JPH03286678A - Picture copying machine - Google Patents

Abstract

PURPOSE:To obtain a high quality picture without uneven density by reading and discriminating the uneven density caused in the print of a test pattern so as to correct the print density characteristic. CONSTITUTION:An input sensor section 1 consists of a photoelectric conversion element such as a CCD and a driver scanning the element and applies read scanning of an original. A picture data of the original (8-bit of each picture element) of the original read by the input sensor section 1 is fed sequentially to an input correction circuit 2. The input correction circuit 2 quantizes a picture data for each picture element into a relevant digital data and the shading correction or the like correcting uneven sensitivity of the CCD sensor or uneven illuminance by a lighting light source is implemented by the digital arithmetic processing.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image copying apparatus that includes at least two print head arrays in which a plurality of printing elements are arranged side by side, and copies and outputs an original image read by the head arrays.

[Conventional technology]

Conventionally, an original is read by driving and scanning a photoelectric conversion element such as a COD, converting it into an image signal, and based on the image signal, driving a plurality of print head arrays in which a plurality of print elements are arranged side by side. An image copying apparatus that prints out reproduced images has been proposed. In a print head array in which a plurality of printing elements of this type of device are lined up, for example, in the case of inkjet printing, ink droplets are ejected from each nozzle depending on the manufacturing precision of the head, usage conditions, etc. It is difficult to make the size of the ink and the ejection angle with respect to the paper uniform, and these conditions change over time and with changes in the environment.

[Problem to be solved by the invention]

However, conventionally, no means has been provided to effectively correct such non-uniform printing characteristics. If the printing characteristics vary significantly from printing element to printing element, there is a problem in that when printing is performed, the uneven printing characteristics directly appear as unevenness on the image. Furthermore, it is known that the appearance of this unevenness differs depending on the printing density.

[Means to solve the problem]

The present invention has been made for the purpose of solving the above-mentioned problems and providing an image copying apparatus that can effectively correct unevenness in the printing characteristics of a print head array and obtain an excellent printed image without density unevenness. This invention has the following configuration as a means for achieving the above-mentioned object. That is, a test pattern generating means for generating a test pattern, a test pattern printing means for printing out the test pattern generated by the test pattern generating means for each head array, and reading the output pattern from the test pattern printing means. a pattern storage means for storing; a calculation means for calculating a correction value for each printing element of the head array from the pattern data stored in the pattern storage means; and a calculation means for calculating a correction value for each printing element of the head array based on the correction value calculated by the calculation means. and a correction means for correcting print density characteristics by selecting an optimum γ correction curve. The printing array is provided for each output color, and the correction means uses an independent γ correction curve group according to each color of the test pattern printing. Alternatively, the correction means uses a group of independent γ correction curves depending on the type of binarization method for printing the test pattern. Furthermore, a test pattern generating means for generating a test pattern, a test pattern printing means for printing out the test pattern generated by the test pattern generating means for each head array, and an output pattern from the test pattern printing means are provided. A pattern storage means for reading and storing, a calculation means for calculating a correction value for each printing element of the head array from the pattern data stored in the pattern storage means, and correcting an image signal based on the correction value calculated by the calculation means. The correction means rewrites the correction value according to selection, and adds the calculation result of the current calculation means to the previous correction value to make a new correction.

[Effect]

With the above configuration, it is possible to correct density unevenness caused by variations in each printing element of the print head array in all gradation ranges, and to provide an image copying apparatus that can obtain excellent printed images without density unevenness. .

【Example】

EMBODIMENT OF THE INVENTION Hereinafter, one Example based on this invention will be described in detail using drawings.

First Embodiment FIG. 1 is a block diagram of an image copying apparatus showing one embodiment of the present invention. In FIG. 1, an input sensor section 1 includes a photoelectric conversion element such as a CCD and a driving device for scanning the photoelectric conversion element, and reads and scans an original. The image data (8 bits for each pixel) of the original read by the input sensor section 1 is sequentially sent to the input correction circuit 2. The input correction circuit 2 quantizes image data for each pixel into corresponding digital data, and performs shading correction and the like to correct uneven sensitivity of the CCD sensor and uneven illuminance due to the illumination light source through digital arithmetic processing. 3 is a pattern generation circuit that generates a test pattern; 4
is a selector that selects either input image data or a test pattern. Further, 5 is an RGB-CMY conversion circuit, and R (red) selected by the selector 4,
G (green) and B (blue) image data are converted into corresponding C (cyan), M (magenta), and Y (yellow) image data using a built-in lookup table 5a. 6 is a black extraction circuit that performs black extraction calculations; 7 is a masking circuit that performs masking processing corresponding to the coloring characteristics of printing ink; 8 has a plurality of correction tables, and selects one of the correction tables to adjust the print density. This is a γ correction circuit that corrects the characteristics, and the correction tables include γ correction tables 8a (for cyan), 8b (for magenta), 8c (for cyan), and 8c ( (for yellow) and 8d (for black). The γ correction curve group in each table is calculated based on the density characteristics obtained by the binarization method during printing of the ink color development characteristic test pattern and the characteristics of variations among the printing elements of the print head array. Therefore, for example, an image copying apparatus having two types of binarization methods is further provided with four correction tables. 9 is a binarization circuit that quantizes multivalued image data into binary data. 10 is a print head array that controls recording dots on/off based on the binary data sent from the binarization circuit 9 to reproduce and print out the image read by the input sensor section 1; 11 is an input correction This is an image memory that stores 8-bit image information read from each pixel from the circuit 2. Further, 12 follows the control procedure stored in the ROM 14,
This is a CPU that controls the entire device of this embodiment, including computation of correction data. 13 is a RAM used as a work area for the CPU 12; 14 is a ROM that stores the above-mentioned programs; and 15 is an unevenness correction data backup RAM that retains the stored contents even if the device is powered off.
The unevenness correction data calculated in U12 is backed up so that it will not be erased even if the device is powered off. FIG. 2 shows the internal configuration of this embodiment having the above configuration. In FIG. 2, a document reading device 200 corresponds to the input sensor unit l in FIG. A photoelectric conversion element (CCD) 206 performs photoelectric conversion to obtain an image signal. The CCD 206 of this embodiment is 25 mm from the front to the back in FIG.
Six pixels are lined up, and each pixel of the CCD 206 is composed of three elements each having R (red), G (green), and B (blue) filters attached to them. A reading unit 203 on which a lamp 204, a lens 205, and a C0D 206 are mounted can move left and right on a rail 207, and the rail 207 can further move on a rail 208 and a rail 209 from the front to the back. In other words, while moving the original on the original platen glass 201 left and right, it is divided into 256-pixel bands and read, then moved 256 pixels in the back direction, and read left and right again.This operation is repeated to read the entire original. It is possible to read. Note that the document pressure plate 202 is for pressing the document against the document platen glass 201. Next, the image signal subjected to various image processing is sent to a printer 210 equipped with a head array 218 corresponding to the print head array 10 of FIG. The printer 210 transfers a roll paper 211 of A1 width to a roller 2.
1.214.215 onto the printing platen 216, and 256 printing elements (inkjet nozzles)
An image is reproduced by ink ejected from a head array 218 arranged vertically in accordance with an image signal. The head array 218 is C (cyan) from the front to the back.
Four inks of M (magenta), Y (yellow), and K (black) are lined up and are arranged together with the ink tank 219 on the carriage 220, and the carriage 220 moves while printing from the front to the back on the rail 221. By doing so, printing is performed in response to the reading operation. and 1
When line printing is performed, the paper is conveyed for one line by a conveyance roller to prepare the paper for the next printing. Note that the cutter 213 is for cutting the roll paper to a required length. The paper on which all lines have been printed is ejected from the paper ejection roller 217 onto the paper ejection tray 222 through the paper ejection port. The process of correcting read image data in this embodiment having the above configuration will be described below. First, the pattern generation circuit 3 generates a 50% (median value of gradation) uniform pattern, which is a test pattern for detecting image density unevenness. This pattern is data of 8 bits per pixel, same as the read image data, and selector 4
is selected as an image signal, passes through each image processing circuit shown in FIG. 1 (unnecessary processing is skipped), and is input to the binarization circuit 9. The binarization circuit 9 performs binarization processing using the error diffusion method and outputs binary data. The print head array 10 (218) prints three lines using this binary data as a drive signal. The printed state of this test pattern is shown in FIG. Here, the reason why we print the test pattern for three lines as shown in Figure 3 is because when the head is driven by the test pattern printing, a temperature change in the head may occur, so the influence of this temperature change may occur. This is to reduce the amount of paper feeding, and to reduce unevenness in paper feeding. Furthermore, it is also used to read the influence of uneven connections between lines at the same time. When printing of this test pattern is completed, the paper ejected from the printer is placed on the layer stacking glass 201, and the image is read by scanning with the C0D 206. FIG. 4 shows this test pattern reading state. The input test pattern image data is stored in image memory 1.
1 is stored. At this time, in the γ correction circuit 8, each color γ correction table 8 stores a group of independent γ correction curves according to each print color of the test pattern as a correction table.
When selecting a, use the R (red) signal to correct the unevenness of the C (cyan) head array, and the B (blue) signal to correct the unevenness of the Y (yellow) head array. When performing unevenness correction for M (magenta) and K (black) head arrays, G (green) signals are stored in the image memory 11, respectively. Thereafter, a correction value is calculated from the image data stored in the image memory 11 (details of the calculation will be described later). The correction data calculated by the arithmetic processing is stored in the backup RAM 15. In this arithmetic processing, during normal image copying, the γ correction circuit 8 uses the correction data stored in the backup RAM 15 to determine whether each printing element (inkjet nozzle) in the correction table 8a is By selecting the optimal γ curve table for density conversion, it is possible to correct the print density characteristics of the print head array itself, and at the same time correct density unevenness caused by variations between each printing element, and to perform density conversion across the entire density gradation range. This allows you to obtain high-quality images with even density. The details of the calculation method will be explained below. In this embodiment, the image data stored in the image memory 11 is 256×1024 pixel data f (i, j)
Each pixel data consists of 8-bit data,
Takes a value from “O” to “255”. Since the image data f (i, j) before this calculation is luminance data, it is first converted into density data g (i+j). Conversion is performed using a correction table 8b consisting of a group of independent γ correction curves according to the type of binarization method created by equation (1) shown below. 255 g(i,j)・−1og(f(i,j)/255)−(1) Then, g
Perform the arithmetic average for i of (i, j), as shown below (
2) Convert to h (j) using equation. In this way, by performing addition and averaging for i in the sub-scanning direction of printing, density data h (j) that accurately reflects the characteristics of each printing element can be obtained. Next, h (j) is sliced at multiple levels as shown in FIG. 5, and the center value J
Find it@r. JC1111t@r" The position of the print head array (J@tart-J@.6) is specified based on this center value Jcenter. This is J5tart"Jc*fitsr-1
28+J **** = J e-nter+ 127
Specify by. Next, in order to reduce positional errors in reading, smoothing of three pixels is performed using equation (3) shown below. p(J) = (h(j-1) + h(j) + h(
j+1) ) / 3 (3) Next, the density data corresponding to each printing element of the print head array is cut out using the following formula. q(k) '' p(Jitart + k) However: 0 to 255) From the data q(k) corresponding to the density of each printing element, use the following formula to determine the density correction value γ(k). r( k) =100- (100X q(k)/T
) +5(k) However, T: Reference correction table 8a
Density when printed with a printing element that matches the characteristics of the γ correction curve, S (k); This is the value that was set in the backup RAM 15 when printing the test pattern, and is the correction data from the previous correction. , or set uniform data, or a value determined by selection. That is, the increase or decrease in density relative to a predetermined value T is expressed as a percentage, and the correction value is increased or decreased by that percentage. As explained above, according to this embodiment, in an image copying apparatus that reads a document and converts it into an image, drives a print head array based on the image signal, and obtains a reproduced image, a uniform pattern is printed. The density unevenness that has occurred is read and determined, the correction data is calculated, and the optimal γ correction curve is selected for each printing element based on the correction data.
By correcting print density characteristics, it has become possible to obtain high-quality images with uniform density across the entire density gradation range.

[Second Embodiment] In the above explanation, the print head array is scanned to perform recording output, and the paper on which the test pattern has been recorded must also be placed on the document placement glass 201 and read. However, the present invention is not limited to the above example, and the print head array may be aligned for one line, eliminating the need for head scanning. FIG. 6 shows the configuration of a second embodiment of the present invention in which the print head array is aligned by one line. In the second embodiment as well, the electrical block configuration is the same as that shown in FIG. 1, and the differences from the first actual flow side will be explained focusing on the mechanism section. In FIG. 6, 601 is a multi-nozzle inkjet head with a density of 400 dpi and 4736 nozzles for each color of C, M, and Y. Each multi-inkjet head 601 has a width of approximately 300 mm, and prints onto a recording material smaller than a standard A3 size (width 297 mm) by selectively ejecting ink as the recording material moves. Images can be recorded on the entire surface of the recording material. Reference numeral 602 denotes a cassette that stores recording paper, which is a recording material.The recording paper is picked up by a pickup roller 603, passes through a second registration roller 606, a guide plate 605, and a second registration roller 606, and is transferred to a conveyor belt 607. It is electrostatically attracted and inkjet recording is performed on the platen 608. Recorded paper is ejected from paper output roller 6.
14, and is discharged to a paper discharge tray 615. In the second embodiment having the above configuration, when performing unevenness correction, the reading system unit 610 is provided on the recording material conveyance system. The reading system unit 610 includes a light source 611, a photoelectric conversion element 612, and a lens 613. The recording paper on which the test pattern has been printed by the inkjet head array 601 is conveyed below the reading unit 610 by a conveyor belt 607. Here, the light source 611 is turned on, and the reflected light from the printed test pattern passes through the lens 613 to the photoelectric conversion element 6.
The light is received at 12. The photoelectric conversion element 612 outputs an image signal according to the amount of received light. By performing the calculation shown in the first embodiment on the image signal, density unevenness can be corrected. With the configuration of the second embodiment as described above, the unevenness correction operation can be performed entirely automatically. As explained above, according to the first embodiment or the second embodiment,
In an image copying device that reads a document and converts it into an image, drives a print head array based on the image signal, and obtains a reproduced image, it prints a uniform pattern, reads and determines the density unevenness that occurs, and generates correction data. An image copying device that can obtain high-quality images with uniform density across the entire density gradation range by calculating the optimum γ curve for each printing element based on the correction data and correcting the print density characteristics. can be provided. At this time, the γ correction circuit 8 uses an independent γ correction curve group depending on each color of the test pattern printing, or uses an independent γ correction curve group depending on the type of the binarization method of the test pattern printing.
By using the correction curve group, a high-quality image without density unevenness can be obtained over the entire density gradation range.

[Third Embodiment] In each of the above embodiments, examples have been described in which the γ correction curve provided in the γ correction circuit 8 is selected to correct the print density characteristics, but the present invention is limited to the above examples. By selecting the optimal straight line for each print head array and converting the density of print data using a separate unevenness correction circuit for printing density unevenness, high-quality images with no density unevenness can be obtained. It may be configured as follows. The block configuration of the third embodiment according to the present invention constructed in this way is shown in FIG. 7. In FIG. 7, the same components as in the first embodiment shown in FIG. is omitted. Note that the mechanism section may employ either mechanism shown in FIG. 2 or FIG. 6. In the third embodiment shown in FIG.
to correct uneven print density. The details of the print density unevenness correction of the third embodiment will be explained below. In this embodiment, as in the first embodiment, the CPU 12 prints out the test pattern generated by the pattern generation circuit 3, reads it, and stores it in the image memory 11. At this time, when performing unevenness correction on the C (cyan) head array, use the R (red) signal, when performing unevenness correction on the Y (yellow) head array, use the B (blue) signal, M (magenta), When performing unevenness correction for a K (black) head array, a G (green) signal is stored in the image memory 11, respectively. Thereafter, correction data is calculated from the image data stored in the image memory 11, and the correction data calculated by the calculation process is stored in the backup RAM 15. During normal image copying, the unevenness correction circuit 19 selects the optimum straight line for each printing element (inkjet nozzle) based on the correction data stored in the backup RAM 15 and performs density conversion. , high-quality images with uniform density can be obtained. The details of the calculation method in the third embodiment will be explained below. Initially, image data f (i, j) which is 8-bit luminance data stored in the image memory 11 as in the first embodiment.
is converted into density data g (i, j). Next, g
Arithmetic averaging is performed for i in (i, j) and converted into density data h (j) that accurately reflects the characteristics of each printing element. Then, find the center value Jc and Wtar, and find the center value J
Print head array position C based on e@llt@r
J gtart “”” J @.6).
Subsequently, three pixels are smoothed using the above-mentioned equation (3), and then density data q (k) corresponding to each printing element of the print head array is cut out using the equation shown below. q(k) ""p(J 5tart + k) ; however, = 0 to 255) Next, in the third embodiment, from the data q (k) for the density of each printing element, the density of the printing element is calculated by the following formula. Calculate the average concentration ΣQ. 1... ΣQ=□Σ q (k) 256 ''' Use this average value to find the density correction value γ(k). That is, r(k) = 100- (100X q(k) /
ΣQ) +5(k) However, S (k) is the value that was set in the backup RAM 15 when printing the test pattern, and the correction data from the previous correction should be set, or uniform data should be set. It is a value that can be set or determined by selection. In other words, the increase or decrease in density is expressed as a percentage, and the correction value is increased or decreased by that percentage, making it possible to select the optimal straight line for each printing element and perform density conversion. As explained above, according to this embodiment, the correction value is rewritten and the value calculated this time is added to the previous correction value as a new correction value, and the unevenness correction circuit 19 optimizes the correction value for each print head array. By selecting the straight line and converting the density of print data, density unevenness can be easily corrected in a short time, and high-quality images can now be obtained. In this way, in an image copying apparatus that reads a document and converts it into an image, drives a print head array based on the image signal, and obtains a reproduced image, a uniform pattern is printed.
By reading and determining the density unevenness that has occurred, calculating correction data, and correcting the image data for each printing element based on the correction data, density unevenness can be easily corrected in a short time, resulting in high-quality images. is now available.

【Effect of the invention】

As explained above, according to the present invention, by reading and determining the density unevenness that occurs when printing a test pattern and correcting the print density characteristics, a high-quality image without density unevenness can be obtained across the entire density gradation range. .

[Brief explanation of the drawing]

1 is a block configuration diagram showing a first embodiment according to the present invention; FIG. 2 is an internal configuration diagram of the first embodiment; FIG. 3 is a diagram showing a printing state of a test pattern of this embodiment; The figure shows the reading state of the printed test pattern of this embodiment. The figure 5 shows the density unevenness data in printing the test pattern. The figure 6 shows the internal configuration of the second embodiment of the present invention. , FIG. 7 is a block diagram of a third embodiment according to the present invention. In the figure, l...input sensor, 2...input correction circuit, 3
... Pattern generation circuit, 5... RGB-CMY conversion circuit, 5b... Lookup table, 6... Black extraction circuit, 7... Masking circuit, 8... γ correction circuit, 8a, 8b... Correction table, 9... Binarization circuit, 10... Print head array, 11... Image memory, 12... CPU, 13... RAM, 14... R
OM, 15...Unevenness correction data backup RAM,
19...Unevenness correction circuit, 200... Original reading device, 206... Photoelectric conversion element, 210... Printer. Figure 2

Claims (4)

[Claims] (1) In an image copying apparatus that includes at least two print head arrays in which a plurality of print elements are arranged side by side and copies and outputs an original image read by the head array, a test pattern generating means that generates a test pattern;
A test pattern printing means for printing out the test pattern generated by the test pattern generation means for each head array, a pattern storage means for reading and storing the output pattern of the test pattern printing means, and a pattern storage means for reading and storing the output pattern of the test pattern printing means; A calculation means for calculating a correction value for each printing element of the head array from the stored pattern data, and an optimum γ correction curve for each printing element selected based on the correction value calculated by the calculation means to determine print density characteristics. An image copying apparatus comprising: a correction means for correcting. (2) The image copying apparatus according to claim 1, wherein the printing array is provided for each output color, and the correction means uses an independent γ correction curve group according to each color of the test pattern printing. Image copying device. (3) The image copying apparatus according to claim 1, wherein the correction means uses a group of independent γ correction curves depending on the type of binarization method for printing the test pattern. (4) In an image copying apparatus that includes at least two print head arrays in which a plurality of print elements are arranged side by side and copies and outputs an original image read by the head array, a test pattern generating means that generates a test pattern;
A test pattern printing means for printing out the test pattern generated by the test pattern generation means for each head array, a pattern storage means for reading and storing the output pattern of the test pattern printing means, and a pattern storage means for reading and storing the output pattern of the test pattern printing means; It has a calculation means for calculating a correction value for each printing element of the head array from the stored pattern data, and a correction means for correcting the image signal based on the correction value calculated by the calculation means, and the correction means can be selected according to the selection. An image copying apparatus characterized in that a correction value is rewritten and a current calculation result by a calculation means is added to a previous correction value to obtain a new correction.