JPH02136244A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To reduce density irregularity by altering the correction characteristics of a correction means for correcting the irregularity of the output characteristics of each head corresponding to the use head range of a multihead indicated by an indication means. CONSTITUTION:The image signal outputted from a smoothing/edge emphasizing part 208 and the image signal after color conversion are inputted to a selector 210 and image data is selected by the selector 210 on the basis of the control signal from a control part 200 corresponding to the effective region of the use head range indicated by a digitizer. A head correction part 211 reads the data of an indicated address and calculates a coefficient having to correct density irregularity from the data and the read pixel density data of a solid pattern to correct input pixel data and outputs the coefficient to each head of a multihead. By this method, regardless of the use head range indicated according to an image forming condition, density irregularity can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that forms images using a multi-head or the like.

[Conventional technology]

Conventionally, for example, in a digital color copying machine using a multi-head, after reading data of each color R, G, and B and converting the read image data into a digital signal,
It processes data and forms images using multi-heads.

[Problem to be solved by the invention]

In such an apparatus, unevenness in density occurs in the output image due to variations in characteristics due to the manufacturing process or variations in characteristics of the materials forming the multi-head.

A first object of the present invention is to provide an image forming apparatus that solves the above-mentioned problems and reduces density unevenness.

Another object of the present invention is to provide an image forming apparatus in which the influence of variations in characteristics due to the manufacturing process or variations in the materials constituting the multi-head is reduced.

Another object of the present invention is to provide an image forming apparatus that can suppress density unevenness in an output image regardless of the usage state of the multi-head.

[Means to solve the problem]

In order to achieve the above-mentioned object, the image forming apparatus of the present invention includes a correction means for correcting variations in output characteristics of each head of a multi-head for image formation, and a correction characteristic of the correction means is changed according to the surroundings of the image forming apparatus. It is characterized by having a means.

〔Example〕

Hereinafter, the present invention will be explained in detail based on Examples.

(Explanation of External Shape) FIG. 1 shows an external view of a digital color copying machine to which the present invention is applied.

The whole can be divided into two parts.

The upper part of Figure 1 shows the color image scanner section 1 (which reads the original image and outputs digital color image data).
The controller section 2 includes a scanner section 1 (hereinafter abbreviated as "scanner section 1"), and a controller section 2 which is built into the scanner section 1 and performs various image processing of digital color image data, as well as having processing functions such as an interface with external devices.

The scanner unit l has a built-in mechanism for reading a three-dimensional object and a sheet original placed downward under the original presser 11, and also for reading a large-sized sheet original.

Further, the operation section IO is connected to the controller section 2, and is used to input various information regarding the copying machine. The controller section 2 instructs the scanner section 1 and the printer section 3 regarding operations according to the input information. Further, when it is necessary to perform complicated editing processing, a digitizer or the like is attached in place of the document presser 11, and this is connected to the controller section 2, thereby making it possible to perform sophisticated processing.

The lower part of FIG. 1 is a printer section 3 for recording the color digital image signal output from the controller section 2 on recording paper. In this embodiment, the printer section 3 is a full color ink jet printer using an ink jet recording head described in Japanese Patent Laid-Open No. 54-59936.

The two parts described above can be separated, and can be installed at separate locations by extending the connecting cable.

(Printer Section) FIG. 2 is a sectional view from the side of the digital color copying machine shown in FIG. 1.

First, an exposure lamp 14, a lens 15, and an image sensor 16 that can read line images in full color.
(in this embodiment, a CCD) reads an original image placed on the original platen glass 17, an image projected by a projector, or a sheet original image produced by the sheet feeding mechanism 12.

Next, various image processing is performed by the scanner section 1 and the controller section 2, and the image is recorded on recording paper by the printer section 3.

In FIG. 2, recording paper is stored in a paper feed cassette 20 that stores cut paper of small standard sizes (A4 to A3 size in this embodiment) and large size (A2 to AI size in this embodiment). It is supplied from a roll paper 29 for carrying out the process.

In addition, by feeding recording sheets one by one through the manual feed port 22 shown in FIG. 1 along the paper feed section cover 21, it is also possible to feed the recording sheets manually from outside the apparatus.

The big up roller 24 is a roller for feeding cut sheets one by one from the paper feed cassette 20, and the fed cut sheets are conveyed to the first feed roller 26 by a cut paper feed roller 25. Ru.

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.

Similarly, the recording paper inserted through the manual feed slot 22 is conveyed to the paper feed roller 26 by the manual feed roller 32.

Pick 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 connected to a paper feed motor (not shown in the drawings, D
It is driven by a C servo motor (using a C servo motor), and can be turned on and off at any time by electromagnetic clutches attached to each roller.

When the printing operation is started in response to an instruction from the controller unit 2, recording paper selectively fed from one of the above-mentioned paper feeding paths is conveyed to the first paper feeding roller 26. In order to eliminate the skew of the recording paper, after creating a predetermined amount of paper loops, the 10th paper feeder 26 is turned on and the recording paper is conveyed to the 20th paper feeder 27.

Between the 10th paper feed roller 26 and the 20th paper feed roller 27, a predetermined amount of paper is applied to the recording paper in order to perform an accurate paper feeding operation between the paper feed roller 28 and the 20th paper feed roller 27. Create a buffer. The buffer amount detection sensor 33 is a sensor for detecting the buffer amount. By creating a buffer in the middle of paper transport, it is possible to reduce the load on the paper feed roller 28 and paper feed roller 27, especially when transporting large-sized recording paper, allowing accurate paper feeding operation. become.

When printing with the recording head 37, the recording head 3
A scanning carriage 34 on which a device 7 or the like is attached performs reciprocating scanning on a carriage rail 36 by a scanning motor 35.

Then, in the outward scan, the image is printed on recording paper,
In the backward scan, the paper feed roller 28 performs an operation to feed the recording paper by a predetermined amount. At this time, while the drive system is detected by the buffer amount detection sensor 33 using the paper feed motor, control is performed so that the buffer amount is always a predetermined amount.

The printed recording paper is discharged to the paper discharge tray 23, and the printing operation is completed.

Next, a detailed explanation of the scanning carriage 3 and the invention will be given using FIG.

In FIG. 3, a paper feed motor 40 is a drive source for intermittently feeding recording paper, and a paper feed motor 40 is a driving source for intermittently feeding the recording paper.
The 20th paper feeder 27 is driven via the 0-ra clutch 43.

The scanning motor 35 moves the scanning carriage 34 to the scanning belt 34.
This is a drive source for scanning in the directions of arrows A and B. 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
-La clutch 43 and paper feed motor 40 are turned on, and the recording paper is conveyed over the platen 39 to the paper feed roller 28.

The recording paper is detected by a paper detection sensor 44 provided on the platen 39.
The sensor information is used for position control, jam control, etc.

When the recording paper reaches the paper feed roller 28, the paper feed number 20-
The clutch 43 and the paper feed motor 40 are turned off, and a suction operation (not shown) is performed from inside the platen 39 to bring the recording paper into close contact with the platen 39.

Prior to the image recording operation on recording paper, the scanning carriage 34 is moved 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. After recording the image for a predetermined length, the scanning carriage 34 is stopped, and conversely, backward scanning is started in the direction of arrow B, and the scanning carriage 34 is returned to the position of the home position conflict sensor 41.

During the backward scan, the paper is fed by the length recorded by the recording head 37 in the direction of arrow C by driving the paper feed roller 28 by the paper feed motor 40.

In this embodiment, the recording head 37 is an ink jet nozzle that uses heat to form air bubbles and uses the resulting pressure to eject ink droplets, and uses four ink jet nozzles with 256 nozzles each assembled. ing.

Scanning carriage 34 is home position sensor 41
When it stops at the home position detected by , the recording head 37 performs a recovery operation. This is a process for stable printing operation, and in order to prevent unevenness at the start of ejection caused by changes in the viscosity of the ink remaining in the nozzles of the print head 37, paper feeding time, internal temperature of the device, etc. This is a process in which pressure is applied to the recording head 37, ink is idly ejected, etc. according to preprogrammed conditions such as ejection time and the like.

By repeating the operations described above, an image is recorded on the entire surface of the recording paper.

(Scanner Section) Next, the operation of the scanner section l will be explained using FIGS. 4 and 5.

FIG. 4 is a diagram for explaining the mechanical mechanism inside the scanner section 1. As shown in FIG.

The CCD unit 18 is a unit composed of a CCD 16, a lens 15, etc., and includes a main scanning motor 50 fixed on a rail 54, a pulley 51, a pulley 52, and a wire 53.
It moves on the rail 54 by a drive system in the main scanning direction consisting of the following, and reads the image on the document platen glass 17 in the main scanning direction. The light shielding plate 55 and the home position sensor 56 are used for position control when moving the CCD unit 18 to the main scanning home position in the correction area 68 in the figure.

The rail 54 rests on rails 65 and 69, and includes a sub-scanning motor 60, pulleys 67, 68, 71-76, and a shaft 72.
73, is moved by a drive system in the sub-scanning direction consisting of wires 66 and 70. Light shielding plate 57, home/bojinyon/
Sensors 58 and 59 are used to move the rail 54 to the home position for sub-scanning in the book mode, in which a document such as a book placed on the document table glass 17 is read, and in the sheet mode, in which the sheet is read. Used for position control.

Sheet feed motor 61. Sheet feed rollers 74 and 75,
The pulleys 62 and 64 and the wire 63 are mechanisms for feeding the sheet original. This mechanism is located on the document table glass 17, and transports the sheet document placed face down to the sheet feed roller 7.
This is a mechanism for feeding a predetermined amount at a time of 4.75.

FIG. 5 is an explanatory diagram of the reading operation in book mode and sheet mode.

In the book mode, the CCD unit 18 is moved to the book mode home position (book mode HP) shown in the correction area 68 in FIG. Start reading the entire surface.

Prior to scanning the original, data settings necessary for processing such as shading correction, black level correction, and color correction are performed in the correction area 68. Thereafter, scanning in the main scanning direction is started by the main scanning motor 50 in the direction of the illustrated arrow. When the reading operation in the area indicated by ■ is completed, the main scanning motor 50
and drive the sub-scanning motor 60,
The correction area 68 of the area is moved in the sub-scanning direction.

Subsequently, similarly to the main scanning of the area (2), processing such as shading correction, black level correction, color correction, etc. is performed as necessary, and the reading operation of the area (2) is performed.

By repeating the above scanning, the entire areas ① to ② are read, and after the reading operation in the area ② is completed, the CCD unit 18 is returned to the book mode home position.

In this embodiment, the document platen glass 17 can read a maximum A2 size document, so in reality it must be scanned more times, but in this explanation, the operation is simplified to make it easier to understand. .

In the seat mode, the CCD unit 18 is moved to the seat mode home position (seat mode H) shown in the figure.
P), and repeatedly reads the sheet document in the area (3) while operating the sheet feed motor 61 intermittently, thereby reading the entire sheet document.

Prior to scanning the document, processing such as shading correction, black level correction, and color correction is performed in the correction area 68, and then scanning in the main scanning direction is started by the main scanning motor 50 in the direction of the arrow shown in the figure. When the forward scanning operation of the area (3) is completed, the main scanning motor 50 is reversed, and during this backward scanning, the sheet feed motor 61 is driven to move the sheet original by a predetermined amount in the sub-scanning direction. Subsequently, the same operation is repeated to read the entire sheet document.

Assuming that the reading operation described above is a reading operation at the same magnification, the area that can be read by the CCD unit 18 is actually a wide area as shown in FIG. this is,
This is because the digital color copying machine of this embodiment has a built-in magnification/reduction function. That is, as explained above, since the area that can be recorded by the recording head 37 is fixed at 256 bits at a time, for example, when performing a 50% reduction operation, the image information of an area of at least double 512 bits is This is because it is necessary. Therefore, the scanner unit l has a built-in function of reading and outputting image information of an arbitrary image area by one main scanning reading.

(Film Projection System) The scanner section 1 of this embodiment can be equipped with a projection exposure means for film projection.

FIG. 6 shows a projector unit 81. which is a projection exposure means on the scanner section l. FIG. 7 is a perspective view of a reflective mirror 80 attached.

The projector unit 81 is a projector for projecting negative film and positive film, and the film is held in a film holder 82 and attached to the projector unit 81. Projector unit 81
The image projected from is reflected by the reflection mirror 80,
Fresnel lens 83 is reached. Fresnel war lens 83
converts this image into parallel light and forms the image on the document table glass 17.

In this way, negative film and positive film images are formed on the document table glass 17 by the projector unit 81, the reflective mirror 80, and the Fresnel lens 83.
image reading becomes possible.

FIG. 7 is a diagram for explaining the film projection system in more detail.

The projector fist unit 81 has a halogen lamp 9.
0, reflection plate 89, condensing lens 91. It is composed of a film holder 82 and a projection lens 92.

The direct light emitted by the halogen lamp 90 and the light reflected by the reflection plate 89 are condensed by a condenser lens 91 and reach the window of the film holder 82 . The film holder 82 has a window slightly larger than one frame of negative film or positive film, so that the film can be loaded inside with plenty of room.

The projection light reaching the window of the film holder 82 passes through the film mounted therein, thereby obtaining a projected image of the film. The projection image thus obtained is optically magnified by the projection lens 92, changed in direction by the reflection mirror 80, and then converted into a parallel light image by the Fresnel lens 83.

The CCD unit 18 inside the scanner 1 reads this image in the book mode described above and converts it into a video signal.

FIG. 8 is a diagram showing an example of the relationship between the film and the projected image formed on the document table glass.

A 22×34 mm film image is shown magnified eight times and focused on the document table glass 17.

(Overall Functional Block Description) Next, the functional blocks of the digital color copying machine of this embodiment will be described using FIG. 9.

The control units 102, 111, and 121 are control circuits that control the scanner unit 1, the controller unit 2, and the printer unit 3, respectively.
It consists of M, data memory, communication circuit, etc. The control units 102 to 111 and the control units 111 to 121 are connected by a communication line, and the control units 102 . 121 performs the operation, the so-called master
Adopts slave control mode.

When the control section 111 operates as a color copying machine, the control section 10. The operation is performed according to input instructions from the digitizer 114.

As shown in FIG. 6, the operation unit IO uses, for example, a liquid crystal (LCD display unit 84) as a display unit, and is equipped with a touch panel 85 made of transparent electrodes on its surface, so that color-related information can be displayed. Selection instructions such as specification and editing operation can be made. In addition, there are keys related to operations, such as a start key 87 for instructing to start a copying operation, a stop key 88 for instructing to stop a copying operation, a reset key 89 for returning the operation mode to the standard state, and a projector key for selecting a projector. Frequently used keys such as 86 are provided independently.

The digitizer 114 is used to input position information necessary for trimming, masking processing, etc., and is connected as an option when complex editing processing is required.

Further, the control unit 111 also controls a control circuit (I/F control unit 112) of a general-purpose parallel interface such as IEEE-488, so-called GP-IB interface, and outputs image data between external devices. , remote control by external devices can be performed via this interface.

Furthermore, the control unit 111 includes a multi-value synthesis unit 106, an image processing unit 107, and a binarization processing unit 1, which perform various processes related to images.
08. Also controls the binary synthesis unit 109 and buffer memory 110.

The control unit 102 controls a mechanical drive unit 105 that controls the drive of the mechanism of the scanner unit 1 described above, an exposure control unit 103 that controls the exposure of a lamp when reading a reflective original, and a halogen lamp when using a projector. The exposure controller 104 controls the exposure control section 90. In addition, the control unit 1
02 is an analog signal processing unit 100.02 that performs various types of processing related to images. It also controls the input image processing section 101.

The control unit 121 includes a mechanical drive unit 105 that controls the drive of the mechanism of the printer unit 3 described above, and a mechanism that absorbs time variations in the mechanical operation of the printer unit 3 and compensates for delays due to the mechanical arrangement of the recording heads 117 to 120. Synchronous delay memory 11
5.

Next, the image processing block in FIG. 9 will be explained along the flow of the image.

The image formed on the CCD 16 is converted into an analog electrical signal by the CCD 16. The converted image information is
The signals are serially processed in the order of red → green → blue and input to the analog signal processing section 100. The analog signal processing unit ioo performs sample and 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. The digital image signal is converted into a digital image signal with a value (in this embodiment, each color has a length of 8 bits) and is output to the input image processing unit 101.

The input image processing unit 101 similarly performs correction processes necessary in the reading system, such as COD 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.
This is a circuit block that performs selection and compositing processing between a serial multi-value digital image signal sent from a serial multi-value digital image signal and a serial multi-value digital image signal sent via a parallel I/F. 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,
This circuit performs 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 output is input to the binarization processing unit 108 and the buffer memory 110, respectively.

The binarization processing unit 108 is a circuit for binarizing a serial multilevel digital image signal, and can select simple binary processing using a fixed slice level, pseudo halftone processing using a dither method, etc. Here, the serial multi-value digital image signal is converted into a four-color binary parallel image signal.

Image data of four colors is sent to the binary synthesis unit 109 and image data of three colors is sent to the buffer memory 110.

The binary synthesis section 109 combines the three-color binary parallel image signals sent from the buffer memory 110 and the binarization processing section 1.
This is a circuit for selecting and combining four-color binary parallel image signals sent from 08 to produce four-color binary parallel image signals.

The buffer memory 110 is a buffer memory for inputting and outputting multivalued images and binary images via a parallel I/F, and has memory for three colors.

The synchronization delay memory 115 of the printer section 3
Absorption of time variations in mechanical operation and recording head 117~
This is a circuit for correcting the delay due to the mechanical arrangement of the recording heads 117 to 120, and internally also generates the timing necessary for driving the recording heads 117 to 120.

The head driver 116 drives the recording heads 117 to 120.
This is an analog drive circuit for driving the recording heads 117 to 120, and internally generates signals that can directly drive the recording heads 117 to 120.

The recording heads 117 to 120 eject cyan, magenta, yellow, and black ink, respectively, to record an image on recording paper.

FIG. 10 is an explanatory diagram of the timing of images between the circuit blocks described in FIG. 9.

Signal BVE is a signal indicating the image effective section for each scan in the main scanning reading operation explained in FIG. Signal B
Full-screen image output is performed by outputting VE multiple times.

The signal VE is a signal indicating the valid section of the image read by the CCD 16 for every l line. Only the signal VE is valid when the signal BYE is valid.

Signal VCK is a clock signal for sending out image data VD. Signal BVE and signal VE also change in synchronization with this signal VCK.

The signal H3 is a signal used when the valid and invalid sections are repeated discontinuously while the signal VE outputs one line.
If the signal VE is continuously valid while outputting one line, it is an unnecessary signal. This is a signal indicating the start of image output of the l line.

Next, the rough signal processing in the image processing section will be explained using FIG. 11.

In FIG. 9, a serial number (for example,
.
1 and converted into parallel signals of Y (yellow), 1M (magenta), and C (cyan), and then sent to the masking unit 20
2 and the selector 203.

The masking unit 202 is a circuit for correcting color cloudiness of output ink, and as shown in FIG.
The following calculation is performed using 0 to 222.

Y, M, C2 Input data Y', M', C', Output data These nine coefficients are corrected for ink cloudiness in a masking section 202 determined by a masking control signal from a control section 200.

Y using Figure 14. To explain only the data, the table RAMs 220 to 222 are switched four times according to the color information during one cycle of input Y image data, so that aII YO* a 21 ” Or a31
Yo, 0 is obtained serially. Similarly for M and C, 812 M 6 , a 32 M 6 , O
and aII CQ +a23co, O are obtained in this order.

Thereafter, the adder 223 performs addition to perform the above-described masking operation and output the colors sequentially.

Next, the black extraction section 204 will be explained using FIG. 15. The input image data is Y, M, C, α (empty)
are input in this order. Here, in the case of 8-bit image data, α is data corrected so that it becomes FFH in hex display (H). Such color sequential image data is input to a comparator 224 and a flip-flop 225. Here, when the data (FFH) of α is input, the data is held by the forced flip-flop 225. Next, the data held in the flip-flop 225 and the image input data are sequentially compared.

Input image data (data held by flip-flop 225) A latch pulse is sent from the latch timing generator 227 to the flip-flop 225 by a signal from the comparator 224, and the input image data is held.

■Image data for pixels (Y.

After the comparison of Y, M, and C) is performed, the minimum image data of Y, M, and C held in the flip-flop 225 is held in the flip-flop 226. In this way, extraction of the minimum values of Y, M, and C, ie, black extraction, is performed on the color-sequential image data, and the extracted black data is output.

Note that the signal processed by the masking section 202 is input to the selector section 203 and the UCR section 205 as a serial signal.

Input image data and image data output from the masking unit 202 are input to the selector 203 .

The selector 203 normally selects input image data based on a selector control signal l sent from the control section 200. If the color correction in the input system is not sufficiently performed, the image data output from the masking section 202 is selected and output by control signal 1. The serial image data output from the selector 203 is input to the black extraction section 204. Y, M in one pixel.

In order to use the minimum value of C as black data, the black extractor 204 detects the minimum values of Y, M, and C as described above with reference to FIG. The detected black data is input to the UCR section 205.

The UCR unit 205 subtracts the extracted black data from each of the Y, M, and C signals. Also, regarding black data,
It is simply multiplied by a coefficient. After correcting the time difference between the black data input to the UCR unit 205 and the image data sent from the masking unit 202, the following calculation is performed.

Y'=Y-alBk M'=M-a2Bk C'=C-a3Bk Bk'=a4Bk Here, Y, M, C, and Bk indicate the extraction unit input data,
Y', M', C', and Bk' indicate extraction unit output data. And the coefficient (a++ a2+ a3+
a4) is determined by the OCR control signal sent from the control section 200.

Next, UCR will be explained using FIG. 16.

The black data enters the coefficient multiplication table RAM 228.

In addition to this, a color mode signal for color discrimination is input from the control section 200. While one pixel of black data is being input, the color mode changes to Y, M, C, and Bk. Based on this color information, the coefficient table is switched for each color, and multiplication is performed independently for each color. The black data multiplied by the coefficient is subtracted from the image data sent in color sequentially by the next subtracter 229 and output.

The data output from the UCR unit 205 is then input to the γ, offset 206.

At the γ, offset 206, gradation correction is performed as shown in the following equation.

y' = b, (y-c,) M' = b2 (M-C2) C' = b3 (CC3) Bk' = b4 (Bk-C4) Here, Y, M, C, Bk are γ, offset part There is large input data, Y', M', C', and Bk' are γ, and there is offset section ratio output data.

Further, the coefficients (b+~b4.c,~C4) in the above equation are determined by the γ and offset control signals sent from the control unit 200.

The signal gradation-corrected by the offset 206 is then sent to the line buffer 20 which stores image data for N lines.
7 is input. This line buffer 207 outputs 5 lines of data necessary for the subsequent smoothing and edge emphasis section 208 in 5 lines in parallel according to the memory control signal sent from the control section 200. These 5 lines worth of signals are input to a spatial filter whose filter size is variable according to a filter control signal from the control unit 200, and smoothed.
Edge enhancement is then performed. In smoothing, as shown in FIG. 12, image noise is removed by setting the average value of the pixel of interest and surrounding pixels as the one-degree value of the pixel of interest.

Next, the smoothing process will be explained using FIG. 17.

Image data is stored line by line in the line buffer 207 in color sequential order. Since this filter is performed in a 5x5 area, color sequential image data is output in 5 lines in parallel. For example, to explain the smoothing process, as shown in FIG. 17, five lines of input color sequential data are added by an adder 230, and then delayed by flip-flops 231-234. Here, the flip-flops 231 to 234 are each configured to be delayed by four pixels by serially connecting four flip-flops. This allows filtering to be performed for each color even if image data is input sequentially. This time, the filter matrix is 5×5, but the size is not specified. The pixel data delayed in this manner is input to the adder 235 and added, and then the division RAM 236 divides the pixel data into 1
/25 and output in color sequential order.

Further, edge enhancement is performed by using the difference between the pixel data of interest and the smoothed signal as an edge signal, and adding this to the pixel data of interest.

The image data output from the smoothing and edge enhancement unit 208 is input to a color conversion unit 209, and color conversion is performed in response to a color conversion control signal from the control unit 200.

The color to be converted, the color to be converted, and the area in which the signal is valid are input in advance from the digitizer device 114 in FIG. 9, and the color conversion unit 209 replaces the image data based on the data.

In this embodiment, a detailed explanation of the color conversion unit 209 will be omitted. The image signal output from the smoothing and edge emphasis section 208 and the image signal after color conversion are input to the selector 210, and the selector control signal 2 selects the image data to be output. 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 input to the buffer memory 110 and the binarization processing section 108 in FIG.

A description of the system input to the buffer memory 110 will be omitted here.

The binarization processing unit 108 will be explained. The image data input to the binarization processing section 108 is input to the head correction section 211 shown in FIG. The head correction section 211 will be explained later. The image signal whose density has been corrected by the head correction section is then sent to the dither section 212.

M, C, and Bk are input serially in 8-bit order.

The dither section 212 uses 6 bits in the main scanning direction for each color.
, 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 control unit 20
The dither control signal from 0 sets the dither matrix size and the dither threshold within the matrix. During operation of the dither circuit, the image reading period signal of the CCDI line is counted in the mechanical main scanning direction, and 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, serial dither threshold values can be obtained by serially switching this memory space to Y, M, C, and Bk. Next, this threshold value is input to a comparator and compared with the image data input from the selector 210 in terms of magnitude.

The output from the comparator is Image data〉Threshold value: 1 Image data ≦ Threshold: 0 is output.

The dither will be explained using FIG. 18.

Counters 237 to 240 are provided for each color so that the dither can be changed for each color. The counter values for the four colors (YD, MD, CD, BkD) are sequentially output to the dither RAM 242 in the order of YD, MD, CD, and BkD by the parallel-serial converter 241. Dayza RAM24
In 2, by switching the upper address using color information,
The dither threshold for each color is changed independently. The dither thresholds output in color sequential manner from the dither RAM 242 in this manner are input to the comparator 243. Comparator 2
43, the image data sent in color sequential order is compared with the dither threshold value sent in color sequential manner, and after being binarized, it is converted by the serial-parallel converter 212 to Y,
M, C.

A signal of 4 bits in total, 1 bit for each Bk, is output.

The binarized data is then converted into parallel 4-bit data in the serial/parallel converter and sent to the buffer memory 110 . and is output to the binary synthesis section 109.

Next, the head correction section 211 will be explained using FIG. 19.

In this case, image data is obtained by outputting a solid pattern of all discharges using a printer in advance and reading the pattern using a portion of the scanner.

Since the solid pattern has different recording characteristics for each element of each head, the image data obtained by reading the solid pattern is
Each element is written to the RAM 255 via the buffer 256. Further, the address of the RAM 255 is determined by a counter 2 that generates an address corresponding to the image data.
53 and is generated in the RAM 255 via the selector 254.
given to. Next, the address of the uneven density image data stored in the RAM 255 is specified via the selector 254, and the data at the specified address is read by the CPU 258 via the buffer 257. Based on the read image data, the CPU 258 performs coefficient calculation to correct density unevenness. In this embodiment, the correction coefficient for each element is determined by the following calculation.

αi: correction coefficient Di: solid pattern read pixel density data and actual input pixel data DT+, then calculation of DTi Xαi is performed to obtain output pixel data. Of course, it is also possible to perform correction by calculations other than those in this embodiment.

The coefficients obtained in this manner are written to addresses corresponding to each recording element of the correction RAM 251 via the selector 250° bidirectional buffer 252. Next, during normal image reading, the input image and the signal from the counter 253 that generates the address are selected by the selector 250 and input to the address of the correction RAM 251. Address assignment is such that input image data is assigned to the lower 8 bits and address data corresponding to each recording element of the head from the counter 253 is assigned to the upper 8 bits. By inputting image data and corresponding address data from the counter 253 to the correction RAM 251, image data corrected according to the characteristics of each recording element of the head can be obtained as an output of the correction RAM 251. This output is input to the dither section 211, binarized, and output. The characteristic data and correction coefficient data for each recording element are Y and M.

This information is stored for all C and Bk heads.

Here, in this embodiment, the correction was performed using the RAM, but the characteristics of the multi-head may be investigated in advance and written in the ROM or the like. Alternatively, the characteristics of each head may be investigated and only the correction coefficients thereof may be written in the ROM, RAM, or the like.

Note that the technology shown in this embodiment is applicable not only to inkjet heads but also to other multi-recording heads such as thermal heads.

As described above, according to this embodiment, by electrically correcting the output density variations of the multi-head due to variations in the manufacturing process and material characteristics, it is possible to increase the production yield and achieve high quality. Moreover, an inexpensive image forming apparatus can be provided.

Next, another embodiment of the head correction section 211 will be described using FIG. 20.

In the case of this embodiment, all 256 nozzles of the recording head 37 are used when enlarging or at the same magnification.
When reducing the number of pixels by 2, the data read by the CCD 16 is multiplied by a reduction rate of 1/2 to control the number of nozzles used for 128 pixels. Therefore, when enlarged or at the same size, 25
Recording is performed using all 6 nozzles, and only half of the 256 nozzles are used during reduction.

FIG. 20 is a block diagram of the head correction section 211 shown in FIG.
OM251' (hereinafter referred to as selection ROM) (F) is an address counter that generates 7 addresses. In this embodiment, the 256-nozzle head is a 10-bit counter so as to count the number corresponding to four colors, that is, a total of 1024 nozzles. Yes, and controlled by signals H5 and VE. Selection ROM251'
, the selection value of the correction amount for each nozzle of the head of each color is written in the color order of C, M, Y, and Bk. Signal H128 is 1b representing the number of used nozzles of the head.
In this embodiment, the it signal is 0 for enlargement and 1 for reduction. The signal H128 is the output of the selection ROM 251 and the correction ROM 253 together with the input image signal VDin.
' will be entered in the address. The correction ROM 253' has a correction curve written in it that indicates how much correction should be made for which nozzle data at which density value, so it can be adjusted for each case of enlargement, same magnification, and reduction according to the input H128 level. A correction value for each density value of the nozzle is output. The correction value output from the correction ROM 253' is input to the adder 256' via the flip-flop 254'. Also, the image signal VD
in is also connected to the adder 256' via the flip-flop 255.
is added to the correction value and sent to the flip-flop 25.
7' and then outputted from the head correction section 211' as VDout. This output is input to the dither section 212' and binarized to the recording head 37.
recorded by.

Next, another embodiment of the configuration shown in FIG. 20 will be described.

A third embodiment will be described using FIG. 21. In the description, the same parts as in FIG. 20 will be given the same numbers and the description will be omitted. Furthermore, since the method of changing the magnification in this embodiment is the same as that in the first embodiment, detailed explanation will be omitted.

In Fig. 20, ROM265' to 268' are C,
M.

This is a characteristic ROM in which characteristic information of density unevenness of 256 nozzles provided in each of the Y and Bk heads is written.In this embodiment, since each head has 256 nozzles, the ROM
Head density unevenness correction data corresponding to the number of nozzles is written in 265' to 268'. V.D.
i n has digital image data of Y and M.

Color component image data for each pixel, such as C, K, Y, M, C, K, is input point by point. Selection RA
M260' takes out data from ROM265' to 268' in accordance with the order of input image data.
Stored. 263' is ROM265' to 268'
This is a bidirectional buffer for writing data retrieved from the RAM 260' into the RAM 260'.

259' is a selector for selecting either the lower 10 bits of the 16-bit address bus address output from the CPU 258' or the 10-bit output of the counter 250'. When writing data to RAM 260', selector 259' is
When reading data from RAM 260', select the output of counter 250'. 262' is a correction RAM into which data is written from the CPU 258'. The selector 261' selects either the 16-bit address from the CPU or the output from the 8-bit flip-flop 252' and 8 bits of the image data input VDin, a total of 16 bits, and inputs it to the correction RAM 262'. be.

A correction table as shown by solid lines or dotted lines 1 to 5 in FIG. 21 is written into the correction RAM by the CPU 258'. Although FIG. 21 shows five types of correction tables indicated by solid lines, there are many more actual correction tables. The correction table for the solid line or points ill~5 mentioned above is in the correction RAM.
262' is selected accordingly.

That is, when the selector 261' selects the B side, 8-bit image data input VDin and 8-bit head density unevenness correction data are input to the RAM 262'; data is used to select the solid lines or dotted lines 1 to 5 described above. Of 1 to 5, the solid line is the data for the same magnification, and the dotted line is the data for the variable magnification.
258', either the dotted line data or the solid line data is written into the correction RAM 262'.

Further, the table written in the correction RAM 262' is written so as to output the correction data ΔA for the input A, and the correction data ΔA is first latched by the flip-flop 254' and sent to the adder 256.
' is added to the input image data A and output as correction amount data A+ΔA via the flip-flop 257'.

Further, the correction table shown in FIG. 21 may be a curved line instead of a straight line.

In this embodiment, a cubic function is used as a preferable example of such a curve, and since the amount of correction for head unevenness can be kept within about ±15%, the following equation is used as a representative so that VDout satisfies the following value.

VDout==aD'in+bD"in+cDin
+dd=0 However, Din: Input density Dout: Output density N: Correction amount Next, the operation of the embodiment shown in FIG. 21, which is corrected as described above, will be explained.

When the power of the apparatus is turned on and before the copy start key is pressed, the selector 259' and the selector 261' each select the input on the A side. As a result, the selection RAM 260 has R.
The data from OM265' to 268' are written in accordance with the order of Y, M, C, K of input image data VDin. Furthermore, before the copy start button is pressed, the correction table indicated by the dotted line or solid line in FIG. 22 is written into the correction RAM 262' depending on the set magnification ratio.

Next, when the copy start key is pressed and copy operation begins, the CPU 258' selectors 259' and 261'
are respectively referred to as the B side, that is, the image control side. When the image signal VDin input from the COD 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 selection data for each nozzle of each color is input. is connected to selector 2 via flip-flop 252'.
61. In the selector 261', the 8 bits of the input image signal VDin are placed in the lower order, and the 8 bits output from the selection RAM 260' are placed in the upper part, and are input to the address A of the correction RAM 262'. After this, the correction RAM 262'
The correction value according to the above formula is calculated by the flip-flop 254'
The signal is input to the adder 256' via the adder 256'. The image signal VDin is also input to the adder 256 via the flip-flop 255', added to the correction value to realize the above-mentioned equation, and outputted from the head correction section 211' as VDout via the flip-flop 257'. This output is input to the dither section 212' and binarized to the recording head 3.
Recorded by 7.

Y in the embodiment described in FIG.

Correction ROM 265' to 26 for each head of M, C, and K
8', even if one of the Y, M, and C heads is replaced, unlike the embodiment explained in FIG. 19, the ROM corresponding to the replaced head is All you have to do is convert. Also, selection RAM 260'
and the correction RAM 262' are configured separately,
Correction RAM according to the range of nozzles used in the head
Since the correction RAM 262' can be rewritten, for example, even if the magnification ratio is frequently changed, it is only necessary to rewrite the correction RAM 262', thereby simplifying the configuration.

According to the two embodiments shown in FIG. 20 and subsequent figures explained above, in addition to the conventional means for electrically correcting variations in the output density of the head, information for determining the nozzle range to be used, such as the magnification ratio, is used. By adding the above-mentioned means for changing the correction amount of the input image data, it is possible to always provide a stable and even image regardless of the range of nozzles used by the recording head.

Further, in the circuit of this embodiment, since the process is carried out in color sequential manner, it is possible to provide a high-quality and inexpensive image forming apparatus since it can be carried out with one circuit without providing a circuit for each color.

Also, in the above embodiment, Y depending on the magnification ratio.

Although the present invention has been applied to a device for changing the range of nozzles used in heads for M, C, etc., the present invention is not limited to changing the magnification ratio, but can be applied to any device that can select the nozzle to be used in a device having multiple nozzles. It can be applied in the same way.

Furthermore, since the above embodiments have been described using an inkjet recording method, an apparatus that performs recording using a multi-nozzle provided with a plurality of nozzles for ejecting ink was shown as an example of a multi-head. In addition to devices having nozzles for ejecting ink, other types of devices using multi-heads, such as multi-heads equipped with multiple heating elements for applying heat for recording using a thermal transfer recording method, are also used. The same can be applied to devices.

As explained above, according to the present invention, since the correction characteristics of the correction means are changed according to the range of use of the multi-head, stable and uniform image formation can be performed regardless of the range of use of the multi-head.

Next, a second example of still another embodiment of the head correction section 211 will be described.
This will be explained using Figure 2.

In this embodiment, since 256 nozzles of the recording head 37 are used to record on the recording paper, recording is completed in units of 256 nozzles (approximately 16 mm). Therefore, depending on the size of the recording paper, it may take up to 10 minutes to record the final line.
Since recording must be done below 1 m.
Controls the number of nozzles used in m units.

In FIG. 22, unlike the head correction section 211 shown in FIG. 20, a preset value for the number of nozzles in use is given by a 4-bit signal NS that controls the number of nozzles in use.

In the selection ROM 251', selection values of correction amounts for each nozzle of each color head are written in the order of colors C, M, Y, and Bk. The signal NS is input to a nozzle selection table ROM 270' (hereinafter referred to as nozzle selection ROM) together with the output of the selection ROM 25bi. Nozzle selection RO
M270' is a table ROM for adjusting the correction amount according to the range of the nozzles used, and in this embodiment, it can be adjusted in units of 1 mm from the top of the head. The nozzle selection ROM 270 has written data for reselecting the correction curve selected by the selection ROM 251 in accordance with the range in which the nozzle is used.

The output of the nozzle selection ROM 270' is input to the address of the correction ROM 253' via the flip-flop 252'. The correction ROM 253' has a correction curve written therein indicating how much to correct the data of which nozzle for which density value, so the selection ROM 251'
The density value is corrected for each nozzle according to the correction curve selected in the nozzle selection ROM 270'.

Further, as shown by the dotted line in FIG. 21, the CPU 258' is configured to determine the paper size set by the operation section, and before the copy start key is pressed, the paper size set by the operation section is changed. Correspondingly, the correction table indicated by the dotted line or solid line in FIG. 22 is written into the correction RAM 262.

Next, when the copy start key is pressed and the copy operation begins, the operation as described above with reference to FIG. 21 is performed.

In particular, in this embodiment, after 1547 minutes of recording is completed and while the printer carriage 34 is returning, the CPU 258 sets the selectors 259' and 261' to the CPU side, and sets the number of nozzles to be used for the next recording scan. is determined and the correction data in the correction RAM 262 is rewritten.

That is, if the next scan uses all 256 nozzles, the CPU 258 determines the correction data indicated by the solid line in FIG. will be written in.

Further, in the above embodiment, the present invention was applied to a head having 256 nozzles, but the present invention can be similarly applied to an apparatus using a full multi-head having nozzles corresponding to the printing width of the recording paper used, for example. Can be done. In this case, for example, when using a head with nozzles for the length of A4 paper (297 mm), the present invention can be applied because the number of nozzles used in the head changes when paper of A4 size or smaller is used.

Also, depending on the human image, there may be parts in the head where constant density data is printed and other parts where nothing is printed.Even in such cases, it is possible to print a constant density by changing the selection of the correction curve. Prevents unevenness in parts,
Can provide high-quality images.

〔Effect of the invention〕

As described above, according to the present invention, density unevenness can be reduced and good image quality can be obtained regardless of the range of heads to be used specified by the image forming conditions.

[Brief explanation of the drawing]

Fig. 1 is an external view of a digital color copying machine to which the present invention is applied, Fig. 2 is a sectional view from the side of the digital color copying machine of Fig. 1, and Fig. 3 is a detailed view of the scanning carriage 3 and the invention. 4 is a diagram for explaining the mechanical mechanism inside the scanner section 1. FIG. 5 is an explanatory diagram of the reading operation in book mode and sheet mode. FIG. 6 is a diagram for explaining the projection exposure on the scanner section l. FIG. 7 is a detailed explanatory diagram of the film projection system, and FIG. 8 is a diagram showing the relationship between the film and the projected image formed on the platen glass. A diagram showing an example of the relationship, Figure 19 is an explanatory diagram of functional blocks of a digital color copying machine to which the present invention is applied, Figure 10 is an explanatory diagram of image timing between circuit blocks, and Figure 11 is an illustration of color image processing. A block diagram of the device, Fig. 12 is a timing chart of smoothing and edge enhancement processing, Fig. 13 is a detailed circuit diagram of the masking section, and Fig. 14 is a
Figure 3 shows the timing chart of each part, Figure 15 shows the detailed circuit diagram of the black extraction part, Figure 16 shows the detailed circuit diagram of the UCR part, Figure 17 shows the detailed circuit diagram of the smoothing part, and Figure 18 shows the detailed circuit diagram of the dither processing part. Detailed circuit diagram, FIG. 19 is a detailed circuit diagram of the head correction section, FIG. 20 is a detailed circuit diagram of another embodiment of the head correction section, and FIG. 21 is a detailed circuit diagram of yet another embodiment of the head correction section. , FIG. 22 is a diagram illustrating a correction table written in the correction RAM 262 shown in FIG. 21, and FIG. 23 is a detailed circuit diagram of still another embodiment of the head correction section. View (film) 776 Nephew. (94 years old &) Ka/4 figure

Claims (3)

[Claims] (1) Correction means for correcting variations in output characteristics of each head of a multi-head for image formation; means for specifying a range of heads to be used in the multi-head according to image forming conditions; An image forming apparatus comprising: means for changing correction characteristics of a correction means. (2) The image forming apparatus according to claim 1, wherein the image forming condition is a printing width condition on a recording material on which an image is to be recorded. (3) The image forming apparatus according to claim 1, wherein the image forming condition is a size condition of a recording material on which an image is to be recorded.