JPH05220977A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To stably output an image free from density irregularity and density stripes in all of gradations by correcting density irregularity using the optimum correction table in each density while a first correction means is changed over corresponding to a density signal within a real time. CONSTITUTION:Herein, density irregularity is corrected according to a correction sequence. That is, printing is performed by operating an operation part of four test patterns (density data =40H/80H/C-H/F-H) different in density. The printing patterns are read using readers themselves and the emitting amount irregularity of the heads corresponding to four densities is estimated. A plurality of the correction tables 1:HS tables corresponding to the respective densities are formed on the basis of the emitting amount irregularity and correction is performed using both of said correction tables and a correction table 2:HS-gamma curve (correction curve : linear).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which corrects density unevenness due to variations in the ejection amount of each nozzle in a recording head. In particular, it is effective for an image forming apparatus using a heating type ink jet recording head in which a plurality of nozzles are arranged and a color image recording apparatus using a plurality of recording heads.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus for recording on a recording medium such as paper or OHP sheet (hereinafter referred to as recording paper or simply paper) has been proposed in the form of mounting recording heads of various recording systems. Has been done. The recording head may be of a wire dot type, a thermal type, a thermal transfer type, an inkjet type, or the like. In particular, the ink jet method, which directly ejects ink onto a recording sheet, is attracting attention as a quiet recording method with low running cost.

In the ink jet recording apparatus, in order to eliminate density fluctuation and density unevenness in the ejection performance, the ejection speed / direction (landing accuracy) and ejection amount VDROP [pl / dot]
In regard to (1), the ejection characteristics were stabilized by the following method.

1. Discharge amount control method This is a divided pulse width modulation method (PWM control method) described in Japanese Patent Application No. 3-4713, etc. proposed by the present applicant.
By varying the pulse width of the pre-pulse in accordance with the temperature of the print head, fluctuations in the ejection amount caused by temperature fluctuations are suppressed.

2. Density unevenness correction method This is a so-called head shading method: HS method of reading density unevenness of a test pattern printed by a recording head and correcting density signals for each nozzle (ejection port).

1. In this method, especially in the serial printing method, since the average ejection amount of the head is controlled, it was possible to eliminate the density fluctuation caused by the temperature fluctuation within the page and between the pages, but the density unevenness of the head itself ( The unevenness in the connecting direction due to the serial printing method), that is, the variation in the ejection amount for each nozzle of the head cannot be corrected. For this reason, it was not possible to completely eliminate the density unevenness in the nozzles of the head, and especially in the image forming apparatus of the serial printing system, density unevenness with the serial joints as the pitch occurred, and it was remarkable in the image with a uniform tone. It was noticeable as unevenness.

[0007] Therefore, in order to make up for the drawback of the method of 1.
In this method, the unevenness correction (HS method) is performed based on a certain fixed output pattern (constant density signal) to reduce the variation in the ejection amount in the nozzles of the head to some extent. In this method, since correction is performed based on the result of reading a pattern with a certain density (a pattern in which nozzles are used with a predetermined print ratio), it is possible to eliminate density unevenness near that density. It was However, in the correction for one fixed density, when the print ratio changes, the frequency of the nozzles used changes from moment to moment.
When the print ratio changes abruptly, or when the print ratio becomes low and the print ratio becomes high, it is not possible to deal with the correction table for one density alone, resulting in density unevenness. Therefore, there has been a need for a method of correcting density unevenness in all areas from low density to high density.

Therefore, when a pictorial color image or the like is printed using an image signal (multi-valued data) from an external device via a reading device or the like, print density unevenness occurs as a result. If printing is performed in this state, a full-color image formed by four colors of cyan, magenta, yellow, and black has density unevenness that is repeated especially at the boundary portion of the serial. In addition, the color balance is partially disrupted in areas such as the uniform-tone blue sky, sunset sky, and human skin, resulting in a change in tint, resulting in uneven color, and poor color reproducibility (color difference). Increase) and deteriorate the image quality. Further, there is a problem that density unevenness occurs even in a single color image such as black, red, blue or green.

Therefore, the present invention has been made in order to solve the above-mentioned problems.
An object of the present invention is to provide an image forming apparatus capable of stably outputting an image without density stripes.

[0010]

In order to achieve the above object, the image forming apparatus of the present invention has a recording head in which a plurality of recording elements are arranged and a recording medium in a direction different from the arrangement direction of the recording heads. In an image forming apparatus that forms an image by relatively moving, a first correction unit that selectively indicates the recording characteristics of each recording element of the recording head for each of a plurality of density regions, and the first correction unit. Second correction means for correcting the density signal based on the recording characteristics instructed by the correction means, and recording instructed by the first correction means according to the density area to which the density signal corresponding to each recording element belongs. And a selecting means for selecting a characteristic.

[0011]

According to the above structure, since the first correction means can be switched in real time according to the density signal (image signal), the uneven density correction can be performed using the optimum correction table for each density, so that the density can be changed from low density to high density. It is possible to uniformly correct the density unevenness up to the density, and it is possible to stably output a pictorial color image.

[0012]

Embodiments of the image forming apparatus of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a processing flow chart that best represents the features of the present invention. Here, 1001 is one or a plurality of recording heads according to the form of the image forming apparatus, and the recording head is composed of multiple nozzles (having a plurality of ejection ports). In this embodiment, four C / M / Y / K inkjet recording heads of a serial recording system are used and applied to a color image forming apparatus. Reference numeral 1003 is a unit for scanning the recording head with respect to the recording medium (recording material) 1002, and 1040 is a conveying unit for the recording medium 1002, and conveys the recording medium 1002 with respect to the recording position of the recording head 1001. 10
Reference numeral 14 is a means for reading a print pattern used for unevenness correction, and in this embodiment, it is also used as a reading means for reading a document and performing image processing. Here, it has a light source (halogen lamp) that irradiates a document (printed matter or a pattern printed on a recording medium) with light and a reading unit (lens and CCD sensor) that reads the reflected light. Reference numeral 1020 denotes a density unevenness correcting unit, which will be described in detail later. However, image recording is performed while performing head unevenness correction processing during normal recording based on the density unevenness data read from the density unevenness correction pattern. There is. Reference numeral 1015 denotes a print control unit, which uses a CPU (microcomputer) to create density unevenness correction data, change drive conditions of the recording head, and perform other printing control.

FIG. 2 is a perspective view of a color ink jet recording image forming apparatus implementing the above method. In the figure, the recording material 40 wound on a roll is the conveyance roller 4
It is held between the sheet feeding roller 43 and the first and second rollers 42 and is fed in the direction 44 by rotating these rollers. Guide rails 46 and 47 are arranged in parallel across the recording material 45, and a recording head unit 49 mounted on a carriage 48 can scan left and right. On the other hand, the guide rail 47 has a slit,
By detecting this slit with a photo sensor provided on the carriage 48, the carriage position and the like can be recognized. The carriage 48 has four color heads 49Y, 49M, and 49 of yellow, magenta, cyan, and black.
C, 49 Bk are mounted, and four color ink tanks are arranged in this. Each head has 128 (400D
It is a multi-nozzle head having a discharge port of PI: Φ = hole diameter equivalent to 20 μm). The recording material 45 is a recording head 49.
Is intermittently fed for each print width (equivalent to 8.128 mm) of
While the recording material 45 is stopped, the recording head 49 scans in the P direction and ejects an ink droplet (maximum drive frequency: 4 KHz, ink ejection amount: about 30 ng / dot) according to the image signal.

FIG. 3 is a perspective view showing the construction of the reading unit and its scanning mechanism in this embodiment. A transparent original plate glass is placed on the scanning portion of the reading unit 60, and the original 2 is set with the printing surface facing downward, and the information of the original is read by the reading unit 60 from below. Is becoming In the figure, reference numeral 60 denotes a reading unit, which slides on a pair of guide rails 61 and 61 'to read an image. The reading unit 60 includes a light source 62 for illuminating a document, a lens 63 for forming a document image on a photoelectric conversion element such as a CCD, and the like. 6
Reference numeral 4 denotes a flexible wire bundle, which supplies electric power to the light source 62 and the CCD, and transmits an image signal from the CCD and other control signals. The reading unit 60 is fixed to a drive transmission unit 65 such as a wire for main scanning (G and H directions) in a direction intersecting the recording medium conveyance direction. The drive transmitting unit 65 in the main scanning direction is stretched between the pulleys 66 and 66 ', and the line information of the image orthogonal to the main scanning G direction is stored in the CCD.
Read with the number of bits corresponding to. After reading the image by a predetermined width, the main scanning pulse motor 67 rotates in the direction opposite to the arrow I. As a result, the reading unit 60 moves in the H direction and returns to the initial position.

Incidentally, 68 and 68 'are carriages,
It slides on guide rails 69 and 69 'for the sub-scanning (F) direction which is substantially orthogonal to the main scanning direction G. Carriage 6
8'is fixed by a fixing member 70 to a driving force transmitting portion 72 for the sub-scanning (F) direction such as a wire stretched over pulleys 71, 71 '. After the main scanning is completed, the pulley 71 is rotated in the direction of arrow H by a sub-scanning drive source (not shown) such as a pulse motor or a servomotor, and a predetermined distance (the same distance d as the read image width in the main scanning G direction). Then, the carriages 68 and 68 'are sub-scanned in the direction of arrow F and stopped. Here, the main scanning G is started again. By repeating the main scanning G, the return J in the main scanning direction, and the sub-scanning F, the entire area of the original image can be read. The document may be fed in the sub-scan direction instead of performing the sub-scan in the reading unit.

Here, the portion related to the density unevenness correction of the present invention will be described. The conventional density unevenness correction method follows a correction sequence as shown in FIG.
That is, only a pattern having a fixed density as shown in FIG. 11 (density data = 80H.4 times printing: irregular 3 lines) is printed, and the ejection amount distribution of the head of each color is estimated from the density. .. Then, a correction table 1: HS table as shown in FIG. 12 is created by calculation,
An image signal (8-bit signal: FF (hex) = 256) as shown in this HS table and FIG. 9A or 9B.
(Dec))) corresponding to the correction table 2: HS_γ curve (correction curve: nonlinear curve, linear curve). At this time, as described above, since the correction table 2: HS_γ table is created with an average head value, it is possible to completely perform density unevenness correction in all gradation expressions from low DUTY to high DUTY. It was impossible.

It should be noted that it is costly to create a non-linear correction curve for each nozzle of the head on the main body side (CPU
However, the correction time (which requires a dedicated printing / correction method for creating HS_γ) becomes long, which is not preferable.

Therefore, in this embodiment, density unevenness is corrected according to the correction sequence shown in FIG. That is,
Four test patterns having different densities as shown in FIG. 19 (four gradations in this embodiment, but the number of gradations may be increased or gradation intervals may be changed as necessary) ( Density data = 40H / 80H / C0H / F0H: irregular 3 lines) is automatically printed by operating an operation unit (not shown). Then, the print pattern is read using its own reading device, and the unevenness in the discharge amount of the head corresponding to each of the four densities (the density unevenness distribution at each density (DUTY) varies depending on the density of the nozzles used). Different: see FIG. 17). Based on this, FIG.
A plurality of correction tables 1: H corresponding to respective densities such as 0
The S table is created, and the correction is performed using both this table and the correction table 2: HS_γ curve (correction curve: linear) as shown in FIG. 9B.

Regarding the circuit configuration and sequence for performing the density unevenness correction described above, the block diagram shown in FIG. 21 and FIG.
This will be described with reference to the sequence flowchart shown in FIG.
In FIG. 21, the image processing unit 801 converts the input image data into an image signal: Si and outputs it to the selector 802. The selector 802 determines the size of the image signal: Si in step S61 of FIG. 22, and switches the switch 803 to change the SRAM (correction table 1) in real time (for each recording element) according to the size of the image signal: Si. )
804 is selected (step S62). Image signal: S
One of the SRAMs 1 to 4 is selected according to the size of i (steps S63 to S66), and the recording (ejection amount) characteristics ( The correction table value) is output.

The correction curve of the HS table (correction table 2) 805 is switched according to the correction table value output for each recording element, and the image signal: Si output from the image processing unit 801 is converted (step S67). .. This makes it possible to correct the density unevenness of the head of each color with a low duty.
It is possible to completely perform in all the gradation expressions from to high DUTY. In the figure, the SRAM
(Correction table 1) 804 is shown representatively for one of the four colors.

Next, the correction algorithm for creating the correction table 1 used in this embodiment will be described in more detail. The purpose of the correction is to converge the print output result of each nozzle to the average density value. For simplicity, the case of the number of recording nozzles N will be described. It is assumed that when each element: nozzle (1 to N) is driven by a uniform image signal: Si and printing is performed, a density distribution is generated in the nozzle direction of this head. First, the density O of the portion corresponding to each recording element
D1 to ODN are measured and the average concentration is: ODAVG = ΣODAVG
/ N is calculated. This average density is not limited to each element,
A method of integrating the reflected light amount to obtain an average value or a known method may be used. If the relationship between the image signal value and the output density of a certain element or a certain element group is as shown in FIG. 4, the signal actually given to this element or this element group is the signal Si.
Correction factor to correct the target concentration: ODAVG: α
Should be set. That is, the signal Si is expressed as α × Si = (ODAV
The correction signal Si corrected to G / ODN) × Si may be given to this element or group according to the input signal Si.
Specifically, it is executed by subjecting the input image signal to table conversion as shown in FIG.

In FIG. 5, a straight line A is a straight line having an inclination of 1, and is a table for outputting an input signal without converting it. The straight line B is a straight line having a slope of α = ODAVG / ODN and is a table for converting an output signal into α · Si with respect to an input signal Si. Therefore, if the image signal corresponding to the Nth recording element is subjected to table conversion such as the straight line B in FIG. Each concentration of the exposed portion becomes equal to ODAVG. If such a process is performed on all the recording elements, density unevenness is corrected and a uniform image can be obtained. That is, it is possible to correct the density unevenness by previously obtaining data as to which table conversion should be performed on the image signal corresponding to which printing element.

FIG. 6 shows a configuration example of the print control system flow having the above configuration. Here, 701 is a reading unit having the reading carriage 60, and 702 is image data (R / G /
B) and 703, an image processing unit that performs processing such as a logarithmic conversion circuit that converts a luminance signal into a density signal, a masking circuit that performs color processing, a UCR circuit, a color balance adjustment circuit, and the like 704.
Is an image signal (C / M / Y / K) after image processing, 705 is a ROM in which a nonuniformity correction conversion table is stored, 706
Is an image signal after unevenness correction, 707 is a binarization circuit, 708
Is a binarized image signal, 709 is a head drive circuit, 71
0 is a head drive signal. A recording head 711 is shown as a representative of the heads 1Y to 1Bk in FIG. Reference numeral 712 is the unevenness reading signal, and 713 is R for holding it.
AM and 715 are CPUs, 716 and 718 that control each part.
Is the unevenness correction signal, and 717-A, B, C and D are unevenness correction R
AM. Further, 720 is a recovery means for maintaining a good ejection state of the recording head 711 by performing suction or the like. Reference numeral 721 is a ROM storing a correction program described with reference to FIG. 8, reference numeral 723 is means for conveying the recording material 45, and reference numeral 725 is means for causing the recording head to scan the recording material.

The image-processed image signal 704 is converted by the unevenness correction table ROM 705 (correction table 2) so as to correct the unevenness of the recording head. The unevenness correction table ROM 705 has 64 correction curves (linear correction: straight line), and the correction curve (either linear or non-linear) is switched according to the unevenness correction signal 718.

FIG. 7 shows an example of the unevenness correction table 2. In the present embodiment, there are 64 correction straight lines each having a different slope from Y = 0.68X to Y = 1.31X by 0.01. , The correction straight line is switched according to the unevenness correction signal 718. For example, when a signal of a pixel to be recorded with an ejection port with a large ejection amount (which results in a large dot diameter on the recording material) is input, a correction straight line with a small inclination is selected, and conversely, a small ejection amount is used. The image signal is corrected by selecting a correction straight line having a large inclination when the ejection port (having a small dot diameter) is selected, and the density unevenness distribution within a certain area is corrected.

Mura correction RAM 717 (correction table 1)
Stores the selection signal of the correction straight line necessary for correcting the unevenness of each head. That is, the unevenness correction signals having 64 kinds of values of 0 to 63 are stored for the number of ejection openings of the print head, and the unevenness correction signal 718 is output in synchronization with the input image signal. Then, the signal 7 in which the unevenness is further corrected by the straight line selected by the unevenness correction signal
Reference numeral 06 denotes a binarization circuit 7 using a dither method, an error diffusion method or the like.
The image is binarized by 07, and the head 711 is driven via the head driver 709 to form a color image without density unevenness. If the density unevenness fluctuates due to long-term use or the head is replaced,
The correction method system may be incorporated as a main body sequence so that the user can easily perform density unevenness correction.

Next, this sequence will be described in detail below. FIG. 8 is a flowchart showing an example of the procedure of unevenness correction processing according to this embodiment. When this procedure is started by pressing the density unevenness correction key (not shown), the ejection stability of the recording head is first secured by head recovery / initialization in step S1. This is the thickening of the ink,
If the density unevenness correction processing is performed as it is when the recording head is not in a normal ejection state due to the inclusion of dust or air bubbles, it may not be possible to recognize the faithful head characteristics (density unevenness distribution state). Is. The recovery condition at this time may be a recovery that is optimized according to various conditions such as the use state and environment, and may be a combination of known recovery conditions (suction, empty discharge, temperature control, drive condition, etc.). In addition,
In addition to the above method, warm-up printing may be performed at the time of printing the test pattern, or a stable area may be read.

Next, in steps S3 and S5, test patterns are printed and read, respectively. In this embodiment, as described above, the density unevenness reading of each density of the pattern as shown in FIG. 19 is performed by the method shown in FIG.
7 (A) / (B) / (C) / (D). Here, the horizontal axis represents the Y direction, that is, the ejection port alignment direction of the recording head, and the vertical axis represents the averaged read densities in the X direction in the arrangement range of the reading elements for each gradation. is there. As described above, since the density distribution does not show a clear rise at both ends of the print area due to the balance with the reading device, the density correction at both ends may not be performed accurately. Therefore, it became possible to solve the problem by considering the rising amount at both ends by the irregular 3-line printing.

The irregular 3-line printing will be described with reference to FIG. X is the scanning direction of the print head, Y is the pixel (nozzle) direction of the print head, and the direction of arrangement of 128 ejection ports. As a printing method, first, printing is performed on the first line with the 99th to 128th nozzles (ejection ports),
Next, the second line is printed using all nozzles, and finally the third line is printed using the 1st to 32nd nozzles. An area surrounded by a dotted line is an area for reading a test image by using a reading device, and in this embodiment, 128 pixels are used, and a warming-up area for printing is provided on the left side of the area. The purpose of using the front and rear 32 nozzles is to take into account the rise of the above-mentioned skipping (which requires accurate reading in order to detect the edge and associate the density unevenness data with the nozzle position). ..

This method will be described with reference to FIG. First, the entire density distribution is captured, and a threshold is set in advance so that a portion where printing is performed and a portion where it is not printed (blank paper portion) can be clearly distinguished (broken line portion in the figure). Next, a nozzle number having a density equal to or higher than a threshold value is calculated, and a position corresponding to a nozzle returned 64 times from that is assigned to the first nozzle, and 2, 3, ...
No. No. is assigned. With such a method, an accurate concentration distribution of the nozzle can be obtained.

However, the number of nozzles on both sides used for irregular 3-line printing is not limited to this number because it depends on the performance of the reading device, but printing is performed in the same state as when printing using all nozzles. It is necessary to control so that it is possible (driving conditions, temperature control, etc.).

The data thus read is 3
The pixel data of 2 + 128 + 32 is once stored in the RAM, and is returned to the data of 128 pixels necessary for the density unevenness of the head for the above-described unevenness correction processing. At this time, as a means for increasing the pixel reading position accuracy, the density data of each pixel is created by weighting the pixels when performing the position allocation in the nozzle direction of the head or performing a smoothing process. good. In the present embodiment, the data obtained by averaging the density data on both sides of the target pixel in the nozzle array direction: Si '= (Si-1 + Si +
Si + 1) / 3 is used. Further, these conditions may be optimized when changing the type of recording medium, ink, etc., and the data processing method, threshold value, etc. may be changed.

In the case of applying the above-mentioned present invention to still another embodiment, if a recording head capable of multi-value printing is used, the multi-value printing recording head has a plurality of dots when performing density inspection printing such as a test pattern. Since one pixel is formed, the change in the print (gradation) density is modulated by increasing or decreasing the number of recording dots of the constituent dots, but the present invention can be effectively applied to this case as well. Further, the correction may be performed more accurately by combining with the ejection amount control and other printing control.

In this way, since the correction table 1 is switched in real time according to the density signal (image signal) and the density unevenness correction can be performed using the optimum correction table 1 for each density, from low density to high density. It is possible to uniformly correct the density unevenness, and it is possible to stably output pictorial color images.

Further, the recording head is not limited to the ink jet type, but other general heads such as a thermal head can be applied.

The present invention provides excellent effects particularly in a recording head and a recording apparatus of the type which utilizes thermal energy among the ink jet recording systems.

Regarding the typical structure and principle thereof, see, for example, US Pat. Nos. 4,723,129 and 4740.
What is done using the basic principles disclosed in 796 is preferred. This method can be applied to both the so-called on-demand type and continuous type, but especially in the case of the on-demand type, a liquid (ink) is used.
By applying at least one drive signal that corresponds to the recorded information and gives a rapid temperature rise exceeding nucleate boiling, to the electrothermal converter arranged corresponding to the sheet or liquid path in which is held, This is effective because heat energy is generated in the electrothermal converter to cause film boiling on the heat acting surface of the recording head, and as a result, bubbles can be formed in the liquid (ink) in a one-to-one correspondence with this drive signal. The liquid (ink) is ejected through the ejection openings by the growth and contraction of the bubbles to form at least one droplet. It is more preferable to make this drive signal into a pulse shape, because the bubble growth and contraction are immediately and appropriately performed, so that the ejection of the liquid (ink) with excellent responsiveness can be achieved. As the pulse-shaped drive signal, U.S. Pat. Nos. 4,463,359 and 43,
Those as described in 45262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the rate of temperature rise on the heat acting surface are adopted, more excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the linear liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned respective specifications. US Pat. No. 4,558,333 and US Pat. No. 4, which disclose a configuration in which a heat acting portion is arranged in a bending region.
The structure using the specification of 459600 is also included in the present invention. In addition, Japanese Laid-Open Patent Publication No. 123670/1984 discloses a configuration in which a common slit is used as a discharge portion of a plurality of electrothermal converters, and an opening for absorbing a pressure wave of thermal energy. The present invention is also effective as a configuration based on JP-A-59-138461, which discloses a configuration that corresponds to the discharge portion.

[0040]

According to the present invention, since the optimum unevenness correction according to the density signal can be performed in real time, the density unevenness correction can be sufficiently performed in all gradations from low density to high density. Therefore, the effect of forming an image by superimposing a plurality of colors, particularly a pictorial color image in which gradation reproducibility is important is great, and color unevenness and density unevenness are eliminated.

In particular, for a color copier of a serial printing system using a plurality of heads and a color printer for multi-value input, it is extremely effective to reduce uneven density due to head nozzle pitch and periodic noise due to connecting lines. effective.

[Brief description of drawings]

FIG. 1 is a drawing showing a schematic configuration of the present invention.

FIG. 2 is a perspective view showing an inkjet recording apparatus.

FIG. 3 is a perspective view showing a reading unit.

FIG. 4 is an explanatory diagram of a mode of unevenness correction of a recording head.

FIG. 5 is an explanatory diagram of a mode of unevenness correction of the recording head.

FIG. 6 is a block diagram showing a configuration of a control system.

7 is a diagram for explaining a correction table 2. FIG.

FIG. 8 is a flowchart illustrating an example of a correction processing procedure.

9A and 9B show correction tables 2, where FIG. 9A is a non-linear type and FIG. 9B is a linear type.

FIG. 10 is a flowchart showing a conventional correction algorithm.

FIG. 11 is a diagram showing a conventional test pattern.

FIG. 12 is a diagram showing a conventional correction table 1.

FIG. 13 is an explanatory diagram of a test pattern for irregular 3-line printing.

FIG. 14 is a density distribution diagram of a test pattern.

FIG. 15 is an explanatory diagram of a test pattern forming method and its reading.

FIG. 16 is a density distribution diagram after reading.

FIG. 17 shows a density distribution for each density signal.

FIG. 18 is a flowchart showing a correction algorithm of this embodiment.

FIG. 19 is a diagram showing a test pattern of the present embodiment.

FIG. 20 is a diagram showing a correction table 1 according to the present embodiment.

FIG. 21 is a block diagram showing a switching configuration of the correction table 1.

22 is a flowchart showing switching control of the correction table 1. FIG.

[Explanation of symbols]

 1001 recording head 1020 unevenness correction means 711 print head 717 unevenness correction RAM 705 unevenness correction table ROM 802 selector 803 switch 804 unevenness correction RAM

Claims (4)

[Claims] 1. An image forming apparatus for forming an image by moving a recording head, in which a plurality of recording elements are arranged, relative to a recording medium in a direction different from an arrangement direction of the recording heads. First correction means for selectively instructing the recording characteristics of each recording element for each of a plurality of density regions, and second correction means for correcting the density signal based on the recording characteristics instructed by the first correction means. An image forming apparatus comprising: a correction unit; and a selection unit that selects a recording characteristic indicated by the first correction unit according to a density region to which a density signal corresponding to each recording element belongs. 2. The first correction means comprises a plurality of correction tables for instructing print characteristics of each print element of the print head for each of a plurality of density areas, and the selection means corresponds to each print element. The image forming apparatus according to claim 1, wherein the plurality of correction tables are selectively selected according to a density area to which the density signal belongs. 3. The image forming apparatus according to claim 1, wherein a plurality of the recording heads are provided, and each of the recording heads has the first correcting unit. 4. The image forming apparatus according to claim 1, wherein the recording head causes a state change in the ink by thermal energy and ejects the ink based on the state change. ..