means. The fixing device 50 fixes the image on the paper P by performing pressure fixing with a pair of fixing rollers 51 and 52 and heat fixing with a halogen lamp 53.

  The paper P subjected to the fixing process by the fixing device 50 is discharged by a paper discharge roller 43 to a paper discharge tray 44 attached to the outer side surface of the housing. When image formation is performed on both sides of the paper P, the paper P on which image formation has been completed on the paper surface is conveyed by the switching gate 45 to the reversing roller 46 below. The reversing roller 46 pinches the trailing edge of the conveyed paper P, reverses the paper P by reverse feeding, and sends it to the refeed conveyance path. The paper P sent out to the refeed conveyance path is conveyed by a plurality of refeeding conveyance means and returns to the transfer position.

  The control unit 70 has a function of controlling the image forming apparatus 1 in an integrated manner, and a microcomputer mainly composed of a CPU, a ROM, a RAM, and an I / O interface can be used. The control unit 70 forms a predetermined image on the paper P by controlling the image forming units 30Y, 30M, 30C, 30K and the like.

  FIG. 2 is a block diagram illustrating a configuration of the image reading apparatus 10 according to the present embodiment. The image reading apparatus 10 is mainly configured by a light source unit 15, a CPU 16, a ROM 17, a RAM 18, a CCD control unit 19, an image processing unit 20, and an image memory 21.

  The light source unit 15 is composed of a plurality of light sources that emit light of different colors, and irradiates the document D with light of a predetermined color selected from the plurality of light sources. In the present embodiment, the light source unit 15 includes three light sources 15R, 15G, and 15B corresponding to three colors of red (R), green (G), and blue (B). For example, LEDs can be used for the individual light sources 15R, 15G, and 15B. Light from each of the light sources 15R, 15G, and 15B is guided by a light guide (not shown) and applied to the document D as line-shaped light corresponding to the main scanning direction.

  The CPU 16 controls the entire image reading apparatus 10. When the CPU 16 reads the program and data stored in the ROM 17, the CPU 16 develops the program and data on the RAM 18, and executes this to execute various processes.

  FIG. 3 is an explanatory diagram showing lighting control of the light source unit 15. In relation to the present embodiment, the CPU 16 performs lighting control for the light source unit 15. Specifically, the CPU 16 sequentially outputs lighting signals to the three light sources 15R, 15G, and 15B (R lighting signal, G lighting signal, and B lighting signal), and sequentially lights the three light sources 15R, 15G, and 15B. Perform the lighting operation. With this lighting operation, RGB light is sequentially irradiated onto the document D (read image) that is transported by the transport drum 26 and relatively moves in the sub-scanning direction (direction intersecting the main scanning direction). This lighting operation is performed once corresponding to the reading operation for one line in the main scanning direction, and the CPU 16 repeatedly performs the lighting operation corresponding to the reading period of the document D (lighting control). Although the lighting order of the three light sources 15R, 15G, and 15B is arbitrary, in this embodiment, lighting is performed in the order of the light sources 15R corresponding to R, the light sources 15G corresponding to G, and the light source 15B corresponding to B. Shall.

  The ROM 17 stores various programs executed by the CPU 16 in the form of program codes readable by the CPU 16. The ROM 17 stores data necessary for executing the program.

  The RAM 18 is a memory serving as a working storage area.

  The CCD controller 19 includes an image sensor CCD, an analog processing circuit (not shown), and the like. The image sensor CCD is a monochrome image sensor in which a plurality of photoelectric conversion elements are arranged in a line for each pixel and arranged substantially parallel to the main scanning direction, and are shared by RGB colors. The reading operation of each element in the image sensor CCD is synchronized based on a main scanning synchronization signal (see FIG. 3).

  As described above, the light (reflected light) that has acted on the document D enters the image sensor CCD. The image sensor CCD performs a reading operation corresponding to the irradiation of light from the light source unit 15, thereby generating an electrical signal corresponding to the intensity of reflected light from the document D as an image (luminance) signal. The generated image signal is converted into a digital signal by an analog processing circuit, and the converted image data is output to the image processing unit 20.

  Here, the image data is a set of pixel values of each pixel, and is density data at a reading position (main scanning line) on the document D by light emitted from the light source unit 15. Each pixel value expresses its density (shading) by, for example, 256 gradations.

  As described above, in the reading operation for one line, the light sources 15R, 15G, and 15B of each color of RGB are sequentially turned on with one lighting operation. As shown in FIG. 3, the CCD controller 19 generates R image data, G image data, and B image data in a line sequential manner. Then, by repeating the lighting operation, three pieces of RGB image data are sequentially generated for each lighting operation.

  In FIG. 3, each of R0, R1, and R2 represents image data (R image data) corresponding to a reading operation by the R light source 15R. Similarly, each of G0, G1, and G2 indicates image data (G image data) corresponding to a reading operation by the G light source 15G, and each of B0, B1, and B2 is a reading operation by the B light source 15B. The corresponding image data (B image data) is shown.

  The image processing unit 20 receives image data from the CCD control unit 19, performs necessary processing on the image data, and stores the image data in the image memory 21. Specifically, the image processing unit 20 inputs RGB image data corresponding to a reading operation for one line, and generates image data for one line based on these three image data. For example, by reading each RGB color in 1800 dpi units, the resolution of the image data for one line corresponds to 600 dpi.

  The image processing unit 20 includes an inter-line correction unit 20a, an edge determination unit 20b, a condition switching unit 20c, a color determination unit 20d, and a resolution conversion unit 20e when this is viewed functionally.

  The interline correction unit 20a inputs RGB image data for one line and performs interline correction. Here, the inter-line correction is a process for correcting a phase shift of the RGB image signal caused by a shift of each RGB reading position (main scanning line). The RGB image data for one line processed by the interline correction unit 20a is output to the edge determination unit 20b, the color determination unit 20d, and the resolution conversion unit 20e, respectively.

  The edge determination unit 20b targets one line of RGB pixels (three pixels in the sub-scanning direction), and the target pixel corresponds to an upstream edge part in the sub-scanning direction or downstream in the sub-scanning direction. It is determined whether it corresponds to a side edge portion or a non-edge portion that does not include an edge. Here, an edge refers to a portion where the amount of change in pixel value between adjacent pixels is large, and is determined by comparing the amount of change with a preset determination value. The upstream edge portion in the sub-scanning direction includes an edge in which the upstream pixel in the sub-scanning direction is white and the downstream pixel is black, and the downstream edge portion in the sub-scanning direction is the sub-scanning direction. This includes an edge in which the upstream pixel in the direction is black and the downstream pixel value is white.

  The condition switching unit 20c holds a plurality of color / black determination conditions. The color black determination condition is for performing color black determination for distinguishing whether the target pixel is color or black, and is used by the color determination unit 20d described later. The condition switching unit 20c can switch the determination width determined as black by the color determination unit 20d by setting the color black determination condition based on the determination result of the edge determination unit 20b.

  The color determination unit 20d performs color black determination as to whether or not the target pixel is black based on the RGB pixel values related to the target pixel and the color black determination conditions set by the condition switching unit 20c (color black Determination unit). In the present embodiment, the color determination unit 20d performs color black determination by converting RGB pixel values related to the target pixel into a predetermined color space. Specifically, the color determination unit 20d generates CbCr color space data in which RGB pixel values related to the target pixel are converted into, for example, a CbCr color space. Here, the color black determination condition described above is a boundary condition for distinguishing between color and black in the CbCr color space. Therefore, the color determination unit 20d compares the CbCr color space data with the color black determination condition to determine whether the target pixel is black or color.

  The color determination unit 20d determines the direction of color shift of the target pixel based on the CbCr color space data (color shift determination unit). The color misregistration is specified as R, Y, C, B, and other five regions based on angles (polar coordinates) defined on coordinates in the CbCr color space.

  When the target pixel is determined to be black by the color determination unit 20d (color black determination unit), the resolution conversion unit 20e increases the resolution of the image data for one line in the sub-scanning direction, and the determination result of the edge determination unit 20b. Depending on the determination result of the color determination unit 20d (color misregistration determination unit), the image is biased upstream in the sub-scanning direction or downstream in the sub-scanning direction (resolution conversion processing). The resolution conversion unit 20e corrects the sub-scanning direction width of the image represented by the image data for one line through such resolution conversion processing.

  The image memory 21 stores image data for one line sequentially generated by the image processing unit 20. The image memory 21 has a capacity capable of storing image data for a plurality of lines corresponding to the maximum size original D that can be read. A group of image data for one line (a set of image data for one line) corresponding to the document D is read by the CPU 16 and output to the control unit 70.

  Hereinafter, prior to description of image processing executed by the image processing unit 20, a mechanism of occurrence of color misregistration in the sub-scanning direction will be described. Here, FIG. 4 is an explanatory diagram showing a mechanism of occurrence of color misregistration in the sub-scanning direction. In the figure, (a) is an explanatory view schematically showing a document D including a read image, and the read image (for example, a black line) is indicated by a black rectangle. In FIG. 2, (b) is an explanatory diagram schematically showing a group of image data for one line corresponding to the reading result of the document D.

  For the document D, a reading operation is performed from top to bottom in the sub-scanning direction for each line. In the reading operation for one line, each RGB color is read in 1800 dpi units. RGB image data is obtained according to the reading operation for one line, and image data for one line corresponding to 600 dpi is obtained based on these image data.

  As shown in FIG. 4A, a total of three black lines (black rectangles) that are read images are arranged on the document D. Specifically, three black lines corresponding to 2 dots (600 dpi) in the sub-scanning direction are arranged at different positions in the sub-scanning direction.

  First, focus on the black line (read image) located first from the left. In one line corresponding to the n-th reading operation, the R main scanning line is white, and the G and B main scanning lines are black. In one line corresponding to the (n + 1) th reading operation, each of the R, G, and B main scanning lines is black. In one line corresponding to the (n + 2) th reading operation, black is displayed on the R main scanning line, and white is displayed on each of the G and B main scanning lines. In this case, the target pixel related to the nth one line corresponds to an upstream edge portion in the sub-scanning direction, the target pixel related to the (n + 1) th first line corresponds to a non-edge portion, and the (n + 2) th 1 The target pixel related to the line corresponds to the downstream edge portion in the sub-scanning direction.

  In the reading result shown in FIG. 4B, the target pixel related to the nth first line becomes red by collecting the RGB pixels. The target pixel related to the (n + 1) th line becomes black by collecting the RGB pixels. In the target pixel relating to the (n + 2) th one line, the RGB pixels are aggregated to be substantially cyan. Thus, color misregistration occurs in each of the nth and n + 2th lines.

  Next, attention is focused on the black line located second from the left. In one line corresponding to the n-th reading operation, the R and G main scanning lines are white, and the B main scanning line is black. In one line corresponding to the (n + 1) th reading operation, each of the R, G, and B main scanning lines is black. In one line corresponding to the (n + 2) th reading operation, the R and G main scanning lines are black, and the B main scanning line is white. In this case, the target pixel related to the nth one line corresponds to an upstream edge portion in the sub-scanning direction, the target pixel related to the (n + 1) th first line corresponds to a non-edge portion, and the (n + 2) th 1 The target pixel related to the line corresponds to the downstream edge portion in the sub-scanning direction.

  In the reading result shown in FIG. 5B, the target pixel related to the nth one line becomes substantially yellow by collecting RGB pixels. The target pixel related to the (n + 1) th line becomes black by collecting the RGB pixels. The target pixel related to the (n + 2) th line is substantially blue by collecting RGB pixels. Thus, color misregistration occurs in each of the nth and n + 2th lines.

  Also, pay attention to the black line located third from the left. In one line corresponding to the (n + 1) th reading operation, each of the R, G, and B main scanning lines is black. In one line corresponding to the (n + 2) th reading operation, each of the R, G, and B main scanning lines is black. In this case, the target pixel related to the (n + 1) th line does not correspond to either the upstream edge portion in the sub-scanning direction or the downstream edge portion in the sub-scanning direction, and corresponds to a non-edge portion. Similarly, the target pixel related to the (n + 2) th one line corresponds to a non-edge portion.

  In the reading result shown in FIG. 4B, the target pixel relating to the (n + 1) th line becomes black by collecting the RGB pixels. Further, the target pixel related to the (n + 2) th one line becomes black by collecting the RGB pixels. Thus, no color misregistration occurs in each of the n + 1th and n + 2th lines.

  As described above, due to the upstream edge portion in the sub-scanning direction, color shift occurs in the red to yellow direction in the target pixel, and in the target pixel due to the downstream edge portion in the sub-scanning direction. ~ Color shift occurs in the cyan direction. However, the tendency of color misregistration due to the edge portion is due to the lighting order of RGB, and when the lighting order is different, the tendency of different color misregistration is shown.

  Also, assuming that the read image is formed in black, what kind of chipping (white portion) is present in the read image within the reading range for one line from the tendency of such color misregistration. Can be judged. For example, when the target pixel corresponds to the upstream edge portion in the sub-scanning direction and the color shift corresponds to red, one line corresponding to 1800 dpi is missing in the read image for one line ( It can be determined that (white) is on the upstream side. Similarly, when the target pixel corresponds to an upstream edge portion in the sub-scanning direction and the color shift corresponds to yellow, two lines corresponding to 1800 dpi are missing in the read image for one line. It can be determined that (white) is on the upstream side.

  Similarly, when the target pixel corresponds to the edge portion on the downstream side in the sub-scanning direction and the color shift corresponds to blue, one line corresponding to 1800 dpi is missing in the read image for one line. It can be determined that (white) is on the downstream side. Similarly, when the target pixel corresponds to the downstream edge portion in the sub-scanning direction and the color shift corresponds to cyan, two 1800 dpi equivalent lines are missing in the read image for one line. It can be determined that (white) is on the downstream side.

  FIG. 5 is a flowchart showing a procedure of image processing in the image reading apparatus 10 applied to the image forming apparatus 1 according to the present embodiment. The processing shown in this flowchart is executed by the image processing unit 20 in response to input of RGB image data corresponding to a reading operation for one line. Further, this process is executed for each pixel in the main scanning direction. Furthermore, it is assumed that the original D introduced into the image reading apparatus 10 has a read image formed in black.

First, in step 1 (S1), the inter-line correction unit 20a performs inter-line correction on the target pixel with respect to one line of RGB pixels (three pixels in the sub-scanning direction). Specifically, the line-to-line correction unit 20a corrects RGB pixel values by the following method.

  In the equation, n indicates a line position in the sub-scanning direction to be read.

  In step 2 (S2), the edge determination unit 20b performs edge determination. Specifically, the edge determination unit 20b determines whether the target pixel corresponds to an upstream edge portion in the sub-scanning direction, a downstream edge portion in the sub-scanning direction, or a non-edge that does not include an edge portion. It is determined whether it corresponds to a part.

  For example, taking the first black line (read image) from the left in FIG. 4A as an example, the target pixel related to the nth one line corresponds to the upstream edge portion in the sub-scanning direction, and n + 2 The target pixel related to the first line corresponds to the downstream edge portion in the sub-scanning direction. Further, the target pixel related to the (n + 1) th line corresponds to a non-edge portion.

  In step 3 (S3), the condition switching unit 20c switches the determination condition. The condition switching unit 20c holds a color black determination condition for the color determination unit 20d to perform color black determination. The condition switching unit 20c holds a standard color black determination condition, a color black determination condition applied to the upstream edge portion, and a color black determination condition applied to the downstream edge portion.

  6A and 6B are explanatory diagrams schematically showing the color black determination condition, in which FIG. 6A shows the standard color black determination condition Cs, and FIG. 6B shows the color black determination condition Cue applied to the upstream edge portion. , (C) shows the color black determination condition Cle to be applied to the downstream edge portion. Each color black determination condition Cs, Cue, Cle is set as a boundary condition for demarcating the boundary between color and black in the CbCr color space. Specifically, when the CbCr space data obtained by converting the target pixel (each pixel of RGB) into the CbCr space is positioned inside the color black determination conditions Cs, Cue, and Cle, the CbCr space data (target pixel) is black. It is determined. On the other hand, when the CbCr space data is positioned outside the color / black determination conditions Cs, Cue, and Cle, the CbCr space data (target pixel) is determined to be color.

  As shown in FIG. 5A, the standard color / black determination condition Cs is set, for example, in a circular shape centered on the origin of the coordinates in the CbCr color space.

  On the other hand, as shown in FIG. 4B, the color black determination condition Cue applied to the upstream edge portion is based on the standard color black determination condition Cs, and the range for black determination is a hue of red to yellow. It has been expanded to. As described above, the upstream edge portion in the sub-scanning direction tends to cause a color shift in the red to yellow direction. According to the color black determination condition Cue, it is easy to determine that the upstream edge portion in the sub-scanning direction is black.

  Further, as shown in FIG. 6C, the color black determination condition Cle applied to the downstream edge portion is based on the standard color black determination condition Cs, and the black determination range is a hue of blue to cyan. It has been expanded to. As described above, the edge portion on the downstream side in the sub-scanning direction tends to cause a color shift in the blue to cyan direction. According to this color black determination condition Cle, it is easy to determine that the downstream edge portion in the sub-scanning direction is black.

  In step 3, the condition switching unit 20c sets the color / black determination condition based on the determination result of the edge determination in step 2. Specifically, the condition switching unit 20c sets the color black determination condition Cue to apply the color black determination condition to the upstream edge when the target pixel corresponds to the upstream edge in the sub-scanning direction. Set. In addition, when the target pixel corresponds to the downstream edge portion in the sub-scanning direction, the condition switching unit 20c sets the color black determination condition to the color black determination condition Cle to be applied to the downstream edge portion. Furthermore, the condition switching unit 20c sets the color black determination condition to the standard color black determination condition Cs when the target pixel corresponds to a non-edge portion. By setting the color black determination condition of the condition switching unit 20c, the determination width determined as black by the color determination unit 20d is switched.

  In step 4 (S4), the color determination unit 20d converts the three pixel values related to the target pixel into CbCr color space data, and compares the converted CbCr color space data with the color black determination condition set in step 3 To do. Then, the color determination unit 20d determines whether or not the CbCr color space data (target pixel) is black (color black determination). In this process, if the CbCr color space data is included inside the color black determination condition set in step 3, the data is determined to be black. On the other hand, if the CbCr color space data is included outside the color black determination condition set in step 3, the data is determined to be color.

  In Step 4, the color determination unit 20d determines the direction of color shift related to the target pixel based on the CbCr color space data (color shift determination). Color misregistration is specified as R, Y, C, B, and five other regions from the angle (polar coordinates) on the coordinates of the data in the CbCr color space.

  In step 5 (S5), the resolution conversion unit 20e increases the resolution of the image data for one line in the sub-scanning direction (resolution conversion process). Then, the resolution conversion unit 20e biases the image to the upstream side in the sub-scanning direction or the downstream side in the sub-scanning direction according to the determination result of the edge determination unit 20b and the determination result of the color misregistration determination of the color determination unit 20d. Let

  In the present embodiment, the image data for one line is 600 dpi, and the resolution conversion unit 20e subdivides the image data for one line into three lines, upper, middle, and lower, by resolution conversion processing. The line image data is converted to a resolution equivalent to 1800 dpi. Here, FIG. 7 is an explanatory diagram showing the concept of resolution conversion processing. In FIG. 7, it is assumed that the pixel value “00” is white and “FF” is black.

  First, a case where the target pixel corresponds to the upstream edge portion in the sub-scanning direction and is determined to be black by the color determination unit 20d will be described. In this case, processing is performed to deviate the image downstream in the sub-scanning direction.

  As a first case, when the target pixel is color-shifted in the red (R) direction, the resolution conversion unit 20e displays an image in the downstream 2/3 range, that is, in the middle and lower two lines. A process of biasing is performed. In this case, the resolution conversion unit 20e develops data in three lines using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, the resolution conversion unit 20e sets “FF” for the lower line. For the intermediate line, the resolution conversion unit 20e sets “3 × (X−85)” when the G pixel value X is 85 or more, and “00” when the G pixel value X is smaller than 85. Set. For the upper line, the resolution conversion unit 20 e sets “3 × (X−170)” when the G pixel value X is 170 or more, and sets “3 × (X−170)” when the G pixel value X is smaller than 170. 00 ”is set.

  As a second case, when the target pixel is color-shifted in the yellow (Y) direction, the resolution conversion unit 20e biases the image to a downstream 1/3 range, that is, one line on the lower side. Process. Similarly, the resolution conversion unit 20e develops data in three lines using the G pixel value that is lit second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, for the lower line, the resolution conversion unit 20e sets “FF” when the G pixel value X is 85 or more, and sets “3 ×” when the G pixel value X is smaller than 85. X ”is set. For the intermediate line, the resolution conversion unit 20e sets “3 × (X−85)” when the G pixel value X is 85 or more, and sets “3 × (X−85)” when the G pixel value X is smaller than 85. 00 ”is set. For the upper one line, the resolution conversion unit 20e sets “00”.

  On the other hand, if the target pixel corresponds to the upstream edge portion in the sub-scanning direction, but does not fall into the above two cases, the resolution conversion unit 20e uses the RGB pixel values and sub-pixels according to the density. Processing to deviate the image downstream in the scanning direction is performed.

  Specifically, for the lower line, the resolution conversion unit 20e sets “FF” when any pixel value X of RGB is larger than 85, and sets “3” when the pixel value X is 85 or less. “X” is set. For the intermediate line, the resolution conversion unit 20e sets “FF” when any pixel value X of RGB is larger than 170, and “3 × (X−85)” when the pixel value X is 170 or less. "Is set. For the upper line, the resolution conversion unit 20e sets “3 × (X−170)” when any pixel value X of RGB is larger than 170, and when the pixel value X is 170 or less. “00” is set.

  In contrast, a case will be described in which the target pixel corresponds to the downstream edge portion in the sub-scanning direction and is determined to be black by the color determination unit 20d. In this case, processing is performed to deviate the image upstream in the sub-scanning direction.

  As a first case, when the target pixel is color-shifted in the cyan (C) direction, the resolution conversion unit 20e performs processing for biasing the image in the upstream one-third range, that is, one line on the upper side. I do. The resolution conversion unit 20e develops data on each line by using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, the resolution conversion unit 20e sets “00” for the lower line. For the intermediate line, the resolution conversion unit 20e sets “3 × (X−85)” when the G pixel value X is 85 or more, and “00” when the G pixel value X is smaller than 85. Set. For the upper line, the resolution conversion unit 20e sets “FF” when the G pixel value X is 85 or more, and sets “3 × X” when the G pixel value X is smaller than 85. To do.

  As a second case, when the target pixel is color-shifted in the blue (B) direction, the resolution conversion unit 20e defocuses the image in the upstream 2/3 range, that is, the middle and upper two lines. To perform the process. The resolution conversion unit 20e develops data on each line by using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, the resolution conversion unit 20e sets “FF” for the upper line. For the intermediate line, the resolution conversion unit 20e sets “3 × (X−85)” when the G pixel value X is 85 or more, and “00” when the G pixel value X is smaller than 85. Set. For the lower line, the resolution conversion unit 20e sets “3 × (X−170)” when the G pixel value X is 170 or more, and the G pixel value X is smaller than 170. “00” is set.

  On the other hand, when the target pixel corresponds to the edge portion on the downstream side in the sub-scanning direction but does not correspond to the above two cases, the resolution conversion unit 20e uses pixel values of each color of RGB, and according to the density thereof Processing to deviate the image to the upstream side in the sub-scanning direction is performed.

  Specifically, for the upper line, the resolution conversion unit 20e sets “FF” when any pixel value X of RGB is larger than 85, and sets “3 × when the pixel value X is 85 or less. X ”is set. For the intermediate line, the resolution conversion unit 20e sets “FF” when any pixel value X of RGB is larger than 170, and “3 × (X−85)” when the pixel value X is 170 or less. "Is set. For the lower line, the resolution conversion unit 20e sets “3 × (X−170)” when any pixel value X of RGB is larger than 170, and the pixel value X is 170 or less. “00” is set in.

  If none of these cases is applicable, the resolution conversion unit 20e increases the resolution using the RGB pixel values. Specifically, the resolution conversion unit 20e replaces the upper line, the intermediate line, and the lower line with a pixel value X obtained by collecting RGB pixel values.

  Through such a resolution conversion process, the resolution conversion unit 20e, based on the determination result of the edge determination unit 20b and the determination result of the color determination unit 20d, the sub-scanning direction of the image represented by the image data for one line Correct the width. Then, this process ends (END).

  As described above, in the present embodiment, the image reading apparatus 10 in the image forming apparatus 1 includes the light source unit 15, the CCD control unit 19, and the image processing unit 20. Here, the light source unit 15 sequentially turns on the RGB light sources 15R, 15G, and 15B each having a different color in response to the reading operation for one line, and the original D (read image) that relatively moves in the sub-scanning direction. ) Are sequentially irradiated with light of each color. The CCD control unit 19 sequentially reads the light of each color that has acted on the read image by the image sensor CCD, and outputs image data of each color (sensor control unit). The image processing unit 20 receives three image data (RGB image data) corresponding to a reading operation for one line from the CCD control unit 19 and generates image data for one line based on these image data. .

  The image processing unit 20 is mainly configured by an edge determination unit 20b, a color determination unit 20d, and a resolution conversion unit 20e. Here, for each color pixel corresponding to the reading operation for one line, the edge determination unit 20b corresponds to the upstream edge portion in the sub-scanning direction or the downstream side in the sub-scanning direction. It is determined whether it corresponds to a non-edge portion. The color determination unit 20d determines the direction of color shift of the target pixel (color shift determination unit), and based on the pixel value of each color related to the target pixel and the color black determination condition for distinguishing whether the target pixel is color or black. Then, the color black / white determination of whether or not the target pixel is black is performed (color black determination unit). When the target pixel is determined to be black by the color determination unit 20d, the resolution conversion unit 20e performs one line based on the determination result of the edge determination unit 20b and the determination result of the color determination unit 20d (color shift determination unit). The width in the sub-scanning direction of the image represented by the image data is corrected (correction unit).

  It can be understood from the tendency of the edge portion and the direction of the color misregistration what kind of chipping (white portion) occurs in the read image within the reading range for one line. Therefore, by referring to the determination result of the edge determination unit 20b and the determination result of color misregistration of the color determination unit 20d, it is represented by the image data for one line so as to correspond to the line width of the read image. The sub-scanning direction width of the image can be corrected. Thereby, it can suppress that the line width of an image expands or a gravity center position shifts | deviates. As a result, deterioration in image quality can be suppressed.

  In the present embodiment, the image processing unit 20 sets the color black determination condition based on the determination result of the edge determination unit 20b, so that the color determination unit 20d (color black determination unit) determines black. It further has a condition switching unit for switching the determination width.

  According to this configuration, the color black determination condition is set to an appropriate condition based on the determination result of the edge portion with respect to the target pixel. With this setting, the determination range determined to be black by the color determination unit 20d is switched. Therefore, in a case where color misregistration occurs, the target pixel corresponding to the edge portion is determined to be black. Adjusted. Thereby, since the sub-scanning direction width of the image can be appropriately corrected, it is possible to suppress deterioration in image quality.

  Further, in the present embodiment, the resolution conversion unit 20e increases the resolution of the image data for one line in the sub-scanning direction, and determines the determination result of the edge determination unit 20b and the determination result of the color determination unit (color misregistration determination unit) 20d. Accordingly, the image is biased to the upstream side in the sub-scanning direction or the downstream side in the sub-scanning direction.

  In particular, the resolution conversion unit 20e determines that the upstream edge portion in the sub-scanning direction is determined, and if the color misregistration in the color direction due to the light source with the earlier lighting order among the plurality of light sources is determined, The image is deviated downstream in the direction. Also, the resolution conversion unit 20e determines that the downstream edge portion in the sub-scanning direction is determined, and if the color misregistration in the color direction due to the light source with the slow lighting order among the plurality of light sources is determined, The image is biased upstream in the direction.

  According to this configuration, it is possible to adjust the width of the image in the sub-scanning direction by increasing the resolution of the image data for one line in the sub-scanning direction. For this reason, it is possible to deviate the image to the upstream side or the downstream side. Thereby, since the line width according to the read image can be reproduced, it is possible to suppress the uncomfortable feeling that the line width of the image is expanded or the position of the center of gravity is shifted. As a result, image quality deterioration can be suppressed.

(Second Embodiment)
The image forming apparatus 1 according to the second embodiment will be described below. The image forming apparatus 1 is different from that of the first embodiment in an image processing method by the image processing unit 20 applied to the image reading apparatus 10. In addition, description is abbreviate | omitted about the point which is common in 1st Embodiment, and it demonstrates centering around difference below.

  In the first embodiment, the resolution conversion unit 20e converts the image data for one line into a resolution equivalent to 1800 dpi by subdividing the image data into upper, middle, and lower lines (resolution conversion processing). . In this embodiment, the resolution conversion unit 20e converts the image data for one line into two upper and lower lines, thereby converting the image data into a resolution equivalent to 1200 dpi. Here, FIG. 8 is an explanatory diagram showing the concept of resolution conversion processing. In FIG. 8, it is assumed that the pixel value “00” is white and “FF” is black.

  First, a case where the target pixel corresponds to the upstream edge portion in the sub-scanning direction and is determined to be black by the color determination unit 20d will be described. In this case, the resolution conversion unit 20e performs a process of biasing the image downstream in the sub-scanning direction.

  As a first case, when the target pixel is color-shifted in the red (R) direction, the resolution conversion unit 20e performs a process of biasing the image to the lower one line. The resolution conversion unit 20e develops data on each line by using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, the resolution conversion unit 20e sets “FF” for the lower line. For the upper line, the resolution conversion unit 20e sets “2 × (X−128)” when the G pixel value X is 128 or more, and “00” when the G pixel value X is smaller than 125. Set.

  As a second case, when the target pixel is color-shifted in the yellow (Y) direction, the resolution conversion unit 20e performs a process of biasing the image to one lower line. The resolution conversion unit 20e develops data on each line by using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, for the lower line, the resolution conversion unit 20e sets “FF” when the G pixel value X is 128 or more, and sets “2 ×” when the G pixel value X is smaller than 128. X ”is set. For the upper line, the resolution conversion unit 20e sets “00”.

  On the other hand, if the target pixel corresponds to the edge portion on the upstream side in the sub-scanning direction but does not correspond to the above two cases, the resolution conversion unit 20e uses the pixel values of each color of RGB, and according to the density thereof Processing to deviate the image downstream in the sub-scanning direction is performed.

  Specifically, for the lower line, the resolution conversion unit 20e sets “FF” when any of the RGB pixel values X is 128 or more, and sets “FF” when the G pixel value X is smaller than 128. 2 × X ”is set. For the upper line, the resolution conversion unit 20e sets “2 × (X−128)” when the RGB pixel value X is 128 or more, and sets “00” when the RGB pixel value X is smaller than 128. "Is set.

  In contrast, a case will be described in which the target pixel corresponds to a downstream edge portion in the sub-scanning direction and is determined to be black by the color determination unit 20d. In this case, processing is performed to deviate the image upstream in the sub-scanning direction.

  As a first case, when the target pixel is color-shifted in the cyan (C) direction, the resolution conversion unit 20e performs a process of biasing the image to the upper one line. In this case, the resolution conversion unit 20e develops data on each line using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, the resolution conversion unit 20e sets “00” for the lower line. For the upper line, the resolution conversion unit 20e sets “FF” when the G pixel value X is 128 or more, and sets “2 × X” when the G pixel value X is smaller than 128.

  As a second case, when the target pixel is color-shifted in the blue (B) direction, the resolution conversion unit 20e performs a process of biasing the black region to the upper one line. The resolution conversion unit 20e develops data on each line by using the G pixel value that is lighted second (middle) in the RGB lighting order related to one lighting operation.

  Specifically, the resolution conversion unit 20e sets “FF” for the upper line. For the lower line, the resolution conversion unit 20e sets “2 × X” when the G pixel value X is 128 or more, and sets “00” when the G pixel value X is smaller than 128. .

  On the other hand, when the target pixel corresponds to the edge portion on the downstream side in the sub-scanning direction but does not correspond to the above two cases, the resolution conversion unit 20e uses pixel values of each color of RGB, and according to the density thereof Processing to deviate the image to the upstream side in the sub-scanning direction is performed.

  Specifically, for the upper line, the resolution conversion unit 20e sets “FF” when any of the RGB pixel values X is 128 or more, and sets “2 ×” when the pixel value X is smaller than 128. X ”is set. For the lower line, the resolution conversion unit 20e sets “2 × X” when the RGB pixel value X is 128 or more, and sets “00” when the X is smaller than 128.

  If none of these cases is applicable, the resolution conversion unit 20e increases the resolution using the RGB pixel values. Specifically, the resolution conversion unit 20e replaces the upper line and the lower line with a pixel value X obtained by collecting RGB pixel values.

  As described above, what kind of chipping (white portion) occurs in the read image within the reading range for one line can be grasped from the tendency of the edge portion and the direction of the color shift. Therefore, by referring to the determination result of the edge determination unit 20b and the determination result of color misregistration of the color determination unit 20d, it is represented by the image data for one line so as to correspond to the line width of the read image. The sub-scanning direction width of the image can be corrected. Thereby, it can suppress that the line width of an image expands or a gravity center position shifts | deviates. As a result, deterioration in image quality can be suppressed.

  Although the image forming apparatus and the image reading apparatus have been described in the embodiments of the present invention, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the invention. Not too long. The image processing apparatus itself that performs the above-described image processing (processing related to the edge determination unit, the color determination unit, and the condition switching unit) also functions as part of the present invention.

  Further, in each of the above-described embodiments, three light sources of RGB are used for the light source unit, and lighting is performed in the order of RGB. However, the types of light sources, the number of light sources, and the lighting order may be different. Here, the color shift described above is caused by the type of light source color and the lighting order thereof. Even when the type of light source, the number of light sources, and the lighting order thereof are different, the present invention is based on the same principle. Can be used.

  In the present embodiment, RGB pixel values are converted into the CbCr color space. However, another color space other than the CbCr color space may be used, and the color black determination may be performed with RGB as it is.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reader 15 Light source unit 16 CPU
17 ROM
18 RAM
DESCRIPTION OF SYMBOLS 19 CCD control part 20 Image processing part 20a Line correction part 20b Edge determination part 20c Condition switching part 20d Color determination part 20e Resolution conversion part 21 Image memory 30Y, 30M, 30C, 30K Image formation part 50 Fixing device 70 Control part

Claims (5)

Corresponding to the reading operation for one line, a lighting operation is performed to sequentially turn on a plurality of light sources that emit light of different colors, and light of each color that has acted on a read image that is relatively moved in the sub-scanning direction is detected by an image sensor. In an image processing apparatus for inputting image data of each color obtained by sequentially reading and generating image data for one line,
For each color pixel corresponding to the reading operation for one line, whether the target pixel corresponds to the upstream edge portion in the sub-scanning direction or the downstream edge portion in the sub-scanning direction, An edge determination unit that determines whether it corresponds to a non-edge part;
A color misregistration determination unit that determines a direction of color misregistration of the target pixel;
Color black determination for performing color black determination as to whether or not the target pixel is black based on a pixel value of each color relating to the target pixel and a color black determination condition for distinguishing whether the target pixel is color or black And
When the target pixel is determined to be black by the color black determination unit, it is represented by the image data for one line based on the determination result of the edge determination unit and the determination result of the color misregistration determination unit. A correction unit for correcting the sub-scanning direction width of the image;
An image processing apparatus comprising:   The color black / black determination condition is set based on a determination result of the edge determination unit, and further includes a condition switching unit that switches a determination width determined as black by the color black determination unit. The image processing apparatus according to 1.   The correction unit increases the resolution of the image data for the one line in the sub-scanning direction, and the upstream side or the sub-scanning direction in the sub-scanning direction according to the determination result of the edge determination unit and the determination result of the color misregistration determination unit. The image processing apparatus according to claim 1, wherein the image is deviated toward a downstream side in the scanning direction. The correction unit is
If an edge portion on the upstream side in the sub-scanning direction is determined and color misregistration in the color direction due to a light source with a fast lighting order among the plurality of light sources is determined, an image is displayed downstream in the sub-scanning direction. Is biased,
If the edge portion on the downstream side in the sub-scanning direction is determined and color misregistration in the color direction caused by a light source with a slow lighting order among the plurality of light sources is determined, an image is displayed on the upstream side in the sub-scanning direction. The image processing apparatus according to claim 3, wherein the image processing apparatus is biased. Corresponding to the reading operation for one line, a light source unit that sequentially turns on a plurality of light sources each having a different color and irradiates light of each color sequentially to a read image that relatively moves in the sub-scanning direction;
A sensor control unit that sequentially reads light of each color that has acted on the read image with an image sensor, and outputs image data of each color corresponding to the plurality of light sources;
An image processing unit that inputs the image data of each color and generates image data for one line;
The image processing unit
For each color pixel corresponding to the reading operation for one line, whether the target pixel corresponds to the upstream edge portion in the sub-scanning direction or the downstream edge portion in the sub-scanning direction, An edge determination unit that determines whether it corresponds to a non-edge part;
A color misregistration determination unit that determines a direction of color misregistration of the target pixel;
Color black determination for performing color black determination as to whether or not the target pixel is black based on a pixel value of each color relating to the target pixel and a color black determination condition for distinguishing whether the target pixel is color or black And
When the target pixel is determined to be black by the color black determination unit, it is represented by the image data for one line based on the determination result of the edge determination unit and the determination result of the color misregistration determination unit. A correction unit for correcting the sub-scanning direction width of the image;
An image reading apparatus comprising: