JP4893079B2 - Boundary value table optimization device, liquid discharge head, liquid discharge device, and computer program - Google Patents

Abstract

In a method of substantially correcting gradation values in a gradation correcting unit, the number of reproducible gradations is substantially reduced. Selection information of a boundary value table for multi-value error diffusion is stored, by ejection condition, in an information storing unit of a liquid ejecting head that can represent one pixel with a large number of liquid droplets. When the liquid ejecting head is mounted, selection information matching an ejection condition is read out and a boundary value table corresponding to the selection information is set for reference by a half toning unit. Consequently, the boundary value table is optimized to correct a gradation characteristic without substantially reducing the number of reproducible gradations.

Description

The invention proposed in the specification relates to a technique for correcting variations in gradation characteristics unique to a liquid discharge head.
The invention proposed by the inventors has aspects as a boundary value table optimization device, a liquid discharge head, a liquid discharge device, and a computer program.

  One of the major factors affecting the image quality of a printing apparatus is gradation characteristics. Hereinafter, the gradation characteristics will be described with reference to FIG. FIG. 1 shows a schematic flow of data processing executed by the printing apparatus. In the case of FIG. 1, the input data is given as RGB format digital data. Assume that the bit length of each color is 8 bits, for a total of 24 bits. In this case, each color of RGB has information of 256 gradations from 0 to 255.

The color conversion unit 1 converts RGB digital data into four colors corresponding to ink colors, that is, Y (yellow), M (magenta), C (cyan), and K (black) digital data (each of 0 to 255). 8 bits).
The halftoning unit 3 converts the digital data after color correction into drive data of the head 5 corresponding to each color.
The head 5 ejects ink droplets based on the drive data and forms a print image on the print medium.

Assume that the density of the output result for the digital data (0 to 255) after the color conversion is required to have a linear relationship as shown in FIG. Ideally, it is not always a straight line.
In addition to the optical density, the numerical value representing the density includes the L * value in the Lab color space, the absolute value of the 1/3 power of X in the XYZ color space, the absolute value of the 1/3 power of Y, and 1 of Z Various values such as an absolute value of the third power and a reading value by a scanner can be used.

Incidentally, the optical density is a logarithm of the degree to which light is not transmitted / reflected to a certain part such as photographic film or photographic paper, and the minimum value is 0.00 (all transmitted / reflected). ) Indicates that the larger the value, the darker.
However, in practice, as shown in FIG. 3, the gradation relationship is often saturated in a high density region.

  Therefore, as shown in FIG. 4, a gradation correction unit 7 is provided after the color conversion unit 1, and a correction operation for canceling the gradation characteristics shown in FIG. 3 is executed. FIG. 5 shows an example of the gradation correction curve. With this gradation correction, the digital data after color conversion and the density of the output result are corrected so as to satisfy the gradation relationship shown in FIG.

However, when the gradation correction shown in the gradation correction unit 7 is executed, the actual number of gradations is greatly reduced as shown in FIG.
One method for suppressing the decrease in the number of gradations is to increase the number of processing bits. For example, there is a method of processing by changing 8-bit digital data to 10-bit or 12-bit digital data.

However, this method has a problem that a large amount of memory is required and the processing speed becomes slow.
These problems are caused by the fact that gradation characteristics as shown in FIG. 3 tend to appear when multi-gradation data is binarized by the error diffusion method.

  On the other hand, the present inventor has proposed a method for improving the appearance of the gradation characteristics by applying a multi-level error diffusion method. Here, the multi-value error diffusion method is an error diffusion method in which the original image data is multi-valued from about 3 values to about 8 values, and density errors generated at that time are distributed to surrounding pixels. In the multilevel error diffusion method, it is common to determine a value obtained by equally dividing the number of gradations of the original image data by the multilevel number as a boundary value.

  However, the visual change when the lowest level is printed from the state where nothing is printed (level 0) (level 1) is larger than the visual change when the level 1 to level 2 is printed. Therefore, if level 0 and level 1, level 1 and level 2, level 2 and level 3, level 3 and level 4 are equally spaced, the image density is ideal for the input signal as shown in FIG. The tendency to deviate greatly from the state will appear.

In view of this, the present inventor has proposed a method (Patent Document 1) for optimizing the boundary value for multilevel error diffusion so that the printing result follows an ideal gradation characteristic curve.
When this method is applied, the image density with respect to the input signal can be close to an ideal relationship as shown in FIG. Note that the gradation characteristics between the boundary values may slightly deviate from the characteristic curve shown in FIG. Therefore, in an actual printing system, a gradation correction unit may be used together for the purpose of finely adjusting the deviation.
JP 2005-252633 A

However, the gradation characteristics of each head generally vary. The causes of variations include, for example, variations in nozzle diameter for ejecting ink droplets, variations in liquid chamber height, variations in heater performance, and the like.
Due to this characteristic variation, there is a problem that even if the gradation characteristics shown in FIGS. 2 and 8 are obtained for a certain head, the same characteristics cannot be obtained for another head.

  Patent Document 2 discloses a technique for solving this problem. That is, while storing a plurality of types of gradation correction data in the gradation correction unit 7, information for selecting these gradation correction data is stored in each head, so that gradation correction suitable for the mounted head is performed. A method of using data at the time of tone correction is disclosed.

However, such a method of correcting a large gradation value using the gradation correction unit has a serious problem that the number of reproducible gradations is greatly reduced as described above.
JP-A-3-252269

Therefore, the inventor proposes a mechanism for optimizing the gradation characteristics without substantially reducing the reproducible gradation width.
That is, a mechanism for optimizing the boundary value table to be selected or created based on the information stored in the liquid ejection head or based on the density of the test pattern actually formed is proposed. In addition, as the boundary value table optimization method, the following four methods are proposed.

(A) Mechanism 1 (selection of boundary value table)
As one mechanism, the inventor proposes a method of reading information for selecting an optimum boundary value table from a plurality of boundary value tables from the information storage unit of the print head.
That is, as a boundary value table optimizing device, a method is proposed in which the following processing functions are mounted.

(A) When information for selecting a boundary value table for multilevel error diffusion is stored for each discharge condition in the information storage unit of the liquid discharge head capable of expressing one pixel with a large number of droplets, the discharge condition is met. Selection information reading unit that reads information to be read from the information storage unit (b) boundary value table setting unit that sets a boundary value table corresponding to the read information for reference of the halftoning unit

(B) Mechanism 2 (Boundary value table generation 1)
As one mechanism, the inventor proposes a method of generating an optimum boundary value table from a set of boundary values read from the information storage unit of the liquid ejection head.
That is, as a boundary value table optimizing device, a method is proposed in which the following processing functions are mounted.

(A) When a set of boundary values for multi-level error diffusion is stored for each discharge condition in the information storage unit of the liquid discharge head capable of expressing one pixel with a large number of droplets, one that matches the discharge condition Boundary value reading unit for reading a set of boundary values from the information storage unit (b) Boundary value table generating unit for generating a boundary value table based on the read set of boundary values (c) A generated boundary value table Boundary value table storage unit for storing (d) Boundary value table setting unit for setting the boundary value table for reference of the halftoning unit

(C) Mechanism 3 (generation of boundary value table 2)
As one mechanism, the inventor proposes a method of generating an optimum boundary value table based on boundary value determination information read from the information storage unit of the liquid ejection head.
That is, as a boundary value table optimizing device, a method is proposed in which the following processing functions are mounted.

(A) When information for determining a set of boundary values for multilevel error diffusion is stored for each discharge condition in the information storage unit of the liquid discharge head capable of expressing one pixel with a large number of droplets, Boundary value determination information reading unit that reads information that matches the discharge conditions from the information storage unit (b) Boundary value determination unit that determines a set of boundary values for multilevel error diffusion based on the read information (c) A boundary value table generating unit that generates a boundary value table based on the set of determined boundary values; (d) a boundary value table storage unit that stores the generated boundary value table; Boundary value table setting section set for reference

(D) Mechanism 4 (Boundary value table generation 3)
As one mechanism, the inventor proposes a method of actually forming a test pattern using a liquid discharge head, optically reading the density, and generating an optimum boundary value table from the read density.
That is, as a boundary value table optimizing device, a method is proposed in which the following processing functions are mounted.

(A) A test pattern signal generator for generating a test pattern signal used for determining a boundary value for multi-level error diffusion according to ejection conditions and directly driving liquid ejection capable of expressing one pixel with a large number of droplets (B) A density reading unit that optically reads the density of the actually formed test pattern. (C) A boundary value table selected or generated based on the read density is set for reference of the halftoning unit. Boundary value table setting section

  By adopting the mechanism proposed by the inventor, even when there is a variation in gradation characteristics between liquid ejection heads (nozzle chips), the gradation characteristics are corrected to an optimized state without reducing the gradation width. Can do.

A technique for optimizing gradation characteristics according to the invention will be described below.
In addition, the well-known or well-known technique of the said technical field is applied to the part which is not illustrated or described in particular in this specification.
The embodiment described below is one embodiment of the present invention and is not limited thereto.

(A) Printing System Hereinafter, a printing system that is an example of a liquid ejection apparatus will be described. In this embodiment, it is assumed that the printing system is an ink droplet ejection device (so-called inkjet printer).
First, the basic structure assumed by the printing system will be described. In the following description, the print head and the signal processing system will be described separately.

(A-1) Print Head This print system uses a print head that ejects ink droplets toward a print medium as a print head. The ink droplet ejection mechanism can be applied to various methods such as a method using a piezo element and a method of heating ink with a heater.
FIG. 9 is a conceptual diagram of the nozzle surface that constitutes the print head 5. Black circles in the figure correspond to individual nozzles. The nozzles are arranged at a pitch corresponding to the printing resolution.

In the case of this embodiment, an area (information storage unit) 51 for storing information necessary for optimizing the boundary value table is mounted.
The information storage unit 51 includes, for example, a semiconductor memory, a resistive element, an arrangement pattern of contact points, a logic circuit, and other structures capable of electrically reading information, as well as optical information such as a printed pattern on the housing surface. A structure that can read out information or a structure that can read out information by mechanical coupling such as a notch can be employed.

The print head shown in FIG. 9 represents the case where the ink colors are four colors (Y, M, C, K). In the case of a print head that can eject a larger number of ink colors, four or more nozzle rows are arranged.
In the case of this embodiment, it is assumed that the print head can form one pixel with a plurality of ink droplets by using one or a plurality of nozzles. That is, one pixel can be expressed with multiple gradations. Note that nozzle rows for four colors can be formed on one print head.

FIG. 10 shows an example of forming one pixel. However, there are actually effects such as displacement of the discharge position and bleeding.
FIG. 10A shows an example in which one pixel region 11 is formed by overlappingly hitting one pixel region 11 while shifting the landing position of the ink droplet 13. In this example, one pixel is formed by four ink droplets 13.

FIG. 10B shows an example in which one pixel region 11 is divided into a plurality of sub-regions and one pixel is formed by ejecting ink droplets for each sub-region. In this example, one pixel region 11 is formed by nine sub-regions.
In either case, one pixel region 11 can be expressed by multi-level gradation.

Further, the print system of the print head may be a line head type or a serial head type.
FIG. 11A shows a line head type print image. This type of print head 5 (nozzle row) is formed to be equal to or longer than the print width of the printing medium 15. In this case, the print head 5 can form a print image without scanning in the print width direction.

  FIG. 11B shows a print image of the serial head type. This type of print head 5 (nozzle row) is formed shorter than the print width of the printing medium 15. In this case, the print head 5 is scanned in the print width direction of the print medium 15 to form a print image.

(A-2) Signal Processing System Next, a schematic configuration common to the signal processing system will be described.
FIG. 12 schematically shows a signal processing system of the printing apparatus. In FIG. 12, parts corresponding to those in FIG.

As shown in FIG. 12, the printing apparatus described below includes a color conversion unit 1, a halftoning unit 3, a print head 5, and a boundary value table optimization unit 21 as main components. Note that the gradation conversion unit is basically unnecessary except that it is used supplementarily in order to increase the correction accuracy of the gradation characteristics.
Although a specific method of realizing the boundary value table optimization unit 21 will be described later, in any case, the function of optimizing the boundary value table used in the multilevel error diffusion processing of the halftoning unit 3 is realized.

  The optimization method includes, for example, a method of selecting an appropriate boundary value table from a plurality of boundary value tables for each print head (ink color and nozzle chip), and an optimum boundary value for each print head (ink color and nozzle chip). There is a method to create a table. In addition, as a method of creating the boundary value table, a method of creating based on the information read from the information storage unit 51 of the print head 5 and a method of creating based on the measured density of the printing result can be considered.

FIG. 12 shows that the boundary value table optimizing unit 21 is provided with information on the gradation characteristics of each head in order to express functions common to these methods.
The optimization of the boundary value table includes both a function for optimizing the shape of the gradation characteristic curve and a function for optimizing the number of ink droplets that define the gradation characteristic curve. In particular, when there is a difference in the maximum density between the heads, the image quality can be stabilized by optimizing the number of ink droplets. The difference in maximum density cannot be corrected by the tone conversion disclosed in Patent Document 2.

(A-3) System Example Hereinafter, a system example of the printing apparatus will be described for each method of realizing the boundary value table optimization unit 21.

(A) System example 1
First, in this system example, a case will be described in which an optimum boundary value table for each head is selected based on selection information read from the print head.

(A-1) System Configuration FIG. 13 shows a system example of the printing apparatus. In FIG. 13, parts corresponding to those in FIGS. 4 and 12 are denoted by the same reference numerals.
The printing apparatus shown in FIG. 13 includes a color conversion unit 1, a gradation correction unit 7, a halftoning unit 3, a print head 5 (information storage unit 51), and a boundary value table optimization unit 21.
In the case of FIG. 13, the gradation correction unit 7 is mounted. This gradation correction unit 7 is for fine gradation adjustment that cannot be corrected by the halftoning unit 3.

FIG. 14 shows a detailed configuration example of the boundary value table optimization unit 21 suitable for application to this system example.
The boundary value table optimization unit 21 used in this system example includes a selection information reading unit 211, a boundary value table setting unit 213, and a boundary value table set storage unit 215.
The selection information reading unit 211 is a processing device that reads from the information storage unit 51 of the print head 5 the selection information of the boundary value table that is optimal for the gradation characteristics unique to each print head.

  The selection information is stored for each head at the time of factory shipment, for example, as ROM data and a resistance value of a variable resistor. For example, it is set for Y ink, M ink, C ink, and K ink. In addition, when a nozzle row corresponding to each ink color is configured by bonding a plurality of nozzle chips as in a line head type print head, selection information can be mounted for each nozzle chip.

Incidentally, the selection information reading unit 211 employs a reading mechanism according to the storage form of the selection information. For example, if the selection information is stored as ROM data, the selection information reading unit 211 is configured by a ROM reader.
The contents of the selection information are specific to the gradation characteristics of each print head, such as the average value of the nozzle diameter and the number of boundary values, in addition to using the identification numbers assigned to the individual boundary value tables prepared on the printing apparatus side. Use information.

  The boundary value table setting unit 213 is a processing device that reads a boundary value table corresponding to the read selection information from the boundary value table set storage unit 215 and sets it for reference by the halftoning unit 3. Of course, the boundary value table is set for each ink color (for each ink attribute). In addition, when the nozzle row is configured by bonding a plurality of nozzle chips, it is of course possible to set for each nozzle chip.

FIG. 15 shows a structural example of the boundary value table set storage unit 215. In the case of FIG. 15, N types (N is a natural number) of selection information and N boundary value tables are stored in association with each other.
Each boundary value table basically has a table structure in which an input signal value (gradation value) is associated with a determination threshold, boundary value L, boundary value H, output value L, and output value H.
The determination threshold is used as a determination criterion for a value (input value) obtained by adding an error component of a peripheral pixel to an input signal value.

The boundary value L is a boundary value assigned when the input value is smaller than the determination threshold. The boundary value H is a boundary value assigned when the input value is larger than the determination threshold.
The output value L and the output value H are the number of ink droplets (quantized value) assigned to the input value smaller than the determination threshold and the input value larger than the determination threshold, respectively.

  The boundary value table setting unit 213 selects a boundary value table most suitable for the tone characteristic of the print head from the plurality of boundary value tables prepared in advance as described above, and sets it for reference by the halftoning unit 3. It is a processing device. By optimizing the boundary value table, the image density reproduced on the printing medium through the multi-value error diffusion processing of the halftoning unit 3 is ideal gradation even if there are variations in gradation characteristics in the print head. It becomes possible to approximate the characteristics.

(A-2) Optimization Operation First, the case where the maximum densities of the print heads corresponding to the respective ink colors are substantially the same will be described.
FIG. 16 shows two print heads having different gradation characteristics. As shown in FIG. 16, the maximum density is almost the same. However, there is a difference in density reproduction characteristics in the intermediate gradation range. Further, it is assumed that the image density tends to be saturated in a high gradation range.

  Therefore, when the boundary value table is optimized according to the gradation characteristics of the print heads, the gradation characteristics of the two print heads are almost ideal gradations without decreasing the gradation width, as shown in FIG. It is corrected to the characteristic. Note that the square symbols in FIG. 17 indicate the seven boundary values that make up the boundary value table 1, and the triangle symbols show the seven boundary values that make up the boundary value table 2. In FIG. 17, the boundary values are extremely shifted in order to clarify the difference in boundary values between the boundary value tables. However, there is a possibility that the boundary value shifts only at one location. In any case, by optimizing the boundary value, the gradation information of the input signal can be reproduced almost as it is.

By the way, the maximum density of the print heads corresponding to each ink color is not limited to being the same.
In this case, correct image density cannot be reproduced even by correcting only the curve shape of the inherent gradation characteristic.

FIG. 18 shows an example in which the maximum density is different. FIG. 18 shows the relationship between the number of ink droplets constituting one pixel and the image density for three types of print heads. As shown in FIG. 18, when the maximum density is different, even if only the boundary value used in the multi-level error diffusion process is optimized, the image quality is deteriorated near the maximum density.
Therefore, when a sufficient maximum number of ink droplets that can be ejected for forming one pixel is secured, a method of determining the number of boundary values so as to make the maximum densities of the respective print heads coincide is adopted.

For example, in FIG. 18, in order to make the maximum density of each print head the same, the boundary value number of the print head A is set to “4”, the boundary value number of the print head B is set to “6”, and the boundary value of the print head C It can be seen that the value number should be set to “5”.
In this case, in the information storage unit 51 of the print head A, the boundary value number “4” is set as selection information of the boundary value table.

In the information storage unit 51 of the print head B, the boundary value number “6” is set as selection information of the boundary value table.
In the information storage unit 51 of the print head B, the boundary value number “5” is set as selection information of the boundary value table.

At this time, if a boundary value table with boundary values “0”, “138”, “212”, “255”, for example, is applied to the print head A with the boundary value number “4”, as shown in FIG. Ideal gradation characteristics can be realized.
For example, if a boundary value table with boundary values “0”, “76”, “134”, “182”, “224”, “255” is applied to the print head B with the boundary value number “6”. The ideal gradation characteristics as shown in FIG. 20 can be realized.

Further, for example, if a boundary value table with boundary values “0”, “100”, “169”, “220”, “255” is applied to the print head C with the boundary value number “5”, FIG. Ideal gradation characteristics as shown can be realized.
Note that FIGS. 19 to 21 illustrate the ideal gradation characteristics so as to be linear, but they are not necessarily linear but may be curved. In that case, a boundary value table determined so that the boundary value is located on the ideal curve is used.

Finally, an example of a boundary value table for each boundary value number is shown. FIG. 22 shows an example of a boundary value table with a boundary value number “4”, FIG. 23 shows an example of a boundary value table with a boundary value number “6”, and FIG. 24 shows an example of a boundary value with a boundary value number “5”.
The threshold value can be set in various ways. In this embodiment, an intermediate value of the boundary value is used. For example, when a value obtained by adding an error calculated from surrounding pixels to the input signal is smaller than a threshold value, the input value is converted into a boundary value L (lower one than the threshold value). As a result, the number of discharges (output value L) corresponding to the boundary value L is output.

  On the other hand, when the value obtained by adding the error calculated from the surrounding pixels to the input signal is larger than the threshold value, the input value is converted to the boundary value H (which is larger than the threshold value). As a result, the number of discharges (output value H) corresponding to the boundary value H is output.

(A-3) Effect of Optimization As described above, the number of gradations can be obtained by adopting a method in which selection information is written in advance in the storage area 51 in order to select an optimum boundary value table corresponding to the print head. The gradation characteristics of each print head can be brought close to an ideal state without reducing the above.
If the selection information reflects the maximum density of the print head and specifies the number of boundary values directly or indirectly, even if there is a variation in the discharge capacity of the print head, it is reproduced on the print medium. The maximum density of each ink can be made substantially the same. As a result, high print quality can be realized regardless of the discharge capability of the print head.

(B) System example 2
In this system example, a case will be described in which a boundary value table optimal for each head is generated based on information read from a print head.

(B-1) System Configuration FIG. 25 shows a system example of the printing apparatus. 25, parts corresponding to those in FIG. 13 are denoted by the same reference numerals.
The printing apparatus shown in FIG. 25 includes a color conversion unit 1, a gradation correction unit 7, a halftoning unit 3, a print head 5 (information storage unit 51), and a boundary value table optimization unit 31.

  In the case of this printing system, the information storage unit 51 of the print head 5 is different from the system example 1 in that a plurality of sets of boundary values necessary for creating the boundary value table are stored for each printing condition. Yes. For this reason, the boundary value table optimizing unit 31 realizes a function of creating a boundary value table based on a set of boundary values read according to printing conditions.

  In the case of this embodiment, the printing conditions are determined by a combination of paper type and printing mode. The print mode is determined by a combination of resolution, print speed, image quality, print content, and other items.

  Incidentally, the resolution is specified as, for example, high resolution, resolution, or the like. Further, the printing speed is designated as, for example, high speed, low speed, or the like. The image quality is specified as, for example, high image quality, normal image quality, draft, or the like. The print content is specified as, for example, a photograph or a document.

  However, a set of boundary values is not always stored for all printing conditions. In such a case, a necessary set of boundary values is created based on the set of boundary values stored for typical printing conditions.

FIG. 26 shows a detailed configuration example of the boundary value table optimization unit 31 suitable for this system example.
The boundary value table optimization unit 31 includes a boundary value reading unit 311, a boundary value table generation unit 313, a boundary value table storage unit 315, and a boundary value table setting unit 317.

  The boundary value reading unit 311 executes a process of reading a set of boundary values that match the printing conditions from the information storage unit 51 of the print head 5. Also in this case, a set of boundary values is stored for each head at the time of factory shipment, for example, as ROM data, a resistance value of a variable resistor, or the like.

  The set of boundary values is set for, for example, Y ink, M ink, C ink, and K ink. In addition, when the nozzle row corresponding to each ink color is configured by bonding a plurality of nozzle chips as in a line head type print head, a set of boundary values should be mounted for each nozzle chip. You can also.

Incidentally, the boundary value reading unit 311 employs a reading mechanism corresponding to the storage form of the boundary value. For example, if the selection information is stored as ROM data, the boundary value reading unit 311 is constituted by a ROM reader.
The boundary value table generation unit 313 executes processing for generating a boundary value table based on the read set of boundary values.

Specifically, the threshold value and output value associated with the boundary value are determined as follows, and the boundary value table is associated with all input signal values.
First, the threshold value is generated as follows. The threshold value is determined as an intermediate value between two adjacent boundary values among a set of boundary values arranged in order of magnitude. Of the two adjacent boundary values, the smaller one is the boundary value L, and the larger one is the boundary value H. In this case, the threshold value is basically calculated based on the following equation. However, round the numbers after the decimal point of the calculation result to an integer.
Threshold = boundary value L + (boundary value H−boundary value L) / 2

In this case, for example, the threshold value corresponding to the boundary value “0” and the boundary value “63” is “32” from “0+ (63-0) / 2”.
Similarly, for example, the threshold value corresponding to the boundary value “63” and the boundary value “127” is “95” from “63+ (127−63) / 2”.

In the boundary value table, the boundary value L (ie, “0”) corresponds to the input signal value “1” to “63” when the added value of the error generated in the surrounding pixels is smaller than the threshold value “32”. When the threshold value is greater than “32”, the boundary value H (ie, “63”) is associated. Similarly, boundary values are associated with other input signal values.
Incidentally, the processing in the case where the added value of the error generated in the surrounding pixels matches the threshold “32” with the input signal value is associated with either the boundary value L or the boundary value H according to the prior setting.

Next, the output value is generated as follows. The number of ink droplets constituting one pixel, that is, “0”, “1”, “2”... Is associated in the order in which the boundary values are arranged in ascending order. The maximum output value is linked to the number of boundary values.
The boundary value table generation unit 313 generates a boundary value table as shown in FIGS.

  The boundary value table storage unit 315 is a storage area for storing the generated boundary value table. The boundary value table storage unit 315 is preferably a non-volatile storage area from the viewpoint of eliminating the need for recalculation. For example, a semiconductor storage device, a magnetic storage device or other storage medium is used. Of course, when power is supplied, if the boundary value is read from the print head 5 and the boundary value table is created again, a volatile storage medium can be used as the storage area.

  The boundary value table setting unit 317 is a processing device that sets the generated boundary value table for reference by the halftoning unit 3. Of course, the boundary value table is set for each ink color. In addition, when a row of nozzles corresponding to each ink color is configured by bonding a plurality of nozzle chips as in a line head type print head, a boundary value table must be set for each nozzle chip. You can also.

  As a result, the image density reproduced on the printing medium through the multi-value error diffusion processing of the halftoning unit 3 can be made close to the ideal gradation characteristics regardless of the variation in gradation characteristics inherent in the print head. it can.

(B-2) Effect of Optimization As described above, if a method of previously writing the optimum boundary value according to the print head into the information storage unit 51 is adopted, an optimum boundary value table is created in the printing system. The gradation characteristics of each print head can be made close to an ideal state.
Further, when the number of boundary values stored in the storage area 51 is set to reflect the maximum density of the print head, even if there is a variation in the discharge capability of the print head, it is reproduced on the print medium. The maximum density of each ink to be produced can be made substantially the same. As a result, high print quality can be realized regardless of the discharge capability of the print head.

(C) System example 3
In this system example, a case will be described in which an optimum boundary value table is generated for each print head based on boundary value determination information read from the print head.

(C-1) System Configuration FIG. 27 shows a system example of the printing apparatus. FIG. 27 shows the same parts as those in FIG.
The printing apparatus shown in FIG. 27 includes a color conversion unit 1, a gradation correction unit 7, a halftoning unit 3, a print head 5 (information storage unit 51), and a boundary value table optimization unit 41.

In the case of this printing system, the information storage unit 51 of the print head 5 is a system example in that information for determining a set of boundary values necessary for creating a boundary value table is stored for each printing condition. 1 and different.
For this reason, the boundary value table optimization unit 41 determines a boundary value based on boundary value determination information that matches the printing conditions, and creates a boundary value table based on the determined set of boundary values. Do both.

  Here, the boundary value determination information refers to information such as average nozzle diameter, print density, and information indicating the characteristics of the print head. That is, in the system example 1, the case where the boundary value table is directly selected based on these pieces of information has been described. However, in this system example, a mechanism for determining a set of boundary values based on the same type of information is employed. The operation after the set of boundary values is determined is the same as that of the system example 2.

FIG. 28 shows a detailed configuration example of the boundary value table optimization unit 41 suitable for this system example.
The boundary value table optimization unit 41 includes a boundary value determination information reading unit 411, a boundary value determination unit 413, a boundary value table generation unit 415, a boundary value table storage unit 417, and a boundary value table setting unit 419.
The boundary value determination information reading unit 411 executes processing for reading boundary value determination information from the information storage unit 51 of the print head 5. Also in this case, the boundary value determination information is stored for each head at the time of factory shipment, for example, as ROM data, a resistance value of a variable resistor, or the like.

  The boundary value determination information here is also set for, for example, Y ink, M ink, C ink, and K ink. In addition, when the nozzle row corresponding to each ink color is configured by bonding a plurality of nozzle chips as in a line head type print head, boundary value determination information may be mounted for each nozzle chip. it can.

Note that the boundary value determination information reading unit 411 employs a reading mechanism corresponding to the boundary value storage form. For example, if the selection information is stored as ROM data, the boundary value determination information reading unit 411 is configured by a ROM reader.
The boundary value determination unit 413 executes processing for determining a set of boundary values for multi-level error diffusion based on the read information. For example, referring to the correspondence table shown in FIG. 29, a set of boundary values corresponding to the boundary value determination information is determined.

Hereinafter, when the boundary value determination information is the print density, the boundary value determination method will be specifically described. Here, it is assumed that “0.51”, “0.98”, “1.36”, “1.60”, “1.88”, and “2.01” are stored as print densities corresponding to levels 1 to 6. The ideal relationship between the gradation value and the density is given by, for example, “density = gradation value × 0.0078”. In this case, the gradation value corresponding to each density is “gradation value = density”. ÷ 0.0078 ”.

The boundary value determination unit 413 calculates an ideal gradation value by substituting the print density read as boundary value determination information into “gradation value = density ÷ 0.0078”. This gradation value is used as a “boundary value” that defines the boundary value table.
Therefore, when the print density is given in the previous example, the corresponding boundary values are “65”, “126”, “174”, “205”, “
Calculated as “241” and “257”.

However, in this example, the maximum boundary value is “
Therefore, the boundary value of level 6 closer to “255” is set to “255”.
The stored print density is “0.8”, “1.4”, “1.8”, “2.1”, “2.2”, “
In the case of 2.3, the boundary values obtained by calculation are “103”, “179”, “231”, “269”, “282”, and “294”. In this case, the boundary value determination unit 413 converts the level 4 boundary value to “
"255" and the boundary value between level 5 and level 6 is not used.

  The boundary value table generation unit 415 executes processing for generating a boundary value table based on the set of boundary values thus obtained. Also in this case, the boundary value table generation unit 415 determines a threshold value and an output value in the same procedure as in the system example 2, and generates a boundary value table associated with all input signal values.

  The boundary value table storage unit 417 is a storage area for storing the generated boundary value table. The boundary value table storage unit 417 is preferably a non-volatile storage area from the viewpoint of reducing the recalculation load. For example, a semiconductor storage device, a magnetic storage device or other storage medium is used. Of course, when power is supplied, if the boundary value is read from the print head 5 and the boundary value table is created again, a volatile storage medium can be used as the storage area.

The boundary value table setting unit 419 is a processing device that sets the generated boundary value table for reference by the halftoning unit 3. Of course, the boundary value table is set for each ink color (for each ink attribute).
In addition, when a nozzle row corresponding to each ink color is configured by bonding a plurality of nozzle chips as in a line head type print head, a boundary value table can be set for each nozzle chip. .

  As a result, the image density reproduced on the printing medium through the multi-value error diffusion processing of the halftoning unit 3 can be made close to the ideal gradation characteristics regardless of the variation in gradation characteristics inherent in the print head. it can.

(C-2) Effect of Optimization As described above, if a method for preliminarily writing information for determining the optimum boundary value according to the print head in the information storage unit 51 is adopted, the printing system An optimum boundary value table can be created to bring the gradation characteristics of each print head closer to an ideal state.

  In addition, when the boundary value determination information stored in the information storage unit 51 is set to reflect the maximum density of the print head, even if there is a variation in the discharge capability of the print head, The maximum density of each ink that is reproduced can be made substantially the same. As a result, high print quality can be realized regardless of the discharge capability of the print head.

(D) System example 4
In this system example, an optimum boundary value is determined based on the actual printing result (measured density) of each head, and a boundary value table that approximates the tone characteristics of the print head corresponding to this boundary value to an ideal characteristic is created. The case of generating will be described.
Therefore, in this system example, it is not necessary to mount or form the information storage unit 51 on the print head 5.

(D-1) System Configuration FIG. 30 shows a system example of the printing apparatus. FIG. 30 shows parts corresponding to those in FIG. 13 with the same reference numerals.
The printing apparatus shown in FIG. 30 includes a color conversion unit 1, a gradation correction unit 7, a halftoning unit 3, a print head 5, a test pattern signal generation unit 61, a print density reading unit 71, and a boundary value table optimization unit 81. To do.

  A configuration unique to this printing system is that a test pattern signal generation unit 61 and a print density reading unit 71 are newly installed, and an optimum boundary value is determined according to the print density actually measured by the boundary value table optimization unit 81. In addition to determining, a function of creating a boundary value table based on the determined set of boundary values is executed.

The test pattern signal generation unit 61 is a processing device that generates a test pattern signal used to determine a boundary value for multilevel error diffusion.
In the case of this embodiment, a test pattern is generated for each printing condition. However, only one type or a representative test pattern can be generated.

  Basically, the test pattern signal uses a pattern corresponding to a boundary value that indicates the characteristics of the print head itself. For example, if the print head is capable of ejecting four ink droplets in one pixel, level 1 solid pattern, level 2 solid pattern, level 3 solid pattern, and level 4 solid pattern 4 Generate types. The number of levels corresponds to the number of ink drops.

  FIG. 31A shows a test pattern example corresponding to this case. Of course, as in the case where a set of boundary values is prepared in advance in the boundary value table optimization unit 81, if the gradation characteristics can be specified by observing the print density of some boundary values, Only a part of the solid coating pattern may be representatively used. An example is shown in FIG. FIG. 31B shows an example in which the saturation state of the high gradation portion is the observation target. That is, FIG. 31B shows a case where a level 3 solid pattern is selected.

  The print density reading unit 71 is a processing device that optically reads the print density of the test pattern and outputs information for determining the boundary value. For example, a scanner is used. Therefore, this printing apparatus is suitable for a multi-function machine in which a scanner is mounted in addition to the print head. However, the print density reading unit 71 can be realized as an external device for the printing apparatus, and can be configured to capture the scan result through the communication terminal of the printing apparatus.

For example, the print density measured for each test pattern is output from the print density reading unit 71 to the boundary table optimization unit 81.
In this embodiment, it is assumed that the output value of the scanner is given by, for example, 8 bits (0 to 255 (assuming that the density of dark objects is high)). In this case, the print density is calculated as “scanner output value × 0.01”.

  For example, as shown in FIG. 31, the print density corresponding to the test pattern is calculated. In the case of FIG. 31A, the print density of the test pattern corresponding to level 1 is calculated as “1.0”. Further, the print density of the test pattern corresponding to level 2 is calculated as “1.2”. Further, the print density of the test pattern corresponding to level 3 is calculated as “1.5”. Further, the print density of the test pattern corresponding to level 4 is calculated as “2.0”. Incidentally, FIG. 31B shows the case where there is only one test pattern. In this case, the print density of the test pattern is calculated as “1.5”.

  However, instead of the print density, the same information as in the other system examples described above may be generated, and the information may be given to the boundary value table optimization unit 81. That is, boundary value table selection information, a set of boundary values, and information for determining a set of boundary values may be given to the boundary value table optimization unit 81.

FIG. 32 shows a detailed configuration example of the boundary value table optimization unit 81 suitable for this system example.
The boundary value table optimization unit 81 includes a boundary value determination unit 811, a boundary value table generation unit 813, a boundary value table storage unit 815, and a boundary value table setting unit 817.
In the case of this example, the boundary value determination unit 811 executes a process of determining a set of boundary values for multilevel error diffusion based on the print density. For example, referring to the correspondence table shown in FIG. 33, a set of boundary values corresponding to the print density is determined.

  For example, when the print density corresponding to the test pattern is measured as “0.51”, “0.98”, “1.36”, “1.60”, “1.88”, “2.01”, the boundary value determining unit 811 performs the measured print Substituting the density into the relational expression given by “gradation value = density ÷ 0.0078”, the corresponding boundary value is calculated. Of course, this relational expression is the case where the ideal relationship between the gradation value and the density is given by “density = gradation value × 0.0078”, and if another relational expression holds, use another relational expression. To do.

When the measured print density is the previous example, the boundary value determination unit 811 outputs “65”, “126”, “174”, “205”, “241”, and “257” as boundary values. However, in this example, the maximum boundary value is “
Therefore, the boundary value of level 6 closer to “255” is set to “255”.

In addition, the measured print density is “0.8”, “1.4”, “1.8”, “2.1”, “2.2”, “
In the case of 2.3, “103”, “179”, “231”, “269”, “282”, and “294” are calculated as boundary values. In this case, the boundary value determination unit 811 converts the boundary value of level 4 to “
"255" and the boundary value between level 5 and level 6 is not used.

  The boundary value table generation unit 813 executes processing for generating a boundary value table based on the read set of boundary values. Also in this case, the boundary value table generation unit 813 determines a threshold value and an output value in the same procedure as in the system example 2, and generates a boundary value table associated with all input signal values.

  The boundary value table storage unit 815 is a storage area for storing the generated boundary value table. The boundary value table storage unit 815 is preferably a non-volatile storage area from the viewpoint of reducing the burden of recalculation. For example, a semiconductor storage device, a magnetic storage device or other storage medium is used. Of course, when power is supplied, if the boundary value is read from the print head 5 and the boundary value table is created again, a volatile storage medium can be used as the storage area.

  The boundary value table setting unit 817 is a processing device that sets the generated boundary value table for reference by the halftoning unit 3. Of course, the boundary value table is set for each ink color. In addition, when a row of nozzles corresponding to each ink color is configured by bonding a plurality of nozzle chips as in a line head type print head, a boundary value table must be set for each nozzle chip. You can also.

  As a result, the image density reproduced on the printing medium through the multi-value error diffusion processing of the halftoning unit 3 can be made close to the ideal gradation characteristics regardless of the variation in gradation characteristics inherent in the print head. it can.

(D-2) Optimization Effect As described above, a test pattern is given to the print head to detect print characteristics (that is, print density is detected), and an optimum boundary value table is generated according to the detection result. As a result, even when the characteristics of the print head change over time, the printing operation can be executed in an optimum state. If this function is used, the boundary value table can be optimized to the gradation characteristics at the time of printing.

  Also in this case, if the boundary value determination information stored in the information storage unit 51 is set to reflect the maximum density of the print head, even if there is a variation in the discharge capacity of the print head, The maximum density of each ink reproduced on the print medium can be made substantially the same. As a result, high print quality can be realized regardless of the discharge capability of the print head.

(B) Application example of printing apparatus Finally, an application example of the printing apparatus will be described.
The printing apparatus described above can be applied to products for various uses.
For example, it can be applied to a kiosk type printing apparatus. FIG. 34 shows a general external configuration of a kiosk type printing apparatus. This type of printing apparatus 91 includes a display area 95 for operation, a media insertion port 97, and a discharge port 99 on the front surface of a housing 93.

  For example, it can be applied to products mainly for home users. FIG. 35 shows a general external configuration of this type of printing apparatus. This type of printing apparatus 101 has a media insertion slot 105 and a display area 107 mounted on the front surface of a housing 103.

  For example, it can be applied to a printing apparatus used in a medical institution. In the case of a printing apparatus used in a medical field, it is used for printing a color image such as a monochrome image or an MRI image like a radiograph. In particular, in the printing apparatus proposed by the inventor, in addition to being able to reproduce the gradation information with almost no loss, it is possible to expect a very high image quality because there is no influence of variations in the maximum density.

(C) Other Embodiments (a) In the embodiment described above, the case where a plurality of sets of boundary value tables are stored for selection has been described.
However, these boundary value tables may be imported later via an external storage medium. That is, it may be added or rewritten later. These boundary value tables may be downloaded from a server such as a manufacturer via network communication such as the Internet.

(B) In the above-described embodiment, a case has been described in which a table in which selection information is associated with a boundary value table is stored in the printing apparatus.
However, the contents of this table may be added or rewritten later. Moreover, you may employ | adopt the mechanism which downloads the content of a table from servers, such as a manufacturer, via network communications, such as the internet.

(C) In the above-described embodiment, the case where the table in which the boundary value determination information and the boundary value are associated is stored in the printing apparatus has been described.
However, the contents of this table may be added or rewritten later. Moreover, you may employ | adopt the mechanism which downloads the content of a table from servers, such as a manufacturer, via network communications, such as the internet.

(D) In the above-described embodiment, the boundary value table selection or generation function has been described mainly from a functional aspect. Needless to say, an equivalent function can be realized as hardware or software.
Further, not only all of these processing functions are realized by hardware or software, but some of them may be realized by using hardware or software. That is, a combination of hardware and software may be used.

(E) In the above-described embodiments, the case where the technology according to the invention is applied to a printing apparatus that ejects ink droplets has been described.
However, the liquid discharge technique described above can also be applied to a liquid discharge head or a liquid discharge apparatus that discharges various dyes as droplets. The technology can also be applied to a liquid discharge head or a liquid discharge device that discharges droplets or the like for forming a protective layer.

The technology can also be applied to a microdispenser that discharges a reagent or the like as droplets and other various measuring devices and test devices. The technique can also be applied to various pattern drawing apparatuses in which droplets are agents that protect members from etching. The technique can also be applied to an apparatus that discharges a DNA-containing solution for detecting a biological sample.
(F) Various modifications can be considered for the above-described embodiments within the scope of the gist of the invention. Various modifications and application examples created based on the description of the present specification are also conceivable.

It is a figure which shows the schematic flow of the data processing performed with a printing apparatus. It is a figure explaining an ideal gradation characteristic. It is a figure explaining the gradation characteristic which is saturated in a high density range. It is a figure which shows the example of a system configuration which correct | amends a gradation characteristic to an ideal state by gradation correction. It is a figure which shows an example of a gradation correction curve. It is a figure which shows an example of the input-output relationship in the case of correct | amending a gradation characteristic by gradation correction. It is a figure which shows the gradation characteristic of the multi-value error diffusion process at the time of setting a boundary value at equal intervals. It is a figure which shows the gradation characteristic of the multi-value error diffusion process at the time of optimizing a boundary value. It is a figure explaining the structural example of a print head. It is a figure explaining the example of formation of 1 pixel. It is a figure explaining the example of a drive of a print head. It is a figure which shows the conceptual structure of the printing apparatus which an inventor proposes. 2 is a diagram illustrating a configuration example of a printing apparatus corresponding to a system example 1. FIG. It is a figure which shows the structural example of a boundary value table optimization part. It is a figure which shows the example of a table which matched selection information and the boundary value table. It is a figure explaining the gradation characteristic before optimizing a boundary value. It is a figure explaining the gradation characteristic after optimizing a boundary value. It is a figure explaining the gradation characteristic when the maximum density varies. It is a figure explaining the example of a gradation characteristic at the time of optimizing the number of boundary values (number of boundary values = 3). It is a figure explaining the example of a gradation characteristic at the time of optimizing the number of boundary values (number of boundary values = 5). It is a figure explaining the example of a gradation characteristic at the time of optimizing the number of boundary values (number of boundary values = 4). It is a figure which shows the example of a boundary value table (number of boundary values = 3). It is a figure which shows the example of a boundary value table (number of boundary values = 5). It is a figure which shows the example of a boundary value table (number of boundary values = 4). 3 is a diagram illustrating a configuration example of a printing apparatus corresponding to a system example 2. FIG. It is a figure which shows the structural example of a boundary value table optimization part. 10 is a diagram illustrating a configuration example of a printing apparatus corresponding to a system example 3. FIG. It is a figure which shows the structural example of a boundary value table optimization part. It is a figure which shows the example of a table which matched boundary value determination information and boundary value. 10 is a diagram illustrating a configuration example of a printing apparatus corresponding to a system example 4. FIG. It is a figure explaining the relationship between a test pattern and printing density. It is a figure which shows the structural example of a boundary value table optimization part. It is a figure explaining the relationship between printing density and a boundary value. It is a figure explaining the external appearance example of a kiosk type printing apparatus. It is a figure explaining the external appearance example of the printing apparatus for home use.

Explanation of symbols

1 color conversion unit 3 halftoning unit 5 print head 7 tone correction unit 21 boundary value table optimization unit 211 selection information reading unit 213 boundary value table setting unit 215 boundary value table set storage unit 31 boundary value table optimization unit 311 boundary Value reading unit 313 Boundary value table generation unit 315 Boundary value table storage unit 317 Boundary value table setting unit 51 Information storage unit 41 Boundary value table optimization unit 411 Boundary value determination information reading unit 413 Boundary value determination unit 415 Boundary value table generation unit 417 Boundary value table storage unit 419 Boundary value table setting unit 61 Test pattern signal generation unit 71 Print density reading unit 81 Boundary value table optimization unit 81 Boundary value table optimization unit 811 Boundary value determination unit 813 Boundary value table generation unit 815 Boundary Value table storage unit 817 Boundary value table Setting section

Claims (16)

The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A boundary value table optimization device used for multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
When a plurality of densities that can be expressed in one pixel by the liquid discharge head are positioned on the ideal input tone value-image density curve in the information holding unit of the liquid discharge head that can express one pixel with a large number of droplets when information for selecting boundary value table for multi-level error diffusion to each tone value set as a boundary value for is stored in the specific print condition, selection information reading for reading the information that matches the printing conditions from the information holding unit And
A boundary value table optimizing device, comprising: a boundary value table setting unit that sets a boundary value table corresponding to the read information for reference to a halftoning unit that executes multilevel error diffusion processing . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A boundary value table optimization device used for multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
When a plurality of densities that can be expressed in one pixel by the liquid discharge head are positioned on the ideal input tone value-image density curve in the information holding unit of the liquid discharge head that can express one pixel with a large number of droplets when a set of boundary values of the boundary value table for multi-level error diffusion sets the gradation value as a boundary value is stored for each printing condition, the information holding unit a set of boundary values that match the printing conditions A boundary value reading unit for reading from
A boundary value table generating unit that generates a boundary value table based on the read set of boundary values;
A boundary value table storage unit for storing the generated boundary value table;
A boundary value table optimizing device, comprising: a boundary value table setting unit that sets the boundary value table for reference to a halftoning unit that executes multilevel error diffusion processing . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A boundary value table optimization device used for multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
When a plurality of densities that can be expressed in one pixel by the liquid discharge head are positioned on the ideal input tone value-image density curve in the information holding unit of the liquid discharge head that can express one pixel with a large number of droplets when information for determining a set of boundary values of the boundary value table for multi-level error diffusion to each tone value set as a boundary value for is stored by the printing conditions, the said information that matches the printing conditions A boundary value determination information reading unit read from the information holding unit;
A boundary value determining unit that determines a set of boundary values for multi-level error diffusion based on the read information;
A boundary value table generating unit that generates a boundary value table based on the set of determined boundary values;
A boundary value table storage unit for storing the generated boundary value table;
A boundary value table optimizing device, comprising: a boundary value table setting unit that sets the boundary value table for reference to a halftoning unit that executes multilevel error diffusion processing . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A boundary value table optimization device used for multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . A test pattern signal generation unit that directly generates a test pattern signal used to determine a boundary value according to printing conditions and directly drives a liquid discharge head capable of expressing one pixel with a large number of droplets;
A density reading unit that optically reads the density of the actually formed test pattern;
A boundary value table setting unit that sets a boundary value table selected or generated based on the read density for reference of a halftoning unit that executes multi-value error diffusion processing; Value table optimization device. A liquid discharge head capable of expressing one pixel with a large number of droplets,
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve. It has an information holding part that saves information to be selected according to printing conditions,
The boundary value table uses a gradation value as a boundary when dividing the number of gradations of the input data as a boundary value, and the input data is compared with a predetermined threshold value within each gradation value range formed by the division. The liquid ejection head is used for multi-value error diffusion processing in which the gradation value is distributed to any boundary value before and after the gradation value range and the boundary value is converted into a corresponding output value . A liquid discharge head capable of expressing one pixel with a large number of droplets,
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . It has an information holding unit that stores a set of boundary values according to printing conditions,
The boundary value table uses a gradation value as a boundary when dividing the number of gradations of the input data as a boundary value, and the input data is compared with a predetermined threshold value within each gradation value range formed by the division. The liquid ejection head is used for multi-value error diffusion processing in which the gradation value is distributed to any boundary value before and after the gradation value range and the boundary value is converted into a corresponding output value . A liquid discharge head capable of expressing one pixel with a large number of droplets,
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . An information holding unit for storing information for determining a set of boundary values for each printing condition;
The boundary value table uses a gradation value as a boundary when dividing the number of gradations of the input data as a boundary value, and the input data is compared with a predetermined threshold value within each gradation value range formed by the division. The liquid ejection head is used for multi-value error diffusion processing in which the gradation value is distributed to any boundary value before and after the gradation value range and the boundary value is converted into a corresponding output value . A liquid discharge head capable of expressing one pixel with a large number of droplets,
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . A test pattern signal used to determine the boundary value is generated according to printing conditions, and has a test pattern signal generation unit that directly drives the print head,
The boundary value table uses a gradation value as a boundary when dividing the number of gradations of the input data as a boundary value, and the input data is compared with a predetermined threshold value within each gradation value range formed by the division. The liquid ejection head is used for multi-value error diffusion processing in which the gradation value is distributed to any boundary value before and after the gradation value range and the boundary value is converted into a corresponding output value . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A liquid ejecting apparatus that performs multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
A liquid discharge head capable of expressing one pixel with a large number of droplets;
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve. An information holding unit for storing information to be selected according to printing conditions;
Be information for selecting the boundary value table, the selection information reading section for reading the information that matches the printing conditions from the information holding unit,
A boundary value table setting unit that sets a boundary value table corresponding to the read information for reference of a halftoning unit that executes multi-level error diffusion processing ;
A liquid ejecting apparatus comprising: a halftoning unit that performs multi-value error diffusion on input image data with reference to a set boundary value table and quantizes the input image data into a corresponding number of droplets. The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A liquid ejecting apparatus that performs multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
A liquid discharge head capable of expressing one pixel with a large number of droplets;
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . An information holding unit for storing a set of boundary values according to printing conditions;
A boundary value reading unit that reads from the information holding unit a set of boundary values that match the printing conditions;
A boundary value table generating unit that generates a boundary value table based on the read set of boundary values;
A boundary value table storage unit for storing the generated boundary value table;
A boundary value table setting unit that sets the boundary value table for reference of a halftoning unit that executes multi-value error diffusion processing ;
A liquid ejecting apparatus comprising: a halftoning unit that performs multi-value error diffusion on input image data with reference to a set boundary value table and quantizes the input image data into a corresponding number of droplets. The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A liquid ejecting apparatus that performs multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
A liquid discharge head capable of expressing one pixel with a large number of droplets;
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . An information holding unit for storing information for determining a set of boundary values for each printing condition;
Is information for determining the set of boundary values, and the boundary value determination information reading unit for reading the information that matches the printing conditions from the information holding unit,
A boundary value determining unit that determines a set of boundary values for multi-level error diffusion based on the read information;
A boundary value table generating unit that generates a boundary value table based on the set of determined boundary values;
A boundary value table storage unit for storing the generated boundary value table;
A boundary value table setting unit that sets the boundary value table for reference of a halftoning unit that executes multi-value error diffusion processing ;
A liquid ejecting apparatus comprising: a halftoning unit that performs multi-value error diffusion on input image data with reference to a set boundary value table and quantizes the input image data into a corresponding number of droplets. The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A liquid ejecting apparatus that performs multi-value error diffusion processing that distributes the boundary value to any one of the boundary values before and after the gradation value range and converts the boundary value into a corresponding output value ,
A liquid discharge head capable of expressing one pixel with a large number of droplets;
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . A test pattern signal generating unit that generates a test pattern signal used for determining a boundary value according to printing conditions and directly drives the liquid ejection head; and
A density reading unit that optically reads the density of the actually formed test pattern;
A boundary value table setting unit that sets a boundary value table selected or generated based on the read density for reference of a halftoning unit that executes multi-value error diffusion processing according to printing conditions;
A liquid ejecting apparatus comprising: a halftoning unit that performs multi-level error diffusion processing on input image data with reference to a set boundary value table and converts the input image data into a corresponding number of ink droplets. The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A computer program that causes a computer to execute multi-value error diffusion processing that distributes the boundary value to any boundary value before and after the gradation value range and converts the boundary value into a corresponding output value ,
When a plurality of densities that can be expressed in one pixel by the liquid discharge head are positioned on the ideal input tone value-image density curve in the information holding unit of the liquid discharge head that can express one pixel with a large number of droplets when information for selecting boundary value table for multi-level error diffusion to each tone value set as a boundary value for is stored in the specific print condition, a process of reading the information that matches the printing conditions from the information holding unit,
A computer program that causes a computer to execute processing for setting a boundary value table corresponding to read information for reference to a halftoning unit that performs multilevel error diffusion processing . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A computer program that causes a computer to execute multi-value error diffusion processing that distributes the boundary value to any boundary value before and after the gradation value range and converts the boundary value into a corresponding output value ,
When a plurality of densities that can be expressed in one pixel by the liquid discharge head are positioned on the ideal input tone value-image density curve in the information holding unit of the liquid discharge head that can express one pixel with a large number of droplets when a set of boundary values of the boundary value table for multi-level error diffusion sets the gradation value as a boundary value is stored for each printing condition, the information holding unit a set of boundary values that match the printing conditions Processing to read from
A process of generating a boundary value table based on the read set of boundary values;
A computer program that causes a computer to execute processing for setting a generated boundary value table for reference to a halftoning unit that performs multilevel error diffusion processing . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A computer program that causes a computer to execute multi-value error diffusion processing that distributes the boundary value to any boundary value before and after the gradation value range and converts the boundary value into a corresponding output value ,
When a plurality of densities that can be expressed in one pixel by the liquid discharge head are positioned on the ideal input tone value-image density curve in the information holding unit of the liquid discharge head that can express one pixel with a large number of droplets when information for determining a set of boundary values of the boundary value table for multi-level error diffusion to each tone value set as a boundary value for is stored by the printing conditions, the said information that matches the printing conditions Processing to read from the information holding unit;
A process of determining a set of boundary values for multi-level error diffusion based on the read information;
Generating a boundary value table based on the set of determined boundary values;
A computer program that causes a computer to execute processing for setting a generated boundary value table for reference to a halftoning unit that performs multilevel error diffusion processing . The gradation value serving as a boundary when dividing the number of gradations of the input data is set as a boundary value, and the gradation value of the input data is compared with a predetermined threshold value within each gradation value range formed by the division. A computer program that causes a computer to execute multi-value error diffusion processing that distributes the boundary value to any boundary value before and after the gradation value range and converts the boundary value into a corresponding output value ,
A boundary value table for multi-level error diffusion in which each gradation value is set as a boundary value when a plurality of densities that can be expressed in one pixel by the liquid ejection head are positioned on an ideal input gradation value-image density curve . A process of generating a test pattern signal used for determining a boundary value according to printing conditions and directly driving a liquid ejection head capable of expressing one pixel with a large number of droplets;
A process for optically reading the density of the actually formed test pattern;
A computer program that causes a computer to execute a process of setting a boundary value table selected or generated based on a read density for reference to a halftoning unit that executes a multilevel error diffusion process .

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