JP2942048B2 - Image forming device - Google Patents

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 for correcting density unevenness due to variations in the discharge amount of each nozzle in a print head. In particular, the present invention 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 performing recording on a recording medium such as paper or OHP sheet (hereinafter referred to as recording paper or simply paper) has been proposed in a form in which recording heads of various recording systems are mounted. Have been. This recording head includes a wire dot type, a thermal type, a thermal transfer type, an ink jet type, and the like. In particular, the ink-jet method, which directly ejects ink onto recording paper, has attracted attention as a quiet recording method with low running cost.

[0003] In order to eliminate the occurrence of density fluctuation and density unevenness in the ejection performance of the ink jet recording apparatus, the ejection speed and directionality (landing accuracy) and the ejection amount VDROP [pl / dot] are required.
Has been stabilized by the following method.

[0004] 1. Discharge amount control method This is a divided pulse width modulation method (PWM control method) described in Japanese Patent Application No. 3-4713 and the like proposed by the present applicant.
By changing the pulse width of the pre-pulse according to the temperature of the recording head, fluctuations in the ejection amount due to temperature fluctuations are suppressed.

[0005] 2. Density unevenness correction method This is a so-called head shading method: HS method in which density unevenness of a test pattern printed by a recording head is read and a density signal for each nozzle (ejection port) is corrected.

[0006] 1. In the method of (1), in particular, in the serial printing method, since the average ejection amount of the head is controlled, it is possible to eliminate the density fluctuation caused by the temperature fluctuation within the page and between the pages. It is not possible to correct for unevenness in the connection direction due to the serial printing method), that is, the variation in the ejection amount of each nozzle of the head. For this reason, the density unevenness in the nozzles of the head could not be completely removed, and particularly in an image forming apparatus of a serial printing system, density unevenness occurs at a pitch of a serial joint and is remarkable in an image of a uniform tone. It was noticeable as unevenness.

Therefore, in order to make up for the disadvantage of the first method,
In the method (1), unevenness correction (HS method) is performed based on a predetermined output pattern (constant density signal), and the variation in the ejection amount in the nozzles of the head has been reduced 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 at a predetermined printing ratio), it is possible to eliminate density unevenness near the density. Was. However, in the correction for one fixed density, when the printing ratio changes, the frequency of the nozzles used changes every moment.
If the printing ratio changes rapidly or the printing ratio becomes low or high, the correction table for one density cannot be used alone, and density unevenness occurs. Therefore, there is a need for a method for correcting density unevenness in all regions 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, unevenness in print density occurs as a result. When printing is performed in this state, a full-color image formed of four colors of cyan, magenta, yellow, and black has density unevenness that is repeated particularly at a boundary between serial portions. In addition, since the color balance is partially disrupted in areas such as the blue sky, sunset sky, and human skin of a uniform tone, the color tone changes and appears as color unevenness, and the color reproducibility decreases (color difference Increase) and lower the image quality. Further, there is a problem that density unevenness occurs even in a monochromatic image such as black, red, blue, or green.

Therefore, the present invention has been made to solve the above-mentioned problem, and has a method of controlling density unevenness in all gradations.
An object of the present invention is to provide an image forming apparatus capable of stably outputting an image having no density streaks.

[0010]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a recording head having a plurality of recording elements arrayed on a recording medium in a direction different from the arrangement direction of the recording heads. In an image forming apparatus that performs image formation by relatively moving, a first correction unit that selectively indicates a recording characteristic of each recording element of the recording head for each of a plurality of density areas; A second correction unit for correcting the density signal based on the recording characteristic specified by the correction unit, and a recording specified by the first correction unit according to a density region to which the density signal corresponding to each recording element belongs. Selecting means for selecting characteristics.

[0011]

According to the above arrangement, the density unevenness can be corrected using the optimum correction table for each density while switching the first correction means in real time according to the density signal (image signal). Density unevenness can be uniformly corrected up to the density, and a pictorial color image can be stably output.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 flowchart showing the features of the present invention best. Here, reference numeral 1001 denotes one or a plurality of recording heads depending on the form of the image forming apparatus, and the recording head is formed of a multi-nozzle (having a plurality of ejection ports). In this embodiment, four ink jet recording heads of C / M / Y / K based on a serial recording method are used and applied to a color image forming apparatus. A unit 1003 scans the print head with respect to the print medium (recording material) 1002, and a transfer unit 1040 for the print medium 1002 conveys the print medium 1002 with respect to the print position of the print head 1001. 10
Reference numeral 14 denotes a unit for reading a print pattern used for unevenness correction. In this embodiment, the unit 14 is used in common with a reading unit for reading a document and performing image processing. Here, a light source (halogen lamp) for irradiating light to a document (a printed matter or a pattern printed on a recording medium) and a reading unit (lens and CCD sensor) for reading reflected light thereof are provided. Reference numeral 1020 denotes a density unevenness correction unit, the method of which will be described in detail later. Based on the density unevenness data read from the density unevenness correction pattern, image recording is performed while performing head unevenness correction processing during normal recording. I have. Reference numeral 1015 denotes a printing control unit, which performs creation of density unevenness correction data, changes in driving conditions of a recording head, and other controls related to printing by a CPU (microcomputer).

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 sheet is held between the sheet feeding roller 43 via the rollers 1 and 42, and is fed in the direction of 44 by rotating these rollers. Guide rails 46 and 47 are set 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 is provided with a slit,
By detecting this slit with a photo sensor provided on the carriage 48, the position of the carriage and the like can be recognized. The carriage 48 has four color heads 49Y, 49M, and 49 of yellow, magenta, cyan, and black.
C, 49Bk are mounted thereon, and ink tanks of four colors are arranged thereon. 128 heads (400D
PI: マ ル チ = a multi-nozzle head having a discharge port with a diameter of 20 μm). The recording material 45 is a recording head 49
Is intermittently fed by the print width (equivalent to 8.128 mm)
While the recording material 45 is stopped, the recording head 49 scans in the P direction and ejects ink droplets (maximum driving 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 platen glass is placed on the scanning portion of the reading unit 60. The document 2 is set with the printing surface facing down, and the information of the document is read by the reading unit 60 from below. Has become. In the figure, reference numeral 60 denotes a reading unit, which reads an image by sliding on a pair of guide rails 61, 61 '. 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 lead bundle for supplying power to the light source 62 and the CCD and transmitting image signals and other control signals from the CCD. 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 with the recording medium conveyance direction. The drive transmission section 65 in the main scanning direction is stretched between pulleys 66 and 66 ′, and the line information of the image orthogonal to the main scanning
Read with the number of bits corresponding to. After reading the image for a predetermined width, the main scanning pulse motor 67 rotates in the direction opposite to the arrow Ι. As a result, the reading unit 60 moves in the H direction and returns to the initial position.

Reference numerals 68 and 68 'denote carriages.
The slider slides on guide rails 69 and 69 'for the sub-scanning (F) direction substantially orthogonal to the main scanning direction G. Carriage 6
8 'is fixed by a fixing member 70 to a driving force transmission unit 72 for the sub-scanning (F) direction such as a wire stretched over the pulleys 71, 71'. After the main scanning is completed, the pulley 71 is rotated in the direction of the arrow H by a sub-scanning driving source (not shown) such as a pulse motor or a servomotor to a predetermined distance (the same distance d as the read image width in the main scanning G direction). The carriage 68, 68 'is 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 document image can be read. In addition, instead of performing the sub-scanning of the reading unit, the document may be fed in the sub-scanning direction.

Here, a part related to the density unevenness correction of the present invention will be described. The conventional density unevenness correction method followed a correction sequence as shown in FIG.
That is, only the pattern of the 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 estimated from the density is estimated. . Then, a correction table 1: an HS table as shown in FIG.
This HS table and an image signal (8-bit signal: FF (hex) = 256 as shown in FIG. 9A or 9B)
(Dec))) Correction Table 2: Correction is performed using both HS_γ curves (correction curves: non-linear curve and linear curve). At this time, as described above, since the correction table 2: HS_γ table is created with average head values, it is possible to completely perform density unevenness correction in all gradation expressions from low DUTY to high DUTY. It was impossible.

It is to be noted that the fact that the non-linear correction curve is created for each nozzle of the head by the main body increases the cost (CPU).
And the correction time (which requires a dedicated printing / correction method for creating HS_γ) is not preferable.

Therefore, in this embodiment, density unevenness is corrected according to the correction sequence shown in FIG. That is,
As shown in FIG. 19, four test patterns having different densities (in this embodiment, four gradations are used, but the number of gradations may be increased or the intervals between gradations 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 ejection amount unevenness of the head corresponding to each of the four densities (density unevenness distribution at each density (DUTY) due to different frequencies of nozzles used depending on the density). Different: see FIG. 17). Based on this, FIG.
A plurality of correction tables 1: H corresponding to respective densities such as 0
An S table is created, and correction is performed using both this table and a correction table 2: HS_γ curve (correction curve: linear) as shown in FIG. 9B.

FIG. 21 is a block diagram showing a circuit configuration and a sequence for performing the above-described density unevenness correction.
This will be described with reference to the sequence flowchart shown in FIG.
In FIG. 21, an image processing unit 801 converts input image data into an image signal: Si and outputs it to a selector 802. The selector 802 determines the size of the image signal: Si in step S61 in 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 of each recording element (discharge amount) are determined according to the density area to which the density signal corresponding to each recording element belongs. Correction table value).

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). . Thereby, the correction of the density unevenness of the head of each color can be performed at a low duty.
To high DUTY in all gradation expressions. Note that, in FIG.
(Correction table 1) 804 is representatively shown for one of the four colors.

Next, a 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 where the number of recording nozzles is N will be described. It is assumed that when printing is performed by driving each element: nozzle (1 to N) with a certain uniform image signal: Si, a density distribution occurs in the nozzle direction of the head. First, the density O of the portion corresponding to each recording element
Measure D1 to ODN and average concentration: ODAVG = ΣODAVG
/ N. This average concentration is not limited to each element,
A method of integrating the amount of reflected light to obtain an average value or a known method may be used. If the relationship between the value of the image signal 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 coefficient to obtain target concentration: ODAVG
Should be determined. That is, the signal Si is expressed as α × Si = (ODAV
G / ODN) × Si, which is a correction signal corrected to Si, may be given to this element or group according to the input signal Si.
More specifically, this is performed by performing a table conversion as shown in FIG. 5 on the input image signal.

In FIG. 5, a straight line A is a straight line having a slope of 1, and is a table for outputting an input signal without any conversion. A straight line B is a straight line having a slope of α = ODAVG / ODN, and is a table for converting an output signal into an input signal Si into α · Si. Therefore, if the image signal corresponding to the N-th recording element is subjected to table conversion such as the straight line B in FIG. Each concentration in the portion to be rendered will be equal to ODAVG. If such processing is performed for all the recording elements, the density unevenness is corrected, and a uniform image is obtained. That is, it is possible to correct the density unevenness by previously obtaining data indicating what table conversion should be performed on an image signal corresponding to which recording element.

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

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

FIG. 7 shows an example of the non-uniformity correction table 2. In this embodiment, there are 64 correction straight lines whose inclinations from Y = 0.68X to Y = 1.31X are different by 0.01 from each other. The correction straight line is switched according to the unevenness correction signal 718. For example, when a signal of a pixel to be recorded at an ejection port having a large ejection amount (resulting in a large dot diameter on a recording material) is input, a correction straight line having a small inclination is selected, and conversely, a correction line having a small ejection amount is selected. In the case of a discharge port (small dot diameter), an image signal is corrected by selecting a correction straight line having a large inclination, and a density unevenness distribution in a certain area is corrected.

Unevenness correction RAM 717 (correction table 1)
Stores a selection signal of a correction straight line necessary for correcting unevenness of each head. That is, the unevenness correction signals having 64 types of values from 0 to 63 are stored for the number of ejection ports of the recording head, and the unevenness correction signal 718 is output in synchronization with the input image signal. Then, the signal 7 whose unevenness has been further corrected by the straight line selected by the unevenness correction signal 7
Reference numeral 06 denotes a binarizing circuit 7 using a dither method, an error diffusion method, or the like.
07, and by driving the head 711 via the head driver 709, a color image without density unevenness is formed. If the density unevenness fluctuates due to long-term use or the head is replaced,
The system of the above-mentioned correction method 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 illustrating an example of a procedure of the unevenness correction processing according to the present embodiment. When this procedure is started by pressing a density unevenness correction key (not shown), first, in step S1, the ejection stability of the recording head is secured by head recovery and initialization. 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 dust or air bubbles, it may not be possible to recognize faithful head characteristics (density unevenness distribution state). It is. The recovery condition at this time may be a recovery optimized according to the use state, the environment, and many other conditions, and may be a combination of known recovery conditions (suction, idle discharge, temperature control, driving conditions, and the like). In addition,
In addition to the above method, warm-up printing may be performed at the time of test pattern printing, or reading of a stable area may be devised.

Next, in steps S3 and S5, the test pattern is printed and read, respectively. In this embodiment, as described above, the result of performing the density unevenness reading of each density of the pattern as shown in FIG.
7 (A), (B), (C) and (D). Here, the horizontal axis is the Y direction, that is, the direction in which the ejection openings of the recording head are arranged, and the vertical axis is the reading density in the X direction averaged 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 printing area due to the balance with the reading device, the density correction at both ends may not be accurately performed. Therefore, the problem can be solved by considering the rising portions at both ends by irregular three-line printing.

The irregular three-line printing will be described with reference to FIG. X is the scanning direction of the print head, and Y is the pixel (nozzle) direction of the print head, which is the direction of arrangement of 128 ejection openings. 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 the nozzles, and finally, the third line is printed using the first to 32nd nozzles. A region surrounded by a dotted line is a region where a test image is read using a reading device. In this embodiment, 128 pixels are used, and a warm-up region for printing is provided on the left side. The purpose of using the 32 nozzles before and after is to take into account the rising edge of the above-described scanning reading (accurate reading is required in order to detect the edge and make the density unevenness data correspond to the nozzle position). .

This method will be described with reference to FIG. First, the entire density distribution is taken in, and a threshold value for clearly distinguishing between a printed portion and a non-printed portion (blank paper portion) is determined in advance (broken line portion in the figure). Next, a nozzle number having a density equal to or higher than the threshold value is calculated, and a position corresponding to the nozzle returned 64 from the nozzle number is allocated to the first nozzle, and 2, 3,.
No. is assigned. With this method, an accurate nozzle density distribution can be obtained.

However, the number of nozzles on both sides used in irregular three-line printing is not limited to this number because it depends on the performance of the reader, but printing is performed in the same state as when printing is performed using all nozzles. It must be controlled so that it can be performed (driving conditions, temperature control, etc.).

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

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

As described above, while the correction table 1 is switched in real time in accordance with the density signal (image signal), the density unevenness can be corrected using the optimum correction table 1 for each density. The density unevenness can be uniformly corrected, and a pictorial color image can be stably output.

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

The present invention provides an excellent effect particularly in a recording head and a recording apparatus of a type utilizing thermal energy among ink jet recording types.

The typical configuration and principle are described in, for example, US Pat. Nos. 4,723,129 and 4,740.
It is preferable to use the basic principle disclosed in the specification of Japanese Patent No. 796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, liquid (ink)
By applying at least one drive signal corresponding to the recorded information and providing a rapid temperature rise exceeding nucleate boiling, to the electrothermal transducer disposed corresponding to the sheet or the liquid path in which is held, This is effective because thermal energy is generated in the electrothermal transducer, and the film is boiled on the heat-acting surface of the recording head. As a result, bubbles in the liquid (ink) can be formed in one-to-one correspondence with the drive signal. The liquid (ink) is ejected through the ejection opening by the growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. Examples of the drive signal in the form of a pulse include those described in U.S. Pat.
Suitable are those described in US Pat. No. 45,262. If the conditions described in U.S. Pat. No. 4,313,124 relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

As the configuration of the recording head, in addition to the combination of the discharge port, the liquid path, and the electrothermal converter (linear liquid flow path or right-angled liquid flow path) as disclosed in the above-mentioned respective specifications, U.S. Pat. No. 4,558,333 and U.S. Pat.
A configuration using the specification of Japanese Patent No. 459600 is also included in the present invention. In addition, Japanese Unexamined Patent Publication (Kokai) No. 123670/1984 discloses a configuration in which a common slit is used as a discharge portion of an electrothermal converter for a plurality of electrothermal converters, and an aperture for absorbing pressure waves of thermal energy. The present invention is also effective as a configuration based on JP-A-59-138461 which discloses a configuration corresponding to a discharge unit.

[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 forming a pictorial color image in which the reproducibility of gradation is important, is remarkable, and the occurrence of color unevenness and density unevenness has been eliminated.

In particular, for a serial printing type color copier / multi-value input color printer using a plurality of heads, it is enormous to reduce the density unevenness due to the head nozzle pitch and the periodic noise due to the streaks. effective.

[Brief description of the drawings]

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

FIG. 2 is a perspective view showing an ink jet recording apparatus.

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

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

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

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

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

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

9A and 9B show a correction table 2, in which FIG. 9A shows a non-linear type, and FIG. 9B shows 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 three-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 reading thereof.

FIG. 16 is a density distribution diagram after reading.

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

FIG. 18 is a flowchart illustrating a correction algorithm according to the present embodiment.

FIG. 19 is a diagram illustrating a test pattern according to the present embodiment.

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

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

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

[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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/01 B41J 2/205

Claims (4)

(57) [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 the arrangement direction of the recording heads. A first correction unit for selectively instructing a recording characteristic of each recording element for each of a plurality of density areas; and a second correction unit for correcting a density signal based on the recording characteristic instructed by the first correction unit. An image forming apparatus comprising: a correction unit; and a selection unit that selects a recording characteristic specified by the first correction unit according to a density area to which a density signal corresponding to each recording element belongs. 2. The image processing apparatus according to claim 1, wherein the first correction unit includes a plurality of correction tables that indicate recording characteristics of each recording element of the recording head for each of a plurality of density areas, and the selection unit corresponds to each recording element. 2. The image forming apparatus according to claim 1, wherein the plurality of correction tables are alternatively selected according to a density area to which a density signal belongs. 3. The image forming apparatus according to claim 1, wherein a plurality of the recording heads are provided, and the first correction unit is provided for each recording head. 4. The image forming apparatus according to claim 1, wherein the recording head causes a state change in the ink by thermal energy, and discharges the ink based on the state change. .