JP2004237725A - Concentration correction method and recording device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide concentration correction method for speedy and highly precise concentration correction and recording device using the method. <P>SOLUTION: A prescribed test pattern image is recorded on recording medium, and a recorded test pattern is optically read in primary resolutions using a sensor. Image quality of the read image is verified. According to the verification results, the prescribed test pattern recorded as above is optically read with the sensor in secondary resolutions which is higher than primary resolutions. Correction data are created by using the read test pattern image. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a density correction method and a printing apparatus to which the method is applied, and more particularly to a density correction method applied to, for example, a printing apparatus equipped with an inkjet print head.

  At present, recording methods applied to recording apparatuses include, for example, a thermal transfer method in which ink of an ink ribbon is transferred to a recording medium such as recording paper by thermal energy, and a method in which flying ink droplets are attached to a recording medium such as paper. There is known an ink jet recording system for performing recording.

  Among them, recording apparatuses employing the ink jet method are widely used in printers, copiers, and the like because of low noise, low running cost, small size of the apparatus, and easy color recording.

  In a recording apparatus using such an ink jet system, it is common to use a recording head in which a plurality of recording elements are integrated and arranged in order to improve the recording speed. The recording element usually includes a nozzle for discharging ink, an ink discharge port, and the like. A major problem in such an ink jet recording apparatus is recording unevenness. Differences in the ink ejection characteristics of a plurality of nozzles cause density unevenness in a printed image.

  Until now, various methods have been proposed for preventing the occurrence of such unevenness and achieving high image quality. For example, the multi-pass printing method is a method in which a print head scans the same area on a print medium a plurality of times to complete printing on the print area. However, in order to take advantage of the multi-pass printing, it is necessary to increase the number of scans of the print head for one print area, that is, the number of divisions, which leads to a decrease in throughput. .

  As a method for suppressing the occurrence of density unevenness without using the divided recording method, there is, for example, a head shading method (for example, see Patent Document 1).

  According to this method, first, a test pattern for determining a preset correction value is recorded on a recording medium using a recording head, and an image of the recorded test pattern is read by a CCD (solid-state imaging device) or the like. The read image is read by a scanner provided, and the read image is appropriately subjected to position correction, and then the image density is assigned to a corresponding raster for each nozzle of the print head. The change in recording density is caused by an error in the ejection amount of each nozzle, a shift in the ejection direction of ink, or bleeding of ink on a recording medium.

Next, a correction value of the recording density corresponding to each nozzle is determined from the density assigned to each raster. Then, the gamma table for each nozzle is changed based on the correction value, or the drive table for each nozzle is changed to adjust the ink ejection amount and the like. With such a correction, for a raster recorded with a high density without correction, a density correction such as an output γ correction is performed so as to reduce the density. The density correction such as the output γ correction is performed to increase the density, thereby reducing the density unevenness.
JP-A-5-69545

  However, the conventional head shading has a problem in that the time required to measure the recording density of the test pattern is long.

  In particular, the number of nozzles of a recent ink jet recording head is as large as several thousands, and the area to be corrected is wide. Furthermore, in order to respond to recent demands for higher image quality, it is required to have high accuracy in measuring the recording density of a test pattern.

  However, in the conventional density correction method, it is necessary to measure a wide range with high accuracy, and thus there is a limit in reducing the measurement time.

  The present invention has been made in view of the above conventional example, and has as its object to provide a density correction method capable of performing density correction quickly and with high accuracy, and a recording apparatus to which the method is applied.

  In order to achieve the above object, the density correction method of the present invention comprises the following steps.

  That is, a density correction method used when performing recording on a recording medium, wherein a recording step of recording a predetermined test pattern image on the recording medium, and a sensor that converts the predetermined test pattern image recorded in the recording step to a sensor. A first reading step of optically reading at a first resolution by using the first reading step; a detecting step of detecting a portion of image quality deteriorated from the image read in the first reading step; A second reading step of optically reading a portion of the predetermined test pattern image having image quality deterioration detected in the detection step at a second resolution higher than the first resolution using the sensor; And a generation step of generating correction data from the image read in the second reading step.

  Now, the configuration of each step included in the above-described method will be described in more detail. In the second reading step, an area near a part where image quality is determined to be degraded in the detecting step is read. In the generation step, at least correction data for a recording element that records a portion determined to have deteriorated image quality in the detection step is generated, and the correction data that has been used so far in the generated correction data. It is desirable to further include a replacement step of replacing

  Further, it is desirable to have a partial reading step of partially reading the predetermined test pattern image at the second resolution even when the image quality is determined to be good as a result of the detection in the detection step.

  Preferably, the recording head is an ink jet recording head. In that case, the inkjet recording head includes an electrothermal converter for generating thermal energy to be applied to the ink in order to discharge the ink using thermal energy, or discharges the ink by mechanical energy. Therefore, it is desirable to provide a piezo element for generating mechanical energy given to the ink.

  Further, the ink jet recording head includes a plurality of nozzle rows for ejecting black, cyan, magenta, and yellow inks.

  Further, the present invention may be realized by applying the method having the above configuration to a recording apparatus. The recording device has the following configuration.

  That is, a recording apparatus that records on a recording medium, a test pattern recording unit that records a predetermined test pattern image on the recording medium, and a first resolution or a first resolution on the image on the recording medium. A reading unit that can read optically at a second resolution that is higher than the first one, and a first unit that controls the reading unit to read the predetermined test pattern image recorded by the test pattern recording unit at the first resolution. Reading control means, detecting means for detecting a portion of image quality degraded from the image read at the first resolution, and detecting means among the predetermined test pattern images recorded by the test pattern recording means A second reading control unit that controls the reading unit to read the portion having the image quality deterioration detected by the second resolution at the second resolution; And having a generating means for generating correction data by using a test pattern image read by the second resolution.

  Therefore, according to the present invention, there is an effect that density correction having both speed and good correction quality can be performed.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  In this specification, “record” (sometimes referred to as “print”) refers not only to the formation of significant information such as characters and figures, but also to the perception of human beings, whether significant or insignificant. Irrespective of whether or not it is made obvious so that it is obtained, a case where an image, a pattern, a pattern, or the like is widely formed on a recording medium or a case where the medium is processed is also described.

  In addition, the term “recording medium” refers to not only paper used in general recording devices, but also a wide range of materials that can accept ink, such as cloth, plastic films, metal plates, glass, ceramics, wood, and leather. Shall be.

  Further, “ink” (sometimes referred to as “liquid”) is to be interpreted broadly as in the definition of “recording (printing)”, and when applied on a recording medium, an image or pattern , A liquid that can be used for forming a pattern or the like, processing a recording medium, or treating ink (for example, coagulation or insolubilization of a colorant in ink applied to a recording medium).

  Further, the term “nozzle” generally refers to an ejection port, a liquid path communicating with the ejection port, and an element that generates energy used for ink ejection, unless otherwise specified.

  FIG. 1 is a top view showing an outline of a configuration of an ink jet recording apparatus (hereinafter, referred to as a recording apparatus) which is a typical embodiment of the present invention.

  As shown in FIG. 1, three ink jet recording heads (hereinafter, referred to as recording heads) 21-1 to 21-3 are mounted on the carriage 20, and each recording head has an ink discharge port for discharging ink. Are arranged in plurality. The recording heads 21-1, 21-2, and 21-3 are recording heads that respectively discharge cyan (C), magenta (M), and yellow (Y) inks. Each of the ink cartridges 22-1, 22-2, and 22-3 includes recording heads 21-1 to 21-3 and an ink tank that supplies ink thereto. In the following description, "21" is used as a reference number when referring to the entire recording head, and "22" is used as a reference number when referring to the entire ink cartridge.

  Here, a configuration in which color recording is performed using three CMY inks is described as an example. However, a recording head that discharges black (Bk) ink, an ink tank that stores Bk ink, and May be added.

  Further, a reflection type density sensor 40 is provided on the carriage 20, so that a test pattern recorded at a predetermined location on a recording medium can be imaged as the carriage 20 moves.

  However, when the present invention is applied to a recording apparatus having a fixed head, for example, a long full-multi type recording head as shown in FIG. 7, the effect is the greatest. This is because, since the number of ink ejection nozzles is large, it takes a long time to create correction data over the entire nozzle area. In FIG. 7, a transport unit such as a transport belt 103 that transports a recording medium 102 is attached to a fixed long inkjet print head 101. Ink is ejected from the inkjet nozzles in accordance with the movement of the recording medium to form an image on the recording medium.

  Control signals and image signals to the recording head 21 are sent from a control circuit of the recording apparatus via the flexible cable 23.

  A recording medium 24 such as plain paper, high-quality exclusive paper, OHP sheet, glossy paper, glossy film, postcard, etc., is sandwiched by discharge rollers 25 via conveyance rollers (not shown), and is driven in the direction of the arrow ( (Sub-scanning direction). On the other hand, the carriage 20 is guided and supported by a guide shaft 27 and a linear encoder 28. The carriage 20 is reciprocated along the guide shaft 27 by the drive of the carriage motor 30 via the drive belt 29. This moving direction is called a main scanning direction.

  A heating element (electric thermal energy converter) for generating thermal energy for ink ejection is provided inside the ink ejection port (liquid path) of the recording head 21. In accordance with the read timing of the linear encoder 28, the heating element is driven based on a recording signal, and an ink droplet is ejected from an ink ejection port of a recording head, and the ink droplet is deposited on a recording medium to form an image. Can be.

  At a home position of the carriage 20 set outside the recording area, a recovery unit 32 having a cap portion 31 is installed. When printing is not to be performed, the carriage 20 is moved to the home position, and the caps 31-1 to 31-3 of the cap unit 31 seal the ink ejection opening surfaces of the corresponding print heads 21-1, 21-2, and 21-3. In addition, clogging due to adhesion of ink due to evaporation of the ink solvent or adhesion of foreign matter such as dust is prevented.

  In addition, the capping function of the cap unit 31 is used for idle discharge in which ink is discharged to the cap unit 31 that is away from the ink discharge port, in order to eliminate discharge failure and clogging of the ink discharge port with low recording frequency. Alternatively, a pump (not shown) is operated in a state of being capped, and ink is sucked from the ink ejection port, and is used for ejection recovery of the ejection port in which ejection failure has occurred. When the recording heads 21-1 to 21-3 pass over the ink receiving section 33 immediately before recording, preliminary ejection is performed to the ink receiving section 33.

  Although not shown, it is desirable to clean the ink ejection port forming surface of the recording head 21 by providing a blade and a wiping member at a position adjacent to the cap portion 31.

  FIG. 2 is a diagram illustrating a configuration of the recording head 21.

  As shown in FIG. 2, the recording head 21 has a number of ink ejection nozzles (hereinafter, referred to as nozzles) in a direction substantially perpendicular to the main scanning direction. FIG. 2 shows an example in which the ink discharge nozzles are formed in one line in each recording head. However, the nozzle lines may be plural lines, and need not be arranged linearly. Further, the interval between the nozzles shown in FIG. 2 is referred to as the resolution of the print head, and is referred to as the nozzle pitch and the nozzle density.

  It is desired that the recording head is moved in the main scanning direction shown in FIG. 2 so that recording corresponding to the width of the nozzle row for ejecting ink can be performed. It may be performed in both directions. The recording head may be prepared by the number of inks used for the recording. For example, full-color recording may be performed with three colors of cyan (C), magenta (M), and yellow (Y). In the case of recording using, dark cyan (C), light cyan (LC), dark magenta (M), light magenta (LM), dark black (Bk), light black (LBk), dark yellow (Y) A recording head that ejects light yellow (LY) and ink of a special color may be prepared.

  The ink jet recording method applicable to the present invention is not limited to the bubble jet method using a heating element (heater). For example, in the case of a continuous type in which ink droplets are continuously ejected and formed into particles, Applicable to charge control type, divergence control type, etc. In addition, in the case of the on-demand type that discharges ink droplets as needed, pressure control method that discharges ink droplets from orifices by mechanical vibration of piezo vibrating element can be applied It is.

  FIG. 3 is a block diagram showing a configuration of a control circuit of the printing apparatus shown in FIG.

  In FIG. 3, 1 is an image data input unit, 2 is an operation unit, 3 is a CPU that performs various processes, 4 is a non-volatile memory that stores various data, and 4a is non-ejection and defective nozzle data corresponding to each nozzle. A recording information storage unit for storing recording information of the head; 4b, a program storage unit for storing various control programs; 5, a RAM; 6, an image data processing unit; 7, an image recording unit for outputting an image; Bus.

  Next, these components will be described in detail.

  The image data input unit 1 serves as an interface for inputting multi-valued image data from an image input device such as a scanner or a digital camera or multi-valued image data stored in a hard disk of a personal computer. The operation unit 2 has various keys for instructing setting of various parameters and start of recording. The CPU 3 controls the entire recording apparatus according to various programs stored in the nonvolatile memory 4.

  The non-volatile memory 4 stores a program for operating the printing apparatus in accordance with a control program and an error processing program, and all the operations of the embodiment described below are operations obtained by executing this program. Note that there are various embodiments of the non-volatile memory 4, such as ROM, FD, CD-ROM, HD, memory card, magneto-optical disk (OMD), EEPROM, FeRAM, MRAM, DVD-ROM, etc. it can. Which storage medium is used depends on the processing speed, cost, and the like required for this recording apparatus. However, the storage area used as the recording information storage unit 4a is preferably a nonvolatile memory such as an EEPROM or an FeRAM, which has a relatively high access speed.

  The RAM 5 is used as a work area for various programs in the nonvolatile memory 4, a temporary save area for error processing, and a work area for image processing. The RAM 5 can copy various tables in the non-volatile memory 4 and then change the contents of the tables and proceed with image processing while referring to the changed tables.

  The image data processing unit 6 can be replaced by the CPU 3 executing a program, but is desirably a dedicated processor in terms of processing speed. The image data processing unit 6 quantizes the multi-valued image data input from the image input unit 1 into N-valued image data for each pixel, and corresponds to the gradation value “T” indicated by each quantized pixel. Generate an ejection pattern. That is, after the input multi-valued image data is subjected to N-value processing, an ejection pattern corresponding to the gradation value “T” is generated. For example, when multi-valued image data expressed by 8 bits (256 gradations) per pixel is input to the image data input unit 1, the image data processing unit 6 sets the gradation value of the output image data to 25 (= 24 + 1). Convert to a value.

  In this embodiment, the multi-valued error diffusion method is used for the T-value processing of the input gradation image data. However, for the T-value processing, for example, an average density storage method, a dither matrix Any halftone processing method can be used. In addition, by repeating the T-value processing for all pixels based on the density information of the image, a binary drive signal of ink ejection and ink non-ejection for each pixel is formed for each nozzle.

  The image recording unit 7 drives the recording head 21 to eject ink based on the ejection pattern generated by the image data processing unit 6 or the image data input from the image input unit 1, and prints a dot image on a recording medium. The bus 8 connects each component in the apparatus and transmits an address signal, data, a control signal, and the like.

  Next, a density unevenness correction method performed in the printing apparatus having the above configuration will be described with reference to FIGS.

  According to this method, first, a test pattern is recorded on a recording medium, a partial density difference of the pattern is detected by optical measurement, and then each nozzle position of the recording head is correlated with density data, and an output image is obtained. In, correction is made so that the part where the density is high is low and the part where the density is low is high, and the drive control of each nozzle is changed to shorten the drive pulse of the nozzle with a large ink discharge amount, So-called head shading, such as raising the drive voltage of a small amount of nozzles, is performed.

  In this embodiment, for the sake of simplicity, only the density correction for a recording head that discharges cyan ink among the three recording heads will be described. The same applies to recording with inks of other colors.

  Needless to say, the correction is performed when the image quality is poor. Although the image quality is improved by the correction, the characteristics of the recording head change over time, and if the ejection state from the nozzle changes, the image quality may deteriorate again. For example, if a phenomenon occurs in which ink is not ejected, an extreme increase or decrease in the amount of ink ejected, or a large shift in the ink ejection position occurs, the image quality is significantly reduced.

  Numerous methods have been proposed as methods for correcting such a phenomenon so as not to occur. A test pattern with a uniform density is recorded and read.This is used to detect density unevenness from the read image and correct it by calculating raster density. There is a method of calculating and correcting the density, and a method of recording a test pattern in which the density changes stepwise and reading it to detect density unevenness. There are various methods for converting raster density into correction data. These methods have advantages and disadvantages depending on the image quality of the image to be corrected, the type of recording medium on which the image is recorded, the type of ink, and the like. Along with this, the measurement accuracy such as the resolution of the captured image is determined.

  By the way, although there is a difference to some extent due to the recent demand for higher image quality, the measurement of the test pattern requires a certain degree of reading accuracy. For example, there are systems that read images at a resolution of 2400 DPI to achieve a certain level of photo quality. However, from the viewpoint of image quality evaluation, there may be a case where a coarser resolution (for example, 600 DPI) may be used. This is because the sensitivity of the human eye is greatly involved. The sensitivity of the human eye is relatively easy to recognize density changes at relatively low frequencies, but relatively insensitive to density changes at high frequencies.

  In view of the above, in this embodiment, the correction requires relatively high-precision measurement, but the image evaluation for determining whether correction is necessary is relatively simple measurement, in other words, an image with a coarse resolution is used. We pay attention to the point of use.

  8 and 9 show examples in which the same image is captured at different resolutions.

  FIG. 8 is a diagram schematically showing a state of reading an image at a high resolution (for example, 2400 DPI), and FIG. 9 is a diagram schematically showing a state of reading the same image at a low resolution (for example, 600 DPI). FIG. 8 and 9 are edited to have the same image size.

  8A and 9A, the ink droplets ejected from the nozzle group 21-1N of the recording head 21-1 adhere to the recording medium 24 as recording dots 24D. I do. However, the positions of these recording dots are somewhat displaced from the expected normal line 24N shown by the dashed line. Because the direction of the ejected droplets is not always linear, some droplets are somewhat upward and some are downward. FIGS. 8B and 9B show the change in the detected density with respect to the nozzle number at the high resolution and the low resolution, respectively. The nozzle number is a number for identifying each nozzle.

  According to the detected density change shown in FIG. 8B, a sharp decrease in the density is clearly seen. This decrease corresponds to the white stripe shown as the reference character a in FIG. In this case, for example, information such as a nozzle position that causes a white stripe can be efficiently acquired.

  On the other hand, according to the detected density change shown in FIG. 9B obtained by reading the image at low resolution, the presence of the image deteriorated portion 24BT such as uneven density can be determined. The position (for example, the portion indicated by reference character a 'in FIG. 9A) cannot be clearly identified. In such a case, the cause of the image deterioration is that the ink ejection amount has decreased in several nozzles corresponding to the image-deteriorated portion, so that the entire portion is a pixel that is colored lightly, or the image-deteriorated portion is It is difficult to determine whether a streak with a strong contrast is generated because one of the corresponding nozzles has become a discharge failure nozzle.

  That is, in the image shown in FIG. 8 having a high reading resolution, it is possible to determine that the image is a white streak caused by the non-ejection of ink from one nozzle. However, in the image shown in FIG. Is a white stripe caused by non-ejection of ink from one nozzle, or a white stripe caused by a small amount of ink ejected from several adjacent nozzles.

  In the case of a white streak caused by ink non-ejection from one nozzle which can be estimated from the image shown in FIG. 8, a method of complementarily printing with nozzles on both sides of the nozzle having an ejection failure is effective for correcting the white streak ( For example, see Japanese Patent Application No. 2002-215847. However, such a determination cannot be made from the image shown in FIG. 9, and correction is performed using several adjacent nozzles including the nozzles that have failed in ejection. Therefore, comparing the two, it can be said that it is more desirable to perform correction based on an image read at high resolution from the viewpoint of high-precision correction.

  However, from the viewpoint of the reading time, when measuring the same range of the image, there is an advantage that the measurement time is significantly shorter when the reading resolution is lower (for example, in the case of FIG. 9). For example, when an image is formed on a line type CCD with two types of optical magnifications (that is, low resolution and high resolution), the larger the magnification, the narrower the measurement range becomes. In this case, the range that can be imaged by one scan is approximately inversely proportional to the magnification. In other words, considering the measurement time, the one with a lower resolution (ie, FIG. 9) is more desirable.

  Therefore, in the present invention, in order to shorten the measurement / detection time, a recording location where density unevenness is a problem, for example, a location where there is a stripe due to an ink non-ejection nozzle or a density unevenness with a large undulation (density defect occurs The step of identifying the portion where the correction is required or monitoring the necessity of correction (image quality evaluation step) and the step of measurement used to generate correction data when correction is necessary (correction data generation step) are separated. Is a low magnification (low resolution), and the latter measurement is performed at a high magnification (high resolution).

  Now, when considering the sensitivity of the human eye to an image, the density change is usually sensitive to low-frequency objects (object), but insensitive to high-frequency changes (for example, RP Dolly and R. Shaw, Noise Perception in Electrophotography, J. Appl. Photogr. Eng., Vol. 5, pp 190-196 (1979)). In other words, since the human eye is a low-pass filter, a system that transmits only relatively low frequency components of the image is sufficient to determine whether the image has a defect. In this embodiment, the optical resolution is set low (for example, 600 DPI) and the measurement is performed for image quality evaluation. However, considering the characteristics of human eyes, the object can still be sufficiently achieved. Then, when the actual correction data is generated after the location (target) to be corrected is determined, only the vicinity of the correction target location is measured again accurately again at a high resolution (for example, 1200, 2400 DPI), Information close to the nozzle resolution is obtained, and data to be fed back to the ejection data of the nozzle is generated based on the information.

  In the processing described below, the correction processing is periodically performed while the actual recording is not being performed.

  FIG. 4 is a flowchart showing the density unevenness correction processing.

  FIG. 5 is a diagram illustrating a state in which a cyan ink is ejected from the recording head 21-1 to record a test pattern, the test pattern is read, and the density is analyzed.

  First, in step S10, a test pattern of 25% duty (that is, ink ejection is generated from 25% of all nozzles of the print head in one cycle of print operation) is printed over the effective print width of the print medium, and in step S20, Then, it is optically evaluated and measured by a reflection type density sensor 40 having a CCD sensor as a light receiving element. However, when the head shading correction has already been performed, the test pattern subjected to the head shading correction is recorded when the test pattern having the 25% duty is printed. By doing so, the head shading correction has already been performed, and the portion where the correction effect has appeared does not need to be determined again as a region where the image quality has deteriorated.

  The optical system of the reflection type density sensor 40 of this embodiment is configured to be able to perform scaled-up and scaled-down imaging. In the case of scaled-down imaging (wide-range measurement mode), resolution is deteriorated, but wide-range measurement is possible. In the case of the (narrow range measurement mode), the imaging range is narrow, but high-precision measurement with high resolution is possible. In the evaluation measurement in step S20, the reflection type density sensor 40 operates in the wide range measurement mode. In the wide range measurement mode, it is possible to capture a pattern having a width of 12 inches × 1 inch at a resolution of 600 DPI in 7 seconds. As discussed previously, the inventor has confirmed through examination that image quality degradation can be detected even at a resolution of 600 DPI, even if the spatial frequency sensitivity of the human eye is considered.

  Next, in step S30, the luminance of the test pattern image captured at the resolution of 600 DPI is integrated in the raster direction, and the projection is performed. The right side of FIG. 5 is a diagram showing the luminance distribution of the projection. If there is no density unevenness in an ideal state, the luminance distribution should be an ideal value (IDEAL) indicated by a solid line with respect to the nozzles of the recording head. However, actually, a value (OBS) deviating from the ideal value is obtained.

  Further, in step S40, the measured value (OBS) is compared with the ideal value (IDEAL), and it is checked whether or not the deviation is within an allowable range. In this embodiment, if the read data is represented by 8-bit data, and if the value deviates from the ideal value by “8” or more, it is determined that the image quality near the location is degraded.

  Here, as a result of the evaluation measurement, if it is determined that the image quality is good, the image quality measurement for correction is not performed, and the process is terminated.

  On the other hand, if it is determined that the image quality of the raster recorded by the specific nozzle is degraded, the process proceeds to step S50, where the correction is performed. For example, in the example shown in FIG. 5, the rasters recorded by the nozzles ABN1 and ABN2 exceed the allowable lower limit (MIN) and the allowable upper limit (MAX), respectively, and it is determined that correction is necessary.

  In step S50, the test pattern is measured again because the measurement accuracy is low to generate correction data using the read result of the test pattern for evaluation measurement recorded in step S10. This is called a correction measurement. In this measurement, the reflection type density sensor 40 is operated in the narrow range measurement mode, and the measurement range is centered on a raster determined to be ejection failure at the time of evaluation measurement (for example, in the vicinity of ABN1 and ABN2 in FIG. 5). Do so. In the narrow range measurement mode, the reflection type density sensor 40 can measure up to a resolution of 2400 DPI, so that highly accurate correction data can be generated.

  Then, in step S60, correction data is generated at the resolution of 2400 DPI read in step S50. More specifically, each raster density is calculated at a resolution of 2400 DPI, and correction data corresponding to a neighborhood including a nozzle determined to be defective or a nozzle determined to be defective is generated.

  Many other methods can be applied as the correction method. For example, measurement may be performed to rewrite a correction pattern at a location where unevenness or a streak is detected. At this time, as shown in Japanese Patent Application No. 2002-215847, a correction may be made in consideration of the coloring characteristics of the ink ejected from the nozzles. In this manner, the recording, measurement, and generation of correction data of a correction pattern can be performed at high speed in the vicinity where unevenness or streaks are detected.

  Finally, in step S70, the corresponding part in the previous correction data is replaced with the correction data generated in step S60.

  Therefore, according to the embodiment described above, a test pattern is read at a low resolution for image quality evaluation, and when the image quality is degraded, the test pattern is read at a high resolution and the correction data is read. Since it is generated, highly accurate correction can be performed quickly for each raster.

  In the above-described embodiment, when the evaluation and measurement result indicates that the image quality is good, the processing is terminated as it is. However, the present invention is not limited to this. For example, a test pattern for partially generating correction data may be used. Measurement may be performed, and correction data may be generated using partially measured data.

For example, even when it is determined that the image quality is good, the correction measurement is partially performed from the upper end as shown in FIG. 6 without ending the processing. Then, at the time of the next evaluation measurement, the correction measurement is further partially performed from the continuation. When there is a recording request, the correction data up to the place where the correction measurement is completed is used. Performing the correction measurement in such a manner as described above has the advantage that the time for one correction process can be reduced, and the correction measurement can be performed efficiently in terms of time.
In the embodiment described above, a pattern having a uniform density of 25% duty is used for image quality evaluation. However, the present invention is not limited to this. For example, another test such as a staircase pattern or a dot pattern may be used. A pattern may be used.

  Furthermore, in the embodiment described above, the same test pattern is used for image quality evaluation and correction, but the present invention is not limited to this. For example, a 100% duty pattern is used for image quality evaluation, Another test pattern such as a staircase pattern or a dot pattern may be used for correction. As described above, it may be more effective to use different test patterns for image quality evaluation and correction.

  Furthermore, in the above-described embodiment, the configuration in which image data is stored at different resolutions using a reflective optical sensor that can be set differently (wide-range measurement mode and narrow-range measurement mode) is used. An example in which evaluation is performed and correction data is generated with high resolution in accordance with the evaluation has been described, but the present invention is not limited to this. For example, (1) image data is read at different resolutions using a single reflective optical sensor that can read at different resolutions, stored, and image quality is evaluated at a low resolution first, and the image is evaluated at a high resolution according to the evaluation. A configuration that generates correction data may be used, or (2) a configuration that stores image data at the same resolution using a single reflection-type optical sensor, performs image processing such as thinning processing, and The image data of the resolution may be obtained, the image quality may be evaluated based on the image data, and the correction data may be generated using the image data of the high resolution which does not perform the thinning process or the like according to the evaluation.

  As described above, when generating correction data, image data having two resolutions, high and low, are used. For the generation of the image data, image data having different resolutions can be generated using optical sensors having different resolutions, Image data may be read at the same resolution, and different image data may be generated in subsequent image processing.

  Furthermore, in the above embodiments, the description has been made assuming that the liquid droplets ejected from the recording head are ink, and the liquid contained in the ink tank is ink, but the contained matter is limited to ink. Not something. For example, an ink tank may contain a processing liquid discharged to a recording medium in order to improve the fixing property and water resistance of the recorded image or to improve the image quality.

  The above-described embodiment includes a means (for example, an electrothermal converter or a laser beam) for generating thermal energy as energy used for causing ink to be ejected, particularly in an ink jet recording system. By using a method that causes a change in the state, it is possible to achieve higher density and higher definition of recording.

  Regarding the typical configuration and principle, it is preferable to use the basic principle disclosed in, for example, US Pat. Nos. 4,723,129 and 4,740,796. 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, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). Applying at least one drive signal corresponding to recording information and providing a rapid temperature rise exceeding nucleate boiling to the electrothermal transducer, thereby causing the electrothermal transducer to generate heat energy, and This is effective because a film in the liquid (ink) corresponding to this drive signal can be formed on a one-to-one basis by causing film boiling on the heat acting surface. By discharging the liquid (ink) through the discharge opening by the growth and contraction of the bubble, at least one droplet is formed. 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 the liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable.

  As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 of the invention relating to the temperature rise rate of the heat acting surface are adopted, more excellent recording can be performed.

  Further, in the above-described embodiment, a serial type recording apparatus that performs recording by scanning a recording head is used. However, a full line type recording apparatus using a recording head having a length corresponding to the width of a recording medium is used. May be. As a full-line type recording head, either a configuration that satisfies the length by a combination of a plurality of recording heads as disclosed in the above specification or a configuration as one integrally formed recording head is used. May be.

  In addition, not only the cartridge-type recording head in which the ink tank is provided integrally with the recording head itself described in the above embodiment, but also the electric connection with the apparatus main body by being attached to the apparatus main body. A replaceable chip-type recording head that can supply ink from the apparatus main body may be used.

  It is preferable to add recovery means for the printhead, preliminary auxiliary means, and the like to the configuration of the printing apparatus described above because the printing operation can be further stabilized. Specific examples thereof include capping means for the recording head, cleaning means, pressurizing or sucking means, preheating means using an electrothermal transducer or another heating element or a combination thereof. It is also effective to provide a preliminary ejection mode for performing ejection that is different from printing, in order to perform stable printing.

  Further, the printing mode of the printing apparatus is not limited to a printing mode of only a mainstream color such as black, and may be a printing head integrally formed or a combination of a plurality of printing heads. The device may be provided with at least one of the full colors.

  In the above-described embodiment, the description has been made on the assumption that the ink is a liquid.However, even if the ink solidifies at room temperature or below, an ink that softens or liquefies at room temperature may be used. Alternatively, in the ink jet system, the temperature of the ink itself is controlled within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. It is sufficient if the ink is sometimes in a liquid state.

  In addition to the above, the recording apparatus according to the present invention may include, as an image output terminal of an information processing apparatus such as a computer, an integrated or separate apparatus, a copying apparatus combined with a reader or the like, and a transmission / reception function. It may take the form of a facsimile machine.

FIG. 1 is an external perspective view illustrating an outline of a configuration of an ink jet recording apparatus according to an embodiment of the invention. FIG. 2 is a diagram illustrating a configuration of a recording head mounted on the inkjet recording apparatus illustrated in FIG. 1. FIG. 2 is a block diagram illustrating a control circuit of the inkjet recording apparatus illustrated in FIG. 1. 9 is a flowchart illustrating density unevenness correction processing. FIG. 5 is a diagram illustrating a state in which a test pattern is recorded by discharging cyan ink by a recording head, and the test pattern is read to analyze a density. It is a figure showing signs of partial correction measurement. 1 is an external perspective view illustrating an outline of a configuration of a full multi-head fixed type inkjet recording apparatus which is a typical embodiment of the present invention. It is a figure which shows the result of reading and measuring a certain image at high resolution (2400 DPI) typically. FIG. 9 is a diagram schematically showing the result of reading and measuring the same image read in FIG. 8 at a low resolution (600 DPI).

Explanation of reference numerals

1 image data input unit 2 operation unit 3 CPU
4 Non-volatile memory 4a Nozzle profile information storage unit 4b Program storage unit 5 RAM
6 Image Data Processing Unit 7 Image Recording Unit 8 Bus 20 Carriage 21, 21-1 to 21-3 Recording Head 22, 22-1, 22-2, 22-3 Ink Cartridge 23 Flexible Cable 24 Recording Medium 25 Discharge Roller 26 Conveying motor 27 Guide shaft 28 Linear encoder 29 Drive belt 30 Carriage motor 31 Cap unit 32 Recovery unit 33 Ink receiving unit 40 Reflective density sensor 101 Full-line inkjet recording head 102 Recording medium 103 Transport belt

Claims (10)

A density correction method used when recording on a recording medium,
A recording step of recording a predetermined test pattern image on the recording medium,
A first reading step of optically reading the predetermined test pattern image recorded in the recording step at a first resolution using a sensor;
A detecting step of detecting a portion having deteriorated image quality from the image read in the first reading step;
Of the predetermined test pattern image recorded in the recording step, a portion having image quality deterioration detected in the detection step is optically read at a second resolution higher than the first resolution using the sensor. A second reading step;
A generation step of generating correction data from the image read in the second reading step.   2. The density correction method according to claim 1, wherein in the second reading step, an area near a portion where the image quality is determined to be degraded in the detecting step is read.   2. The density correction method according to claim 1, wherein in the generation step, correction data is generated for at least a recording element that records a portion determined to have deteriorated image quality in the detection step.   2. The density correction method according to claim 1, further comprising a replacement step of replacing previously used correction data with the correction data generated in the generation step.   2. The method according to claim 1, further comprising a partial reading step of partially reading the predetermined test pattern image at the second resolution even when the image quality is determined to be good as a result of the detection in the detecting step. The density correction method described in 1. A recording device that performs recording on a recording medium,
Test pattern recording means for recording a predetermined test pattern image on the recording medium,
Reading means for optically reading an image on the recording medium at a first resolution or a second resolution higher than the first resolution;
First reading control means for controlling the reading means to read the predetermined test pattern image recorded by the test pattern recording means at the first resolution;
Detecting means for detecting a portion having deteriorated image quality from the image read at the first resolution;
A second reading unit that controls the reading unit to read, at the second resolution, a portion of the predetermined test pattern image recorded by the test pattern recording unit that has image quality deterioration detected by the detection unit; Control means;
Generating means for generating correction data using the test pattern image read at the second resolution.   7. The recording apparatus according to claim 6, wherein the second reading control unit controls to read an area near a portion where the image quality is determined to be degraded by the detecting unit.   7. The recording apparatus according to claim 6, wherein the generation unit generates correction data for a recording element that records at least a portion determined to have deteriorated image quality by the detection unit.   7. The recording apparatus according to claim 6, further comprising a replacement unit that replaces the correction data used so far with the correction data generated by the generation unit. A third reading control unit that controls the reading unit to partially read the predetermined test pattern image at the second resolution even when the image quality is determined to be good as a result of the verification by the detecting unit. The recording device according to claim 6, further comprising:

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