JP2002374416A - Printer and density correcting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely make density corrections of a plurality of half-tone processings without making the time needed for a density measuring processing long. SOLUTION: A patch pattern is generated with half-tones of a dither 1 and printed on a form (S402) and the density values of respective density levels of the printed patch pattern of the dither 1 are measured (S403) by using a scanner 119 and density characteristics to the input density of the dither 1 are computed (S404) and a density correction table for the dither 1 for correcting the input density level is generated (S405) and set in a density correction table area 113c in a RAM 113 (S406). Then a patch pattern is generated with half-tones of a dither 2 and a density correction table for the dither 2 for correcting its input density level is generated (S413) and then sets in a density correction table area 113c in the RAM 113 (S414).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus and a density correction method, and more particularly, to a printing apparatus and a density correction method. 1. Field of the Invention The present invention relates to a printing apparatus provided with a density correction unit for performing a density correction method.

[0002]

2. Description of the Related Art In a conventional printing apparatus, density correction for a density level of a formed image in order to eliminate color fluctuation due to density fluctuation due to aging changes is performed at a plurality of density levels obtained by performing a specific type of halftone processing. The patch pattern is printed on paper, the density is measured by an external reading device such as a scanner, and the density characteristic of the halftone processing is measured based on the measured density value. Thus, a density correction table is created so that the density correction is performed, and the density correction is performed using the density correction table. Further, the density correction of the halftone processing in which the measurement is not performed is performed using the density correction table of the measured halftone processing.

[0003]

However, in such a conventional printing apparatus, since the density fluctuation varies depending on the type of the halftone processing, the accuracy of the density correction in the halftone processing without measurement is insufficient. There was a problem. Further, performing the density measurement processing a plurality of times for each type of halftone processing has a problem in that the printing speed is reduced.

The present invention has been made in view of such a problem, and an object of the present invention is to accurately perform density correction of a plurality of halftone processes without increasing the time required for the density measurement process. It is an object of the present invention to provide a printing apparatus and a density correction method capable of simultaneously measuring density fluctuations of a plurality of halftone processes and improving the durability of a plurality of density correction tables.

[0005]

According to the present invention, in order to achieve the above object, the invention according to claim 1 has a plurality of halftone processes, and all halftone processes for which density correction is desired. In a printing apparatus provided with density correction means for repeatedly performing density correction on a process, the density correction means includes a sufficient number of density level patch patterns to obtain density characteristics with respect to an input density level of a designated halftone process. A patch pattern printing means for printing the patch pattern on paper, a patch pattern measuring means for measuring the density of the patch pattern printed on the paper by the patch pattern printing means, and a halftone based on the density value measured by the patch pattern measuring means. A density characteristic calculating means for obtaining a density characteristic of the processing, and a density characteristic calculated by the density characteristic calculating means is a specified density characteristic.
A density correction table creating means for creating an input density level correction table for halftone processing, and a density correction table setting means for setting a density correction table for halftone processing created by the density correction table creating means are provided. And

[0006] The invention described in claim 2 is the invention according to claim 1.
And a density correction halftone setting means for setting the type and number of halftones each time a density correction table is set by the density correction means; and The patch pattern forming region dividing unit that divides the image into the number of halftones set by the tone setting unit and allocates each halftone region, and performs each halftone process on the region allocated by the patch pattern forming region dividing unit. It is characterized by having a patch pattern forming means for forming patch patterns of several density levels performed, and a density measuring means for measuring the density of the patch pattern formed by the patch pattern forming means using a sensor.

[0007] Further, the invention according to claim 3 is based on claim 2.
In the invention described in the above, for all the halftone processing to be corrected, the density measurement is performed at the time when the density correction table is set by the density correction means, and each halftone processing whose density is measured by the density measurement means is performed. Is determined to which density level is corrected by the corresponding halftone density correction table, and the sensor measurement value of each halftone measured by the density measuring means is converted to the density level of each halftone. It is characterized by having sensor reference value determining means for setting a reference density level and a sensor reference value.

[0008] The invention described in claim 4 is the invention according to claim 3.
In the invention described in the above, after the sensor reference value determination means is performed, the density measurement means is performed at a specified timing, and compares the measured sensor measurement value of each halftone with the sensor reference value. Density fluctuation amount calculating means for calculating the density fluctuation amount of each halftone by the increase / decrease thereof, and the density fluctuation amount calculated by the density fluctuation amount calculation means, the density characteristic of each halftone is defined as a specified density characteristic. And a density correction table correcting means for correcting the density correction table of the corresponding halftone.

According to a fifth aspect of the present invention, there is provided a printing apparatus having a plurality of halftone processes and a density correction step of repeatedly performing density correction for all halftone processes for which density correction is desired. In the density correction method, a patch pattern printing step of printing on a sheet a patch pattern of a sufficient number of density levels to obtain density characteristics with respect to an input density level of a designated halftone process; A patch pattern measuring step of measuring the density of the patch pattern printed on the patch pattern, and a density value measured in the patch pattern measuring step,
A density characteristic calculation step for calculating the density characteristic of the halftone processing, and a density correction table generation for generating an input density level correction table for the halftone processing so that the density characteristic calculated in the density characteristic calculation step becomes a specified density characteristic And a density correction table setting step of setting a density correction table for halftone processing created in the density correction table creation step.

The invention described in claim 6 is the same as the invention in claim 5
In the invention described in (1), each time a density correction table is set in the density correction step, a density correction halftone setting step of setting the type and number of halftones; Dividing into the number of halftones set by the tone setting step, and assigning each halftone area as a patch pattern forming area dividing step; and applying each halftone processing to the area assigned by the patch pattern forming area dividing step. A patch pattern forming step of forming patch patterns of several density levels is performed, and a density measuring step of measuring the density of the patch pattern formed by the patch pattern forming step using a sensor.

The invention described in claim 7 is the same as the claim 6.
In the invention described in the above, for all the halftone processes to be corrected, the density measurement is performed at the time when the density correction table is set in the density correction step, and each halftone processing whose density is measured in the density measurement step is performed. The density level is determined to which density level is corrected by the corresponding halftone density correction table, and the sensor measurement value of each halftone measured in the density measurement step is
Each has a reference density level of each halftone and a sensor reference value determining step as a sensor reference value.

[0012] The invention described in claim 8 is the same as in claim 7.
In the invention described in the above, after the sensor reference value determination step is performed, the density measurement step is performed at a specified timing, and compares the measured sensor measurement value of each halftone with the sensor reference value. The density fluctuation amount calculation step of calculating the density fluctuation amount of each halftone by the increase / decrease, and the density fluctuation amount calculated in the density fluctuation amount calculation step, the density characteristics of each halftone are defined as the specified density characteristics. And a density correction table correction step of correcting the density correction table of the corresponding halftone.

According to a ninth aspect of the present invention, there is provided a program for causing a computer to execute the steps according to any one of the fifth to eighth aspects.

According to the present invention, it is possible to accurately perform the density correction of a plurality of halftone processes without increasing the time required for the density measurement process. Also,
In the printing apparatus, the density fluctuations of a plurality of halftone processes can be measured at the same time, and the durability of the plurality of density correction tables can be improved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining a control configuration in an embodiment of a printing apparatus (hereinafter, referred to as a printer) according to the present invention. In the figure, reference numeral 101 denotes a host computer, and color information, characters, graphics, image images,
The print information such as the number of copies to be printed is sent to the printer 102. A scanner 119 measures the density of a density correction scanner patch pattern described later.

The printer 102 includes an image processing unit 103,
A printer engine 114 that forms an actual image based on an image signal sent from the image processing unit 103 and a density measuring unit 115 that measures a density value of a density level are roughly classified.

The main configuration and operation of the image processing section will be described below. In the image processing unit 103,
Reference numeral 104 denotes an interface for controlling transmission / reception of print information to / from the host computer 101, and reference numeral 105 denotes a reception buffer for holding input print information. In the object generation unit 106, information such as colors, characters, graphics, and image images, which are print information input from the host computer 101, is converted into intermediate information (hereinafter, referred to as an object) and stored in the object buffer 107. At this time, if the print information is color-related data such as a gray level setting, a color level setting, and a multi-valued image image, the data correction unit 116 described later corrects the density level using a density correction table.

Next, based on the object stored in the object buffer 107, the rendering unit 108
Generates a bit image to be rendered. At this time, the dither processing unit 110 performs halftone processing to reduce the output gradation. The generated bit image is stored in the band buffer 109. In this way, the bit image stored in the band buffer 109 is transmitted from the printer engine 114 and is formed on a recording medium.

Reference numeral 112 denotes a central processing unit (CP)
In U), various processes are determined and controlled according to the program stored in the ROM 111. 111 is ROM
(Read only memory), which stores various control programs 111a including the programs shown in the flowcharts of FIGS. 2, 4, 6, 7, 12, and 14.

Reference numeral 113 indicates that the CPU 112
The RAM (random access memory) used as a work area stores data and status information for performing determination control of each process according to the program stored in the storage unit 1, and stores halftone designation data 113b and a density correction table 113c to be described later. is there.

The density value of the scanner patch pattern measured by the scanner 119 is converted into a density correction table in a
The type and number of the measured halftones stored in the density correction table area 113c of 113 are set in the halftone designation area 113b of the RAM 113. A density measurement pattern forming unit 118, which will be described later, forms a plurality of density level patch patterns of a specified halftone, and the density measurement unit 115 uses a sensor to measure the density value of the patch pattern formed by the density measurement pattern formation unit. The density correction table correction unit 117 described later calculates the density fluctuation amount from the measured value, corrects the density correction table, and performs data correction.
In step 6, data density correction is performed.

Hereinafter, the printing process according to the present embodiment will be described with reference to the flowchart shown in FIG.
Note that the control program for realizing the processing shown in the flowchart shown in FIG. 2 is stored in the ROM 111 and executed by the CPU 112 as described above.

In FIG. 2, first, print data is received from the host computer 101 (S201), and held in the reception buffer 105 (S202). Then, data for one processing unit is extracted from the reception buffer 105 (S
203), it is determined whether or not all data has been extracted (S204). If it is determined that the data processing has not been completed, it is determined whether the data processing for one page has been completed (S205).

If it is determined that the printing has not been completed, it is determined whether the print data is color-related data such as color information or a color image (S206). If it is determined that the data is color-related data, the data correction unit 116 corrects the density level using a density correction table (S207). Then, an object is created (S20).
8) and store it in the object buffer 119 (S20)
9) Return to step S323 to retrieve the next data.

On the other hand, if it is determined in step S206 that the data is not color-related data, it is determined whether or not the data is mask data such as a character or a figure (S210). If it is determined that the object is the mask data, an object of the mask data is created (S208), and the process returns to step S209. On the other hand, if it is determined that the data is not mask data, print data processing is performed according to the type of data (S21).
1) Return to step S203.

If it is determined in step S205 that one page of data has been completed, rendering processing is performed based on the object held in the object buffer 107 (S212), and a bit image is transmitted to the printer engine 114. Then, a printing process for printing on paper is performed (S213). Step S2
If it is determined in 04 that the data is completed, the processing is terminated.

Next, a scanner density correction process according to the present embodiment will be described with reference to FIGS. In the present embodiment, two types of halftone processing for performing density correction, dither 1 and dither 2, are used.

FIG. 3 is a diagram showing an example of a patch pattern for scanner density correction. On a sheet of paper, Y, M, C, and K print areas are formed, and in each color area, a patch pattern of 2% in halftone input density level to be corrected is formed.
This patch pattern is printed on paper by a command from the host computer or a test print function of the printing apparatus.

FIG. 4 is a flowchart showing the scanner density correction processing. First, it is determined whether or not to correct the halftone of dither 1 (S401). If it is determined that the correction is to be performed, the patch pattern shown in FIG. Print on top (S402),
The density value of each density level of the printed dither 1 patch pattern is measured using the scanner 119 (S403), and the density characteristic of the dither 1 with respect to the input density level is calculated from the measured density value of each density level of the patch pattern. (S40
4) A dither 1 density correction table for correcting the input density level so that the density characteristics become the specified density characteristics is created (S405), and the dither 1 density correction table is stored in the RAM 1
13 (S4).
06). Then, dither 1 is added to the halftone designation area 113b as the type of halftone for which the density correction has been performed (S40).
7), the number of corrected data is counted up (S40).
8).

Next, it is determined whether or not to correct the halftone of dither 2 (S409). If it is determined that the correction is to be performed, the patch pattern shown in FIG. Then, printing is performed on paper (S410), the density value of each density level of the printed dither 2 patch pattern is measured using the scanner 119 (S411), and from the measured density value of each density level of the patch pattern, A density characteristic for the input density level of dither 2 is calculated (S412),
A density correction table of dither 2 for correcting the input density level so that the density characteristic becomes the specified density characteristic is created (S41).
3) The density correction table for dither 2 is set in the density correction table area 113c of the RAM 113 (S414).
Then, dither 2 is added to the halftone designation area 113b as the type of halftone for which the density correction has been performed (S415), and the number of corrected halftones is counted up (S416).

On the other hand, if it is determined in step S401 that dither 1 is not to be corrected, the process proceeds to step S4.
Go to 09. If it is determined in step S409 that dither 2 is not to be corrected, the process ends.

FIG. 5 shows an example of the density characteristic.
The solid line in (a) indicates that the patch pattern of FIG. 3 shown in step 404 of FIG.
Is a density characteristic with respect to the input density level obtained from the measured density value. The dashed line in FIG. 5A is a predetermined density characteristic which is determined in advance and is a linear characteristic. In order to change the density characteristic of the dither 1 shown by the solid line in FIG. 5A to the linear characteristic shown by the broken line in FIG. 5A, as shown by the solid line in FIG.
A density correction table for replacing the input density level with the corrected density level is created (a density correction table for dither 1). With respect to the density measurement value of dither 2, the density characteristics are similarly calculated, and a density correction table for dither 2 is created.

Next, a density measuring process in the printing apparatus according to the present embodiment will be described with reference to FIGS. FIG. 6 is a flowchart illustrating an example of the density measurement process. First, a patch pattern for performing density measurement is formed (S601). The density of the formed patch pattern is measured by a sensor in the printer (S602).

FIG. 7 is a flowchart showing the patch pattern forming process (S601) of FIG. As shown in step 408 in FIG. 4, two types of dither, dither 1 and dither 2, for which scanner density correction has been performed are designated in the halftone designation data 113b (S701). When the patch pattern formation area for the density measurement of the printer is an area in which a patch pattern of eight points for each color as shown in FIG. 8 can be formed, as shown in FIG. , And the upper portion is assigned as a dither 1 region and the lower portion is assigned as a dither 2 region (S702). Then, as shown in FIG. 10, a patch pattern having a density level of 20%, 40%, 60%, and 80% by dither 1 is formed in the upper region, and a density pattern of 20% by dither 2 is formed in the lower region. 40%, 60% and 80% patch patterns are formed (S703).

FIG. 11 shows the density measurement process (S60) of FIG.
It is a figure showing an example of 2). In the printer 102, the density of the patch pattern (FIG. 10) formed in the above-described patch pattern forming area on the intermediate transfer body 1101 is measured by the sensor 1102, and the measured density value is sent to the image processing unit 103. Note that the density measurement processing is performed continuously with the scanner density correction processing shown in FIG. 4 and the power supply is turned on and the specified number of prints is set. After printing the number of
This is performed at a predetermined time, for example, a predetermined elapsed time such as every 30 minutes, or at a timing such as an environmental change such as an in-machine temperature and humidity.

FIG. 12 is a flowchart showing an example of the sensor reference value setting process. The sensor reference value setting process
The density level value and the sensor measurement density value measured in the density measurement processing shown in FIG. 6 which is performed continuously with the sensor density correction processing shown in FIG. 4 are received from the density measurement unit 115 (S1).
201) First, the density level value of dither 1 is shown in FIG.
The input density level value of the input density level axis of FIG. 5B corresponding to the corrected density level value of the corrected density level axis of FIG. 5B is obtained and set as the reference density level of dither 1 (S1202). At the same time, the sensor measurement value is set as the sensor reference value of dither 1 (S1203).

The sensor reference value is indicated by ● (black dot) shown in FIG.
Becomes In this sensor reference value setting process, a sensor reference value is similarly set for the density level value measured by dither 2 and the sensor measurement density value.

Next, referring to FIGS. 14 and 15, FIG.
The operation of the density correction table correction unit shown in FIG. FIG. 14 is a flowchart showing the density correction table correction processing, in which a sensor measurement value is received from the density measurement unit 115 (S1401).
Is compared with the sensor reference value of the same density level set in the sensor reference value setting processing shown in (1), the amount of density fluctuation from the sensor reference value is determined (S1402), and the density characteristic corrected by the density correction table is obtained from the density fluctuation amount. Then, the density correction table of the dither 1 is corrected so that the density characteristics become the specified density characteristics (linear characteristics) (S1403). Similarly, for the dither 2, the density correction table of the dither 2 is corrected.

FIG. 15 shows an example of the density correction table correction processing. The horizontal axis in FIG. 15A indicates the input density level, and the vertical axis indicates the density value corrected by the density correction table. A dashed line is a density characteristic at the time of creating the density correction table, which is a specified density characteristic. ● on the wavy line indicates the sensor reference value, and 値 (white point) indicates the sensor measurement value. The density difference between the sensor reference value and the sensor measurement value is the density variation. The density characteristic corrected by the current density correction table from the density fluctuation amount becomes the density characteristic indicated by the solid line in FIG.

When correction is performed so that the density characteristic indicated by the solid line in FIG. 15A becomes a specified density characteristic (linear characteristic),
A density correction table indicated by a solid line in FIG. The density correction table shown by the solid line in FIG.
15B is a correction table of the input density level corrected by the density correction table indicated by the solid line in FIG. 15B, and includes a density correction table indicated by a solid line in FIG. 15B and a density correction table indicated by a solid line in FIG. When the density correction table is corrected by synthesizing the density correction table, the density correction table shown by the solid line in FIG.

The color data input from the host computer is converted into YMCK data, and the density level is always corrected by using the specified density correction table for halftone processing (solid line in FIG. 15B). Printing can be performed with colors having standard density characteristics.

As described above, the present invention has a plurality of halftone processes, and repeatedly performs scanner density correction for all halftone processes for which density correction is to be performed. A sufficient number of density level patch patterns are printed on paper to obtain density characteristics for the density level, and the density of the printed patch pattern is measured using a scanner. Calculate the characteristics, create an input density level correction table for the halftone process so that the calculated density characteristics become the specified density characteristics, set the created density correction table for the halftone process in the printing device, and in the printing device Each time a density correction table is set by scanner density correction, the type and number of halftones are set, and an area where a patch pattern can be formed in the printing apparatus is Divided into the specified number of halftones and assigned as each halftone area, forming a patch pattern of several density levels where each halftone process was performed in the assigned area, and using the formed patch pattern as a sensor When the density correction table is set for all halftone processes for which density is to be measured and correction is to be performed, density measurement is performed, and the measured density level of each halftone is set to the corresponding halftone. It is also determined which density level has been corrected by the density correction table, and the measured sensor values of each halftone are used as the reference density level and sensor reference value of each halftone, respectively. It is performed at the timing, and the sensor measurement value of each measured halftone is compared with the sensor reference value, and the density fluctuation amount of each halftone is calculated based on the increase / decrease, and the calculated density change is calculated. By correcting the density correction table of the corresponding halftone so that the density characteristic of each halftone becomes the specified density characteristic according to the amount, a plurality of halftones can be obtained without increasing the time required for the density measurement process. The density correction of the processing can be performed with high accuracy. Further, in the printing apparatus, it is possible to simultaneously measure the density fluctuations of the plurality of halftone processes, and it is possible to improve the durability of the plurality of density correction tables.

In this embodiment, the density correction 2 is performed.
Although the number of types can be set, an arbitrary number of types can be set, and a density correction table is created by the scanner correction process of the number of types, and the patch pattern formation area is divided and measured according to the number of types, Any type of density correction table can be created and corrected. In addition, the color correction of the color printer is used.
The present invention is also effective for devices such as AX. Further, although the density levels for measuring the density in the printing apparatus are eight density levels, the present invention is also effective in a printing apparatus that measures an arbitrary density level.

[0044]

As described above, according to the present invention, the density correcting means forms a sufficient number of density level patch patterns on a sheet to obtain density characteristics with respect to the input density level of the designated halftone processing. Patch pattern printing means for printing, patch pattern measurement means for measuring the density of the patch pattern printed on the paper by the patch pattern printing means, and the density value measured by the patch pattern measurement means,
Density characteristic calculating means for obtaining the density characteristic of the halftone processing, and density correction table generating means for generating an input density level correction table for the halftone processing so that the density characteristic calculated by the density characteristic calculating means becomes a specified density characteristic. And a density correction table setting means for setting a density correction table of the halftone processing created by the density correction table creating means, so that a plurality of patch patterns of the halftone processing can be measured in one density measurement process. It is possible to accurately perform the density correction of a plurality of halftone processes having excellent durability without increasing the time required for the density measurement process.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining a control configuration in a printing apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a print information processing method according to the embodiment.

FIG. 3 is a diagram illustrating an example of a scanner correction patch pattern according to the embodiment.

FIG. 4 is a flowchart illustrating a scanner correction processing method according to the embodiment.

FIG. 5 is a diagram illustrating an example of a scanner density correction table creation process according to the embodiment.

FIG. 6 is a flowchart illustrating an example of a density measurement process according to the embodiment.

FIG. 7 is a flowchart illustrating a pattern forming process according to the embodiment.

FIG. 8 is a diagram illustrating an example of a ぱ patch pattern formation region in the present embodiment.

FIG. 9 is a diagram illustrating an example of division of a patch pattern formation area according to the present embodiment.

FIG. 10 is a diagram illustrating an example of two types of dither patch pattern formation in the present embodiment.

FIG. 11 is a diagram illustrating an example of a density measurement process according to the present embodiment.

FIG. 12 is a flowchart illustrating an example of a sensor reference value setting process according to the embodiment.

FIG. 13 is a diagram illustrating an example of a sensor reference value setting process according to the present embodiment.

FIG. 14 is a flowchart illustrating an example of a density correction table correction process according to the embodiment.

FIG. 15 is a diagram illustrating an example of a density correction table correction process according to the present embodiment.

DESCRIPTION OF SYMBOLS 101 Host computer 102 Printer 103 Image processing unit 104 Interface 105 Reception buffer 106 Object generation unit 107 Object buffer 108 Rendering unit 109 Band buffer 110 Dither processing unit 111 ROM 111a Control program 112 CPU 113 RAM 113a Work area 113b Intermediate Key designation area 113c Density correction table area 114 Printer engine 115 Density measurement unit 116 Data correction unit 117 Density correction table creation unit 118 Pattern formation unit 119 Scanner 120 Scanner density correction unit 1101 Intermediate transfer body 1102 Sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C061 AR01 KK18 KK25 KK28 2C262 AA24 AB07 BB01 BB36 BC01 BC10 EA04 FA13 GA02 2H027 DA09 DB01 DE07 EB03 EB04 EC03 EC06 EC20 5B057 AA11 CA08 CA12 CA16 CB08 CH11 CE17 CE16 DB02 DB06 DB09 DC22 5C077 LL18 MM27 MP01 MP08 NN08 PP15 PQ12 PQ22 PQ23 TT02

Claims (9)

[Claims] 1. A printing apparatus comprising a plurality of halftone processes, and a density correction unit for repeatedly performing density correction for all halftone processes for which density correction is to be performed, wherein the density correction unit includes a designated density correction unit. Patch pattern printing means for printing, on a sheet, patch patterns of a sufficient number of density levels to obtain density characteristics with respect to the input density level of the halftone processing; and density of the patch pattern printed on the sheet by the patch pattern printing means , A density characteristic calculating means for obtaining a density characteristic of the halftone processing based on the density value measured by the patch pattern measuring means, and a density characteristic calculated by the density characteristic calculating means. Density correction table creating means for creating an input density level correction table for halftone processing so that
A printing apparatus comprising: a density correction table setting unit configured to set a density correction table for halftone processing created by the density correction table creating unit. 2. A density correction halftone setting means for setting the type and number of halftones each time a density correction table is set by the density correction means, and an area in which the patch pattern can be formed is defined by the density correction halftone. The patch pattern forming area dividing means is divided into the number of halftones set by the setting means and assigned as each halftone area, and each halftone process is performed on the area assigned by the patch pattern forming area dividing means. A patch pattern forming means for forming patch patterns of several density levels, and density measuring means for measuring a density of the patch pattern formed by the patch pattern forming means using a sensor. The printing device according to claim 1. 3. A density measurement is performed for all halftone processes to be corrected when the density correction table is set by the density correction means, and each halftone density measured by the density measurement means is measured. The density level is determined to which density level is corrected by the corresponding halftone density correction table, and the sensor measurement value of each halftone measured by the density measuring means is used as a reference for each halftone. The printing apparatus according to claim 2, further comprising a sensor reference value determining unit that determines a density level and a sensor reference value. 4. After the sensor reference value determining means is performed, the density measuring means is performed at a prescribed timing, and compares the measured sensor measurement value of each halftone with the sensor reference value; The density fluctuation amount calculated by the density fluctuation amount calculating means for calculating the density fluctuation amount of each halftone by the increase and decrease, and the density characteristic of each halftone becomes a prescribed density characteristic by the density fluctuation amount calculated by the density fluctuation amount calculating means. 4. The printing apparatus according to claim 3, further comprising a density correction table correction unit configured to correct the density correction table of a corresponding halftone. 5. A density correction method for a printing apparatus having a plurality of halftone processes and a density correction step of repeatedly performing density correction for all halftone processes for which density correction is to be performed. A patch pattern printing step of printing on a sheet a patch pattern of a sufficient number of density levels to obtain a density characteristic with respect to an input density level of the processing; and measuring the density of the patch pattern printed on the sheet by the patch pattern printing step A patch pattern measuring step to be performed, a density characteristic calculating step of obtaining a density characteristic of halftone processing based on the density values measured in the patch pattern measuring step, and a density characteristic calculated in the density characteristic calculating step becomes a specified density characteristic. In this way, a density correction table is created to create an input density level correction table for halftone processing. Steps and the density correction process in the printing apparatus being characterized in that a density correction table setting step of setting a density correction table for halftone processing created by the concentration correction table creation step. 6. A density correction halftone setting step of setting the type and number of halftones each time a density correction table is set in the density correction step, and setting the area in which the patch pattern can be formed to the density correction halftone. Dividing into the number of halftones set in the setting step, and allocating each patch pattern forming area as each halftone area, and performing each halftone process on the area allocated in the patch pattern forming area dividing step A patch pattern forming step of forming patch patterns of several density levels, and a density measuring step of measuring the density of the patch pattern formed by the patch pattern forming step using a sensor. 6. A density correction method in the printing apparatus according to 5. 7. A density measurement is performed for all halftone processing to be corrected when a density correction table is set in the density correction step, and each halftone density measured in the density measurement step is calculated. The density level is determined to which density level is corrected by the corresponding halftone density correction table, and the sensor measurement value of each halftone measured in the density measurement step is used as a reference for each halftone. 7. The method according to claim 6, further comprising a step of determining a sensor reference value to be a density level and a sensor reference value. 8. After the sensor reference value determination step is performed, the density measurement step is performed at a specified timing, and compares the measured sensor measurement value of each halftone with the sensor reference value; The density fluctuation amount calculation step of calculating the density fluctuation amount of each halftone by the increase and decrease, and the density fluctuation amount calculated by the density fluctuation amount calculation step makes the density characteristic of each halftone a prescribed density characteristic. 8. A density correction method for a printing apparatus according to claim 7, further comprising a density correction table correction step of correcting the density correction table of a corresponding halftone. 9. A program for executing the steps according to claim 5 on a computer.