JP4383622B2 - Image forming apparatus and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus and a control method therefor, and more particularly to an image forming apparatus that corrects an output density during image formation and a control method therefor.
[0002]
[Prior art]
In general, in a printing apparatus that prints and outputs an image on a recording sheet, the color of a printed image may fluctuate due to density fluctuations due to aging of the apparatus.
[0003]
Therefore, in the conventional printing apparatus, in order to eliminate the influence of the density fluctuation, the density correction with respect to the density level of the formed image is performed as follows.
[0004]
That is, at a predetermined timing, several patch patterns having specific density levels are formed on the photoconductor or intermediate transfer body, and the input density level is standardized based on the density value obtained by measuring the patch pattern with a sensor. A density correction table for correcting density values has been created. At the time of actual image formation, the color density variation in the printed image is suppressed by adjusting the input density level using this density correction table.
[0005]
Further, when the density correction is performed in the conventional image forming apparatus, several patch patterns of the same density level are used in order to reduce the measurement error of the patch pattern density formed on the photosensitive member or the intermediate transfer member. It was formed in several places, and the average value of these measured values was used as the measured concentration value.
[0006]
[Problems to be solved by the invention]
However, in the conventional image forming apparatus, only a few specific density levels are measured when the density correction table is created, so that the density correction for all input density levels is not always sufficient.
[0007]
Further, even if the density level is the same, an error occurs between the density of the patch pattern formed on the photoconductor or the intermediate transfer body in the apparatus and the density actually formed on the recording paper. Therefore, as in the above-described conventional example, the density correction table created based on the density value measured on the photoconductor or intermediate transfer body can sufficiently correct the image formed on the recording paper. could not.
[0008]
Further, when patch patterns having the same density level are formed in several places as in the conventional case, the number of density levels that can be measured as a whole is reduced, so that density characteristics for all input density levels can also be obtained. Is difficult, and sufficient density correction cannot be performed on the formed image.
[0009]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus and a control method therefor that can appropriately perform density correction of a formed image in all image input density levels in the image forming apparatus. Objective.
[0010]
It is another object of the present invention to provide an image forming apparatus and a control method thereof that can shorten the rise time of the apparatus while enabling appropriate density correction immediately after the power is turned on.
[0011]
Further, it is possible to provide an image forming apparatus and a control method therefor that can obtain density characteristics with respect to all input density levels more accurately by increasing the number of density levels of measurable patch patterns and appropriately enable density correction of a formed image. With the goal.
[0012]
[Means for Solving the Problems]
As a means for achieving the above object, a method for controlling an image forming apparatus according to the present invention includes the following steps.
[0013]
  That is, an image forming apparatus for correcting the density level of image information with reference to a density correction table when a toner image carried on an image carrier is transferred to a recording medium to form an image on the recording medium. In the control method, a first density correction table is created based on a scanner measurement value obtained by reading a pattern printed on a recording medium by the image forming apparatus with a scanner connected to the image forming apparatus. A first pattern having a plurality of density levels including a halftone density level is formed on the image carrier, and the density value of the first pattern measured by a sensor is used. A table correction step for correcting the first density correction table, and a patch pattern having a patch pattern having a density level higher than that of the first pattern. Of the pattern formed on the image bearing member, based on the concentration value of the second pattern measured by the sensor, and a second table generation step of generating a second density correction table, a,Determining whether the first density correction table has already been created by the first table creation step;The first density correction table has already been createdIt was judgedThe table correction step is executed, and the first density correction table is not created.It was judgedIn this case, the second table creation step is executed.
[0016]
  As a means for achieving the above object, an image forming apparatus according to the present invention comprises the following arrangement.
[0017]
  That is, in an image forming apparatus that corrects a density level of image information with reference to a density correction table when a toner image carried on an image carrier is transferred to a recording medium to form an image on the recording medium. A first table for creating a first density correction table based on a scanner measurement value obtained by reading a pattern printed on a recording medium by the image forming apparatus with a scanner connected to the image forming apparatus. A patch pattern having the same density level of the first pattern formed by forming a first pattern having a patch pattern of a plurality of density levels including a halftone density level on the image carrier and measured by a sensor. Table correction means for correcting the first density correction table based on a density value determined as an average value of the measured values, and the first parameter. A second pattern having a patch pattern with a density level higher than that of the image pattern is formed on the image carrier, and a second density correction table is formed based on the density value of the second pattern measured by the sensor. A second table creation means for creatingIt is determined whether or not the first density correction table has already been created by the first table creation means, and if it is determined that the first density correction table has already been created, the table correction means is used. Operate and operate the second table creating means when it is determined that the first density correction table is not created..
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.
[0019]
[First Embodiment]
<Basic processing in this embodiment>
First, in order to help understanding the detailed description of the present embodiment, basic processing in the present embodiment will be described.
[0020]
In this embodiment, first, a patch pattern having a predetermined gradation, which is a measurement image, is printed on paper, and the density value of each patch pattern is obtained by reading the paper with a scanner. A density correction table for correcting so as to present is prepared in advance.
[0021]
Next, in the printer, a patch pattern having a predetermined gradation is formed on a photosensitive member or an intermediate transfer member, and the density is measured by a sensor. Based on the measurement result and the density correction table, a measurement reference density value (sensor reference value) by a sensor in the printer is set in advance.
[0022]
The above is the initial processing for density correction in the present embodiment.
[0023]
Based on the density variation obtained by forming a patch pattern in the printer at a predetermined timing during use of the printer, measuring its density with a sensor, and comparing the sensor measurement value with a sensor reference value. The density correction table is corrected.
[0024]
Thereby, it is possible to perform density correction in consideration of a change with time in the printer.
[0025]
Details of this embodiment will be described below.
[0026]
<Device configuration>
FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus (hereinafter referred to as a printer) in the present embodiment.
[0027]
In FIG. 1, reference numeral 101 denotes a host computer, which sends print information for performing print processing such as color information, characters, graphics, images, and the number of copies to the printer 102. Reference numeral 103 denotes a scanner, which scans a document and generates image data, and measures the density of a density correction patch pattern which will be described later.
[0028]
The printer 102 includes an image processing unit 215, a printer engine 217 that forms an image on a recording sheet based on an image signal sent from the image processing unit 215, and a density value of a patch pattern formed based on a specific density level. Are roughly divided into a density measuring unit 216 that measures the density and a table storage device 218 that stores density correction tables and sensor reference values.
[0029]
Hereinafter, main configurations and operations of the image processing unit 215 will be described.
[0030]
First, an image forming system in the image processing unit 215 will be described.
[0031]
Reference numeral 201 denotes an interface that controls transmission / reception of print information to / from the host computer 101, and 202 denotes a reception buffer that holds input print information.
[0032]
Reference numeral 203 denotes an object generation unit that converts print information input from the host computer 101 such as colors, characters, graphics, and image images into intermediate information (hereinafter referred to as an object) and stores it in the object buffer 204. At this time, if the print information is color-related data such as gray level setting, color level setting, multi-value image, etc., density level correction using a density correction table is performed in a density correction unit 208 described later. .
[0033]
Next, based on the object stored in the object buffer 204, the rendering unit 205 generates a bit image to be rendered, and stores the bit image in the band buffer 206. At this time, the gradation of the bit image (output image) is reduced to the output gradation in the printer engine 217 by performing pseudo halftone processing in the dither processing unit 207.
[0034]
In this way, the bit image stored in the band buffer 206 is sent to the printer engine 217 and formed on the recording medium.
[0035]
A central processing unit (CPU) 213 determines and controls various processes according to programs stored in the ROM 212. A ROM (Read Only Memory) 212 stores various control programs 212a including a program for realizing the processing shown in the flowchart of FIG.
[0036]
Reference numeral 214 denotes a RAM (Random Access Memory), which stores data for the CPU 213 to perform judgment control of each process in accordance with a program stored in the ROM 212, and is used as a work area.
[0037]
Next, a density control system in the image processing unit 215 will be described. Here, an outline will be described, and details thereof will be described later.
[0038]
First, a density correction table is created in the scanner density correction unit 209 based on the density value of the patch pattern printed by the printer engine 217 and measured by the scanner 103. Thereafter, the density measuring unit 216 measures the density value of a patch pattern formed on a drum (described later) in the printer 102 based on a plurality of density levels including halftones at a predetermined timing, and the sensor density correcting unit 210 Based on the measured value, the concentration fluctuation amount is obtained. Then, the correction table correction unit 211 corrects the previously created density correction table based on the density fluctuation amount.
[0039]
The table storage device 218 stores the density correction table corrected as described above and the sensor reference value set when the density correction table is created.
[0040]
<Print processing>
Hereinafter, the print processing in the present embodiment will be described with reference to the flowchart shown in FIG. 2 is stored in the ROM 211 as described above, and is executed by the CPU 212.
[0041]
In FIG. 2, first, print data is received from the host computer 101 (S301) and held in the reception buffer 202 (S302). Then, one processing unit of data is extracted from the reception buffer 202 (S303), and it is determined whether or not all data extraction has been completed (S304). If it is determined that the processing has not been completed, it is determined whether or not the data processing for one page has been completed (S305).
[0042]
If it is determined that the data processing for one page has not been completed, it is determined whether the print data is color-related data such as color information or a color image image (S306). For example, the density correction processing unit 208 corrects the density level of each color of the print data using the density correction table (S307).
[0043]
Here, in the present embodiment, the density correction table referred to in the density correction unit 208 is capable of optimally converting the density level by sufficiently considering the current density characteristics including the temporal change in the current printer 102. It is corrected.
[0044]
Next, an object of the print data is created (S308) and stored in the object buffer 204 (S309), and the process returns to step S303 to retrieve the next data.
[0045]
On the other hand, if it is determined in step S306 that the data is not color-related data, it is determined whether the data is mask data of characters, graphics, or the like (S310). If it is determined that the data is mask data, an object of mask data is created (S308), and the process returns to step S309. On the other hand, if it is determined that it is not mask data, print data processing corresponding to the type of data is performed (S311), and the process returns to step S303.
[0046]
On the other hand, if it is determined in step S305 that one page of data has been completed, rendering processing is performed based on the object held in the object buffer 204 (S312), and the created bit image is transmitted to the printer engine 217. Then, a printing process for printing on the recording paper is performed (S313).
[0047]
If it is determined in step S304 that the processing for all data has been completed, the printing process is terminated.
[0048]
<Scanner density correction process (density correction table creation process)>
Next, scanner density correction processing according to the present embodiment will be described with reference to FIGS. 3, 4, and 5. That is, a density correction table is created so that the scanner measured density value is corrected to an ideal value (linear).
[0049]
FIG. 3 is a diagram illustrating an example of a scanner density correction patch pattern in the present embodiment. According to the figure, the scanner density correction patch pattern has a sufficient number of patch patterns for each color (Y, M, C, K) to obtain density characteristics for the input density level (00H to FFH). It can also be seen that patch patterns of the same density level are arranged at different positions in order to eliminate errors due to density unevenness on the paper. This patch pattern is printed out on a recording sheet by the printer engine unit 217 based on a command from the host computer 101 or a test print function of the printer 102.
[0050]
FIG. 4 is a flowchart showing the scanner density correction process.
[0051]
First, the patch pattern shown in FIG. 3 is printed on a recording sheet by the printer 102 (S401), and the density value is actually measured for all density levels of the formed patch pattern by reading the sheet with the scanner 103. (S402).
[0052]
Then, in order to remove the density unevenness on the recording paper, the scanner density correction unit 209 averages the measured density values of the patches having the same density level, and further calculates the measured density values of the patches having the preceding and following density levels. The measured density value is corrected by using the moving average to calculate (S403). Then, based on the corrected measured density value of each density level patch, the density correction table is created by interpolating the data between the patches so that the density characteristic with respect to the input density level becomes a predetermined density characteristic (S404).
[0053]
By the processing in steps S401 to S404, a patch pattern having a sufficient number of density levels to obtain density characteristics with respect to the input density level is printed on the recording paper, and the density of the patch pattern is measured using the scanner 103. A density correction table for obtaining density characteristics from the measured density values and correcting the input density level so that the density characteristics become a predetermined density characteristic is created.
[0054]
Thereafter, a sensor reference value setting process for setting a measurement reference value (hereinafter referred to as sensor reference value) of the density sensor in the density measurement unit 216 in the printer 102 is performed (S405). Specifically, first, the patch pattern formed in the printer 102 is measured by the density sensor in the density measuring unit 216. This measuring method will be described later. Then, the sensor density correction unit 210 corrects the measurement value, and the correction table correction unit 211 sets the obtained sensor measurement value and density level as a sensor reference value in the density measurement unit 216.
[0055]
Then, the density correction table and the sensor reference value obtained by the above processing are stored in the table storage device 218 (S406).
[0056]
In the present embodiment, the scanner density correction process shown in FIG. 4 is performed prior to the actual print process.
[0057]
<< Density correction table creation process >>
FIG. 5 is a diagram illustrating an example of density characteristics referred to in the present embodiment.
[0058]
The solid line in FIG. 5A is the density characteristic obtained by a series of measurement value correction processes shown in steps S401 to S403 in FIG. That is, the patch pattern shown in FIG. 3 is printed on the paper in the printer 102, the density value of the patch pattern is measured by reading the paper with the scanner 103, and the measurement value is corrected by the scanner density correction unit 209. The obtained density characteristics with respect to the input density level.
[0059]
A broken line in FIG. 5A is a density characteristic exhibiting a linear characteristic for performing ideal image formation. This characteristic is hereinafter referred to as a predetermined density characteristic.
[0060]
In this embodiment, in order to correct the density characteristic obtained by actual measurement (solid line in FIG. 5A) to a predetermined density characteristic (dashed line in FIG. 5A), in step S404, the input density level is corrected. A density correction table is created so that is replaced with a correction density level. An example of this density correction table is shown by the solid line in FIG.
[0061]
<< Sensor reference value setting process >>
FIG. 6 is a flowchart showing an example of the sensor reference value setting process in step S405 of FIG.
[0062]
The correction table correction unit 211 receives the density level value to be measured and the measured density value from the sensor density correction unit 210 (S701). Then, the input density level value corresponding to the density level value is obtained by referring to the density correction characteristic (density correction table) with the density level value corresponding to the correction density level axis in FIG. Is set as a reference density level (S702). At the same time, a measured density value measured by a sensor in the density measuring unit 216 described later is held as a sensor reference value corresponding to the reference density level (S703).
[0063]
In FIG. 7, the set sensor reference values (three points in this example) are indicated by ● (black dots). A broken line shown in FIG. 7 is a density characteristic linearly corrected by the density correction table. That is, immediately after the density correction table is set, the sensor density measurement value follows a linear characteristic, so it is appropriate to set this as the sensor reference value.
[0064]
<In-printer density measurement process>
Hereinafter, the density measurement process in the printer according to the present embodiment will be described with reference to FIG. This processing corresponds to the concentration measurement processing in step S701 in FIG.
[0065]
FIG. 8 is a diagram schematically illustrating an example of the in-printer density measurement process. In the figure, reference numeral 601 denotes a patch pattern of several halftone density levels in the density level (00H to FFH), which is formed for each color (Y, M, C, K). Here, it is assumed that patch patterns having density levels of 30H, 60H, and 90H are formed for each color.
[0066]
In the printer 102, for example, a patch pattern 601 of each color is formed on an intermediate transfer member 602, and the density of the patch pattern is measured by a sensor 603. The sensor 603 is configured by, for example, a combination of a near infrared light source that irradiates the drum and a photo sensor.
[0067]
The measured density value (hereinafter referred to as sensor measurement value) is sent to the sensor density correction unit 210 in the image processing unit 215.
[0068]
The density measurement by the sensor 603 is performed not only when the printer 102 is installed, but also when the power is turned on, when a predetermined number of sheets is printed (for example, after printing 50 sheets or every 200 sheets), every predetermined time (for example, 30). Etc.), and at a timing such as a fluctuation of an environmental value such as the in-machine temperature / humidity over a predetermined amount.
[0069]
Further, the density measurement of the patch pattern may be realized by measuring the image density on another member such as on the photosensitive drum.
[0070]
<Correction table correction process>
Hereinafter, density correction table correction processing in the correction table correction unit 211, which is a feature of the present embodiment, will be described with reference to FIGS.
[0071]
The correction table correction process, as described as the density measurement timing by the sensor 603, is a timing such as when the power is turned on, when printing a predetermined number of sheets, every predetermined time, fluctuation of an environmental value such as in-machine temperature / humidity over a predetermined amount Is executed. Thereby, it is possible to perform correction appropriately corresponding to the change with time of the printer 102.
[0072]
FIG. 9 is a flowchart showing the correction process of the density correction table in the correction table correction unit 211.
[0073]
First, the correction table correction unit 211 receives a sensor measurement value from the sensor density correction unit 210 (S901). This process is the same as step S701 in FIG. 6 described above. Next, the sensor measurement value is compared with the sensor reference value of the same density level set in step S405 of FIG. 4, and the density fluctuation amount from the sensor reference value is obtained for all density levels (S902). Then, based on the density fluctuation amount, the density characteristic after correction by the density correction table is obtained, and the density correction table is corrected so that the density characteristic becomes a predetermined density characteristic (linear characteristic) (S903).
[0074]
FIG. 10 is a diagram illustrating an example in which density variation occurs. In FIG. 10A, the horizontal axis represents the input density level, and the vertical axis represents the density value after correction by the density correction table. A broken line in the figure indicates a characteristic when the density correction table is created, that is, a predetermined density characteristic. The black circle (●) plotted on the broken line indicates the sensor reference value, and the white circle (◯) indicates the actual sensor measurement value. Therefore, the difference between the sensor reference value and the sensor measurement value is obtained as the density fluctuation amount. The density characteristics corrected by the current density correction table based on the density fluctuation amount are as shown by the solid line in FIG.
[0075]
In order to perform correction so that the density characteristic indicated by the solid line in FIG. 10A becomes a predetermined density characteristic (linear characteristic), a correction table indicated by the solid line in FIG. 10B is obtained. In the correction table shown by the solid line in FIG. 10B, the input density level corrected by the density correction table created in the initial state as shown by the solid line in FIG. It is a table for correcting. Therefore, the optimum density correction table for the current printer 102 is obtained by combining the correction table indicated by the solid line in FIG. 10B and the correction table indicated by the solid line in FIG. As shown by the solid line.
[0076]
As described above, in this embodiment, at a predetermined timing, a patch pattern is formed in the printer 102 to obtain the sensor measurement value, and the density fluctuation amount is calculated by comparing the sensor measurement value with the sensor reference value. Based on the density fluctuation amount, the density correction table is corrected so as to obtain a predetermined density characteristic.
[0077]
Therefore, the color data input from the host computer 101 is converted into YMCK data, and the density correction unit 208 corrects the density level based on the corrected density correction table as shown by the solid line in FIG. As a result, it is possible to always perform printing with colors having standard density characteristics.
[0078]
<Density correction processing at power-on>
Next, with reference to FIG. 11, the density correction processing at the time of power-on in this embodiment will be described.
[0079]
FIG. 11 is a flowchart showing the correction process of the density correction table when the power is turned on.
[0080]
When the power of the printer 102 is turned on, the density correction table and the sensor reference value stored in the table storage device 218 in advance are read by the scanner density correction process shown in FIG. 4 (S1101). These are reset as the density correction table and sensor reference value in the correction table correction process shown in FIG. 9 (S1102). Then, the sensor measurement value is received by performing the in-printer density measurement process shown in FIG. 8 (S1103) (S1104), and the correction table correction process shown in FIG. 9 is executed (S1105).
[0081]
As described above, according to the present embodiment, by correcting the density correction table at an appropriate timing, the printer 102 eliminates the individual difference and the density difference in the initial state, and further, due to the density variation with time. Color variations with always optimal gradation can be achieved by eliminating variations in color.
[0082]
In addition, when the power is turned on, the density correction table correction process can be performed without executing the scanner density correction process again. Therefore, it is possible to perform appropriate density correction while shortening the rise time of the apparatus.
[0083]
[Second Embodiment]
Hereinafter, a second embodiment according to the present invention will be described.
[0084]
FIG. 12 shows the configuration of the printer in the second embodiment. In the figure, the same processing units as those in FIG. 1 shown in the first embodiment are given the same reference numerals, and the description thereof is omitted. That is, the table storage device 218 is removed from the configuration of FIG. 1 shown in the first embodiment.
[0085]
The operation of each processing unit in the second embodiment is basically the same as that of the first embodiment described above. Hereinafter, a characteristic process of the second embodiment that is different from the first embodiment will be described.
[0086]
<Scanner density correction processing>
FIG. 13 is a flowchart showing scanner density correction processing in the second embodiment.
[0087]
First, the patch pattern shown in FIG. 3 is printed on the recording paper by the printer 102 (S2401). Subsequently, in the first embodiment, the in-printer density measurement process shown in FIG. 8, that is, the density of the patch pattern having a plurality of density levels formed on the intermediate transfer body 602 is measured using the sensor 603 (see FIG. S2402).
[0088]
Thereafter, the recording paper printed and output in step S2401 is read by the scanner 103, and the density values are actually measured for all density levels of the formed patch pattern (S2403).
[0089]
Then, in order to remove the density unevenness on the recording paper, the scanner density correction unit 209 averages the measured density values of the patches having the same density level, and further calculates the measured density values of the patches having the preceding and following density levels. The measured density value is corrected by using the moving average by using (S2404). Based on the corrected measured density value of each density level patch, the density correction table is created by interpolating the data between the patches so that the density characteristic with respect to the input density level becomes a predetermined density characteristic (S2405).
[0090]
Thereafter, the sensor measurement value and the concentration level measured in step S2402 are set as a sensor reference value in the concentration measurement unit 216 (S2406).
[0091]
In the second embodiment, the same processing as in the first embodiment described above is performed except for the scanner density correction processing described above.
[0092]
As described above, according to the second embodiment, immediately after the patch pattern is printed on the recording medium, the patch pattern density in the printer is measured and the sensor reference value is set. Density measurement errors based on the difference from the sensor reference value measurement timing, density fluctuations due to changes over time, and the like can be minimized.
[0093]
[Third Embodiment]
The third embodiment according to the present invention will be described below.
[0094]
The configuration of the printer in the third embodiment is shown in FIG. In the figure, the same processing units as those in FIG. 12 shown in the second embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0095]
In other words, FIG. 14 shows a configuration in which a correction table control unit 219 is provided in place of the sensor density correction unit 210 and the correction table correction unit 211 is removed from the configuration of FIG. 12 shown in the second embodiment. Yes. The correction table control unit 219 creates a sensor density correction table or corrects the scanner density correction table based on the density values of a plurality of density levels including halftones measured by the density measuring unit 216.
[0096]
The density correction unit 208 corrects the density level of the input image data based on the sensor density correction table or the scanner density correction table.
[0097]
In the first and second embodiments described above, an example in which the scanner density correction unit 209 creates a density correction table and corrects it at a predetermined timing has been described. On the other hand, in the third embodiment, the correction table control unit 219 corrects the scanner density correction table if the scanner density correction unit 209 has already been set, and creates the sensor density correction table if not set. . Accordingly, in the third embodiment, in order to distinguish these density correction tables, they will be described as a “scanner density correction table” and a “sensor density correction table”, respectively. This corresponds to the density correction table in the first and second embodiments.
[0098]
The operation of each processing unit in the third embodiment is basically the same as that in the first or second embodiment described above. Hereinafter, a characteristic process of the third embodiment that is different from the first and second embodiments will be described.
[0099]
<Scanner density correction process (scanner density correction table creation process)>
FIG. 15 is a flowchart showing scanner density correction processing in the third embodiment.
[0100]
First, the patch pattern shown in FIG. 3 is printed on a recording sheet by the printer 102 (S3401), and the sheet is read by the scanner 103, whereby the density value is actually measured for all density levels of the formed patch pattern. (S3402).
[0101]
Then, in order to remove the density unevenness on the recording paper, the scanner density correction unit 209 averages the measured density values of the patches having the same density level, and further calculates the measured density values of the patches having the preceding and following density levels. Using the moving average, the measured density value is corrected (S3403). Then, based on the measured density value of each corrected density level patch, a scanner density correction table is created by interpolating data between patches so that the density characteristic with respect to the input density level becomes a predetermined density characteristic (S3404). .
[0102]
The density characteristics shown by the solid line in FIG. 5A are obtained by the processing shown in steps S3401 to S3403 as in the first embodiment. Also in the third embodiment, in order to correct the density characteristic obtained by actual measurement (solid line in FIG. 5 (a)) to a predetermined density characteristic (dashed line in FIG. 5 (a)), FIG. A scanner density correction table indicated by a solid line in b) is created, and the input density level is replaced with the correction density level using the table.
[0103]
<In-printer density measurement process>
FIG. 16 is a diagram schematically illustrating an example of the in-printer density measurement process according to the third embodiment. In the printer 102, for example, patch patterns 3601 of several halftone density levels in the density level (00H to FFH) are formed on the intermediate transfer body 602 for each color (Y, M, C, K). Here, in the third embodiment, although details will be described later, a patch pattern 3601 formed on the intermediate transfer member according to the timing at which the density measurement process in the printer is executed is one of those shown in FIGS. 19 and 22. Switch to the pattern.
[0104]
The formed patch pattern 3601 of each color is measured by the sensor 603, and the obtained density value (sensor measurement value) is sent to the correction table control unit 219 in the image processing unit 215.
[0105]
<Correction table control processing>
FIG. 17 is a flowchart illustrating an example of density correction table control processing in the correction table control unit 219.
[0106]
First, the scanner density correction unit 209 determines whether a scanner density correction table has already been created and set (S3701). If it is determined that it is not set, a multiple density level measurement process described later is performed (S3702), and the process ends. On the other hand, if it is determined in step S701 that the scanner density correction table is set, a limited density level measurement process described later is performed (S3703), and the process is terminated.
[0107]
<< Multiple concentration level measurement process >>
Next, the multiple density level measurement process shown in step S3702 of FIG. 17 will be described with reference to FIGS.
[0108]
FIG. 18 is a flowchart illustrating an example of the multiple density level measurement process.
[0109]
18, first, a multi-density level patch pattern shown in FIG. 19 is created (S3801), and the density measurement unit 216 measures the density of the patch pattern using a sensor as shown in FIG. 16 (S3802). Then, a sensor density correction table is created (S3803).
[0110]
FIG. 19 is a diagram illustrating an example of a multiple density level patch pattern.
[0111]
In the density measuring unit 216, when the patch patterns that can be formed are 8 patterns for each color, patch patterns of 8 different density levels 30H, 40H, 50H, 60H, 70H, 80H, 90H, and A0H are formed for each color. This is an example in which the highlight level is emphasized and the density level is allocated so that the density characteristics of the entire density level (00H to FFH) can be obtained. The patch pattern formed here is measured as shown in FIG.
[0112]
<<< Sensor density correction table creation process >>>
With reference to FIG. 20, the sensor density correction table creation processing shown in step S3803 of FIG. 18 will be described.
[0113]
The black dots (（) plotted in FIG. 20A are measured density levels (sensor measured values) in the patch patterns of the eight different density levels shown in FIG. Based on these eight points, when the overall sensor density characteristic in the current state is obtained, the density characteristic indicated by the solid line in FIG. 20A is obtained. The broken line in FIG. 20A indicates a predetermined density characteristic that is a target for density correction, and exhibits a linear characteristic.
[0114]
The solid line in FIG. 20B shows the corrected density level value in the sensor density correction table. In the third embodiment, in order to correct the density characteristic (FIG. 20 (a) solid line) actually obtained based on the measured value of the sensor 603 to the predetermined density characteristic (dashed line in FIG. 20 (a)), the sensor A density correction table is created as shown by the solid line in FIG.
[0115]
Thus, when the scanner density correction table is not set, the sensor density correction table is created based on multi-level patch patterns, that is, based on more accurate density characteristics for all input density levels. At the time of printing, the color data input from the host computer 101 is converted into YMCK data, and the density correction unit 208 corrects the density level based on the sensor density correction table. Thereby, it is possible to sufficiently correct the formed image.
[0116]
<< Limited concentration level measurement process >>
Next, the limited density level measurement process shown in step S3703 of FIG. 17 will be described with reference to FIG. 21, FIG. 22, and FIG.
[0117]
In FIG. 21, first, the limited density level patch pattern shown in FIG. 22 is created (S4101), and the density measuring unit 216 measures the density of the patch pattern using a sensor as shown in FIG. 16 (S4102). .
[0118]
Then, after the scanner density correction table is set in the scanner correction processing unit 209, it is determined how many times the correction table control process is performed (S4103). If this is the first time, that is, if the first sensor measurement by the density measuring unit 216 is performed after setting the scanner correction table, a sensor reference value setting process is performed (S4104), and the process is terminated. On the other hand, if it is the second time or later, a scanner density correction table correction process is performed (S4105), and the process ends.
[0119]
FIG. 22 is a diagram illustrating an example of the limited density level patch pattern.
[0120]
In the density measurement unit 216, when the patch patterns that can be formed are eight patterns for each color, the different density levels are limited to three points, 30H, 60H, and 90H, and patch patterns having the same density level are formed at a plurality of locations. In this way, the same density level is formed at a plurality of locations, and the average value of the measurement values obtained by the sensor is used as the sensor density measurement value, so that the influence of the sensor error can be minimized.
[0121]
<<< Sensor reference value setting process >>>
The sensor reference value setting process shown in step S4104 of FIG. 21 will be described.
[0122]
The sensor reference value set in the third embodiment is obtained, for example, as shown in FIG. That is, the three black dots (●) plotted in FIG. 7 are the first when the correction table control unit 219 performs the first process after the scanner correction table is set, that is, after the scanner correction table is set. When the sensor measurement is performed by the density measuring unit 216, three density levels (sensor density measured values) obtained by measuring and averaging the patch patterns of the limited density level shown in FIG. 22 are shown. The sensor concentration measurement value at this time is set as a sensor reference value at each of the concentration levels 30H, 60H, and 90H.
[0123]
The broken line shown in FIG. 7 is the density characteristic linearly corrected by the scanner density correction table. That is, for the first sensor measurement after the scanner density correction table is set, the sensor density measurement value follows a linear characteristic, so it is appropriate to set this as the sensor reference value.
[0124]
<<< Scanner Density Correction Table Correction Process >>>
The scanner correction table correction process shown in step S4105 of FIG. 21 will be described with reference to FIG.
[0125]
FIG. 23 is a flowchart illustrating an example of the scanner density correction table correction process.
[0126]
When the correction table control process is performed in the correction table control unit 219 after the scanner correction table is set, first, the sensor density measurement value measured by the density measurement unit 216 in step S4102 is received (S4401). . Then, the sensor density measurement value is compared with the sensor reference value of the same density level set in the sensor reference value setting process shown in step S4104 of FIG. 21, thereby obtaining the density fluctuation amount from the sensor reference value (S4402). . Then, the density characteristic based on the scanner correction table is changed by the amount of density fluctuation, and the scanner density correction table is corrected so that the density characteristic becomes linear (S4403).
[0127]
Note that the specific correction method of the scanner density correction table in step S4403 is the same as the correction method of the density correction table described with reference to FIG.
[0128]
As described above, by correcting the scanner density correction table at a predetermined timing, the color data input from the host computer 101 is converted into YMCK data during printing, and the density correction unit 208 corrects the scanner density correction table corrected. By correcting the density level based on the above, it is possible to always perform printing with a color having a standard density characteristic.
[0129]
As described above, according to the third embodiment, when the density correction by the scanner is not performed (when the scanner density correction table is not set), the number of density levels that can be measured by the density measuring unit 216 is increased. As a result, the density characteristics for all input density levels can be obtained more accurately. Therefore, by creating a sensor density correction table based on the density characteristics, it is possible to perform sufficient correction on the formed image.
[0130]
On the other hand, when the density correction by the scanner has already been performed (when the scanner density correction table is already set), the influence of the sensor measurement error can be suppressed. By correcting the density correction table, it is possible to eliminate the difference in density between individuals and to eliminate the variation in color due to the density variation with time.
[0131]
In the third embodiment, the concentration level measurable by the concentration measuring unit 216 is described as eight or three points. However, the number of measurement levels of the present invention is not limited to this, and an arbitrary number of concentration levels can be measured. Needless to say, the present invention is also applicable to the printing apparatus.
[0132]
<Modification>
In each embodiment described above. In particular, color correction in a color printer has been described as an example, but the present invention can be similarly applied to density adjustment in a monochrome printer. Needless to say, the target device is not limited to a printer but is effective for devices that require density adjustment of a formed image when performing image formation, such as a copying machine and a facsimile.
[0133]
Further, although an example of forming an image input from a host computer has been described, image formation based on image data read by a scanner, for example, may be performed.
[0134]
Further, although the density level is described as 00H to FFH, the present invention is not limited to this range, and is effective in an image forming apparatus capable of setting an arbitrary level. Further, the density level to be measured is not limited to three points for each color, and any number of density levels may be measured.
[0135]
[Other Embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device You may apply to.
[0136]
Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or CPU) of the system or apparatus. Needless to say, this can also be achieved by the MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.
[0137]
Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.
[0138]
When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.
[0139]
【The invention's effect】
As described above, according to the present embodiment, the density correction of the formed image in the image forming apparatus can be appropriately performed for all input density levels.
[0140]
In addition, it is possible to shorten the rise time of the apparatus while enabling appropriate density correction immediately after the power is turned on.
[0141]
In addition, by increasing the number of density levels of the patch pattern that can be measured, the density characteristics for all input density levels can be obtained more accurately, and the density correction of the formed image can be appropriately performed.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a printer according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating print processing according to the present exemplary embodiment.
FIG. 3 is a diagram illustrating an example of a patch pattern in the present embodiment.
FIG. 4 is a flowchart showing scanner density correction processing in the present embodiment.
FIG. 5 is a diagram illustrating an example of density characteristics in the present embodiment.
FIG. 6 is a flowchart showing sensor reference value setting processing in the present embodiment.
FIG. 7 is a diagram illustrating an example of a sensor reference value in the present embodiment.
FIG. 8 is a diagram illustrating an example of an in-printer density measurement process in the present embodiment.
FIG. 9 is a flowchart showing density correction table correction processing in the present embodiment.
FIG. 10 is a diagram illustrating an example of density characteristics in the present embodiment.
FIG. 11 is a flowchart showing density correction table correction processing at the time of power-on in the present embodiment.
FIG. 12 is a block diagram illustrating a configuration of a printer according to a second embodiment of the invention.
FIG. 13 is a flowchart illustrating scanner density correction processing according to the second embodiment.
FIG. 14 is a block diagram illustrating a configuration of a printer according to a third embodiment of the invention.
FIG. 15 is a flowchart illustrating scanner density correction processing according to the third embodiment.
FIG. 16 is a diagram illustrating an example of an in-printer density measurement process according to the third embodiment.
FIG. 17 is a flowchart showing density correction table control processing in the third embodiment.
FIG. 18 is a flowchart showing multiple density level measurement processing in the third embodiment.
FIG. 19 is a diagram illustrating an example of a patch pattern for measuring multiple density levels in the third embodiment.
FIG. 20 is a flowchart showing sensor density correction table creation processing in the third embodiment.
FIG. 21 is a flowchart showing limited density level measurement processing in the third embodiment.
FIG. 22 is a diagram illustrating an example of a limited density level measurement patch pattern according to a third embodiment.
FIG. 23 is a flowchart showing scanner correction table correction processing in the third embodiment.
[Explanation of symbols]
101 Host computer
102 Printer
103 Scanner
201 interface
202 Receive buffer
203 Object generator
204 Object buffer
205 Rendering part
206 Band buffer
207 Dither processor
208 Density correction unit
209 Scanner density correction unit
210 Sensor density correction unit
211 Correction table correction unit
212 ROM
213 CPU
214 RAM
215 Image processing unit
216 Concentration measurement unit
217 Printer Engine
218 Table storage device
219 Correction table control unit
601 Patch pattern
602 Intermediate transfer member
603 sensor

Claims (4)

Image forming apparatus control method for correcting density level of image information with reference to density correction table when transferring toner image supported on image carrier to recording medium and forming image on recording medium Because
First table creation for creating a first density correction table based on a scanner measurement value obtained by reading a pattern printed on a recording medium by the image forming apparatus with a scanner connected to the image forming apparatus Process,
A first pattern having patch patterns of a plurality of density levels including a halftone density level is formed on the image carrier, and the first density is determined based on a density value of the first pattern measured by a sensor. A table correction process for correcting the correction table;
A second pattern having a patch pattern having a density level higher than that of the first pattern is formed on the image carrier, and a second pattern is obtained based on the density value of the second pattern measured by the sensor. A second table creation step for creating a density correction table;
Have
It is determined whether or not the first density correction table has already been created by the first table creation process, and the table correction process is performed when it is determined that the first density correction table has already been created. And executing the second table creation step when it is determined that the first density correction table has not been created.   The first pattern includes a plurality of patch patterns having the same density level, and in the table correction step, an average value of a plurality of patch patterns having the same density level measured by the sensor is used as a density value. The method of controlling an image forming apparatus according to claim 1. The table correction step includes
A reference value setting step of setting a reference value of the sensor based on a measured value of the first pattern by the sensor if the step is a first execution after the execution of the first table creation step; ,
If the process is the second or subsequent execution after the execution of the first table creation process, the first density correction is performed based on the measured value of the first pattern by the sensor and the reference value of the sensor. A first table correction step for correcting the table;
The method of controlling an image forming apparatus according to claim 1, further comprising: An image forming apparatus that corrects a density level of image information with reference to a density correction table when a toner image carried on an image carrier is transferred to a recording medium to form an image on the recording medium. ,
First table creation for creating a first density correction table based on a scanner measurement value obtained by reading a pattern printed on a recording medium by the image forming apparatus with a scanner connected to the image forming apparatus Means,
A first pattern having patch patterns of a plurality of density levels including a halftone density level is formed on the image carrier, and the measured values of patch patterns having the same density level of the first pattern measured by a sensor are measured. Table correction means for correcting the first density correction table based on a density value determined as an average value;
A second pattern having a patch pattern having a density level higher than that of the first pattern is formed on the image carrier, and a second pattern is obtained based on the density value of the second pattern measured by the sensor. A second table creation means for creating a density correction table;
Have
It is determined whether or not the first density correction table has already been created by the first table creation means, and if it is determined that the first density correction table has already been created, the table correction means is used. An image forming apparatus that operates and operates the second table creation means when it is determined that the first density correction table is not created .

Images