JP6442985B2 - Image processing apparatus and image reading apparatus - Google Patents

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, and the image signal is digitally converted and input to the image processing unit as image data. Then, the image processing unit generates image data for one line by collecting the pixel values of each color of RGB.

  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

  In this type of image reading apparatus, since the reading position of each color on the document is different in the sub-scanning direction, there is a problem in that color misregistration occurs at the edge portion of the image and image quality deteriorates.

  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. Here, for each color pixel corresponding to the reading operation for one line, the image processing apparatus corresponds to the upstream edge portion in the sub-scanning direction or the downstream side in the sub-scanning direction. Based on an edge determination unit that determines whether it corresponds to an edge portion or a non-edge portion, a pixel value of each color related to the target pixel, and a color black determination condition that distinguishes whether the target pixel is color or black The color black determination unit that determines whether the target pixel is black and the color black determination condition are set based on the determination result of the edge determination unit. And a condition switching unit that switches the determination range.

Here, in the first invention, when the condition switching unit is determined to correspond to the standard color black determination condition used when it is determined to correspond to the non-edge portion and to the upstream edge portion in the sub-scanning direction. The color black determination condition used for the first color black that is set so that the hue caused by the color of the light source with the earlier lighting order among the plurality of light sources is determined to be black than the standard color black determination condition The determination condition and the color black determination condition used when it is determined to correspond to the downstream edge portion in the sub-scanning direction, and the hue caused by the color of the light source whose lighting order is slow among the plurality of light sources It is preferable to have a second color black determination condition set so as to determine black rather than the color black determination condition. In this case, the light source with the earliest lighting order is at least one light source excluding the light source that lights up at the latest, and the light source with the slow lighting order is at least one light source except at least the light source that lights up at the earliest. desirable.

In the first aspect of the invention, the condition switching unit includes a standard black / black determination condition used when it is determined to correspond to a non-edge portion, an upstream edge portion in the sub-scanning direction, and a downstream side in the sub-scanning direction. It is a color black determination condition used when it is determined that it corresponds to the edge part, and the hue caused by the color of the light source in the middle of the lighting order among the plurality of light sources, and the light source with the fast lighting order among the plurality of light sources It is preferable to have a third color black determination condition set so that the hue caused by the color of the light source with a slow lighting order is determined to be a color rather than the standard color black determination condition. In this case, the plurality of light sources are preferably composed of three light sources, and the light source in the middle of the lighting order is preferably the light source that lights second. Further, it is desirable that the light source with the fast turn-on order is at least one light source except the light source that is turned on at the latest, and the light source with the slow turn-on order is at least one light source except at least the light source that is turned on at the earliest. .

In the first invention, when the condition switching unit is determined to correspond to a standard color black determination condition used when it is determined to correspond to a non-edge portion and to an edge portion on the upstream side in the sub-scanning direction. Fourth color black determination that is set to determine the hue that is caused by the color of the light source that is lighted up late among the plurality of light sources as the color black determination condition to be used is determined to be a color than the standard color black determination condition. This is a color black determination condition used when it is determined that the condition corresponds to the downstream edge portion in the sub-scanning direction, and the hue caused by the color of the light source with the earlier lighting order among the plurality of light sources is changed to the standard color. It is preferable to have a fifth color black determination condition set so as to determine a color rather than a black determination condition. In this case, the light source with the earliest lighting order is at least one light source excluding the light source that lights up at the latest, and the light source with the slow lighting order is at least one light source except at least the light source that lights up at the earliest. desirable.

Further, according to the first aspect of the present invention, for the target pixel determined to be black by the color black determination unit, the density for performing density correction based on the pixel value of the pixel corresponding to the color of the light source in the middle of the lighting order among the plurality of light sources. It is preferable to further include a correction unit. In this case, the plurality of light sources are preferably composed of three light sources, and the light source in the middle of the lighting order is preferably the light source that lights second.

  According to the second aspect of the invention, in response to a reading operation for one line, a plurality of light sources each having a different color are sequentially turned on, and light of each color is sequentially irradiated onto a read image that moves relatively 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 by an image sensor, and outputs image data of each color, and image processing that inputs image data of each color and generates image data for one line And an image reading apparatus. 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. Based on an edge determination unit that determines whether it corresponds to an edge portion or a non-edge portion, a pixel value of each color related to the target pixel, and a color black determination condition that distinguishes whether the target pixel is color or black The color black determination unit that determines whether the target pixel is black and the color black determination condition are set based on the determination result of the edge determination unit. And a condition switching unit that switches the determination range.

  According to the present invention, 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 width determined to be black by the color black determination unit is switched, so that the target pixel corresponding to the edge portion is adjusted to be determined to be black. As a result, color misregistration that occurs at the edge portion can be suppressed, so that 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 of a read image in which color misregistration occurs Explanatory drawing which shows typically the black-and-white determination condition which concerns on 2nd Embodiment. Explanatory drawing which shows typically the black-and-white determination condition which concerns on 3rd Embodiment. Explanatory drawing which shows typically the black-and-white determination condition which concerns on 3rd Embodiment.

(First embodiment)
FIG. 1 is an explanatory diagram schematically illustrating a configuration of an image forming apparatus 1 according to the first embodiment. An 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 a 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 device 10 reads an image of the document D conveyed by the conveyance drum 26. The image reading apparatus 10 irradiates the original D with the light source unit 15 at the original reading position RP. The reflected light reflected by the document D is guided by a plurality of mirrors 11, 12, and 13 and 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 performs predetermined processing on the image signal to create image data. 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 photoconductive 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 conveyance 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 black determination unit 20d, and a density correction unit 20e when this is functionally grasped.

  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 black determination unit 20d, and the density correction 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 black determination unit 20d performs color black determination as to whether or not the target pixel is black based on the RGB pixels related to the target pixel and the color black determination condition set by the condition switching unit 20c. In this embodiment, the color black determination unit 20d performs color black determination by converting each pixel value of RGB related to the target pixel into a predetermined color space. Specifically, the color black determination unit 20d generates CbCr color space data obtained by converting each pixel value of RGB related to the target pixel 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 black 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 density correction unit 20e performs correction to replace the target pixel determined to be black by the color black determination unit 20d with black according to the density of the read image. This correction is performed on the basis of the pixel value of the color that lights second (middle) in the RGB lighting sequence related to one lighting operation. In this embodiment, since lighting is performed in the order of R, G, and B, the target pixel is replaced with black according to the density of the G pixel value (density correction process). The reason for paying attention to the pixel value of the color in the middle of the lighting order is that when considering blurring of the optical system, for black pixels, the color in the middle of the lighting order, that is, the color at the center of gravity in the sub-scanning direction has the highest density. It is because it is thought that it is expressing correctly. Note that if the target pixel is an edge portion, the same amount of edge enhancement processing can be performed on each of the RGB pixels.

  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.

  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.

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 corrected.

  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. 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 black 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 black determination unit 20d is switched.

  In step 4 (S4), the color black determination unit 20d converts the three pixel values related to the target pixel into CbCr color space data, and converts the converted CbCr color space data and the color black determination condition set in step 3 Compare. The color black determination unit 20d determines whether the CbCr color space data (target pixel) is color or black. 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 5 (S5), the color black determination unit 20d determines whether or not the determination result in step 4 is black. If the determination result is black, an affirmative determination is made in step 5, and thus the process proceeds to step 6 (S6). On the other hand, if the determination result is color, a negative determination is made in step 5, and thus the process proceeds to step 7 (S7).

  In step 6, the density correction unit 20e performs density correction processing on the target pixel determined to be black. Specifically, the density correction unit 20e replaces the target pixel with black according to the density of the G pixel value in the second lighting order (middle). This monochrome information is associated with the target pixel, whereby image data for one line is generated. Then, this process ends (END).

  On the other hand, in step 7, the image processing unit 20 collects RGB pixel values related to the target pixel, and specifies color information of the target pixel. This color information is associated with the target pixel, whereby image data for one line is generated. 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 the reading operation for one line from the CCD control unit, 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 black determination unit 20d, and a condition switching unit 20c. Whether the target pixel corresponds to an upstream edge portion in the sub-scanning direction or a downstream edge portion in the sub-scanning direction with respect to RGB pixels for one line as an object, It is determined whether it corresponds to a non-edge portion. The color black determination unit 20d performs color black determination as to whether or not the target pixel is black based on the pixel value of each color relating to the target pixel and the color black determination condition for distinguishing whether the target pixel is color or black. Do. The condition switching unit 20c sets the color black determination condition based on the determination result of the edge determination unit 20b, thereby switching the determination width determined as black by the color black determination unit 20d.

  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 width determined as black by the color black determination unit 20d is switched, and thus the target pixel corresponding to the edge portion is adjusted to be determined as black. As a result, color misregistration that occurs at the edge portion can be suppressed, so that deterioration in image quality can be suppressed.

  In the present embodiment, the condition switching unit 20c is determined to correspond to the standard color black determination condition Cs used when it is determined to correspond to the non-edge portion and the upstream edge portion in the sub-scanning direction. Color black determination condition (first color black determination condition) Cue and color black determination condition (second color black determination condition) Cle used when determined to correspond to the downstream edge portion in the sub-scanning direction. And have.

  Here, the first color / black determination condition Cue is a standard color / black determination based on the hue caused by the color of the light source (first light source or first / second light source) with the fast lighting order among the three light sources. The condition Cs is set so as to be determined to be black. That is, the first color black determination condition Cue is a red to yellow hue caused by the colors of the R light source 15R and the G light source 15G that are lighted up earlier in RGB than the standard color black determination condition Cs. Is set to be judged. On the other hand, the second color / black determination condition Cle is a standard color / black determination condition Cs based on the hue caused by the color of the light source (2 · 3rd light source or the third light source) whose lighting order is slow among the three light sources. Rather than black. In other words, the second color black determination condition Cle is a blue to cyan hue caused by the colors of the B light source 15B and the G light source 15G, which are slow in lighting order, out of RGB, which is blacker than the standard color black determination condition Cs. Is set to be judged.

  The upstream edge portion in the sub-scanning direction tends to cause a color shift in the red to yellow direction, but the first color / black determination condition Cue is a target pixel corresponding to the upstream edge portion in the sub-scanning direction. It tends to be determined as black. For this reason, since the target pixel corresponding to the upstream edge portion is determined to be black by the color black determination unit 20d, it is possible to suppress the occurrence of a color shift in the red to yellow direction. Further, although there is a tendency to cause a color shift in the blue to cyan direction on the downstream edge portion in the sub-scanning direction, the second color black determination condition Cle is an object corresponding to the downstream edge portion in the sub-scanning direction. The pixel tends to be easily determined to be black. For this reason, since the target pixel corresponding to the downstream edge portion is determined to be black by the color black determination unit 20d, it is possible to suppress a color shift in the blue to cyan direction.

  In the present embodiment, the image processing unit 20 corresponds to the color of the light source (second light source) whose lighting order is the middle of the three light sources for the target pixel determined to be black by the color black determination unit 20d. It further has a density correction unit 20e that performs density correction based on the pixel value of the pixel. That is, the density correction unit 20e performs density correction based on the pixel value of the pixel corresponding to the color of the G light source 15G in the middle of the lighting order of RGB.

  According to this configuration, the density of the target pixel determined to be black is corrected based on the pixel value at the center of gravity of the target pixel. Accordingly, the pixel value replaced with black by the color black determination is also corrected to the pixel value corresponding to the read image. As a result, it is corrected to black (monochrome) according to the density of the pixel value of the read image. As a result, it is possible to reduce the uncomfortable feeling that the line width of the image is felt thick or the position of the center of gravity of the image is shifted.

(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.

  Consider a case where the pixel of the second (middle) color ("G" in this embodiment) has an edge on each of the upstream side and the downstream side and causes a color shift in the magenta direction or the green direction. 7A shows a black line having a line width corresponding to the main scanning line (for example, 1800 dpi), and the G pixel has edges on the upstream side and the downstream side, respectively. That is, the target pixel corresponds to an upstream edge portion in the sub-scanning direction and a downstream edge portion in the sub-scanning direction. On the other hand, (b) shows a white line having a line width corresponding to the main scanning line (for example, 1800 dpi), and the G pixel has an edge on each of the upstream side and the downstream side. That is, the target pixel corresponds to a downstream edge portion in the sub-scanning direction and an upstream edge portion in the sub-scanning direction. When such a black line or white line overlaps with the G reading position (main scanning line) that is lit in the middle, in the former case, a color shift occurs in the magenta direction, and in the latter case, the color moves in the green direction. Cause a gap.

  In principle, color misregistration occurs in such a case, but it is generally considered that such a condition is very rarely satisfied. Therefore, in the present embodiment, the scene in which the pixel of the second (middle) color (“G” in the present embodiment) has edges on the upstream side and the downstream side, that is, the target pixel is in the sub-scanning direction. In the scene corresponding to the upstream edge portion and the downstream edge portion in the sub-scanning direction, it is made easier to determine the hues of green and magenta as colors compared to the standard color / black determination condition Cs.

  Therefore, as one of the features of the present embodiment, the condition switching unit 20c further holds a color black determination condition Ca that is applied to the upstream and downstream edge portions. As shown in FIG. 8, the color black determination condition Ca is based on the standard color black determination condition Cs and expands the color determination range for the hues of green (G) and magenta (M). . As described above, when the G pixel that is lit second (middle) has edges on the upstream side and the downstream side, the target pixel is easily determined to be a color by using the color black determination condition Ca. .

  As described above, in the present embodiment, the condition switching unit 20c uses the standard color black determination condition Cs used when it is determined to correspond to the non-edge portion, the upstream edge portion in the sub-scanning direction, and the downstream in the sub-scanning direction. A color black determination condition (third color black determination condition) Ca that is used when it is determined to correspond to the side edge portion.

  Here, the third color black determination condition Ca includes the hue caused by the color of the light source in the middle of the lighting order (second light source) among the three light sources, and the light source with the fast lighting order among the three light sources ( The hue resulting from the colors of the first light source) and the light source with the slow lighting order (third light source) is set to be determined to be a color rather than the standard color black determination condition Cs. That is, the third color black determination condition Ca includes the hue caused by the color of the G light source 15G (second light source) in the middle of the lighting order of RGB and the R light source 15R of the fastest lighting order of RGB. And the hue caused by the color of the B light source 15B whose lighting order is slow are set so as to be determined to be a color than the standard color black determination condition Cs.

  For an image with a narrow line width, a situation in which the line width is emphasized thickly, or a white line is filled with black is also assumed. In addition, it is rare that edges occur on the upstream side and the downstream side of the G pixel. Therefore, according to the configuration of the present embodiment, the scene as described above is configured not to be determined to be black compared to the first embodiment. In this manner, by allowing color misregistration, priority can be given to reproducibility in the entire target pixel. Thereby, it is possible to suppress a decrease in image quality.

  The color black determination condition Ca shown in the present embodiment and the color black determination conditions Cue and Cle shown in the first embodiment can be used in combination. That is, the condition switching unit 20c, when it is determined that the target pixel corresponds to the upstream edge portion in the sub-scanning direction, the color black determination condition Cue shown in the first embodiment and the color shown in the present embodiment. In combination with the black determination condition Ca, a color black determination condition having both characteristic determination characteristics may be set. Similarly, when it is determined that the target pixel corresponds to an edge portion on the downstream side in the sub-scanning direction, the condition switching unit 20c displays the color black determination condition Cle shown in the first embodiment and the present embodiment. The color black determination condition Ca may be set in combination with the color black determination condition Ca.

(Third embodiment)
Hereinafter, the image forming apparatus 1 according to the third embodiment will be described. 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. Note that description of points that are the same as in the first embodiment will be omitted, and hereinafter, differences will be mainly described.

  FIG. 9 is an explanatory diagram of the color black determination condition Cb1 applied to the upstream edge portion according to the third embodiment. As described above, at the upstream edge portion in the sub-scanning direction, there is a tendency for color shift from red to yellow, and color shift from blue to cyan is unlikely to occur. Therefore, the color black determination condition Cb1 shown in FIG. 9 is based on the standard color black determination condition Cs, and extends the range in which the hues of blue (B) and cyan (C) are determined to be color.

  FIG. 10 is an explanatory diagram of the color black determination condition Cb2 applied to the downstream edge portion according to the third embodiment. As described above, at the downstream edge portion in the sub-scanning direction, there is a tendency for color shift from blue to cyan, and color shift from red to yellow is unlikely to occur. Therefore, the color black determination condition Cb2 shown in FIG. 10 is based on the standard color black determination condition Cs, and the range in which the colors of red (R) and yellow (Y) are determined as colors is expanded.

As described above, in this embodiment, the condition switching unit 20c adds the standard color black determination condition Cs to the color black determination condition (the fourth color black determination condition used when it is determined to correspond to the upstream edge portion in the sub-scanning direction). Color black determination condition) Cb1 and a color black determination condition (fifth color black determination condition) Cb2 used when it is determined to correspond to the downstream edge portion in the sub-scanning direction.

  Here, the fourth color black determination condition Cb1 determines that the hue caused by the color of the light source (third light source) whose lighting order is slow among the three light sources is a color more than the standard color black determination condition Cs. Is set to That is, the fourth color black determination condition is set so that the hue caused by the color of the B light source 15B whose lighting order is late among RGB is determined to be a color more than the standard color black determination condition Cs. On the other hand, in the fifth color black determination condition Cb2, the hue caused by the color of the light source (first light source) whose lighting order is early among the three light sources is determined to be a color more than the standard color black determination condition Cs. Is set to That is, the fourth color black determination condition is set so that the hue caused by the color of the R light source 15R in the lighting order of RGB among the RGB is determined to be a color more than the standard color black determination condition Cs.

  According to this configuration, the color black determination conditions Cb1 and Cb2 are optimized in accordance with the tendency of color misregistration. Thus, the determination by the color black determination unit 20d can be appropriately performed.

  The color black determination conditions Cb1 and Cb2 shown in the present embodiment and the color black determination conditions Cue and Cle shown in the first embodiment can be used in combination. That is, the condition switching unit 20c, when it is determined that the target pixel corresponds to the upstream edge portion in the sub-scanning direction, the color black determination condition Cue shown in the first embodiment and the color shown in the present embodiment. The black determination condition Cb1 may be combined to set a color black determination condition having both characteristic determination characteristics. Similarly, when it is determined that the target pixel corresponds to an edge portion on the downstream side in the sub-scanning direction, the condition switching unit 20c displays the color black determination condition Cle shown in the first embodiment and the present embodiment. The color black determination condition Cb2 may be combined to set a color black determination condition having both characteristic determination characteristics. Similarly, the color black determination condition Ca shown in the present embodiment may be further combined with the technique shown in the second embodiment.

  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. Further, the image processing apparatus itself that performs the above-described image processing (processing relating to the edge determination unit, the color black 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.

  In addition to the method shown in the present embodiment, the following processing may be added in order to suppress erroneous black / white determination.

  For example, in the case where the color black determination condition shown in the present embodiment is performed for the target pixel, the present embodiment is provided on the condition that the upstream target pixel is determined to be black by the standard color black determination condition Cs. The processing of the condition switching unit 20c and the color black determination unit 20d shown may be performed.

  Further, when the line width of the read image is thin, the condition switching shown in the present embodiment is performed when the color misregistration direction regarding the upstream edge portion and the color misregistration direction regarding the downstream edge portion are the same. The processing of the unit 20c and the color black determination unit 20d may be canceled.

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 Interline correction part 20b Edge determination part 20c Condition switching part 20d Color black determination part 20e Density correction part 21 Image memory 30Y, 30M, 30C, 30K Image forming part 50 Fixing device 70 Control part

Claims (7)

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;
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
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;
An image processing apparatus comprising: The condition switching unit
A standard black-and-white determination condition used when it is determined to correspond to the non-edge portion;
It is a color black determination condition used when it is determined that it corresponds to the upstream edge portion in the sub-scanning direction, and the hue caused by the color of the light source with the earlier lighting order among the plurality of light sources is the standard color. A first color black determination condition set to determine black as compared to the black determination condition;
It is a color black determination condition used when it is determined that it corresponds to the downstream edge portion in the sub-scanning direction, and the hue caused by the color of the light source whose lighting order is slow among the plurality of light sources is the standard color. A second color black determination condition set to determine black as compared to the black determination condition;
I have a,
The light source with the earlier lighting order is at least one light source excluding the light source that is turned on at the latest time,
The image processing apparatus according to claim 1, wherein the light source with the slow lighting order is at least one light source excluding a light source that is lighted at least earliest . The condition switching unit
A standard black-and-white determination condition used when it is determined to correspond to the non-edge portion;
A color black determination condition used when it is determined to correspond to an upstream edge portion in the sub-scanning direction and a downstream edge portion in the sub-scanning direction, and the light source in the middle of the lighting order among the plurality of light sources The hue caused by the color of the light source and the hue caused by the color of the light source with the fast lighting order and the light source with the slow lighting order among the plurality of light sources are determined to be colors than the standard color black determination condition. The set third color black judgment condition,
Have
The plurality of light sources are composed of three light sources,
The light source in the middle of the lighting sequence is the light source that lights second,
The light source with the earlier lighting order is the light source that is lighted first,
The image processing apparatus according to claim 1 or 2, wherein the light source having a slow lighting order is a light source that is lighted third . The condition switching unit
A standard black-and-white determination condition used when it is determined to correspond to the non-edge portion;
It is a color black determination condition used when it is determined that it corresponds to the upstream edge portion in the sub-scanning direction, and the hue resulting from the color of the light source with the slow lighting order is selected from the plurality of light sources. A fourth color black determination condition set so as to be determined to be a color than the black determination condition;
It is a color black determination condition used when it is determined to correspond to the downstream edge portion in the sub-scanning direction, and the hue caused by the color of the light source in the lighting order among the plurality of light sources is determined as the standard color A fifth color black determination condition set so as to be determined to be a color than the black determination condition;
I have a,
The light source with the earlier lighting order is at least one light source excluding the light source that is turned on at the latest time,
The image processing apparatus according to claim 1 or 2 , wherein the light source with the slow lighting order is at least one light source excluding a light source that lights at least earliest .   The condition switching unit
  A standard black-and-white determination condition used when it is determined to correspond to the non-edge portion;
  It is a color black determination condition used when it is determined that it corresponds to the upstream edge portion in the sub-scanning direction, and the hue caused by the color of the light source whose lighting order is slow among the plurality of light sources is determined as the standard A fourth color black determination condition set so as to be determined to be a color than the color black determination condition;
  It is a color black determination condition used when it is determined that it corresponds to an edge portion on the downstream side in the sub-scanning direction, and the hue caused by the color of the light source with the earlier lighting order among the plurality of light sources is determined as the standard A fifth color black determination condition set so as to be determined to be a color than the color black determination condition;
The image processing apparatus according to claim 3, further comprising: The target pixel determined to be black by the color black determination unit further includes a density correction unit that performs density correction based on the pixel value of the pixel corresponding to the color of the light source in the middle of the lighting order among the plurality of light sources. And
The plurality of light sources are composed of three light sources,
The image processing apparatus according to any one of claims 1 to 5 , wherein the light source in the middle of the lighting order is a light source that is lighted second . Corresponding to the reading operation for one line, a light source unit that sequentially lights a plurality of light sources each having a different color and sequentially irradiates light of each color 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;
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
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;
An image reading apparatus comprising: