JP7516985B2 - Image forming apparatus and control program - Google Patents

Description

The present invention relates to an image forming apparatus and a control program.

Image forming devices use electrophotography to print toner images on paper. If a user finds that the image printed on the paper is defective or dirty, they reprint using new paper. Reprinting wastes paper and toner.

In order to eliminate this waste of reprinting, a technology has been released that uses white toner to correct images on paper that already has an image printed on it, while preserving the areas without defective images.

For example, the technology of Patent Document 1 has a printer that prints images and a correction image creation unit that creates data for correcting images. A first image printed on paper and a second image obtained by correcting the first image are input as data to the correction image creation unit. The correction image creation unit compares the first image and the second image, detects first difference pixels that are present in the first image but not in the second image, and second difference pixels that are present in the second image but not in the first image, and generates an erased image for erasing the first difference pixels and an additional image for adding the second difference pixels. The printer makes the erased image invisible by printing the created erased image with white toner that is close to the color of the paper, and then prints the additional image with black toner. In this way, the technology of Patent Document 1 uses the paper on which the first image is printed as is to obtain a printout in which the first image is corrected.

JP 2018-141885 A

However, the technology in Patent Document 1 only corrects the image itself printed on the paper, and does not take into consideration the possibility of printing a new image while correcting defects such as stains on the paper being used.

The present invention has been made in consideration of the above circumstances, and aims to provide an image forming device and control program that can correct defects such as stains on the paper on which a new image is to be printed and print a new image.

The above object of the present invention is achieved by the following means:

(1) a correction area determination unit that analyzes the first image data corresponding to each of the acquired printing sheets and determines a correction area;
a correction signal generating unit that generates a second exposure signal for correction based on the determined correction area;
an output control unit that generates a corrected third exposure signal by correcting a first exposure signal generated from print data of a print job with the second exposure signal;
an image forming section that forms an image on the paper based on the third exposure signal;
An image forming apparatus comprising:

(2) The paper for printing is white paper, colored paper, or paper on which a base image for overprinting has been printed,
the first image data is read image data obtained by reading the paper;
The image forming apparatus according to (1) above, wherein the correction area determination unit determines the correction area by comparing the first image data with reference image data stored in advance.

(3) the image forming section includes a plurality of image forming units each developing a toner of at least yellow, magenta, cyan, and black colors,
The image forming apparatus according to (2) above, wherein the output control section generates the third exposure signal by performing a logical sum of the first exposure signal and the second exposure signal in each of the image forming units.

(4) the first image data is read image data obtained by reading the blank paper,
The image forming apparatus according to (2) or (3) above, wherein the correction area determination unit uses image data composed of uniform standard pixel values corresponding to the color of the white paper as the reference image data.

(5) The image forming section includes a plurality of image forming units for developing yellow, magenta, cyan, and black toners, respectively, and further includes a white image forming unit for developing white toner,
said paper for printing is blank,
the correction area determination unit compares the reference image data, which is configured with uniform pixel values, with pixel values of the read image data obtained by reading the white paper, and determines an area in which pixels having a difference of a predetermined value or more are consecutive as the correction area for white;
The image forming apparatus according to (4) above, wherein the correction signal generation section generates the second exposure signal of the image forming unit for white based on the determined correction area for white.

(6) The paper for printing is colored paper;
the correction area determination unit uses image data composed of uniform standard pixel values corresponding to the color of the colored paper as the reference image data,
the correction area determination unit compares the reference image data, which is composed of uniform pixel values, with pixel values of the read image data obtained by reading the color paper, and determines an area in which pixels having a difference of a predetermined value or more are consecutive as the correction area for the color of one or more of the image forming units corresponding to the pixel values of the reference image data;
The image forming apparatus according to (2) or (3) above, wherein the correction signal generation section generates the second exposure signal of the image forming unit for the color based on the determined correction area for the color.

(7) The image forming section includes a plurality of image forming units for developing yellow, magenta, cyan, and black toners, respectively, and further includes a white image forming unit for developing white toner,
The image forming apparatus according to (6) above, wherein the correction signal generation section generates the second exposure signal for the image forming unit for white based on the determined correction area.

(8) The paper for printing is a paper on which a base image for overprinting is printed,
the correction area determination unit uses original image data used for printing the base image as the reference image data,
the correction area determination unit compares the original image data with pixel values of read image data obtained by reading the printed paper, and determines an area in which pixels having a difference of a predetermined value or more are consecutive as the correction area for the color of one or more of the image forming units corresponding to the pixel values of the reference image data;
The image forming apparatus according to (2) or (3) above, wherein the correction signal generation section generates the second exposure signal of the image forming unit for the color based on the determined correction area for the color.

(9) The image forming section includes a plurality of image forming units for developing yellow, magenta, cyan, and black toners, respectively, and further includes a white image forming unit for developing white toner,
The image forming apparatus according to (8) above, wherein the correction signal generation section generates the second exposure signal for the image forming unit for white based on the determined correction area.

(10) An image forming device according to any one of (2) to (9) above, in which the correction signal generation unit generates a second exposure signal for correction by correcting the exposure signal for a plurality of pixels included in the determined correction area and for pixels surrounding the correction area.

(11) A control program executed by a computer to control an image forming apparatus including a printing unit that forms an image on a sheet,
A step (a) of analyzing first image data corresponding to each of the acquired printing sheets and determining a correction area;
(b) generating a second exposure signal for correction based on the determined correction area;
(c) generating a corrected third exposure signal by correcting a first exposure signal generated from print data of a print job with the second exposure signal;
and (d) forming an image on the paper by an image forming unit based on the third exposure signal.

(12) The paper for printing is blank paper, colored paper, or paper on which an image for overprinting has been printed,
the first image data is read image data obtained by reading the paper;
The control program according to (11) above, wherein in the step (a), the correction area is determined by comparing the first image data with reference image data stored in advance.

According to the image forming device and control program of the present invention, a second exposure signal for correction is generated based on a correction area determined by analyzing the acquired first image data, a first exposure signal generated from the print data of the print job is corrected with the second exposure signal to generate a corrected third exposure signal, and an image is formed on paper based on the third exposure signal. In this way, if there are defects such as stains on the paper on which a new image is to be printed, these can be corrected and a new image can be printed.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a hardware configuration of the image forming apparatus. FIG. 2 is a block diagram showing a hardware configuration of the image forming apparatus. 5 is a flowchart showing a printing process executed by a control unit of the image forming apparatus. 1A and 1B are schematic diagrams for explaining defective printed matter that occurs when there is a defect such as a stain on the printing paper. FIG. 6 is a schematic diagram for explaining a correction image for correcting (erasing) the defective portion in FIG. 5(b). 11A and 11B are schematic diagrams for explaining composite image data for simultaneously correcting a defective portion and printing. 11A and 11B are schematic diagrams for explaining composite image data for simultaneously correcting a defective portion and printing. FIG. 11 is a flow diagram showing the flow of data in a printing process using blank or colored paper. 11 is a timing chart showing a process of generating a third exposure signal for correction on a blank sheet of paper. 13 is a timing chart showing a process of generating a third exposure signal for correction in a color paper (Y color). FIG. 4 is a flow diagram showing the flow of data in a printing process using printed paper. 10 is a timing chart showing a process of generating a third exposure signal for correction on printed paper. FIG. 13 is a schematic diagram showing a configuration of an image forming apparatus according to a modified example.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that in the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted. Also, the dimensional ratios in the drawings have been exaggerated for the convenience of explanation, and may differ from the actual ratios.

Figure 1 is a schematic diagram showing the configuration of an image forming device 1 according to an embodiment of the present invention. Figures 2 and 3 are block diagrams showing the hardware configuration of the image forming device 1. As shown in Figure 1, the image forming device 1 includes a device main body 10a, a paper feed device 10b, and a reading device 10c.

The paper feed device 10b is equipped with a plurality of paper feed trays 145c to 145d (hereinafter, these are also collectively referred to as paper feed trays 145), and conveys paper 300 stored therein from these paper feed trays. The surface (image forming surface) of the conveyed paper 300 is read by the reading unit 16 arranged on the conveying path 141, and read image formation data is generated. For example, if the paper 300 is white or colored paper, dirt on the surface is detected by image analysis of the read image data. In addition, when overwriting a printed paper on which a base image has been printed (hereinafter referred to as "overprinting"), if the paper 300 is a printed paper printed by another image forming device, etc., dirt is detected by analyzing the read image data generated by reading it, or printing defects are detected by comparing it with the original image data. After passing through the transport path 141, the paper 300 is transported to the transport path 142 of the downstream device body 10a, where an image is formed on the image forming surface.

As shown in Figures 2 and 3, the image forming device 1 includes a control unit 11, a memory unit 12, an image forming unit 13, a paper feed and transport unit 14, an operation display unit 15, a reading unit 16, a printer controller 17, and a synchronization signal generation circuit 18 (see Figure 3).

(Control unit 11)
As shown in Fig. 3, the control unit 11 includes a CPU 111, a control memory 112, an image control circuit 113, a page memory 114, and a buffer 115. The image control circuit 113 includes a memory control ASIC (ASIC: Application Specific Integrated Circuit) and a print ASIC. The page memory 114 is connected to the memory control ASIC, and the memory control ASIC controls input and output of data. The buffer 115 is connected to the print ASIC, and the print ASIC controls input and output of data. The page memory 114 or the buffer 115 may be provided inside the circuit of the memory control ASIC or the print ASIC, respectively.

The CPU 111 comprehensively controls the overall operation of the image forming device 1 by executing various programs stored in the control memory 112 or the storage unit 12. The CPU 111 also functions as a correction area determination unit, a correction signal generation unit, and an output control unit by executing the programs. Note that the image control circuit 113 may be configured to assume some or all of the functions of the correction signal generation unit and the output control unit.

The "correction area determination unit" determines the correction area by analyzing the read image data (first image data) of the paper 300 to be printed, obtained by reading by the reading unit 16. In this case, (a) the correction area is determined by comparing the first image data with the reference image data. Or (b) when using a paper 300 that has already been printed, and when part of the image is to be rewritten, an area that matches an area specified by a user, etc. is determined as the correction area.

When the correction area determination unit determines the correction area by the former comparison (a), there are mainly three methods (a1) to (a3) below. (a1) In the first method, the pixel value of the reference image data stored in advance is compared with the pixel value of each pixel of the first image data, pixels (candidate pixels) with a difference of a predetermined value (threshold value) or more are extracted, and the area (clustering) where the extracted candidate pixels are continuous is determined as the correction area. For example, when using white paper, if the pixel value of a pixel of any of the image data of each color of RGB of the read image data is equal to or less than a preset threshold value (high density), it is extracted as a candidate pixel. Then, the area where the candidate pixels are continuous is determined as the correction area. The threshold value may be a threshold value obtained by storing a correspondence table of paper type and paper color (pixel value) in the storage unit 12 and adding a predetermined offset to the color of the paper type specified by the user, etc. The scanned image data in RGB format may be converted to GS (Gray Scale) or YMCK (or YMCKW) before the correction area is determined. In the latter case, if the pixel value of any of the YMCK pixels is equal to or greater than a threshold (high density), it is extracted as a candidate pixel and the correction area is determined.

(a2) In the second method, the average density (color) of the paper is determined from the read image data obtained by reading one or more sheets of the same type as the paper being used using the reading unit 16, etc. Then, an offset value that takes variation into account is added to this determined density and the resulting density is set as the threshold value. In this case, a uniform threshold value is applied to the entire image data.

(a3) In the third and final method, when overprinting, the original image data used for printing on the printed paper is obtained, and this is compared with the scanned data of the paper on a pixel-by-pixel basis. Pixels with a difference of a certain amount or more (which may be high or low density) are extracted as candidate pixels, and if these pixels are consecutive, they are determined to be the correction area. Note that proof image data (hereinafter, these are collectively referred to as "reference image data") may be used instead of the original image data. Proof image data is selected by the user from among the papers (printed papers) on which the printed image (base image) is printed. The user visually checks the paper with the printed base to confirm that it is a good product, and the scanned image data obtained by reading the paper of the confirmed image with this image forming device 1 or an external reading device is used as the proof image data. When comparing pixel values in (a3) above on a pixel-by-pixel basis, if the resolution of the scanned image data of the paper 300 differs from the resolution of the reference image data (original image data or proof image data), the user converts the resolution to match one of them. In the following, to avoid complicating the explanation, the resolutions of the reference image data, print image data, image forming unit 13 (writing unit 1302), etc. are all described as being the same resolution.

The "correction signal generating unit" generates a second exposure signal for correction based on the determined correction area. For example, a second exposure signal is generated for the image forming unit 130 to apply overwriting toner to erase (make invisible) stains to pixels in the same area as the correction area. For example, a second exposure signal is generated for a white image forming unit (image forming unit 130 (W) described later) to erase stains on a white sheet of paper. This second exposure signal may be a signal that corrects the exposure signal for pixels in an area the same as the size of the correction area (i.e., a signal that applies toner or increases the amount of toner applied to increase the density of the pixels). Alternatively, the area may be expanded (thickened) to the pixels around the correction area in consideration of the variation in position during image formation, and a second exposure signal that corrects the exposure signal for the expanded area may be generated. The periphery refers to pixels that are adjacent to and continuous with the correction area in the main scanning direction and/or sub-scanning direction. For example, it refers to pixels that are continuous with a distance of 1 mm (e.g., several tens of pixels in front and behind at 1200 dpi) in the main scanning direction.

The "output control unit" generates a third exposure signal from a first exposure signal generated from the print image data of the print job and a second exposure signal generated by the correction signal generation unit. For example, the third exposure signal is generated by taking the logical sum of the first exposure signal and the second exposure signal for each pixel. By processing the exposure signal in this way and generating image data for correction, image processing can be performed quickly with a simple configuration, and defects can be efficiently corrected.

(Image forming unit 13)
1 again, the image forming section 13 includes a plurality of image forming units 130 (Y to W), an intermediate transfer belt 131, a secondary transfer section 132, and a fixing section 133.

The image forming section 13 forms images by a well-known electrophotographic process using toner. The image forming units 130 (Y-W) correspond to the toners Y (yellow), M (magenta), C (cyan), K (black), and W (white), respectively. Each image forming unit 130 includes a photoconductor drum 1301, a writing unit 1302, a developing device 1303, a charging electrode (not shown), a cleaner (not shown), and the like. Each image forming unit 130 uses a different color of toner in the developing device 1303, but is otherwise identical in configuration.

In this embodiment, as described later, when a W toner is used as the bottom layer (contacting the paper) of toner for correction (erasing), and Y, M, C, and K toners corresponding to the print image data (first exposure signal) are layered on top of it, it is preferable to configure the W toner and the color toners so that the W toner and the other YMCK color toners do not completely melt and become integrated. For example, it is preferable that the color toner has excellent melting properties and sharp melting properties that melt at low temperatures and in a short time, while the W toner has a storage elastic modulus of the binder resin that is 5 times or more the storage elastic modulus of the binder resin of the color toner at the softening temperature of the binder resin of the color toner. By making it 5 times or more, it is possible to prevent to some extent the W toner from melting and mixing with the color toners during heat fixing.

Each writing unit 1302 includes a laser diode (LD), a polygon mirror, an index sensor, and a control circuit that controls a motor that drives the polygon mirror (none of which are shown). The index sensor detects the laser light reflected and irradiated by the polygon mirror, and outputs a polygon rotation synchronization signal. The output CLK (clock) signal output by the synchronization signal generation circuit 18, which will be described later, is synchronously controlled based on the polygon rotation synchronization signal output by the index sensor.

The photoconductor drum 1301 is exposed at the exposure position by a laser (indicated by a dashed arrow in FIG. 1) emitted from the writing unit 1302. For Y color, the electrostatic latent image formed on the surface of the photoconductor drum 1301 by exposure is developed with toner by the corresponding Y color developing device 1303, forming a Y color toner image on the surface of the photoconductor drum 1301. Similarly, the image forming units 130 for other colors form electrostatic latent images by the corresponding writing units 1302, which are developed with toner by the corresponding M, C, K, and W color developing devices 1303, forming M, C, K, and W color toner images on the surface of the photoconductor drum 1301. The formed toner images of each color are primarily transferred onto the intermediate transfer belt 131 and superimposed to form a full-color toner image. This full-color toner image is transferred by the secondary transfer unit 132 onto the surface of the paper 300 sent from either the paper feed device 10b or the paper feed tray 145a, b of the device main body 10a itself. The image is then fixed onto the surface of the paper 300 by applying heat and pressure in the downstream fixing unit 133.

The distance from the exposure position of each photoconductor drum 1301 to the primary transfer position is set to be the same. In addition, the distance between adjacent photoconductor drums in the direction along the surface of the intermediate transfer belt 131 (height direction) is the same, and the photoconductor drums 1301 are arranged at equal intervals in the height direction. Therefore, the relative distance between the exposure positions of each photoconductor drum 1301 is equal to the distance between the photoconductor drums (hereinafter simply referred to as the "drum distance"). In such a case, when exposing pixels at the same position on the paper 300, the exposure timing differs for Y, M, C, K, and W in that order by the drum distance.

(Paper feeding and conveying section 14)
The paper feed conveying unit 14 includes the above-mentioned multiple paper feed trays 145a to 145e. The paper feed conveying unit 14 also includes conveying paths 141 to 143. A multiple number of sheets of paper 300 are stacked in each of the paper feed trays 145, and the topmost sheet of paper 300 is fed one by one. The paper feed conveying unit 14 includes multiple pairs of conveying rollers arranged along the conveying paths 141 to 143, and a drive motor (not shown) that drives the rollers. For example, the paper feed conveying unit 14 conveys the paper 300 fed from the paper feed tray 145d to the reading position of the reading unit 16 on the conveying path 141, the transfer position of the secondary transfer unit 132, or the downstream paper output tray 144.

(Operation display unit 15)
An operation display unit 15 is disposed on the top of the device main body 10a. The operation display unit 15 receives operations from the user and displays information. The operation display unit 15 for this purpose may have any configuration, such as a touch panel in which an operation section and a display section are integrated, or a configuration in which hard keys such as buttons and keys are combined with a liquid crystal display device, etc.

(Reading unit 16)
The reading unit 16 is disposed on the conveying path 141, reads an image on the paper 300 conveyed by the paper feed conveying unit 14, and generates read image data. The same reading unit may be disposed below the conveying path 141 so that both sides can be read simultaneously (one pass). The reading unit 16 includes a sensor array, a lens optical system, an LED (Light Emitting Diode) light source, and a housing for housing these. The sensor array is a color line sensor in which multiple optical elements (e.g., CCD (Charge Coupled Device)) are arranged in a line along the main scanning direction, and the reading area in the width direction corresponds to the full width of the paper 300. The optical system is composed of multiple mirrors and lenses. Light from the LED light source passes through the document glass and irradiates the surface of the paper 300 passing through the reading position on the conveying path 141. An image formed by the surface reflected light at this reading position is guided by the optical system and formed on the sensor array. The resolution of the reading unit 16 is in the range of 100 to 1200 dpi, for example, 600 dpi or 1200 dpi.

(Printer controller 17)
The printer controller 17 acquires a print job sent from a terminal device 900 configured as a PC (personal computer) or the like. Then, the print data (image data) described in PDL (Page Description Language) or PDF format included in this print job is rasterized by the printer controller 17 and converted into image data for each page in raster format, and temporarily stored in the page memory 114. The read image data generated by the reading unit 16 described above and correction image data described later are also temporarily stored in the page memory 114.

(Synchronization signal generation circuit 18)
The synchronous signal generating circuit includes one or more crystal oscillators and generates the output CLK.

(Printing process)
The printing process in this embodiment will be described below with reference to Fig. 4 to Fig. 7. Fig. 4 is a flow chart showing the printing process executed by the control unit 11 of the image forming apparatus 1, and Fig. 5 to Fig. 7B are schematic diagrams for explaining the first to third exposure signals of the correction process for a defective image in this printing process.

(Example of print output)
Before describing the printing process, the first to third exposure signals used in the printing process will be described with reference to FIGS. 5 to 7B.

Figure 5 is a schematic diagram for explaining defective prints that occur when the print paper has defects such as stains. Figure 5(a) shows paper 310 before printing and paper 510 after printing when ideal paper, i.e., paper without stains, is used to print using print image data 410 by image forming device 1. Here, paper 310 is a printed sheet of paper with a Y-colored base image formed on the lower half of the blank paper. The base image is a rectangular image of uniform density in a light Y color.

In the illustrated example, the print image data 410 is composed of image data for the colors Y, K, and W, and there is no image data for the colors M and C (zero value, i.e. NULL). In FIG. 5(a), the composition of the image data for each color is shown in a speech bubble. Note that the area where the image data for W is located (area to be exposed) is shown shaded for display purposes. The exposure signal formed by the image data for each color is referred to below as the "first exposure signal." This first exposure signal 4100 is sent to the writing unit 1302 for each color at a predetermined timing.

Figure 5(b) shows an example of output when stained unprinted paper 311 is used in a comparative example. As can be seen from a comparison with Figure 5(a), if there is a stain, the stain remains on printed paper 511, resulting in a defective final print.

Figure 6 is a schematic diagram for explaining a correction image for correcting (erasing) the defective portion in Figure 5 (b). The correction area determination unit of the control unit 11 determines the correction area corresponding to the stains (four in the example shown in Figure 5 (b)) on the unprinted paper 311 by comparing the read image data read from the paper 311 with the reference image data. Specifically, the difference between the read image data and the original image data as the reference image data used to print the printed image on the unprinted paper 311 is calculated, and the correction area is determined from pixels with a difference of a predetermined value or more. For example, the correction area determination unit extracts pixels with a density difference of a predetermined value or more (dark density due to stains) as candidate pixels by comparing pixel values after YMCK format conversion. Then, the pixels with consecutive candidate pixels are grouped (clustered), and a group with a predetermined or greater area (or number of pixels) is determined as the correction area. For example, an area of 1 mm square or more is determined as the correction area.

Next, the correction signal generating unit of the control unit 11 generates a second exposure signal 4200 for correction for the corresponding pixel group at the same position as the correction area, or for this pixel group and the surrounding pixels adjacent to it.

In the example shown in FIG. 6, in the image data for correction 420 (corresponding to the second exposure signal 4200), an image for stain correction (stain erasure) is formed in the pixel group corresponding to the correction area and the surrounding pixels in the image data for W color. The shape of the correction image may be the same as the shape of the correction area, or may be a shape obtained by enlarging (thickening) it to the periphery, or may be a predetermined shape (circle or rectangle) set to a size that includes the correction area. In the following, an example will be described in which a rectangular correction image is formed. As shown in the speech bubble in FIG. 6, the correction image corresponds to the image of the paper 311 before printing (including the image for erasing W color; the same applies below). Specifically, for the two stains on the lower side, correction images for Y and W colors are generated corresponding to the color (Y color) of the paper 311 at that position, and for the two stains on the upper side, correction images for W color are generated corresponding to the color (white paper) of the paper 311 at that position.

Figures 7A and 7B are schematic diagrams for explaining composite image data for simultaneously correcting defective areas and printing. As shown in Figure 7A, the output control unit of the control unit 11 generates composite image data 430 by combining the above-mentioned print image data 410 and correction image data 420.

The third exposure signal 4300 of the composite image data 430 is generated by correcting the first exposure signal 4100 of the print image data 410 with the second exposure signal 4200 of the correction image data 420 by the output control unit, as described below. For example, the third exposure signal 4300 is generated by performing a logical OR on the first and second exposure signals 4200 on a pixel-by-pixel basis. Note that, for the sake of explanation, FIG. 7A and FIG. 7B show composite image data 430 on a page-by-page basis, but in this embodiment, such page image data is not generated, but the exposure signal is synthesized on the exposure signal to generate the third exposure signal. This allows image processing to be performed at high speed with a simple configuration compared to generating image data for each page.

As shown in FIG. 7B, the image forming unit 13 forms an image on the paper 311 using composite image data 430, which is a composite of a correction image corresponding to stains on the paper 311 before printing, and outputs the printed paper 512, which is a normal printout in which the defects have been corrected (erased). In the printing process described below, such first to third exposure signals are used to output a normal printout.

(Printing process)
(Step S201)
Returning to the description of Fig. 4, the control unit 11 accepts a print job. For example, the control unit 11 accepts a print job sent from the terminal device 900. The print job includes a job ticket that describes print settings such as information on the type of paper used for printing, and print data.

(Steps S202 and S203)
The printer controller 17 performs a rasterization process on the print data acquired in step S201, generates raster data, and stores it in the page memory 114. Image data is transferred from the page memory 114 connected to the memory control ASIC to the buffer 115 of the print ASIC line by line in order from the top. The image data for each line transferred from the page memory 114 is composed of image data of five colors, Y, M, C, K, and W, and is stored in the buffer 115 for each color after being subjected to Front processing when simultaneously transferred line by line. This Front processing includes image processing of gamma correction, screen correction, density balance, and two-dimensional position correction. The image data stored in each buffer 115 is read out line by line from the buffer 115 in synchronization with the HV signal (vertical effective signal) during a period when the VV signal (vertical effective signal) for each color described later is effective as a first exposure signal, and is sent to each LD of the corresponding writing unit 1302 (Y to W). When this is read out, rear processing is performed on the image data of each line, which is related to image position adjustment such as leading edge timing adjustment and offset adjustment.

(Step S204)
The control unit 11 identifies the paper 300. For example, the control unit 11 conveys the paper 300 from the paper feed tray 145 selected in accordance with the job ticket.

(Step S205)
The control unit 11 reads the image of the image forming surface of the paper 300 by the reading unit 16, and obtains read image data (hereinafter referred to as "first image data"). Note that image data designated by the user may be used as the first image data. For example, the paper is read in advance by an external reading device, and the obtained read image data is used. In this case, the read image data obtained by continuously reading a plurality of sheets, for example, one cassette of 500 sheets, of paper using a reading device with an ADF is used. Specifically, the obtained read image data for a plurality of pages is stored in the storage unit 12, and the paper 300 is loaded into the paper feed tray 145 in the order in which it was read. Then, every time the paper 300 is transported for image formation using the paper 300, the corresponding read image data is read from the storage unit 12.

(Step S206)
The correction area determination unit of the control unit 11 determines the correction area by analyzing the first image data acquired in step S205. The correction area can be determined by any of the three methods described above, namely (a1) a preset reference value, (a2) a reference value calculated from the read image data, and (a3) a comparison with the original image data at the time of overprinting, or a combination of these methods. For example, as shown in FIG. 6, the correction area is determined by comparing the read image data (first image data) obtained by reading the paper 311 before printing with the reference image data by the method (a3). At this time, the first image data obtained by reading in RGB format may be converted to YMCK format before being compared with the reference image data.

(Step S207)
The correction signal generating section of the control section 11 generates a second exposure signal for a correction area corresponding to dirt or the like. As shown in the second exposure signal 4200 of the correction image data 420 in Fig. 6 described above, second exposure signals of Y color and W color for correction (erasure) are generated according to the reference image data (paper color of the pre-printed paper 311, or pixel value of the pixel at the correction area position of the base image). For example, for the W color for erasure, an exposure signal with a pixel value of 255/255 is generated, and for the Y color, an exposure signal with the same pixel value as the pixel value of the Y color of the base image is generated.

(Step S211)
The output control unit of the control unit 11 corrects the first exposure signal obtained in step S203 with the second exposure signal obtained in step S207 to generate a third exposure signal. Specifically, the output control unit generates the third exposure signal by taking a logical sum for each pixel. For example, in an 8-bit (255 gradations) pixel signal, if the pixel value of the first exposure signal is 0/255 (NULL) and the second exposure signal is 255/255 (FULL), the third exposure signal becomes 255/255 by logical sum. Also, if the first exposure signal is 8/255 and the second exposure signal is 128/255, the third exposure signal becomes 128/255.

In the case of intermediate density PWM, the logical sum differs depending on how the exposure signal is distributed within one pixel. This distribution can be left justified, center justified, or right justified. For example, in the case of PWM 50%, of the 10 nsec section equivalent to one pixel, exposure is performed in the first half (upstream side in the main scanning direction) of 0 to 5 nsec for left justification, exposure is performed in the second half (downstream side in the main scanning direction) of 5 to 10 nsec for right justification, and exposure is performed in the middle section of 2.5 to 7.5 nsec for center justification. It is preferable to configure the first exposure signal and the second exposure signal to be distributed to the left, right, or vice versa, so that they are alternated. In this case, if the first exposure signal is 8/255 and the second exposure signal is 128/255, the logical sum of the third exposure signal will be 136/255. On the other hand, if the first and second exposure signals are both configured with the same distribution, for example both centered, and the first exposure signal is 8/255 and the second exposure signal is 128/255, the third signal, which is the logical sum, will be 128/255.

(Step S212)
The image control circuit 113 sends the third exposure signal obtained in step S211 to the writing units 1302 (Y to W) of each color at the respective timings, and forms an image on the paper 300 conveyed in step S204.

(Step S213)
After the above image formation is performed, if the print job is not completed and there is printing to be performed on the next sheet, the process returns to steps S202 and S204, and the subsequent processes are performed. Note that, when printing on a sheet repeatedly using the same print data, the processes of steps S202 and S203 can be omitted, and the first exposure signal used in the previous printing can be repeatedly used.

In this way, in the image forming device according to this embodiment, a second exposure signal for correction is generated based on the correction area determined by analyzing the acquired first image data, the first exposure signal generated from the print data of the print job is corrected with the second exposure signal to generate a corrected third exposure signal, and an image is formed on paper based on the third exposure signal. In this way, if there are defects such as stains on the paper on which a new image is to be printed, these can be corrected (erased) and a new image can be printed. Furthermore, since the third exposure signal for correction is generated by processing the exposure signal, correction can be performed without generating composite image data for correction for each page (composite image data 430 in FIG. 7A), and image processing can be performed quickly with a simple configuration.

(Example)
Next, a specific example of the exposure signal generation process in the above-described embodiment will be described with reference to FIGS.

(First embodiment)
In the first embodiment, a case where white paper or colored paper is used will be described. Fig. 8 is a flow diagram showing the flow of data in a printing process using white paper or colored paper, and Figs. 9 and 10 are timing charts showing the process of generating a third exposure signal for correction when using white paper and colored paper, respectively.

Figure 8 shows the printing process along with the data flow, and corresponds to the flowchart in Figure 4. In Figure 8, data corresponding to Figures 5 to 7B (print image data 410, etc.) are given the same numbers to replace the explanation.

(Step S701)
The conveyed blank paper 312 (or colored paper) is read by the reading unit 16 to generate first image data 601 .

(Steps S702 and S703)
The correction area determination unit of the control unit 11 compares the first image data 601 with the reference image data 602 to determine a correction area, thereby generating image data for correction 420 and storing it in the page memory 114. This process corresponds to steps S206 and S207 in Fig. 4 and Fig. 6, and a description thereof will be omitted.

(Step S704)
The image control circuit 113 of the control unit 11 reads the image data from the page memory 114 in response to the read signal, temporarily stores it in a buffer 115, and outputs an exposure signal to the writing unit 1302 for each line of the main scan, with the timing synchronized by a delay circuit in the image control circuit 113.

(Step S711)
The control unit 11 performs the above-mentioned image processing of gamma correction, screen correction, density balance, and two-dimensional position correction, as well as image position adjustment, on the image data 410 for printing.

(Step S712)
The image control circuit 113 acquires the first exposure signal 4100 and the second exposure signal 4200 for each line by synchronizing the timing, and generates a third exposure signal 4300 by taking a logical sum for each pixel.

(Step S713)
The writing units 1302 (Y to W) of the image forming section 13 perform exposure in response to the input third exposure signal, and form a print image 513 made of toner of each color on the white paper 312 .

(Example of processing a blank sheet)
Next, with reference to FIG. 9, a process for generating an exposure signal when a blank sheet is used in the printing process of FIG. 8 will be described.

In the example of Figure 9 (the same applies to Figures 10 and 12 described below, hereafter simply referred to as Figure 9, etc.), the VV signal is generated by the start signal of the print job, and one High period corresponds to one page of an image. Also, one High period of the HV signal corresponds to one main scan line. One cycle of the output CLK corresponds to the exposure period of one pixel. Also, in the example of Figure 9, etc., the timing of each color is shown aligned along the vertical axis, but in reality, the exposure timing differs by the amount of the distance between the drums. Furthermore, the first to third exposure signals are PWM signals corresponding to the pixel value (for example, 255 means full lighting during the exposure period, and 128 means 50% exposure).

In addition, examples such as Figure 9 show examples in which, not only for the third exposure signal but also for the second exposure signal, a correction area is determined on the exposure signal and the second exposure signal is generated without generating page image data for correction for each page (such as image data 420 in Figure 6).

In FIG. 9, a correction area is determined for stains on a white sheet of paper, and a correction area of the image data 420 for correction using white toner is determined according to the pixel values of the reference image, i.e., the color of the paper (white). In FIG. 9, the correction areas for Y to K and the second exposure signal are not generated in the printing process for white paper (all NULL signals) and are not used, so they are shown grayed out (light text). As shown in FIG. 9, the correction area determination unit compares the first image data with the reference image data and extracts pixels whose difference is greater than a predetermined value. This reference image data is composed of uniform pixel values corresponding to the white color of the paper. For example, the pixel values of YMCK in the first image data converted to YMCK format are compared with the pixel values of YMCK corresponding to the white color of the paper (for example, all 0 (zero)), and the difference between them is taken. Then, pixels whose difference is greater than the predetermined value (high density) are determined as candidate pixels. For example, if the difference between any pixel values is equal to or greater than the predetermined value of 20/255, it is extracted as a candidate pixel, and if a certain number of these pixels are consecutive in the main scanning direction, they are determined as a correction area.

Then, the correction signal generating section of the control section 11 (for example, the image control circuit 113) expands the W correction area, for example, to several tens of adjacent pixels (equivalent to 0.5 mm each before and after) on the same line in the main scanning direction, and generates a second exposure signal. The W exposure signal is PWM 100% (255/255).

The output control unit of the control unit 11 (for example, the image control circuit 113) takes the logical sum of the first exposure signal and the second exposure signal for each color to generate a third exposure signal. Specifically, the third exposure signal is generated by the logical sum of the first exposure signal and the second exposure signal for W color. In this way, by using the exposure signal to determine the correction area and generate a correction signal, if there are defects such as stains on the paper, these can be corrected and a new image can be printed.

(Example of processing colored paper (yellow))
Next, referring to Fig. 10, the generation process of the exposure signal when colored paper is used in the printing process of Fig. 8 will be described. Note that the type and number of target colors differ depending on the hue of the colored paper, but in the following, for ease of explanation, the colored paper will be described as a light-colored paper with the same hue as the Y toner. Therefore, the colors to be processed in the correction image data are two colors, W and Y (similar to the second exposure signal in Fig. 6).

In the example shown in Figure 10, Y color is also processed, so the correction area and second exposure signal for Y color are shown. Note that M, C, and K colors are not processed, as in Figure 9, so the correction areas and second exposure signals for these colors are omitted in Figure 10.

In the signal generation process of FIG. 10, as in the example of FIG. 9, the correction area determination unit compares the first image data with the reference image data and extracts pixels with a difference greater than a predetermined value. This reference image data is composed of uniform pixel values that correspond to the light yellow color of the paper. For example, in RGB format (8 bit (0-255)), it is (0,0,20), and in Y,M,C,K format (8 bit (0-255)), it is (20,0,0,0). For example, the YMCK pixel values in the first image data converted to YMCK format are compared with the YMCK pixel values (20,0,0,0) that correspond to the light yellow color of the paper, and the difference between them is taken. Then, pixels with a difference greater than the predetermined value (higher density) are determined as candidate pixels. For example, if the Y pixel value is 40/255 or more (i.e. the difference is 20/255 or more), or if the pixel value of any of the C, M, and K pixels is 20/255 or more (i.e. the difference is 20/255 or more), it is extracted as a candidate pixel, and if a certain number of such pixels are consecutive, it is determined to be a correction area. By comparing the pixel values of each pixel in the first image data with the pixel values of this reference image data, pixels with a difference greater than a certain value (whether the density is high or low) are determined to be correction areas.

Next, the correction signal generating section of the control section 11 (e.g., the image control circuit 113) expands the correction area for the Y and W colors, and generates a second exposure signal that is expanded to, for example, several tens of adjacent pixels before and after the same line in the main scanning direction.

The exposure signal for W at this time is PWM 100% (255/255) as in FIG. 9, but the PWM for Y is set to 8% (=20/255) to correspond to the light paper color. The PWM for Y is set by the control unit 11 according to the pixel value of the reference image. For example, it is set to the same value as the pixel value of the reference image data. The PWM for W is set to 100% as in FIG. 9 when the difference is positive, that is, when the density of the dirty part is high. On the other hand, when the density of the dirty part is low, W may not be used as follows. For example, when the pixel value of Y in the reference image is 5/255 and the color of the paper is 20/255, the PWM for Y is set to the difference of 15/255, and the PWM setting value for W is 0/255 because it is not necessary.

The output control unit of the control unit 11 takes the logical sum of the first exposure signal and the second exposure signal for each color to generate a third exposure signal. Specifically, it takes the logical sum of the first exposure signal and the second exposure signal for each of the Y and W colors to generate a third exposure signal for each of the Y and W colors. In this way, by determining the correction area and generating the correction signal using the exposure signal, high-speed signal processing can be performed with a simple configuration, thereby achieving high-speed image processing, and in addition, if there are defects such as stains on the paper, these can be corrected and a new image can be printed.

Second Example
(Example of processing of overprinted paper)
In the second embodiment, a description is given of overprinting using a printed sheet on which a base image is printed. Fig. 11 is a flow diagram showing the flow of data in the overprinting printing process, and Fig. 12 is a timing chart showing the generation process of a third exposure signal for correction in the overprinting sheet.

Steps S801 to S813 of the second embodiment shown in FIG. 11 correspond to steps S701 to S713 of the first embodiment (FIG. 9), respectively, and these embodiments basically perform similar processing, but the second embodiment differs from the first embodiment in two ways: (1) alignment processing, and (2) no expansion processing (thickening) to the surrounding pixels of the correction area. In the former (1) alignment, for the first image data obtained by reading the base image, characteristic objects or registration marks (e.g., multiple cross marks formed near the corners of the paper) formed in the base image and the edges of the paper are detected by image recognition, and the image formation position relative to the paper is grasped. Then, by comparing this with the reference data, alignment (shift, rotate, magnification adjustment, etc.) with the reference image data is performed. The reference image data here is the original image data of the base image, or proof image data obtained by reading a sample printed paper.

(Step S801)
The conveyed printed paper 313 is read by the reading unit 16 to generate first image data 603 .

(Steps S802 and S803)
The correction area determination unit of the control unit 11 performs a registration process on the first image data 603 with the reference image data 604, and then compares pixels at corresponding positions to determine a correction area, thereby generating image data for correction 420 and storing it in the page memory 114. Note that this correction area is not expanded to adjacent pixels, as described below, except when the base image is a simple pattern, for example, a uniform color like the pre-printing paper 310 in FIG.

(Step S804)
Here, the same process as in step S704 in FIG. 9 is performed, and an exposure signal is output to the writing unit 1302 for each main scanning line by synchronizing the timing.

(Steps S811 to S814)
9, the control unit 11 performs various image processing on the overwrite image data 411, acquires the first exposure signal 4101 and the second exposure signal 4201 by matching the timing for each line, and takes a logical sum for each pixel to generate a third exposure signal 4301. Then, the writing units 1302 (Y to W) of the image forming unit 13 perform exposure according to the input third exposure signal, and form a print image 514 formed with toner of each color on the printed paper 313 on which the base image has been printed.

(Example of processing of overprinted paper)
Next, referring to FIG. 12, the generation process of the exposure signal in the printing process of FIG. 11 when using a printed paper will be described. In the overprinting paper, each color is mostly used, so the colors to be processed in the correction image data are four colors, W, Y, M, and C. Note that K color is not easily used as a color for correction (stain removal), so it is excluded from the processing target in the example of FIG. 12. Note that K color may be included as a target. For example, when printing a negative image, that is, when using a dark color paper such as black and printing characters, lines, etc. in light colors (W color, Y color, etc.), K color may also be a processing target.

In the signal generation process of FIG. 12, as in the examples of FIG. 9 and FIG. 10, the correction area determination unit compares the first image data with the reference image data for each pixel, and extracts pixels with a difference greater than a predetermined value as candidate pixels. This reference image data is original image data corresponding to the base image, or proof image data, and has different pixel values for each position. For example, when there is a difference of 10/255 or more, it is extracted as a candidate pixel, and when a certain number of such pixels are consecutive, it is determined to be a correction area.

Next, the correction signal generating section of the control section 11 (for example, the image control circuit 113) generates second exposure signals for the colors Y to C and W. The second exposure signal for W at this time is PWM 100% (255/255) as in Figures 9 and 10, but the PWM for Y to C has a value according to the pixel value at each position of the reference image data (base image). For example, it is set to the same value as the pixel value of the reference image data.

The output control unit of the control unit 11 takes the logical sum of the first exposure signal and the second exposure signal for each color to generate a third exposure signal. Specifically, it takes the logical sum of the first exposure signal and the second exposure signal for each of the colors Y to C and W to generate a third exposure signal for each of the colors Y to C and W. In this way, by determining the correction area and generating the correction signal using the exposure signal, high-speed signal processing can be performed with a simple configuration, thereby achieving high-speed image processing, and if there are any defects such as printing abnormalities or stains on the printed paper, these can be corrected and a new image can be printed.

The configuration of the image forming device 1 described above is the main configuration described in explaining the features of the above embodiment, but is not limited to the above configuration and can be modified in various ways within the scope of the claims. Furthermore, the configuration of a typical image forming device 1 is not excluded.

For example, in the image forming device 1 of FIG. 1, the reading unit 16 is disposed upstream of the image forming unit 13 in the transport path, but the reading unit may be disposed on the downstream transport path. FIG. 13 is a schematic diagram showing the configuration of an image forming device 1b in a modified example. In the image forming device 1b, a reading device 10d and a transport device 10e are connected downstream of the device main body 10a. The reading device 10d is provided with reading units 16a and 16b that respectively read images on the front and back sides of the paper 300 transported along the transport path. After the base image is printed by the image forming unit 13, the paper 300 transported from the paper feed tray 145a is read by the reading unit 16a, and read image data (first image data) is generated. In addition, when the base image is not printed, the image is read by the reading unit 16a without image formation by the image forming unit 13, and read image data (first image data) is generated. In this case, a large number of sheets of paper 300 (for example, 500 sheets per cassette) are transported continuously, turned over by the transport device 10e, and stacked in the same order on the paper output tray 144. After that, the paper 300 and the scanned image data are associated with each sheet on a cassette basis as specified by the user, and then the printing process shown in FIG. 8 can be performed.

In addition, while the image forming apparatuses 1 and 1b are shown as examples equipped with an image forming unit 130 for W, this may be omitted and the image forming apparatus may be configured with general image forming units 130 for Y, M, C, and K. In this case, for example, the above-mentioned printing process can be performed on Y-color paper, with Y-color being the processing target for correction (erasure).

The means and methods for performing various processes in the image forming apparatuses 1 and 1b according to the above-described embodiments can be realized by either a dedicated hardware circuit or a programmed computer. The above programs may be provided by a computer-readable recording medium such as a USB memory or a DVD (Digital Versatile Disc)-ROM, or may be provided online via a network such as the Internet. In this case, the programs recorded on the computer-readable recording medium are usually transferred to and stored in a storage unit such as a hard disk. The above programs may also be provided as standalone application software, or may be incorporated into the software of the device as one of its functions.

1, 1b image forming device,
10a device main body 10b paper feed device 10c, 10d reading device 10e conveying device 11 control unit,
111 CPU,
112 control memory,
113 Image control circuit,
114 page memory,
115 Buffer,
12 Storage section 13 Image forming section 130 Image forming unit 1301 Photoconductor drum 1302 Writing unit 1303 Developing device 131 Intermediate transfer belt 132 Secondary transfer section 133 Fixing section 14 Paper feed conveying section 15 Operation display section 16, 16a, 16b Reading section 17 Print controller 18 Synchronization signal generating circuit 900 Terminal device

Claims (12)

a correction area determination unit that analyzes the first image data corresponding to each of the acquired printing sheets and determines a correction area;
a correction signal generating unit that generates a second exposure signal for correction based on the determined correction area;
an output control unit that generates a corrected third exposure signal by correcting a first exposure signal generated from print data of a print job with the second exposure signal;
an image forming section that forms an image on the paper based on the third exposure signal;
An image forming apparatus comprising: the image forming section includes a plurality of image forming units each developing a toner of at least yellow, magenta, cyan, and black colors,
The paper for printing is white paper, colored paper, or paper on which a base image for overprinting has been printed,
the first image data is read image data obtained by reading the paper;
The image forming apparatus according to claim 1 , wherein the correction area determination unit determines the correction area by comparing the first image data with reference image data stored in advance. 3. The image forming apparatus according to claim 2, wherein the output control section generates the third exposure signal by a logical sum of the first exposure signal and the second exposure signal in each of the image forming units. the first image data is read image data obtained by reading the blank paper,
4. The image forming apparatus according to claim 2, wherein the correction area determination section uses image data constituted by uniform standard pixel values corresponding to a color of the white paper as the reference image data. the image forming section includes a plurality of image forming units for developing yellow, magenta, cyan, and black toners, respectively, and further includes a white image forming unit for developing white toner;
said paper for printing is blank,
the correction area determination unit compares the reference image data, which is configured with uniform pixel values, with pixel values of the read image data obtained by reading the white paper, and determines an area in which pixels having a difference of a predetermined value or more are consecutive as the correction area for white;
The image forming apparatus according to claim 4 , wherein the correction signal generating section generates the second exposure signal of the image forming unit for white based on the determined correction area for white. The paper for printing is colored paper,
the correction area determination unit uses image data composed of uniform standard pixel values corresponding to the color of the colored paper as the reference image data,
the correction area determination unit compares the reference image data, which is composed of uniform pixel values, with pixel values of the read image data obtained by reading the color paper, and determines an area in which pixels having a difference of a predetermined value or more are consecutive as the correction area for the color of one or more of the image forming units corresponding to the pixel values of the reference image data;
4. The image forming apparatus according to claim 2, wherein the correction signal generating section generates the second exposure signal of the image forming unit for the color based on the determined correction area for the color. the image forming section includes a plurality of image forming units for developing yellow, magenta, cyan, and black toners, respectively, and further includes a white image forming unit for developing white toner;
The image forming apparatus according to claim 6 , wherein the correction signal generating section generates the second exposure signal for the image forming unit for white based on the determined correction area. The paper for printing is a paper on which a base image for overprinting is printed,
the correction area determination unit uses original image data used for printing the base image as the reference image data,
the correction area determination unit compares the original image data with pixel values of read image data obtained by reading the printed paper, and determines an area in which pixels having a difference of a predetermined value or more are consecutive as the correction area for the color of one or more of the image forming units corresponding to the pixel values of the reference image data;
4. The image forming apparatus according to claim 2, wherein the correction signal generating section generates the second exposure signal of the image forming unit for the color based on the determined correction area for the color. the image forming section includes a plurality of image forming units for developing yellow, magenta, cyan, and black toners, respectively, and further includes a white image forming unit for developing white toner;
The image forming apparatus according to claim 8 , wherein the correction signal generating section generates the second exposure signal for the image forming unit for white based on the determined correction area. 10. The image forming apparatus according to claim 2, wherein the correction signal generation unit generates a second exposure signal for correction by correcting an exposure signal for a plurality of pixels included in the determined correction area and for pixels surrounding the correction area. A control program executed by a computer that controls an image forming apparatus having a printing unit that forms an image on a sheet,
A step (a) of analyzing first image data corresponding to each of the acquired printing sheets and determining a correction area;
(b) generating a second exposure signal for correction based on the determined correction area;
(c) generating a corrected third exposure signal by correcting a first exposure signal generated from print data of a print job with the second exposure signal;
and (d) forming an image on the paper by an image forming unit based on the third exposure signal. The paper for printing is blank paper, colored paper, or paper on which an image for overprinting has been printed,
the first image data is read image data obtained by reading the paper;
The control program according to claim 11 , wherein in the step (a), the correction area is determined by comparing the first image data with reference image data stored in advance.