JP2010136060A - Image forming apparatus and program for correcting uneven density - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which corrects uneven density precisely in a short period of time, and also to provide a program for correcting uneven density. <P>SOLUTION: Based on the read data of a test pattern 200, the output density corresponding to an input pixel value at a measurement point is measured and plotted in the coordinate system of the input pixel value-output density, and then the output density is complemented between the measurement points thus obtaining a measured density curve 204. A pixel value D1 required for obtaining the target value X of an input pixel value D0 is calculated on the measured density curve 204, and a correction LUT 1 sets a translation pixel value of D0 at D1. A displacement (a) arises between the D1 obtained based on the complement value and a pixel value D1' which can actually obtain the output density X. From a second measured density curve 204 based on the read data of a test pattern 200 which is based on the correction LUT 1, a pixel value D2 required for obtaining the target value X is calculated. Regarding that the displacement (a') of the D0 and D2 is substantially identical to the displacement (a), the displacement (a') is made to correspond with the D1, and a pixel value D3 which is displaced from the D1 by the displacement (a') is set as the translation pixel value of D0 by a correction LUT 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and a density unevenness correction program.

  The present invention relates to an image forming apparatus that forms an image using a recording head in which a plurality of recording elements are arranged, and forms a test pattern in a state in which density unevenness correction is performed based on previously generated correction data. Based on the read data, calculate the correction amount obtained from the ratio of the average density of all the discharge ports in the print head and the concentration of the target discharge port, and calculate the current correction amount and the correction amount used so far. An image forming apparatus that calculates correction data by multiplication or addition has been proposed (see, for example, Patent Document 1).

Further, in the input / output characteristics of each nozzle, a straight line connecting the lowest measured value of the highest luminance (input luminance 255) and the highest measured value of the lowest luminance (input luminance 0) is taken as the measured luminance average value and corresponds to each nozzle. There has been proposed a printing apparatus that corrects an input pixel value by adding a correction value such that the pixel value of the pixel becomes an average value (see, for example, Patent Document 2).
Japanese Patent No. 2938929 JP 2007-38435 A

  It is an object of the present invention to provide an image forming apparatus and a density unevenness correction program that can correct density unevenness in a short time with high accuracy compared to a case without this configuration.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention comprises a plurality of recording elements arranged along a predetermined direction, and the recording is performed according to image information indicating an input pixel value. Image forming means for driving an element to form an image, reading means for reading an image formed by the image forming means and outputting read data, and predetermined for measuring an output density corresponding to an input pixel value First control means for controlling the image forming means so that a reference image having a plurality of density patterns for different pixel values is formed, and read data obtained by reading the reference image with the reading means The output density for each of the plurality of density patterns is calculated based on the output density, and the output density corresponding to the pixel value between the predetermined different pixel values is calculated based on the calculated output density. First correction information for calculating a completed complementary value and converting the input pixel value to a first pixel value corresponding to the same output density or complementary value as the output density target value corresponding to the input pixel value is provided. First correction information generation means for generating, and controlling the image forming means so that an input pixel value is converted into the first pixel value based on the first correction information to form the reference image And calculating the output density and the complementary value based on the read data obtained by reading the reference image formed by the second control means and the control of the second control means by the reading means, Using the shift amount between the second pixel value corresponding to the output density or the complementary value and the input pixel value corresponding to the output density target value corresponding to the input pixel value as the shift amount in the first correction information, The deviation of the first pixel value It is configured to include a second correction information generation means for generating a second correction information for converting the input pixel value to the third pixel value min corrected.

  According to a second aspect of the present invention, the third pixel value is a value obtained by subtracting the input pixel value from the second pixel value and adding the first pixel value to the first pixel value. A value obtained by subtracting the input pixel value from a value obtained by adding the second pixel value to a value, or a value obtained by adding the second pixel value to a value obtained by subtracting the input pixel value from the first pixel value. It can be.

  According to a third aspect of the present invention, the first correction information and the second correction information are generated when a predetermined condition is satisfied, and when the predetermined condition is not satisfied. The second correction information can be generated using the first correction information generated when the predetermined condition is satisfied. According to a fourth aspect of the present invention, the case where the predetermined condition is satisfied may be a case where a recording head composed of a plurality of recording elements arranged along the predetermined direction is replaced. it can.

  According to a fifth aspect of the present invention, when the second correction information is generated, the second control means uses the third correction information as the first correction information. The correction information obtained by changing the first pixel value is used as the pixel value, the formation of the reference image by the second control unit, and the generation of the second correction information by the second correction information generation unit. It can be repeated multiple times.

  According to a sixth aspect of the present invention, there is provided a density nonuniformity correction program for forming a reference image having a plurality of density patterns for different predetermined pixel values for measuring an output density corresponding to an input pixel value. As described above, a plurality of recording elements arranged along a predetermined direction are provided, and an image forming unit that drives the recording elements according to image information indicating input pixel values to form an image is controlled. Output for each of the plurality of density patterns based on the read data obtained by reading the image formed by the image forming means and reading the reference image with the control means and the reading means that outputs the read data Calculating a density, and based on the calculated output density, calculating a complementary value that complements an output density corresponding to a pixel value between the predetermined different pixel values, First correction information generating means for generating first correction information for converting the input pixel value to a first pixel value corresponding to an output density or complementary value equal to a target value of an output density corresponding to a force pixel value And a second control unit that controls the image forming unit so that the reference image is formed by converting the input pixel value to the first pixel value based on the first correction information; The output density and the complementary value are calculated based on the read data obtained by reading the reference image formed by the control of the second control means by the reading means, and the output density corresponding to the input pixel value A shift amount between the second pixel value and the input pixel value corresponding to the same output density or complementary value as the target value is used as the shift amount in the first correction information, and the first pixel value is used as the shift value. Before the third pixel value corrected by the amount Is a program for functioning as a second correction information generation means for generating a second correction information for converting the input pixel value.

  As described above, according to the image forming apparatus according to claim 1 and the density unevenness correction program according to claim 6, the density unevenness is corrected with high accuracy in a short time compared to the case where the present configuration is not provided. The effect that it can be obtained.

  Further, according to the image forming apparatus of the second aspect, it is possible to easily calculate the pixel value to be converted and correct the density unevenness in a short time with high accuracy compared to the case where the present configuration is not provided. The effect is obtained.

  Further, according to the image forming apparatus of the third aspect, it is possible to obtain an effect that density unevenness correction according to the situation can be performed as compared with the case where the present configuration is not provided.

  Further, according to the image forming apparatus of the fourth aspect, it is possible to obtain an effect that the density unevenness correction according to the situation can be performed as compared with the case where the present configuration is not provided.

  Further, according to the image forming apparatus of the fifth aspect, it is possible to obtain an effect that the density unevenness can be corrected with higher accuracy than in the case where the present configuration is not provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, the case where the image forming apparatus of the present invention is applied to an ink jet type droplet discharge apparatus will be described.

  FIG. 1 is a schematic diagram showing an overall configuration of an ink jet type droplet discharge apparatus 10 according to the present embodiment.

  The droplet discharge device 10 includes a recording head array 12. The recording head array 12 includes a cyan ink liquid (C), a magenta ink liquid (M), a yellow ink liquid (Y), a black ink liquid (K), and a processing liquid (T). Correspondingly, five recording heads 14C, 14M, 14Y, 14K, and 14T are provided.

  The recording heads 14 </ b> C, 14 </ b> M, 14 </ b> Y, 14 </ b> K, and 14 </ b> T are long recording heads called FWA (Full Width Array) whose width is substantially equal to the width of the recording paper 16. The recording heads 14 </ b> C, 14 </ b> M, 14 </ b> Y, 14 </ b> K, and 14 </ b> T are fixed, and eject the respective ink droplets and processing droplets from the ejection nozzles onto the recording paper 16 that is being conveyed. An image is formed based on the data. The treatment liquid is colorless or light-colored, and the ink liquid of each color is dropped on the recording paper 16 and then dropped so as to overlap, thereby reducing ink bleeding and improving the image quality.

  The recording heads 14C, 14M, 14Y, 14K, and 14T are respectively connected to ink cartridges 18C, 18M, 18Y, 18K, and 18T that store CMYK ink liquids and processing liquids by pipes (not shown), respectively. Are supplied to the recording heads 14C, 14M, 14Y, 14K, and 14T. As the ink, various known inks such as water-based ink, oil-based ink, and solvent-based ink can be used.

  In addition, the droplet discharge device 10 includes a conveyance belt 19 that is an endless belt below the recording head array 12. The conveyor belt 19 is wound around the drive rolls 20A and 20B, and is driven to rotate in the A direction, which is the clockwise direction in FIG. 1, by the rotational force of the drive rolls 20A and 20B. The conveying belt 19 when facing the recording head array 12 is flat, and the recording paper 16 is conveyed to the flat area, and ink droplets are applied to the recording paper 16 from the recording heads 14C, 14M, 14Y, and 14K. As a result, an image is formed. At this time, the recording heads 14C, 14M, 14Y, and 14K discharge ink droplets from the discharge nozzles to the recording paper 16 with a time difference. As a result, the ink droplets of the respective colors are superimposed on the recording paper 16, and an image is formed.

  Further, the droplet discharge device 10 includes a charging roll 22 on the upstream side in the driving direction from the region of the conveying belt 19 facing the recording head array 12. A predetermined voltage is applied to the charging roll 22, and the charging roll 22 is driven while sandwiching the conveyance belt 19 and the recording paper 16 with the driving roll 20 </ b> A, thereby applying a charge to the recording paper 16. The recording paper 16 that has been charged by the charging roll 22 is electrostatically attracted to the transport belt 19 and is transported along with the circumferential drive of the transport belt 19.

  The recording paper 16 is accumulated in a paper feed tray 24 provided on the lower side inside the droplet discharge device 10. The recording paper 16 is taken out from the paper feed tray 24 one by one by the pick-up roll 26, and is transported to the transport belt 19 by the recording paper transport unit 30 having a plurality of transport rollers 28.

  A peeling plate 32 is disposed on the downstream side in the driving direction of the conveying belt 19 in FIG. 1 from the portion facing the recording head array 12. The peeling plate 32 peels the recording paper 16 from the transport belt 19. The recording paper 16 peeled off from the transport belt 19 is transported by a plurality of discharge rollers 36 constituting a discharge transport section 34 and is discharged to a paper discharge tray 38 provided at the upper part of the droplet discharge device 10.

  A cleaning roll 40 capable of sandwiching the conveyance belt 19 with the drive roll 20B is disposed on the downstream side in the rotation direction of the conveyance belt 19 in FIG. The cleaning roll 40 cleans the surface of the conveyor belt 19.

  In addition, the recording paper 16 having an image formed on one side may be transported to the transport belt 19 again by the reverse transport unit 44 including a plurality of reversing rollers 42, and an image may be formed on the other surface. it can. The reverse conveyance unit 44 branches from the discharge conveyance unit 34 and is arranged so as to convey the recording paper 16 to the recording paper conveyance unit 30.

  An optical sensor 46 is disposed on the upstream side in the rotational direction from the position where the peeling plate 32 is disposed on the downstream side in the rotational direction of the conveyor belt 19 in FIG. 1 with respect to the portion facing the recording head array 12. The optical sensor 46 is composed of, for example, a CCD line sensor or a CCD area sensor, and reads, for example, a test pattern image for correcting the density of ink ejected by the ejection nozzle at a predetermined reading resolution. The optical sensor 46 is configured to have substantially the same width as the print width of the recording head 14, and reads an image on the entire surface of the recording paper 16 when the recording paper 16 is conveyed.

  FIG. 2 is a diagram illustrating a main part of a control system of the droplet discharge device 10.

  The droplet discharge device 10 includes a CPU 100 that controls the entire droplet discharge device 10. The CPU 100 includes a ROM 102, a RAM 104, a hard disk storage device 106, an image data input unit 108, an operation display unit 110, an image formation control unit 112, an image data processing unit 114, an optical sensor 46, and a bus 116 such as a control bus or a data bus. Connected through.

  The ROM 102 stores a control program for controlling the droplet discharge device 10 and nozzle characteristic data (such as a correction LUT described later) for each discharge nozzle. The RAM 104 is used as a work space for processing various data. The hard disk storage device 106 stores image data, test pattern data for forming a test pattern image, various data relating to image formation, and the like.

  The image data input unit 108 receives input of image data from a personal computer (not shown). The input image data is transmitted to the hard disk storage device 106.

  The operation display unit 110 includes a touch panel in which an operation function and a display function are integrated, and operation buttons for a user to perform various operations. The operation display unit 110 receives an operation such as start of image formation on the recording paper 16 and notifies the user of the control state of the droplet discharge device 10 and the like.

  The image formation control unit 112 controls the recording heads 14C, 14M, 14Y, 14K, 14T, the conveyance belt 19 and the like in order to form an image on the recording paper 16 based on the image data.

  The image data processing unit 114 performs predetermined image processing such as ink density adjustment on the image data stored in the hard disk storage device 106. Further, the image data processing unit 114 processes read data obtained by reading the test pattern with the optical sensor 46, and performs an ink density correction lookup for correcting the ink density of the image formed on the recording paper 16. A table (hereinafter referred to as “correction LUT”) is generated.

  Next, a correction LUT generation method according to the first embodiment will be described. Note that the density unevenness correction process executed in the present embodiment is the same process for each of the recording heads 14C, 14M, 14Y, 14K, and 14T. explain.

  As shown in FIG. 3, the test pattern 200 includes a plurality of density patterns 202 for detecting density unevenness. The density pattern 202 is formed in a belt-like shape having a width substantially the same as the print width of the recording head in the ejection nozzle arrangement direction and a predetermined width in the paper transport direction for each density pattern of different densities. Each density pattern 202 is arranged at a predetermined interval in the paper transport direction, and is given a number such as density pattern 202 (1), density pattern 202 (2),... Density pattern 202 (n) from the top. n is the number of steps of the density pattern, and can be an arbitrary number, for example, 8 steps or 16 steps. Each density pattern 202 includes, for example, the density pattern 202 (1) as an input pixel value d1, the density pattern 202 (2) as an input pixel value d2,..., And the density pattern 202 (n) as an input pixel value dn. Furthermore, it corresponds to a predetermined input pixel value.

  The optical sensor 46 sequentially reads the test pattern 200 from the density pattern 202 (1) along the paper conveyance direction. Based on the read data, the output density for n stages corresponding to the input pixel value for each ejection nozzle. Measure. The input pixel values d1 to dn at which the output density is measured are referred to as “measurement points”.

  As shown in FIG. 4, the output density measured by reading from each density pattern 202 at the position corresponding to the target discharge nozzle in the coordinate system with the input pixel value on the horizontal axis and the output density on the vertical axis is measured for each measurement point. The measured concentration curve 204 is obtained by complementing the output density between each measurement point by linear interpolation or the like. Also, the average value of the output density at each measurement point of all the discharge nozzles is plotted in the coordinate system for each measurement point, and the output density is complemented between each measurement point by linear interpolation or the like to obtain the target density curve 206. Although the target density curve 206 is an average of the output densities of all the discharge nozzles here, the maximum value, the minimum value, the mode value, etc. of the output density may be used.

  In order to create a correction LUT such that the measured density curve 204 approaches the target density curve 206, a first correction LUT (hereinafter referred to as “correction LUT1”) is first generated. Here, a method of generating the correction LUT1 will be described by focusing on the input pixel value D0. A measurement point di (i is an arbitrary natural number from 1 to n) corresponding to the input pixel value D0 in FIG. 4 and a measurement point d (i + 1) portion are enlarged and shown in FIG. In FIG. 5, only the output density target value X of the input pixel value D0 is displayed, and the display of the target density curve 206 is omitted.

  As shown in FIG. 5, in order to obtain the target value X for the input pixel value D0, the pixel value D1 having an output density X on the measured density curve 204 is required. Therefore, it is determined that the input pixel value D0 is converted to D1 in the correction LUT1. This is expressed as “LUT1 (D0) = D1”, and D1 is referred to as “conversion pixel value” in the correction LUT1. Here, it is considered that the measured density curve 204 is ideally an ideal measured density curve 208 indicated by a broken line in FIG. 5, and the converted pixel value D1 obtained based on the complementary value obtained by linear interpolation and the actual output density. There is a shift amount a between the pixel value D1 ′ from which X can be obtained.

  Therefore, in order to further correct the value corresponding to the deviation amount a, a second correction LUT (hereinafter referred to as “correction LUT2”) is generated. The input pixel value is corrected by the correction LUT1, and the test pattern 200 is output and read by the optical sensor 46, and the measured density curve 204 and the target density curve 206 are obtained in the same manner as described above.

  As in the case of the correction LUT1, the measurement point di and measurement point d (i + 1) portions corresponding to the input pixel value D0 are enlarged and shown in FIG. The output density measured for the first time is indicated by a white circle (◯), and the output density measured for the second time after correction by the correction LUT 1 is indicated by a black circle (●).

  As in the case of the correction LUT1, when the pixel value for obtaining the target value X is obtained from the second measured density curve 204, the pixel value D2 is obtained. The difference between the input pixel value D0 and the pixel value D2 at this time is defined as a shift amount a '. The shift amount a 'is regarded as substantially the same as the shift amount a in the correction LUT1, and the converted pixel value D1 in the correction LUT1 is further corrected.

  Here, since the point plotted as the output density of the input pixel value D0 in FIG. 6 is actually the output density of the converted pixel value D1, the shift amount a ′ between the input pixel value D0 and the pixel value D2 is expressed as follows. Corresponding to the converted pixel value D1, a pixel value D3 having a value shifted from D1 by the shift amount a ′ is calculated. Then, in the correction LUT2, it is determined that the input pixel value D0 is converted to the pixel value D3. This is expressed as “LUT2 (D0) = D3”, and D3 is referred to as “conversion pixel value” in the correction LUT2. Since the shift amount a 'is considered to be substantially the same as the shift amount a in FIG. 5, the converted pixel value D3 can be considered to be substantially the same as the pixel value D1' in FIG. That is, the first measured density curve 204 becomes closer to the target density curve 206 by converting the input pixel value D0 to the converted pixel value D3 and correcting it.

“LUT2 (D0) = D3” can be further expressed by the following equation.
LUT2 (D0) = D3
= D1 + (D2-D0) (1)
= (D1 + D2) -D0 (2)
= D1-D0 + D2 (3)
As described above, the expression (1) indicates that the conversion pixel value D3 in the correction LUT2 is calculated by associating the shift amount a ′ (= (D2−D0)) with the conversion pixel value D1 in the correction LUT1. ing. In addition, the input pixel value D3 is calculated using an expression that does not have a term corresponding to the shift amount a ′ directly on the expression by exchanging the order of the terms as in Expression (2) and Expression (3). Also good.

  Note that, when the pixel value D2 is calculated from the second measured density curve 204, since it is calculated using the complementary value, a similar shift amount is generated although the value is smaller than the shift amount a in the correction LUT1. . Therefore, the generation of the correction LUT2 is repeated to reduce the deviation amount, thereby improving the density unevenness correction accuracy.

  In the above description, the input pixel value D0 has been described. However, the same processing is performed for each input pixel value to generate the correction LUT1 and the correction LUT2. For the input pixel value corresponding to the measurement point, the converted pixel values in the correction LUT1 and the correction LUT2 are calculated by the above method, and for the input pixel value corresponding to other than the measurement point, the input pixel value corresponding to the measurement point. The conversion pixel value may be calculated by complementing the conversion pixel values calculated for the above by linear interpolation or the like.

  Next, with reference to FIG. 7, a processing routine for correcting density unevenness in the present embodiment will be described. This routine is started when the CPU 100 executes a density unevenness correction program stored in the ROM 102 when an instruction signal for instructing density unevenness correction is input.

  In step 300, it is determined whether or not the recording head 14 has been replaced. In this embodiment, when the recording head 14 is replaced, the correction LUT 1 is generated and stored in a predetermined storage area, and thereafter, the correction stored in the predetermined storage area is performed unless the recording head 14 is replaced. Assume that LUT1 is used. Therefore, in order to determine the presence or absence of the correction LUT1, it is determined whether or not the recording head 14 has been replaced. If the recording head 14 has been replaced, the process proceeds to step 302. If the recording head 14 has not been replaced, the process proceeds to step 308. Whether or not the recording head 14 has been replaced is determined by checking if the correction LUT 1 has not yet been generated after the recording head 14 has been replaced by setting a flag to that effect. It can be judged by doing. Further, the correction LUT1 stored in a predetermined storage area when the recording head 14 is replaced is deleted, and it is determined whether or not the correction LUT1 exists in this storage area. Alternatively, it may be determined that the recording head 14 has been replaced.

  In step 302, the test pattern 200 is output. Here, since the correction LUT 1 does not exist, the test pattern 200 is output in a state where the density unevenness is not corrected. Next, in step 304, the output test pattern 200 is read by the optical sensor 46, and read data is output.

  Next, in step 306, based on the read data, the measurement density curve 204 and the target density curve 206 for each ejection nozzle are calculated, and a correction pixel value corresponding to each input pixel value is calculated to generate a correction LUT1. And stored in a predetermined storage area.

  Next, in step 308, “1” is set to the variable i. The variable i is a value indicating the number of generations when the correction LUT2 described later is repeatedly generated. In addition, the number of times the correction LUT2 is generated is “n”, and n is set in this step. The number of repetitions n may be a predetermined value, for example, or may be a value input from the operation display unit 110 by the user. Further, as a density unevenness correction mode, for example, a plurality of modes such as a mode with a repetition count of 5 and a mode with a repetition count of 2 are provided, and the repetition count corresponding to the selected mode is set as the value of n. You may do it. Alternatively, the value of the number of repetitions n may be set according to the elapsed time from the previous density unevenness correction to the current density unevenness correction.

  Next, in step 310, the input pixel value is converted into a converted pixel value determined by the correction LUT1, and the test pattern 200 is output. Next, in step 312, the output test pattern 200 is read by the optical sensor 46 and read data is output.

  Next, in step 314, the measured density curve 204 and the target density curve 206 for each ejection nozzle are calculated based on the read data, and the converted pixel values corresponding to the respective input pixel values are converted into the above (1) to (3). ) To generate a correction LUT2_i by calculation based on any of the equations.

  Next, in step 316, it is determined whether there is a print job waiting to be printed. This is because when there is a print job waiting to be printed, the execution of the print job is given priority over the generation of the correction LUT 2 to correct the density unevenness correction with higher accuracy. If a print job is input from the external personal computer or the like to the image data input unit 108, it is determined that there is a print job waiting for printing, and the process proceeds to step 326. If there is no print job waiting for printing, Proceed to step 318.

  In step 318, it is determined whether or not the variable i has reached n. If i = n, it is determined that the number of times the correction LUT 2 has been generated has been completed by the number set in step 308, and the process proceeds to step 326. If the variable i is not yet n, the process proceeds to step 320, where the input pixel value is converted to the converted pixel value determined by the correction LUT2_i, and the test pattern 200 is output. Next, in step 322, the output test pattern 200 is read by the optical sensor 46 to output read data. Next, in step 324, the variable i is incremented by 1, and the process returns to step 314.

  If it is determined in step 316 that there is a job waiting for printing, or if it is determined in step 318 that the generation of the correction LUT 2 has been repeated n times, the process proceeds to step 326, and in step 314. A correction LUT is generated by combining the generated correction LUT2_i and a correction LUTy generated by other processing (not shown). The density unevenness correction in the present embodiment is a process mainly for correcting low frequency density unevenness. For example, in order to correct high frequency density unevenness or density unevenness due to a non-ejection nozzle, Other density unevenness correction processing is performed. The final correction LUT is generated by combining the correction LUTy generated by such other processing and the correction LUT2_i in the present embodiment.

In order to generate the correction LUT by combining the correction LUT2_i and the correction LUTy, for example, the converted pixel value by the correction LUT2_i is used as the input pixel value of the correction LUTy as shown in equation (4).
LUT (D0) = LUTy (LUT2_i (D0)) (4)
Here, when the correction LUT2_i and the correction LUTy are determined as in the expressions (5) and (6), the input pixel value D0 is converted into the pixel value D4 by the correction LUT.

LUT2_i (D0) = D3 (5)
LUTy (D3) = D4 (6)

  Note that the method of generating the correction LUT by combining the correction LUT2_i and the correction LUTy is an example. For example, other methods may be used, such as using the converted pixel value by the correction LUTy as the input pixel value of the correction LUT2_i. Good.

  Next, in step 328, the generated correction LUT is transferred, stored in a predetermined storage area, and the process is terminated.

  As described above, in the present embodiment, a correction value LUT2 is generated by calculating a value corresponding to the shift amount in the correction LUT1 by a simple method and further correcting the correction value. Therefore, the correction value is set based on the ratio between the target value and the measured density. Compared to the case where the correction value is calculated by calculating and adding or multiplying the correction values calculated by repeated correction, the density unevenness can be corrected with high accuracy in a short time. Further, it is possible to perform density unevenness correction with higher accuracy by repeatedly generating the correction LUT2. Further, since the correction LUT1 and the correction LUT2 use different conversion pixel value calculation methods, the density unevenness correction process can be flexibly performed in accordance with the processing status of the droplet discharge device, the presence or absence of replacement of the printhead, and the like. it can.

  In the present embodiment, a case has been described in which whether or not to generate the correction LUT1 is determined based on whether or not the recording head has been replaced. However, whether or not the user generates the correction LUT1 from the operation display unit. It is also possible to input a selection signal for selecting and to make a determination based on this selection signal, or to make a determination based on the elapsed time from the previous density unevenness correction to the current density unevenness correction.

  In addition, although the liquid droplet ejection apparatus according to the present embodiment has been described with respect to the case where an image (including characters) is formed on a recording paper, the recording medium is not limited to the recording paper, and the ejection is performed. The liquid is not limited to the ink liquid, and may be used in other liquid droplet ejection recording apparatuses such as a pattern forming apparatus that ejects liquid droplets onto a sheet-like substrate for forming a pattern such as a semiconductor or a liquid crystal display. Can be applied.

  In this embodiment, the case where the image forming apparatus of the present invention is applied to a droplet discharge device has been described. However, the present invention can also be applied to an LED printer or a thermal printer. An LED printer to which the present invention is applied has a plurality of light emitting elements arranged in a predetermined direction as recording elements, and forms an electrostatic latent image on a photoreceptor by causing the light emitting elements to emit light according to input pixel values. An exposure unit and a development unit that develops an electrostatic latent image formed on the exposure unit to form an image. Then, by converting the input pixel value into the converted pixel value based on the correction LUT, the light emission amount for each light emitting element is changed, and the density of the image formed by the developing unit is corrected. The thermal printer to which the present invention is applied has a plurality of thermal heads arranged in a predetermined direction as recording elements, applies a voltage to the recording elements according to the input pixel value, and presses the recording elements against the thermal paper. Thus, an image is formed. Then, by converting the input pixel value to the converted pixel value based on the correction LUT, the voltage applied to the recording element is changed, and the density of the formed image is corrected.

It is the schematic which shows the whole structure of the droplet discharge apparatus which concerns on this Embodiment. It is a block diagram which shows the principal part of the control system of the droplet discharge apparatus which concerns on this Embodiment. It is a figure which shows an example of a test pattern. It is a diagram which shows a measurement density | concentration curve and a target density | concentration curve. It is a figure for demonstrating calculation of the conversion pixel value in correction | amendment LUT1. It is a figure for demonstrating calculation of the conversion pixel value in correction | amendment LUT2. It is a flowchart which shows the processing routine of density | concentration unevenness correction in this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Droplet discharge device 14 Recording head 46 Optical sensor 112 Image formation control part 114 Image data processing part 200 Test pattern 202 Density pattern 204 Measurement density curve 206 Target density curve D0 Input pixel value D1 Conversion pixel value in correction LUT1 (first Pixel value)
D2 pixel value (second pixel value)
Conversion pixel value (third pixel value) in D3 correction LUT2

Claims (6)

An image forming unit including a plurality of recording elements arranged along a predetermined direction, and driving the recording elements in accordance with image information indicating an input pixel value to form an image;
Reading means for reading an image formed by the image forming means and outputting read data;
First control means for controlling the image forming means so that a reference image having a plurality of density patterns for different predetermined pixel values for measuring an output density corresponding to an input pixel value is formed;
The output density for each of the plurality of density patterns is calculated based on read data obtained by reading the reference image with the reading unit, and the predetermined different pixel values are calculated based on the calculated output density. A complementary value that complements the output density corresponding to the pixel value in between is calculated, and the input pixel is set to the first pixel value corresponding to the same output density or complementary value as the target value of the output density corresponding to the input pixel value. First correction information generating means for generating first correction information for converting a value;
Second control means for controlling the image forming means so as to form the reference image by converting an input pixel value to the first pixel value based on the first correction information;
The output density and the complementary value are calculated based on the read data obtained by reading the reference image formed by the control of the second control means by the reading means, and the output corresponding to the input pixel value The shift amount between the second pixel value corresponding to the same output density or complementary value as the target density value and the input pixel value is used as the shift amount in the first correction information, and the first pixel value is used as the shift amount. Second correction information generating means for generating second correction information for converting the input pixel value into a third pixel value corrected by a shift amount;
An image forming apparatus including:   A value obtained by subtracting the input pixel value from the second pixel value is added to the first pixel value, and the second pixel value is added to the first pixel value. The image forming apparatus according to claim 1, wherein a value obtained by subtracting the input pixel value from the obtained value or a value obtained by adding the second pixel value to a value obtained by subtracting the input pixel value from the first pixel value. .   When the predetermined condition is satisfied, the first correction information and the second correction information are generated, and when the predetermined condition is not satisfied, the predetermined condition is satisfied The image forming apparatus according to claim 1, wherein the second correction information is generated using the first correction information generated in step 1.   4. The image forming apparatus according to claim 3, wherein the case where the predetermined condition is satisfied is a case where a recording head composed of a plurality of recording elements arranged along the predetermined direction is replaced.   When the second correction information is generated, the second control means uses the first pixel value as the first correction information to the third pixel value of the second correction information. 5. The method according to claim 1, wherein the correction information is changed, and the formation of the reference image by the second control unit and the generation of the second correction information by the second correction information generation unit are repeated a plurality of times. The image forming apparatus according to claim 1. Computer
A plurality of recording elements arranged along a predetermined direction so that a reference image having a plurality of density patterns for different predetermined pixel values for measuring the output density corresponding to the input pixel value is formed. A first control unit that controls an image forming unit that drives the recording element according to image information indicating an input pixel value to form an image;
Based on read data obtained by reading an image formed by the image forming unit and reading the reference image by a reading unit that outputs read data, an output density for each of the plurality of density patterns is calculated. Based on the calculated output density, a complementary value is calculated by complementing the output density corresponding to the pixel value between the predetermined different pixel values, and the same output as the target value of the output density corresponding to the input pixel value First correction information generating means for generating first correction information for converting the input pixel value into a first pixel value corresponding to a density or a complementary value;
Second control means for controlling the image forming means so as to form the reference image by converting an input pixel value to the first pixel value based on the first correction information;
The output density and the complementary value are calculated based on the read data obtained by reading the reference image formed by the control of the second control means by the reading means, and the output corresponding to the input pixel value The shift amount between the second pixel value corresponding to the same output density or complementary value as the target density value and the input pixel value is used as the shift amount in the first correction information, and the first pixel value is used as the shift amount. Second correction information generating means for generating second correction information for converting the input pixel value into a third pixel value corrected by a shift amount;
Density unevenness correction program to make it function.

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