JPH03189158A - Image forming device - Google Patents

Abstract

PURPOSE:To improve quality of a reproductive image by a method wherein a recording head is so selected that overlap of residual density irregularity is minimized based on a residual density irregularity data of a recording head which is stored in a storing means. CONSTITUTION:A color copying machine 306 forms a gradation pattern based on a constant density gradation pattern data generated with a pattern generator 305. An image read scanner 307 reads an image printed with the digital color copying machine 306. A frame memory 304 stores the read image data, and a secondary recorder 301a as a storage means stores a residual density irregularity data of a multinozzle ink jet head. A computer device 301 as a head selectively means selects a recording head so that overlap of residual density irregularity is minimized based on the residual density irregularity data stored in the secondary recorder 301a.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus having a recording head in which a plurality of ejection ports are arranged in correspondence with the width of recording paper. [Prior Art 1] Conventionally, this type of image forming apparatus only performs density unevenness correction on a multi-nozzle inkjet head in which a plurality of ejection ports are arranged corresponding to the width of recording paper. [Problems to be Solved by the Invention] However, even though it appears that the density unevenness has been corrected, it is actually not fully corrected, so that minute density unevenness remains in the multi-nozzle inkjet head alone. For this reason, multiple multi-nozzle inkjet heads are used to eject multiple colors of ink, for example, cyan, magenta, yellow, and black, onto the same recording paper. When performing full color printing, minute residual density unevenness may be located at the same nozzle position. In such cases, the density unevenness due to color mixing becomes very thick (
This poses a problem in that it stands out and degrades the quality of the formed image. An object of the present invention is to provide an image forming apparatus that can solve the above problems and improve the quality of reproduced images. [Means for Solving the Problems 1] In order to achieve such an object, the present invention provides an image forming apparatus having a recording head in which a plurality of ejection ports are arranged corresponding to the width of recording paper. The apparatus includes a storage means for storing residual density unevenness data, and a head selection means for selecting recording/positioning based on the residual density unevenness data stored in the storage means so that the overlap of the remaining density unevenness is minimized. It is characterized by [Function] In the present invention, residual density unevenness data of the recording head is stored in the storage means, and based on the residual density unevenness data stored in the storage means, the recording head is adjusted so that the overlap of the remaining density irregularities is minimized. Select by selection means selection. [Embodiment 1] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the invention. In FIG. 1, 305 is a pattern generator that generates a gradation pattern of constant density. The pattern generated by the pattern generator 305 is
As shown in the figure, gradation data of constant density spans three lines. The pattern generator 305 is 33%,
Each density data of 50% and 75% can be selected and generated. Reference numeral 306 is a multi-nozzle inkjet type digital color copying machine that uses only one head of the printer shown in FIG. It forms the An image reading scanner 307 reads the image printed by the digital color copy 1'j 1306. A frame memory 304 stores image data read by the image reading scanner 307. 301 is a computer device, which serves as head selection means;
Based on the residual density unevenness data stored in the secondary printing device 301a, printheads are selected so that the overlap of the remaining density unevenness is minimized. Reference numeral 301a denotes a secondary recording device within the computer device 301, which serves as storage means for storing residual density unevenness data of the multi-nozzle inkjet head. (Pattern Generator 305) FIG. 2 shows the configuration of the pattern generator 105 shown in the first diagram. In FIG. 2, a control unit 401 is equipped with a microprocessor and generates patterns, sends image data to the printer 305, and controls the printer 306. Reference numeral 402 denotes a constant density pattern generation unit, which generates multi-value density data of a constant density under the control of the control unit 401. A head correction unit 203 corrects the multi-value data generated by the constant density pattern generation unit 402. The head correction unit 403 is composed of RAM and can be easily rewritten, so if you want to perform correction again after the head correction processing is completed, you can simply write the correction data to the RAM and the processing will be faster. It is possible to aim for A dither unit 404 converts the binary data corrected by the head correction unit 203 into binary data using a dither method. 405 is a parallel-to-serial converter that converts parallel signals into serial signals. Note that the head correction section 403, dither section 404, and parallel-to-serial conversion section 405 have the same configuration as the head correction sections 411 and 412 of the scanner section shown in FIG. As a result, completely equivalent head correction can be performed even if the result of the correction performed by the head correction section 203 in the pattern generator 105 is stored in the ROM and inputted into the head correction section 211 of the scanner section of the actual machine. Further, the density unevenness correction data is transferred by the computer device 301 to the head correction section 403 via the control section 401. After confirming that the correction has been properly performed, the data is transferred to the PROM writer 302 and converted into ROM. Next, the computer device 301 when performing head correction
The control procedure will be explained below. The head to be corrected is transferred to the digital color copying machine 30.
6. The color of the ink used may be the most sensitive color depending on the characteristics of the image reading scanner 307. In this example, black is used. Next, the operator instructs the computer device 301 to print out without applying head correction. This command is accepted by the control unit 401 of the pattern generator 305, and the control unit 401 starts processing. At this time, the head correction section 40 performs no head correction calculation.
Through data is written in 3, and a 50% density pattern is printed in only 3 lines as shown in FIG. After the operator places this output image on the document reading section of the image reading scanner 307, the operator again commands the computer device 301 to perform head correction. When the computer device 301 receives this command, it operates the frame memory 304 and the image reading skill 307, and writes the image output to the frame memory 304. The reading area at this time is, as shown in FIG. 3, the image for three lines and the non-printing area before and after it. The number of images to be read is 512 pixels in the H scan direction, and 10 pixels in the ■ scan direction.
It has 24 pixels. Since one pixel is 8-bit multi-value data, a total of 512 kbytes is written into the frame memory 304. The reading pixel density of the image reading scanner 307 and the printing pixel density of the digital color copying machine 306 are both set to 400 dpi. Next, based on the image data written in the frame memory 304, the average density of each pixel in the H scan direction is calculated, and (2) the density in the scan direction is determined for each pixel. As a result, the density curve shown in FIG. 3 is obtained in the computer device 301. After that, identify areas where the density is thick (fluctuations) and identify an image area for 3 lines.The image area is identified.
Head correction calculation is started using the image of the second line (center line) as the calculation target. As shown in Fig. 4, the head correction calculation calculates whether each pixel is large or small with respect to the reference value at 50% density. is 256). As a result of the calculation, if the density is higher than the standard value, create correction data that lowers the density, and if the density is lower than the standard value, create correction data that increases the density. When the above calculations are completed, 256 bytes of correction data for each nozzle of the head are obtained.Then, this correction data is sent to the head correction section 4 of the pattern generator 305.
03, and based on the written correction data, a 50% density pattern shown in FIG. 3 is printed by the digital color copying machine 306. Then, the operator visually checks the printed image, and if the result of the check is satisfactory, instructs the computer device 301 to write this data into the PROM writer 302. When the writing is completed, the operator writes the written ROM
Remove the head together with the head. On the other hand, if the operator determines that the correction is insufficient as a result of visual judgment, the corrected image is read again by the image reading scanner 307 and the same processing as described above is performed. At this time, the computer device 301 is instructed that this is the second correction (thereby, it adds or subtracts the previous correction data and calculates to set the correction amount to a smaller value. After that, the image is printed again. The operator visually checks it again and decides whether or not to correct it again.If the operator decides to correct it again as a result of the judgment, the same process as the second correction is repeated.Usually, at most several times. With this, the density unevenness correction for one head is completed. When the density unevenness correction is completed, the computer device 30
1 stores the final density unevenness data of this head together with the identification code of the head, such as the manufacturing lot number. Thereafter, the same procedure is performed for each head to correct density unevenness. Therefore, in this embodiment, two
Based on the final residual density unevenness data of each head stored in a storage device such as a disk, software is installed that automatically selects combinations of heads so that the remaining density unevenness of each head does not overlap. has been
Heads are automatically sorted as shown in FIG. 4 as an example. In this embodiment, the operator instructs the computer device 301 to start sorting when all the density unevenness corrections for all the heads to be processed in that manufacturing lot are completed, so that the processing is performed for all the heads at that time, and the combination of heads is performed. We have adopted a method that determines all of the following. If it is not possible to find a combination in which the remaining density unevenness does not overlap for all the heads, you can choose to use a combination in which the overlap of the unevenness is as small as possible, or to remove a specific head and perform the process. (1) The image reading scanner 307 and the digital color copying machine device 306 are specially designed, and the configuration is such that the output from the digital color copying machine 306 is automatically read and then the paper is automatically ejected. By repeating the correction until the density unevenness of each nozzle is below a certain value,
It is now possible to perform head correction completely automatically, making work even more efficient. (2) In this embodiment, the application is explained as an inkjet full-color digital color copying machine that prints four colors overlapping, but the application is not limited to this. Applicable if applicable. (Digital color copying machine 306) (FIG. 5) FIG. 5 shows the digital color copying machine 306 shown in the first figure. In the figure, 1 is a color image scanner that reads an original image and outputs digital color image data to an external device. Reference numeral 3 denotes a printer section that records the color digital image signal output from the color image scanner 1 on recording paper. The printer section 3 is a full-color inkjet printer using a recording head of the inkjet recording method described in Japanese Patent Laid-Open No. 54-59936. The color image scanner 1 and the printer section 3 can be separated, and by extending the connection cable, they can be installed at a separate location. (Printer section 3) (FIG. 6) FIG. 6 is a sectional view of the digital color copying machine 306 shown in FIG. The exposure lamp 14, the lens 15, and the CC016 capable of reading line images in full color read the original image placed on the original table glass 17, the projected image by the projector, or the sheet original image by the sheet feeding mechanism 12. . Next, various types of image processing are performed on the read image by the scanner section 1 and the controller section 2, and the image is recorded on recording paper by the printer 3. The recording paper comes from a paper feed cassette 20 that stores cut sheets of small standard sizes, in this embodiment A4 to A3 sizes, and rolls for recording large sizes, A2 to AI sizes in this embodiment. It is supplied from paper 29. Further, by inserting the recording sheets one by one through the manual feed slot 22 shown in FIG. 5 along the paper feed section cover 21, paper feeding from outside the apparatus, that is, manual paper feeding is possible. The cut paper from the paper cassette 20 is
The cut sheets are fed one by one by the roller 24, and the fed cut sheets are transferred to the feed tube 10-ra 26 by the cut sheet feed roller 25.
transported to. The roll paper 29 is sent out by a roll paper feed roller 30, cut into a standard length by a cutter 31, and then transferred to the paper feed number 10.
- It is conveyed to La 26. Further, the recording paper inserted through the manual feed slot 22 is conveyed to the 10th paper feed roller 26 by the manual feed roller 32. Big up roller 24, cut paper feed roller 25
, the roll paper feed roller 30, the 10th paper feed roller 26, and the manual feed roller 32 are driven by a paper feed motor (not shown) (in this embodiment, a DC servo motor is used), and each roller It is controlled on and off at any time by an attached electromagnetic clutch. When the printing operation is started by an instruction from the controller unit 2, the recording paper selectively fed from any of the above-mentioned paper feeding paths is conveyed to the paper feeding path 26. In order to eliminate the skew of the recording paper, after a predetermined amount of paper loops have been made, the paper feed number 10-ra 26 is turned on and the paper feed number 20-2 is turned on.
The recording paper is conveyed to the roller 27. In order to perform accurate paper feeding operation between the paper feeding roller 28 and the paper feeding roller 27,
A buffer is created by slackening the recording paper by a predetermined amount between the 10th sheet feeder 26 and the 20th sheet feeder 27. The buffer amount is detected by the buffer amount detection sensor 33. By constantly creating a buffer during paper conveyance, the load on the paper feed roller 28 and paper feed roller 27 is reduced, especially when large-sized recording paper is conveyed, allowing accurate paper feed operation. I have to. When printing with the inkjet recording head 37, a scanning carriage 34 on which the recording head 37 etc. are attached is used.
is scanned back and forth on a carriage rail 36 by a scanning motor 35. In the forward scan, an image is printed on the recording paper, and in the backward scan, the recording paper is fed by a predetermined amount by the paper feed roller 28. At this time, the drive system is controlled by the paper feed motor based on the buffer amount detected by the buffer amount detection sensor 33 so that a predetermined buffer amount is always maintained. The printed recording paper is discharged to the paper discharge tray 23, and the printing operation is completed. (Around the scanning carriage 34) (FIG. 7) Next, the area around the scanning carriage 34 will be explained in detail. In FIG. 7, a paper feed motor 40 is a drive source for intermittently feeding the recording paper, and the paper feed motor 40 is a driving source for intermittently feeding the recording paper, and is connected to the paper feed 20-ra 27 via each feed roller 28 and the paper feed 20-ra clutch 43.
It is what drives the. The scanning motor 35 is a driving source for causing the scanning carriage 34 to scan in the directions of arrows A and B via the scanning belt 34. In this embodiment, since accurate paper feeding control is required, pulse motors are used for the paper feeding motor 40 and the scanning motor 35. When the recording paper reaches paper feed number 20-27, paper feed number 20
-Ra clutch 43 and paper feed motor 40 are turned on, and the recording paper is conveyed over platen 39 to paper feed roller 28. The recording paper conveyed on the platen 39 is detected by a paper detection sensor 44 on the platen 39, and the sensor information is used for position control, jam control, and the like. When the recording paper reaches the paper feed roller 28, the paper feed number 20-
The clutch 43 and paper feed motor 40 are turned off,
The recording paper is sucked from inside the platen 39 by a suction motor (not shown), and the recording paper is brought into close contact with the platen 39. Prior to the image recording operation on the recording paper, the scanning carriage 3
4 to the position of the home position sensor 41,
Next, forward scanning is performed in the direction of arrow A, and cyan, magenta, yellow, and black inks are ejected from the recording head 37 from predetermined positions to record an image. When the image recording for a predetermined length is completed, the scanning carriage 34 is stopped, and after stopping, backward scanning is started in the direction of arrow B, and the scanning carriage 34 is returned to the home position.
Return to the position of the position sensor 41. During this backward scanning, the paper feed roller 28 is driven by the paper feed motor 40 to feed the paper in the direction of arrow C by the length recorded by the recording head 37. The inkjet recording head 37 is configured to form bubbles using heat and use the resulting pressure to eject ink droplets. Four inkjet recording heads 37 are used, and 256 nozzles are assembled into one recording head. When the scanning carriage 34 is detected by the home position sensor 41 and stopped at the home position, recovery processing of the recording head 37 is performed. This recovery process is performed using preprogrammed settings such as paper feeding time, internal temperature, and ejection time in order to prevent unevenness at the start of ejection caused by changes in the viscosity of ink remaining in the nozzles of the recording head 37. This is a process in which pressure is applied to the recording head 37, ink is idly ejected, etc. according to conditions. Thereafter, the same operation is repeated and the image is recorded on the entire surface of the recording paper. (Scanner Section 1) (FIGS. 8 and 9) In FIG. 8, the CCD unit 18 is composed of a CGD 16, a lens 15, and the like, and reads an image on the document table glass 17 in the main scanning direction. The drive system in the main scanning direction is a main scanning motor 50 identified on the rail 54,
It is composed of a pulley 51, a pulley 52, and a wire 53, and moves the CCD unit 18 on a rail 54. The light shielding plate 55 and the home position sensor 56 are used for position control when the CCD unit 18 is moved to the main scanning home position within the correction area 68 shown in FIG. The rail 54 is connected to the rails 65 and 6 by a drive system in the sub-scanning direction.
9. You will be guided up the stairs. The drive system in the sub-scanning direction includes a sub-scanning motor 60, pulleys 67, 68, 71, 76, and shafts 72, 73.
, wire 66.70. The light shielding plate 57 and the home position sensors 5g and 59 set the home position for sub-scanning either in a book mode for reading a document such as a book placed on the platen glass 17, or in a sheet mode for reading a sheet. ni rail 54
It is used for position control when moving. Sheet feed motor 61, sheet feed roller 74°75,
The pulleys 62, 64 and the wire 63 constitute a mechanism for feeding the sheet original. A sheet original placed with the original surface facing downward on the original table glass 17 is fed by sheet feed rollers 74 and 75 by a predetermined amount. Next, reading operations in book mode and sheet mode will be explained. (a) In the book mode, the CCD unit 1 is placed at the book mode home position (book mode HP) in the correction area 68 shown in FIG.
8 and start reading the document from the book mode HP. The original is placed on the original table glass 17. Prior to scanning the original, data necessary for processing such as shading correction, black level correction, color correction, etc. is set in the correction area 68. Thereafter, the CCD unit 18 is driven by the main scanning motor 50 to move the area (2) shown in FIG. 9 in the direction of the arrow, that is, in the main scanning direction. When the reading of area ■ is completed, the main scanning motor 50 is reversed, the sub-scanning motor 60 is driven, and the CCD unit 18 is moved to the correction area 68 of area ■.
will be moved to Next, in the same way as when main scanning area ■,
If necessary, perform shading correction, black level correction,
Then, processing such as color correction is performed, and area (■) is read. Thereafter, similar scanning is repeated to read areas (1) to (2). Then, after reading area ■, the CCD
Return unit 18 to book mode/home position. In this embodiment, since a maximum A2 size document can be read, scanning must actually be performed more times, but in this explanation, the operation is simplified to make it easier to understand. (b ) In the sheet mode, the CCD unit 18 is moved to the sheet mode home position (sheet mode HP), that is, area ■, and the sheet original is read repeatedly while being operated intermittently by the sheet feed motor 61, and the entire sheet original is read. Prior to scanning, processing such as shading correction, black level correction, and color correction is performed in the correction area 68, and then the CCD unit 18 is moved by the main scanning motor 50 in the direction of the arrow shown in the figure to move the CCD unit 18 in the main scanning direction. Then, after the outbound reading operation of area ■ is completed,
The main scanning motor 50 is reversed, and the sheet feed motor 61 is driven during the backward scan to move the sheet original by a predetermined amount in the sub-scanning direction. Thereafter, the same operation is repeated to read the entire sheet document. If the same size reading is performed in this way, C
The area that can be read by the CD unit 18 is actually a wide area, as shown in FIG. This is because the digital color copying machine of this embodiment has a magnification/reduction function. That is, as mentioned above, the area that can be recorded by the sink jet recording head 37 is fixed at 256 bits at a time, so when reducing the image by 50%, for example, the image information of an area of 512 bits, which is at least twice as large, will be reduced. This is because it becomes necessary. Therefore, the scanner section 1 has a function of reading and outputting image information of an arbitrary image area by one main scan reading. (Film Projection System) (FIGS. 10 and 11) This is a perspective view when a projector unit 81 and a reflecting mirror 80 are attached to the scanner section 1. The projector unit 81 projects negative film and positive film, and is composed of a halogen lamp 90, a reflecting plate 89, a condensing lens 91, a film holder 82, and a projection lens 92, as shown in FIG. The direct light from the halogen lamp 90 and the reflected light from the reflection plate 89 are collected by a condenser lens 91 and transmitted through the film, and the projected image on the film is optically magnified by the projection lens 92. ing. The film holder 82 holds negative/positive film and can be attached to the projector unit 81. The film holder 82 holds one for negative film and one for positive film.
It has a window that is slightly larger than the size of the frame, allowing for plenty of room to load the film. The reflecting mirror 80 reflects the image projected from the projector unit 81. Fresnel lens 83 is reflective mirror 8o
The reflected image is converted into parallel light and placed on the document table glass 1.
The image is formed on 7. This image is read in book mode by a CCD unit 18 in the scanner 1, and converted into a video signal by the CCD unit 18. The 22mm x 34mm film image and the projected image magnified 8 times on the platen glass are shown in the first image.
Shown in Figure 2. (Description of overall functional blocks) (FIG. 13) The functional blocks of the digital color copying machine of this embodiment will be explained. The control units 102, 111, and 121 are control circuits that are composed of a microcomputer, program ROM, data memory, communication circuit, etc., and control the scanner unit 1, controller unit 2, and digital color copying machine unit 3, respectively. It is. Between the control units 102 and 111 and between the control units 111 and 121,
A so-called master slew 1 control mode is adopted in which the control units 102 and 121 operate according to instructions from the control unit 111 and are connected through a communication line. When operating as a color copying machine, the control section 111 operates according to input instructions from the operation section IO and the digitizer 114. The operation unit 10 has a touch panel 85 made of transparent electrodes on the surface of the LCD display unit 84, and the touch panel 85 allows selection instructions such as designation of specified editing operations regarding colors. The operation unit 10 includes keys related to operations, such as a start key 87 for instructing the start of a copying operation;
Frequently used keys such as a stop key 88 for instructing to stop the copying operation, a reset key 89 for returning the operation mode to the standard state, and a projector key 86 for selecting a projector are provided independently. The digitizer 114 is used to input positional information necessary for trimming, masking, etc., and is connected as an option when complex editing processing is required. The control unit 111 is, for example, a control circuit of a general-purpose parallel interface such as IEEE-488, so-called GP-IB interface, that is, the I/F control unit 11
2, and image data input/output between external devices and remote control by the external devices can be performed via this interface. The control unit 111 also includes a multi-value synthesis unit 106, an image processing unit 107, a binarization processing unit 10g, which performs various processes related to images.
It controls the binary synthesis section 109 and the buffer memory 110. The control unit 102 includes a mechanical drive unit 105 that drives and controls the mechanism of the scanner unit 1, an exposure control unit 103 that controls exposure of a lamp when reading a reflective original, and an exposure control unit that controls exposure of a halogen lamp 90 when using a projector. Control unit 10
4. Further, the control unit 102 controls an analog signal processing unit 100 that performs various types of processing regarding images, and an input image processing unit 101. The control unit 121 absorbs time variations in the mechanical operation of the mechanical drive unit 105 that drives and controls the mechanisms of the digital color copying machine unit 3 and the mechanical operation of the digital color copying machine unit 3. The synchronization delay memo IJ115 for correcting the delay is controlled. Next, the image processing section shown in FIG. 13 will be explained. The COD 16 converts the formed image into an analog electrical signal. The converted image information is serially processed in the order of red → green → blue. The analog signal processing unit 100 performs sample hold, dark level correction, dynamic range control, etc. for each color of red, green, and blue, and then performs analog-to-digital conversion (A/D conversion) and serial multi-color processing. It converts into a digital image signal of a value (in this embodiment, each color has a length of 8 bits). The input image processing unit 101 similarly performs correction processing necessary in the reading system, such as CCD correction and γ correction, on the serial multi-valued digital image signal. The multi-value synthesis section 106 of the controller section 2 is connected to the scanner section 1.
Serial multilevel digital image signals sent from
A serial multi-value digital image signal sent via a parallel I/F is selected and synthesized. The selectively combined image data is sent to the image processing unit 107 as a serial multi-level digital image signal. The image processing unit 107 performs smoothing processing, edge enhancement, black extraction, masking processing for color correction of recording ink used in the recording heads 117 to 120, and the like. The serial multilevel digital image signal is processed by a binarization processing unit 10.
8 and buffer memory 110, respectively. The binarization processing unit 10g binarizes the serial multilevel digital image signal, and can select either simple binary processing using a fixed slice level, pseudo halftone processing using a dither method, etc. There is. Here, the serial multi-value digital image signal is converted into a four-color binary parallel image signal. The four-color image data is input to the binary synthesis section 109, and the three-color image data is input to the buffer memory 110. The buffer memory 110 is a buffer memory for inputting and outputting multivalued images and binary images via a parallel I/F, and has memories for three colors. The binarization processing unit 108 combines the binary parallel image signal from the buffer memory 110 and the four-color binary parallel image signal from the binarization processing unit 108 and converts it into a four-color binary parallel image signal. do. The synchronization delay memory 115 of the printer section 3
absorbs time variations in mechanical operation of the recording head 117.
The delay due to the mechanical arrangement of the recording heads 117 to 120 is corrected, and timing signals necessary for driving the recording heads 117 to 120 are generated. The head driver 116 drives the recording heads 117 to 120, and generates a signal that can directly drive the recording heads 117 to 120. The inkjet recording heads 117 to 120 eject cyan, magenta, yellow, and black ink, respectively, to record an image on recording paper. (Timing of each part shown in FIG. 13) (FIG. 14) FIG. 14 shows an example of the timing of each part shown in FIG. 13. Signal BVE is a signal indicating an image valid section for each main scan. A full-screen image is output by outputting the signal BVE multiple times. The signal VE is a signal indicating a valid section of the image read by the CCD 16 for each line. When signal BVE is valid, only signal VE is valid. Signal VCK is a clock signal for sending out image data VD. Signal BVE and signal VE change in synchronization with this signal VCK. The signal HS is a signal used when a valid section and an invalid section are discontinuously repeated while the signal VE is output for one line. If the signal VE is continuously valid while one line is output, it is an unnecessary signal. This is a signal indicating the start of one line of image output. (Image processing section 107) (FIG. 15) FIG. 15 shows the configuration of the image processing section 107 shown in FIG. 13. The image processing unit 107 shown in FIG.
, (in this order) (hereinafter referred to as input image data), the serial-to-parallel converter 201 converts the image data into
The signal is converted into parallel signals of yellow (Y), magenta (M), and cyan (C), and sent to the masking unit 202 and the selector 203. The masking unit 202 corrects the cloudy color of the output ink, and performs calculation based on the following equation (1). Y, M, C: Input data Y', M', C': Output data, digital data from A/D converter 11O is B,
G, R, B, G, R, . . . are output in this order. The obtained digital data is converted into complementary color data Y, M, C by the complementary color conversion circuit 120.
, Y, M, C... are output in this order. Since the input image data and the subsequent image data have different frequencies, the obtained color sequential color image data is frequency-converted by the time-axis conversion unit 200a according to the time-axis conversion control signal sent from the control unit 200. is performed and output. The output image data (hereinafter referred to as input image data) is processed by the serial-parallel converter 201.
The signals are converted into Y, M, and C parallel signals and sent to a masking unit 202 and a selector 203, and the masking unit 202 corrects the color cloudiness of the output ink based on equation (1). After the ink cloudiness is corrected by the masking unit 202 determined by the masking control signal from the control unit 200, the selector unit 203 and U
It is input to the CR section 205. Input image data and image data output from the masking unit 202 are input to the selector 203 . The input image data is selected by the selector 203 based on the selector control signal 1 sent from the normal control section 200. If the color correction in the input system is not sufficiently performed, the image data from the masking unit 202 is selected and output by the control signal 1. The serial image data output from the selector 203 is
The black extraction unit 204 extracts Y at one pixel. In order to set the minimum value of M, C as black data, Y, M, C
The minimum value of is detected, and the detected black data is sent to the UCR unit 2.
05 is input. The UCR unit 205 subtracts the extracted black data from each of the Y, M, and C signals, and simply multiplies the black data by a coefficient. The time difference between the black data input to the OCR unit 205 and the image data sent from the masking unit 202 is corrected, and calculation is performed based on the following equation (2). Here, Y, M, C, Bk: extraction unit input data Bk'
:Extraction unit output data Then, the coefficient a + + a2* as + a4 is determined by the OCR control signal sent from the control unit 200. The data output from the UCR unit 205 is input to the γ-offset unit 206, and the γ-offset unit 206 performs gradation correction based on the following equation (3). Here, Y, M, C, Bk: γ/offset section input data Bk
': γ・Offset unit output data Also, the coefficients blb, ~ClC4 in equation (3) are γ sent from the control unit 200.
- Determined by the offset control signal. The signal whose gradation has been corrected by the γ/offset section 206 is N9
The line buffer 207 stores 12 minutes of image data, and the line buffer 207 causes the control unit 200 to
5 lines of data necessary for the smoothing and edge emphasizing section 208 in the subsequent stage are outputted in 5 lines in parallel by a memory control signal from . These five lines of signals are sent to the control unit 200.
A filter control signal is input to a spatial filter with a variable filter size, and after smoothing, edge enhancement is performed. By smoothing, as shown in FIG. 16, the average value of the pixel of interest and surrounding pixels is set as the density value of the pixel of interest,
Image noise is removed. Further, the difference between the pixel data of interest and the smoothed signal is used as an edge signal, and the edge signal is added to the pixel data of interest to perform edge enhancement. Note that a detailed explanation of the smoothed edge enhancement unit 208 will be omitted. The smoothed and edge-enhanced image data is processed by the color conversion unit 20.
9 performs color conversion based on a color conversion control signal from the control unit 200. The digitizer device 114 in FIG. 9 inputs in advance the color to be converted, the color to be converted, and the area in which the signal is valid, and the image data is replaced by the color conversion unit 209 based on the data. Note that a detailed explanation of the color conversion unit 209 will be omitted. The smoothed, edge-enhanced image signal and the color-converted image signal are input to the selector 210, and the selector 210 selects image data to be output based on the selector control signal 2. Which image data to select is determined by specifying a valid area input from the digitizer device 114. The image signal selected by the selector 210 is sent to the buffer memories 110 and 2 shown in FIG.
The data is input to the value conversion processing unit 108. Note that a description of the system input to the buffer memory 110 will be omitted. Next, the binarization processing section 108 will be explained. The image data input to the binarization processing unit 108 is
The signal is input to the head correction section 211 shown in the figure. The head correction section 211 will be explained later. The image signal whose density has been corrected by the head correction section is sent to the dither section 212 in the order of Y, M, C, Bk in serial 8.
It is input in bits. The dither unit 212 has 6 bits in the main scanning direction for each color.
t, has a memory space of 6 bits in the sub-scanning direction (or 4 bits in the main scanning direction and 8 bits in the sub-scanning direction), and the dither unit 212 calculates the dither matrix size and the size based on the dither control signal from the control unit 200. , and the dither threshold in the matrix. When the dither circuit operates, the image reading period signal of one line of the CCD is counted in the mechanical main scanning direction, the image video clock is counted in the sub-scanning direction, and the set dither threshold value in the memory space is read out. Also, this memory space is serially Y,
It is switched to M, C, and Bk to obtain a serial dither threshold. The obtained threshold value is input to a comparator (not shown), and this comparator compares the threshold value with the image data input from the selector 210. A comparator (not shown) outputs image data〉threshold value: 1 image data≦threshold value 20, and the output data is converted into parallel 4 bft data by a serial-parallel converter, and then transferred to the buffer memory 110 shown in FIG. and binary synthesis section 1
It is output on 09. (Head correction section 211) (FIG. 23) FIG. 23 shows the configuration of the head correction section 211 shown in FIG. 15. In FIG. 23, ROM265 to 268 are ROMs,
C,M. Characteristic information on density unevenness of 256 nozzles making up the Y and Bk recording heads is written. ROM26
In numbers 5 to 268, head density unevenness correction data corresponding to 256 nozzles is written. Digital color component image data for each pixel is input point-sequentially into VDin in the order of Y, M, C, Bk, Y, M, C, Bk. The selection RAM 260 stores ROMs 265 to 268 in accordance with the order of input image data.
The data read from is stored. 263 is a bidirectional buffer for writing data read from the ROMs 265 to 268 into the RAM 260. 259 is a selector, 16 output from CPU 25g.
Either the lower IO bit of the bit address bus address or the 10-bit output of the counter 250 is selected. Selector 259 is RA
When writing data to M260, the output of CPO 258 is selected, and when reading data from RAM 260, counter 250 is selected. 262 is a correction RAM into which data is written from the CPU 258. 261 is a selector that receives a 16-bit address from the CPU or a total of 16 bits, including the output from the 8-bit flip-flop 252 and the 8-bit image data input VDin.
One of the bits is selected and input to the correction RAM 262. The correction RAM 262 includes a 24th
The correction table shown by solid lines and broken lines in the figure is for CPU 25g.
Written by. Although five correction tables are shown by solid lines in FIG. 24, there are actually more correction tables. The correction tables indicated by solid lines or broken lines 1 to 5 are correction R
It is selected depending on the data input to AM262. That is, when the B side is selected by the selector 261, the 8-bit image data input VDin and the 8-bit head density unevenness correction data are input to the RAM 262. Among these, 8-bit density unevenness correction data is used to select solid lines or broken lines 1 to 5 shown in FIG. Note that the solid line is the data for the same magnification, and the dotted line is the data for the variable magnification, and either the broken line or the solid line data is written into the correction RAM 262 by the CPU 25g depending on the range of nozzles used in the head. In addition, the table written in the correction RAM 262 is
The correction data ΔA for the input A is written so as to be output, and the correction data ΔA is sent to the flip-flop 254.
The data is once latched by the adder 256, added to the input image data A, and outputted via the flip-flop 257 as correction amount data A+ΔA. Note that the correction table is not a straight line as shown in FIG. 24 (or may be a curved line. A preferable example of such a curve is a cubic function, and the amount of correction for head unevenness is ±15%.
Therefore, the output concentration VDout is expressed by the following equation (4).
It can be expressed as VDout = aD”in+bD”in+cDin+
d - (4) d=0 where Din: input density N: correction amount Next, a control procedure by the CPo 258 of the head correction section shown in FIG. 23 will be explained. Before the power of the device is turned on and the copy start key is pressed, the selector 259 and the selector 261
Select the input on the A side. Therefore, the data from the ROMs 265 to 268 are stored in the selection RAM 260 as Y and M of the input image data VDin.
, C, Bk in this order. In addition, before the copy start button is pressed, the correction table shown in the broken line or solid line shown in FIG.
write to. Then, when the copy start key is pressed and the copy operation starts, the selectors 259 and 261 select B.
In other words, select the input on the image control side. When the image signal VDin input from the CCD is input to the head correction unit 211, the address output by the counter 250 is input to the address of the selection RAM 260 via the selector 259, and the selection data for each color nozzle is input to the flip-flop 252. is input to the selector 261 via. The selector 261 sets the 8 bits of the input image signal VDin to the lower order and the 8 bits output from the selection RAM 260 to the upper order, and inputs them to the address A of the correction RAM 262. After this,
The correction value according to the above-mentioned formula read from the correction RAM 262 is sent to the adder 256 via the flip-flop 254.
The image signal VDin is input to the adder 256 via the flip-flop 255. Then, it is added to the correction value to realize the above-mentioned equation, and is outputted from the head correction unit 211 as VDout via the flip-flop 257. This output is input to the dither section 212, binarized, and recorded by the recording head 37. The head correction section shown in FIG. 23 includes Y, M, C, Bk.
Since each head has a correction ROM 265 to 268, when any one of the Y, JC, and Bk heads is replaced, the R corresponding to the replaced head is
All you need to do is replace the OM, and the ROM is compatible with each head.
can be prepared in advance using a jig. Since the image forming apparatus of this embodiment uses a jig for correcting density variations between nozzles of a multi-nozzle inkjet head, it is possible to correct and process a large number of heads in a short time. In addition, it is possible to stably supply a multi-nozzle inkjet head without causing large variations in image quality from head to head.Furthermore, after correction is completed, recording is performed so that slight density unevenness that remains does not overlap. I decided to sort out the heads, so
It is possible to suppress the emphasis on density unevenness due to the overlapping of these minute density uneven portions between a plurality of heads, and it is possible to prevent density unevenness, especially when color printing is performed using two or more colors. [Effects of the Invention] As explained above, according to the present invention, since the heads are selected so that slight density unevenness remaining after correction does not overlap, the quality of reproduced images can be improved. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the pattern generator 305 shown in the first diagram, FIG. 3 is a diagram showing an example of a gradation pattern, and FIG. 4 is a head FIG. 5 is a diagram showing the external shape of the digital color copying machine shown in FIG. 1. FIG. 6 is a sectional view showing the structure of the digital color copying machine shown in FIG. 8 is a diagram showing the mechanical mechanism inside the scanner section 1. FIG. 9 is an explanatory diagram explaining the reading operation in book mode and sheet mode. FIG. 10 is a diagram showing the projector attached to the scanner section 1. A perspective view showing the unit 81 and the reflecting mirror 80, FIG. 11 is a block diagram showing the configuration of the film projection system shown in No. 1O, and FIG. 12 is an example of the relationship between the film and the projected image formed on the platen glass. FIG. 13 is a diagram showing the configuration of an image processing system of a digital color copying machine according to an embodiment. FIG. 14 is a diagram showing an example of the timing of each part shown in FIG. 13. FIG. 15 is an image shown in FIG. FIG. 16 is a diagram showing an example of a signal waveform during smoothing and edge enhancement; FIG. 17 is a block diagram showing the configuration of the masking section 202 shown in FIG. 15; FIG. 13 is a timing chart showing an example of the timing of each part shown in FIG. 19; FIG. 19 is a block diagram showing the configuration of the black extraction unit 204 shown in FIG. 15; FIG. 20 is a block diagram showing the configuration of the OCR unit 205 shown in FIG. 15; 22 is a block diagram showing the structure of the dither section 212 shown in the 15th drawing. FIG. 23 is a block diagram showing the structure of the head correction section 211 shown in the 15th drawing. FIG. 24 is a diagram showing an example of a correction table written in the correction RAM 262 shown in FIG. 01 02 04 05 06 07 ... Computer device, ... PROM writer, ... Frame memory, ... Pattern memory, ... Printer, ... Image reading scanner. Pixel number (head nozzle number) Fig. 4 Fig. 6 Fig. 5 Ruled area / 76 m Fig. 12 Fig. 14 Fig. 16 Fig. 17 Fig. 24

Claims (1)

[Scope of Claims] 1) In an image forming apparatus having a recording head in which a plurality of ejection ports are arranged corresponding to the width of recording paper, a storage means for storing residual density unevenness data of the recording head; and the storage means. Based on the residual density unevenness data stored in
An image forming apparatus comprising: head selection means for selecting recording heads so that overlap of residual density unevenness is minimized.