JP3580150B2 - Image processing apparatus and method, and printing apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, image data having a gradation value for each pixel forming an image within a predetermined gradation number range is converted to a gradation value at an output gradation number which is a gradation number lower than the gradation number. The present invention relates to an image processing apparatus, an image processing method, and a recording medium on which a program for the image processing is recorded, and a printing apparatus for printing an image using the image processing technique.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an output device of a computer, there has been proposed an ink jet printer that forms dots by using several colors of ink ejected from a plurality of nozzles provided in a head and records an image. It is widely used for printing in multiple colors and multiple tones. In such a printer, usually, only two gradations of dot on / off can be taken for each pixel. Accordingly, an image is printed after image processing for expressing the gradation of the original image data by the dispersibility of dots, that is, so-called halftone processing.
[0003]
In recent years, in order to enrich the gradation expression, there has been proposed an ink-jet printer, which is a so-called multi-value printer, capable of expressing two or more gradations of ON / OFF for each dot. For example, a printer capable of expressing three or more types of densities for each dot by changing the dot diameter and the ink density, and a multi-gradation can be expressed by superposing a plurality of dots for each pixel It is a printer. Even in such a printer, halftone processing is required because the gradation of the original image data cannot be sufficiently expressed in each pixel unit.
[0004]
Various methods have been proposed for such halftone processing, and typical methods include an error diffusion method and a dither method. In general, the error diffusion method controls the generation of dots so as to minimize the local error that occurs between the density expressed by turning on and off the dots and the density to be expressed. is there. On the other hand, the dither method has a characteristic that high-speed processing is possible because the processing is relatively simple. Conventionally, halftone processing has been performed by selectively using processing that is deemed appropriate according to the purpose of printing an image from various processings including an error diffusion method and a dither method.
[0005]
[Problems to be solved by the invention]
However, when these processes are used in a multi-valued printer, the halftone process by the dither method can perform a process with excellent image quality so that the gradation expression of the multi-valued printer aiming at high image quality can be sufficiently utilized. It was difficult. On the other hand, halftone processing by the error diffusion method also has the following problem.
[0006]
As an example of a multi-value printer, a printer capable of forming two types of dots, a small-diameter dot (referred to as a small dot) and a large-diameter dot (referred to as a large dot), will be described as an example. FIG. 17 shows an example in which an image is printed by the printer according to the embodiment. For convenience of illustration, FIG. 17 shows dot formation for 8 × 8 pixels. In FIG. 17, a small circle “径” means a small dot. A large-diameter “●” means a large dot. In FIG. 17, a predetermined density is expressed by forming eight small dots and four large dots.
[0007]
FIG. 18 shows another example in which an image is printed by a multilevel printer. The meanings of the symbols in FIG. 18 are the same as those in FIG. 17 and 18, since the number of formed small dots and the number of large dots are equal, the densities expressed in this area are equal. However, in FIG. 17, the small dots and the large dots are formed so as to be evenly dispersed, respectively, whereas in FIG. 18, the small dots and the large dots are not formed so as to be evenly dispersed as in FIG. That is, in FIG. 18, the occurrence of large dots is locally biased. Generally, large dots are more visible than small dots. Accordingly, when the bias related to the generation of large dots occurs as shown in FIG. 18, the dots become more conspicuous, and such bias is recognized as unevenness by human eyes, and the image quality deteriorates.
[0008]
The conventional error diffusion method can be applied to a multilevel printer in the following manner. For example, consider a case where ternarization is performed by an error diffusion method. At this time, the correction is performed by adding the quantization error diffused from the peripheral processed pixels to the gradation data of the target pixel to be processed. By comparing the corrected result with the two threshold values, it is ternaryized to one of dot off, small dot on, and large dot on. By increasing the threshold value for comparison, the present invention can be similarly applied to four-valued or more.
[0009]
When the conventional error diffusion method is applied to a multi-value printer in such a manner, the formation of dots is controlled so as to locally minimize the density error, but when viewed only with small dots or large dots, The formation of dots could not be controlled while ensuring sufficient dispersibility of each dot. For this reason, for example, the occurrence of large dots may be biased as shown in FIG. 18, and the image quality may be reduced as described above. Since a multi-value printer is originally intended to enhance the image quality by enriching the gradation expression, such a decrease in the image quality cannot be overlooked.
[0010]
Further, another problem has occurred in the halftone processing by the error diffusion method. FIG. 13 is a graph showing the relationship between the gradation value of the input image data and the dot recording rate. The graph indicated by the curve LD1 in FIG. 13 shows the recording rate of large dots when the formation of small dots and large dots is determined by the error diffusion method. As shown in FIG. 13, it can be seen that the recording rate of large dots sharply decreases around the gradation values dp1 and dp2. Although the gradation value at which such a phenomenon occurs varies depending on the threshold value used in the error diffusion method, the density evaluation value of each dot, and the like, a portion where the dot recording rate sharply changes at any gradation value appears. Such a gradation value at which the recording rate of large dots changes abruptly changes the granularity of the printed image abruptly, thereby causing false contours and the like, thereby deteriorating the image quality. As described above, such a decrease in image quality was not overlooked.
[0011]
In the above example, a multi-value printer capable of forming two types of small dots and large dots has been described. However, a similar problem occurs if the multi-value printer is capable of expressing three or more gradation values for each pixel. I was Further, since the above-mentioned problem relates to so-called halftone processing, it has been expected that similar problems will occur in various printing apparatuses other than the above-described ink jet printer that require halftone processing.
[0012]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and prevents the image quality from being deteriorated due to a bias in dot generation or a sudden change in the generation rate, and converts the original image data into three-valued data. It is an object of the present invention to provide a technique for multileveling. It is another object of the present invention to provide a printing apparatus that enables high-quality printing by applying such technology.
[0013]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of the problems described above, the present invention employs the following configurations.
The image processing apparatus according to the present invention includes:
With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. An image processing apparatus for performing
It is possible to determine the presence or absence of formation of at least some of the two or more types of dots, and to provide two or more types of multi-value conversion means having different properties.
For at least some of the two or more types of dots, two or more of the multivalued means are used in accordance with a predetermined parameter related to the property of the multivalued means. The point is to determine whether or not dots are formed.
[0014]
The image processing method of the present invention includes:
With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. An image processing method to be performed,
It is possible to determine the presence or absence of formation of at least some of the two or more types of dots, and prepare two or more types of multi-valued means having different properties,
For at least some of the two or more types of dots, two or more of the multivalued means are used in accordance with a predetermined parameter related to the property of the multivalued means. The point is to determine whether or not dots are formed.
[0015]
In such an image processing apparatus and image processing method, for at least some of the dots, the presence / absence of dot formation is determined using two or more types of multi-valued means. As a method of using two or more types of multi-value generating means, for example, there is a method in which when a parameter takes a certain value, the presence or absence of dot formation is determined by preferentially using one multi-value converting means. In other words, when it is determined that the dot should be formed by the priority multi-value generating means, a method may be adopted according to the result, and in other cases, the dot formation is determined again by the other multi-value converting means. it can. Of course, the multi-value conversion means which is prioritized according to the value of the parameter may be switched. Further, as another method, the presence or absence of dot formation may be determined by integrating the results of multi-level conversion by two or more types of multi-level conversion means. For example, the presence / absence of dot formation may be determined based on the logical sum of the results of the respective multi-level conversion means, or the presence / absence of dot formation may be determined based on the logical product.
[0016]
Conventionally, each type of multi-value conversion means used to determine whether or not each dot is formed is one type. For example, even if a multi-valued means using the error diffusion method and the dither method is prepared, it is usual to select and use only one of them for each image data. On the other hand, the image processing apparatus and the like according to the present invention greatly differ in that two or more types of multi-level converting means are used in determining whether or not each dot is formed. The two or more types of multi-value conversion means used here have different properties. Examples of the properties include various properties such as a property that image quality is excellent and a property that high-speed processing is possible. In the image processing apparatus and the like of the present invention, by using two or more types of multi-level quantization means having different properties in this way, it is possible to perform multi-level quantization utilizing the properties of each multi-level quantization means. Conversely, since the image processing can be performed while complementing the drawbacks of each multi-level quantization unit with the other multi-level quantization units, image processing suitable as a whole can be realized. The determination of the presence / absence of dot formation using two or more types of multi-value conversion means as described above may be a part of the dots to be subjected to image processing.
[0017]
In the image processing apparatus,
The multi-value conversion means having the different properties,
First multi-level conversion means for performing multi-level conversion of the three or more values by error diffusion;
Means for determining the presence or absence of formation of at least some of the two or more types of dots and multi-leveling the input image data to two or more values, and And a second multi-level converting means that can assign to the area of the image with higher dispersibility than the error diffusion.
In a predetermined range of gradation values, dot formation is performed by using the result of multi-level quantization by the second multi-level quantization unit with priority over the result of multi-level quantization by the first multi-level quantization unit. The presence or absence can be determined.
[0018]
For example, as one of the multivalue means having different properties, a multivalue means using an error diffusion method is used. This makes it possible to perform multi-value processing utilizing the characteristic of the error diffusion method, which is capable of performing multi-value processing with excellent image quality. On the other hand, when multi-valued conversion of three or more values is performed by error diffusion, as described above with reference to FIG. 18, there is a possibility that some dots have poor dispersibility and are locally aggregated. Therefore, in the above-described image processing apparatus, as the second multi-valued means, a multi-valued means capable of allocating dots with higher dispersiveness than error diffusion is prepared. The presence / absence of dot formation is determined by giving priority to the multi-value conversion means of 2. In this case, the dispersibility of the dots is ensured at the gradation value to which the second multi-level conversion means has priority, and the multi-level conversion excellent in the image quality can be performed by the error diffusion method in the other areas. High image quality multi-leveling can be performed.
[0019]
Here, the first multi-level converting means performs the multi-level processing by an error diffusion method that also reflects a density error generated between the result of the multi-level processing by the second multi-level converting means and the image data. It is desirable to use a means for performing the conversion.
[0020]
As is well known, the error diffusion method performs multi-level conversion while diffusing a density error generated between a multi-level conversion result and a gradation value of image data in a multi-level processed pixel to unprocessed pixels. As a result, local density errors can be minimized. Here, in the image processing apparatus of the present invention, when the error diffusion method is applied as the first multi-valued means, the density error generated in the pixel for which the presence or absence of the dot is determined by the first multi-valued means. It is also possible to adopt a mode in which only the light is diffused. On the other hand, as described above, it is also possible to apply the error diffusion method in such a manner that the density error generated by the second multi-level converting means is also reflected.
[0021]
If the error diffusion method is applied in the latter mode, the local density error including the density error generated by the second multi-level quantization unit can be minimized, and higher quality image processing is realized. be able to. In particular, it is possible to appropriately eliminate the density error in the vicinity of the boundary between the area where the multi-level quantization is performed by the second multi-level quantization unit and the area where the multi-level quantization is performed by the error diffusion method. The effect of improving image quality is great. Further, the effect of improving the image quality is also great in a region where the multi-level conversion by the second multi-level conversion unit and the multi-level conversion by the error diffusion method are mixed in a fine cycle.
[0022]
In the image processing apparatus of the present invention, various means can be considered as the multi-value conversion means having higher dispersibility than the error diffusion method. For example, the second multi-level conversion means may be a means for performing multi-level conversion by a dither method.
[0023]
The multi-value conversion means based on the dither method determines dot formation based on a magnitude relationship between a threshold value specified for each pixel by a so-called dither matrix and a gradation value of image data. As the threshold value is smaller, dots are more likely to be formed. Therefore, by using a dither matrix in which the dispersibility of the smaller threshold value is increased, the dispersibility of the dots can be ensured. Examples of the dither matrix that ensures such dispersibility include a so-called bull-noise mask type dispersion matrix.
[0024]
Further, as another multivalued means having high dot dispersibility, the second multivalued means includes:
Storage means for storing a relationship between the tone value of the image data and a predetermined parameter relating to the dispersibility of dots determined to be formed by the second multi-level converting means;
A second image data generating unit that generates second image data from the image data by converting a gradation value of the image data into the predetermined parameter with reference to the stored relationship;
The second image data may be multivalued by error diffusion and error diffusion means for determining whether or not the dot is formed by error diffusion.
[0025]
In the above-described method, the error diffusion method is used as the second multi-level converting means. However, while the error diffusion method used as the first multi-level conversion means performs multi-level conversion based on image data, the error diffusion method as the second multi-level conversion means is generated from image data. The difference is that the image data is the second image data. As described above, the second image data is data obtained by changing the gradation value of the image data to a predetermined parameter related to the dot dispersion. In the error diffusion method, when binarization is performed, sufficient dispersibility is ensured. In the above-described image processing apparatus, since the on / off determination of a specific dot for which dispersibility is to be ensured, that is, binarization is performed by using the above parameters, the dispersibility of the dot can be ensured. . As the predetermined parameter related to the dot dispersibility, for example, a recording rate of each dot set for each gradation value can be used.
[0026]
In the above-described image processing apparatus, the image processing apparatus includes, as the multi-level conversion unit, a first multi-level conversion unit based on an error diffusion method, and a second multi-level conversion unit having higher dot dispersion than the error diffusion method. The multi-level conversion means determines whether or not dots among the two or more types of dots including dots whose dispersibility in the image area significantly affects the image quality after multi-level conversion are formed. It may be a means for performing multi-value conversion of a value or more.
[0027]
According to such an image processing apparatus, of the two or more types of dots for which the presence or absence of dot formation is to be determined, at least the dots whose dispersibility affects the image quality are determined by the second multi-level quantization unit. Value conversion can be performed. The dispersibility of such dots can be ensured, and the image quality after multi-leveling can be improved. At the same time, other dots can be multi-valued only by the error diffusion method without performing the second multi-value conversion means. By doing so, it is also possible to quickly perform processing for these dots.
[0028]
Examples of the dots whose dot dispersibility affects the image quality include dots having a high density per unit area. Specifically, there are a dot having a large diameter, a dot formed by using a high-density ink, a dot which is to be formed on the same pixel a plurality of times, and the like.
[0029]
Further, in the image processing apparatus, the image processing apparatus includes, as the multi-level converting means, a first multi-level converting means based on an error diffusion method, and a second multi-level converting means having higher dot dispersibility than the error diffusion method.
The predetermined gradation value in which the result of the multi-level quantization by the second multi-level quantization unit is prioritized is the multi-valued dot dispersibility for which the presence or absence of formation is determined by the second multi-level quantization unit. It can be a gradation value that includes a gradation value that significantly affects the image quality after image formation.
[0030]
In this case, the dot multiplicity is preferentially used for the tone value at which the dot multiplicity affects the image quality, so that the dot multiplicity is ensured. As a result, it is possible to perform high-quality multi-value quantization. The gradation value at which the dot dispersibility affects the image quality is, for example, a gradation value at which recording of the dot is started.
[0031]
Furthermore, in this case,
At least one of the dots whose presence / absence can be determined by both the first multi-level quantization means and the second multi-level quantization means in at least some of the predetermined gradation values. It is preferable that the probability of formation by the second multi-level quantization means is set higher than the probability of formation by the first multi-level quantization means.
[0032]
By doing so, of the dots formed at the gradation values to which the second multi-level quantization means has priority, the dots formed in accordance with the determination by the second multi-level conversion means become dominant. The dispersibility of dots can be ensured more reliably.
[0033]
In the image processing device of the present invention,
As multi-value conversion means having different properties,
First multi-level conversion means for performing multi-level conversion of the three or more values by error diffusion;
With respect to at least some of the two or more types of dots, the first multi-level conversion unit controls the probability of forming the dots as a whole so as to maintain continuity with respect to changes in tone values of the image data. Two types of multi-level conversion means including a second multi-level conversion means capable of determining the formation of the dot with a probability complementing a change in the probability of a determination to be made;
At least in the gradation values at which the dots are formed, the presence / absence of dot formation may be determined by preferentially using the second multi-value processing means over the first multi-value processing means. it can.
[0034]
In such an image processing apparatus, as one of the multivalued means having different properties, a multivalued means using an error diffusion method is used. This makes it possible to perform multi-value processing utilizing the characteristic of the error diffusion method, which is capable of performing multi-value processing with excellent image quality. On the other hand, when multi-valued conversion of three or more values is performed by error diffusion, as described above with reference to FIG. 13, there is a possibility that a portion where the dot recording rate sharply changes with respect to the gradation value may occur. is there. Therefore, in the above-described image processing apparatus, the first multi-level converting means serves as the second multi-level converting means so that the probability of forming the dot as a whole maintains continuity with respect to a change in the gradation value of the image data. A second multi-level converting means capable of determining the formation of the dot with a probability complementing a change in the probability of making a determination to be formed by the converting means is prepared, and the second multi-level converting means is given priority. The presence or absence of dot formation is determined. This makes it possible to maintain the continuity of the dot recording rate as a whole by the complementing action of the second multi-level quantization means, and to perform multi-level quantization with excellent image quality.
[0035]
The probability that complements the change in the probability that the first multi-level conversion unit makes a determination to form is, for example, the second value in the case of a tone value at which the dot recording rate by the first multi-level conversion unit sharply decreases. Is set so that the dot recording rate by the multi-level converting means is increased. As the second multi-value means, various multi-value means such as a dither method and an error diffusion method can be applied. In this case, it is desirable to use the second image data generated by converting the gradation value of the image data into the dot recording rate by the second multi-level converting unit. Further, in the image processing apparatus, it is needless to say that it is preferable to reflect the result of the multi-level quantization by the second multi-level quantization unit in the error diffusion method as the first multi-level quantization unit.
[0036]
In the image processing device of the present invention,
Dither multi-leveling means for determining whether or not each dot is formed by a dither method for at least some of the two or more types of dots;
When it is determined that any dot should not be formed by the dither multi-level converting means, the two or more types of dots including the dot which is a determination target of the formation by the dither multi-level converting means are subjected to error diffusion. An error diffusion multi-leveling means for determining whether or not each dot is formed may be provided.
[0037]
In such an image processing apparatus, the presence / absence of dot formation is determined by using two multivalued means having different properties, namely, a dither method and an error diffusion method. Basically, the dither method is used with priority, and the multi-value conversion by the error diffusion method is performed only when it is determined that a dot is not formed by the dither method. As described above, the dither method has characteristics such as the ability to secure the dispersibility of dots. Therefore, according to the above-described image processing apparatus, the image processing apparatus ensures high-quality image processing by securing the dispersibility of dots. It can be performed. Further, in the above image processing apparatus, it is needless to say that it is preferable that the error diffusion method reflects the result of the multi-value quantization by the dither method.
[0038]
Further, in the image processing apparatus of the present invention,
Storage means for storing, for at least some of the two or more types of dots, the relationship between the tone value of image data and the recording rate of the dots;
A second image data generating unit configured to generate a second image data from the image data by obtaining a recording rate of the dot according to a gradation value of the image data with reference to the relationship;
First error diffusion multi-valued means for multi-valued the second image data by error diffusion to determine whether or not at least some of the dots are formed;
When the first error diffusion multi-value generating means determines that no dot should be formed, the two types including the dot subjected to the formation determination by the first error diffusion multi-value converting means are used. The above-mentioned dots may be provided with a second error diffusion multi-value means for judging whether or not each dot is formed by converting the image data into multi-values by error diffusion.
[0039]
According to such an image processing apparatus, multi-level processing is performed using multi-level processing by error diffusion in two stages. The above-described first error diffusion is to multi-value the second image data set based on the dot recording rate, and the second error diffusion is to multi-value the input image data. is there. As described above, when the second image data is multi-valued, multi-valued processing can be performed while ensuring dot dispersibility. Therefore, according to the image processing apparatus, high-quality image processing is realized as a whole. can do. Further, in the above image processing apparatus, it is needless to say that it is preferable to reflect the result of the multi-level quantization by the first error diffusion method in the second error diffusion method.
[0040]
As an invention using the various image processing apparatuses described above, there is a printing apparatus that forms dots according to data processed by the image processing apparatus and prints an image, as described below.
[0041]
The printing apparatus of the present invention
With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. A printing apparatus that prints an image according to the image data by forming respective dots on a print medium in accordance with the result of the multi-value processing,
Image data input means for inputting the image data,
Two or more types of multi-value quantization means capable of determining the presence or absence of formation of at least some of the two or more types of dots;
Dot forming means for forming a dot on a print medium according to the determination result of the presence or absence of dot formation by the multi-valued means,
According to a predetermined parameter related to the property of the multi-level converting means, one of the multi-level converting means is preferentially used to determine whether or not to form a dot and print an image. Is the gist.
[0042]
In such a printing device,
The multi-value conversion means having the different properties,
First multi-level conversion means for performing multi-level conversion of the three or more values by error diffusion;
Means for determining whether or not at least some of the two or more types of dots are formed from the input image data and performing multi-level conversion to two or more values. Two types of multi-level converting means, comprising: a second multi-level converting means capable of assigning dots to the image area with higher dispersiveness than error diffusion;
In a predetermined range of gradation values, dot formation is performed by using the result of multi-level quantization by the second multi-level quantization unit with priority over the result of multi-level quantization by the first multi-level quantization unit. An image can be printed by determining the presence or absence.
[0043]
According to these printing apparatuses, since the above-described image processing apparatus is internally provided, high-quality image processing can be performed, and high-quality printing can be realized. The printer used here is a so-called multi-value printer capable of forming two or more types of dots. The two or more types of dots are dots having different densities per unit area. For example, dots having different diameters, dots formed with inks having different densities, and dots to be formed on the same pixel a plurality of times are planned. And the like.
[0044]
The above-described image device of the present invention can also be configured by realizing the above-described multi-value conversion by a computer, and thus the present invention can also take an aspect as a recording medium on which such a program is recorded.
[0045]
The recording medium of the present invention
With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. A computer-readable recording medium for recording a program for performing,
For at least some of the two or more types of dots, a function of determining the presence or absence of the formation of each of the dots by two or more types of multi-value bins having different properties;
A function of judging the presence or absence of dot formation by giving priority to the result of one of the multi-levels in accordance with predetermined parameters related to the two or more types of multi-levels. This is a recording medium on which a program to be realized is recorded.
[0046]
In such a recording medium,
A first multi-value function for determining whether or not each dot is formed by a dither method for at least some of the two or more types of dots;
When it is determined that none of the dots should be formed by the first multi-level conversion function, the two or more types of dots including the dot that has been determined to be formed by the first multi-level conversion function Alternatively, the recording medium may be a recording medium on which a program for realizing a second multi-value function for determining whether or not each dot is formed by error diffusion is recorded.
[0047]
Further, for at least some of the two or more types of dots, data storing the relationship between the tone value of image data and the recording rate of the dots,
A function of generating second image data from the image data by obtaining a recording rate of the dot in accordance with a gradation value of the image data with reference to the data;
A first multi-value function that multi-values the second image data by error diffusion and determines whether or not at least some of the dots are formed;
When it is determined that none of the dots should be formed by the first multi-level conversion function, the two or more types of dots including the dot that has been determined to be formed by the first multi-level conversion function Alternatively, a recording medium may be provided in which a program for realizing a second multi-level function of multiplying the image data by error diffusion and determining whether or not each dot is formed is recorded.
[0048]
The above-described image processing apparatus of the present invention can be realized by executing the program recorded on each of the recording media by the computer. Examples of the storage medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, and an internal storage device of a computer (a memory such as a RAM or a ROM). ) And external storage devices, such as various computer readable media. The present invention also includes an aspect as a program supply device that supplies a computer program for realizing the multi-value function of the image processing device to a computer via a communication path.
[0049]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples.
(1) Device configuration
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus and a printing apparatus according to an embodiment of the present invention. As shown, the scanner 12 and the color printer 22 are connected to the computer 90. When a predetermined program is loaded and executed on the computer 90, the computer 90 functions as an image processing apparatus, and also functions as a printing apparatus together with the printer 22. The computer 90 includes the following units interconnected by a bus 80, centering on a CPU 81 that executes various arithmetic processes for controlling operations related to image processing according to a program. The ROM 82 previously stores programs and data necessary for the CPU 81 to execute various arithmetic processes, and the RAM 83 temporarily reads and writes various programs and data necessary for the CPU 81 to execute various arithmetic processes. Memory. The input interface 84 controls input of signals from the scanner 12 and the keyboard 14, and the output interface 85 controls output of data to the printer 22. The CRTC 86 controls signal output to the CRT 21 capable of color display, and the disk controller (DDC) 87 controls transmission and reception of data with the hard disk 16, the flexible drive 15, or a CD-ROM drive (not shown). The hard disk 16 stores various programs loaded and executed in the RAM 83 and various programs provided in the form of device drivers.
[0050]
In addition, a serial input / output interface (SIO) 88 is connected to the bus 80. The SIO 88 is connected to the modem 18, and is connected to the public telephone line PNT via the modem 18. The computer 90 is connected to an external network via the SIO 88 and the modem 18. By connecting to a specific server SV, it is also possible to download a program required for image processing to the hard disk 16. In addition, it is also possible to load a necessary program from a flexible disk FD or a CD-ROM and cause the computer 90 to execute the program.
[0051]
FIG. 2 is a block diagram illustrating a software configuration of the printing apparatus. In the computer 90, an application program 95 operates under a predetermined operating system. A video driver 91 and a printer driver 96 are incorporated in the operating system, and image data FNL to be transferred to the printer 22 is output from the application program 95 via these drivers. An application program 95 for retouching an image reads an image from the scanner 12 and displays the image on the CRT display 21 via the video driver 91 while performing predetermined processing on the image. The data ORG supplied from the scanner 12 is original color image data ORG read from a color original and composed of three color components of red (R), green (G), and blue (B).
[0052]
When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives the image information from the application program 95, and receives the image information from the application program 95 in a signal that can be processed by the printer 22 (here, each color of cyan, magenta, yellow, and black). Into a multi-valued signal). In the example shown in FIG. 2, the printer driver 96 includes a resolution conversion module 97, a color correction module 98, a color correction table LUT, a halftone module 99, and a rasterizer 100.
[0053]
The resolution conversion module 97 serves to convert the resolution of the color image data handled by the application program 95, that is, the number of pixels per unit length into a resolution that can be handled by the printer driver 96. Since the image data whose resolution has been converted in this manner is still image information of three colors of RGB, the color correction module 98 refers to the color correction table LUT and uses the cyan (C) and magenta colors used by the printer 22 for each pixel. (M), yellow (Y) and black (K). The color-corrected data has a gradation value in a width of, for example, 256 gradations. The halftone module 99 executes a halftone process for expressing such gradation values in the printer 22 by forming dots in a dispersed manner. The halftone module 99 in the present embodiment is included in at least the image processing device in the present invention. The image data processed in this manner is rearranged by the rasterizer 100 in the order of data to be transferred to the printer 22, and output as final image data FNL. In the present embodiment, the printer 22 only plays a role of forming dots in accordance with the image data FNL, and does not perform image processing. However, it goes without saying that these processes may be performed by the printer 22.
[0054]
Next, a schematic configuration of the printer 22 will be described with reference to FIG. As shown in the drawing, the printer 22 includes a mechanism for transporting a sheet P by a paper feed motor 23, a mechanism for reciprocating a carriage 31 in the axial direction of a platen 26 by a carriage motor 24, and a print head mounted on the carriage 31. The control circuit 40 controls the paper feed motor 23, the carriage motor 24, the print head 28, and the operation panel 32 to exchange signals with each other. .
[0055]
The mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 includes an endless drive belt between a carriage shaft 24 and a slide shaft 34 laid parallel to the platen 26 and holding the carriage 31 in a slidable manner. A pulley 38 on which the carriage 36 is extended and a position detection sensor 39 for detecting the origin position of the carriage 31 are provided.
[0056]
The carriage 31 can be mounted with a cartridge 71 for black ink (Bk) and a cartridge 72 for color ink containing three color inks of cyan (C), magenta (M), and yellow (Y). . A total of four ink discharge heads 61 to 64 are formed on the print head 28 below the carriage 31, and at the bottom of the carriage 31, an introduction pipe 67 (which guides ink from the ink tank to each color head). (See FIG. 8). When the cartridge 71 for black (Bk) ink and the cartridge 72 for color ink are mounted on the carriage 31 from above, the introduction pipe 67 is inserted into the connection hole provided in each cartridge, and the ejection heads 61 to 64 from each ink cartridge. Can be supplied to the printer.
[0057]
A mechanism for discharging ink and forming dots will be described. FIG. 4 is an explanatory diagram showing a schematic configuration inside the ink discharge head 28. When the ink cartridges 71 and 72 are mounted on the carriage 31, the ink in the ink cartridge is sucked out through the introduction pipe 67 by utilizing the capillary phenomenon as shown in FIG. The print heads 28 are guided to the respective color heads 61 to 64 of the print head 28. When the ink cartridge is mounted for the first time, the operation of sucking ink into the heads 61 to 64 of the respective colors is performed by a dedicated pump. In this embodiment, a pump for suction and a cap for covering the print head 28 at the time of suction are provided. The illustration and description of such a configuration are omitted.
[0058]
As will be described later, the heads 61 to 64 for each color are provided with 48 nozzles Nz for each color (see FIG. 6), and each of the heads 61 to 64 is one of the electrostrictive elements for each nozzle. An excellent piezo element PE is arranged. FIG. 5 shows the structure of the piezo element PE and the nozzle Nz in detail. As shown in the upper part of FIG. 5, the piezo element PE is installed at a position in contact with the ink passage 68 that guides the ink to the nozzle Nz. As is well known, the piezo element PE is an element that distorts the crystal structure due to the application of a voltage and converts electro-mechanical energy very quickly. In the present embodiment, by applying a voltage having a predetermined time width between the electrodes provided at both ends of the piezo element PE, the piezo element PE expands by the voltage application time as shown in the lower part of FIG. One side wall 68 is deformed. As a result, the volume of the ink passage 68 contracts in accordance with the expansion of the piezo element PE, and the ink corresponding to the contraction is discharged as particles Ip at a high speed from the tip of the nozzle Nz. Printing is performed by the permeation of the ink particles Ip into the paper P mounted on the platen 26.
[0059]
FIG. 6 is an explanatory diagram showing the arrangement of the inkjet nozzles Nz in the ink ejection heads 61 to 64. The arrangement of these nozzles consists of four sets of nozzle arrays that eject ink for each color, and 48 nozzles Nz are arranged in a staggered manner at a constant nozzle pitch k. The positions of the nozzle arrays in the sub-scanning direction coincide with each other. Note that the 48 nozzles Nz included in each nozzle array need not be arranged in a staggered manner, and may be arranged on a straight line. However, the arrangement in a staggered manner as shown in FIG. 6 has the advantage that the nozzle pitch k can be easily set small in manufacturing.
[0060]
Although the printer 22 of the present invention includes the nozzles Nz having a constant diameter as shown in FIG. 6, three types of dots having different diameters can be formed using the nozzles Nz. This principle will be described. FIG. 7 is an explanatory diagram showing the relationship between the driving waveform of the nozzle Nz when ink is ejected and the ink Ip ejected. The drive waveform indicated by a broken line in FIG. 7 is a waveform when a normal dot is ejected. In the section d2, once a voltage lower than the reference voltage is applied to the piezo element PE, the piezo element PE is deformed in the direction of increasing the cross-sectional area of the ink passage 68, contrary to the description with reference to FIG. Therefore, as shown in the state A of FIG. 7, the ink interface Me called a meniscus is in a state recessed inside the nozzle Nz. On the other hand, when a low voltage is suddenly applied as shown in the section d2 using the drive waveform shown by the solid line in FIG. 7, the meniscus is greatly depressed inward as compared with the state A as shown in the state a. Next, when the voltage applied to the piezo element PE is made positive (section d3), ink is ejected based on the principle described above with reference to FIG. At this time, large ink droplets are ejected as shown in states B and C from the state where the meniscus is not much depressed inward (state A). As shown in state c, a small ink droplet is ejected.
[0061]
As described above, the dot diameter can be changed according to the change rate when the drive voltage is lowered (section d1, d2). In this embodiment, a driving waveform for forming a small dot IP1 having a small dot diameter and a medium dot IP2 having a second dot diameter are determined based on such a relationship between the driving waveform and the dot diameter. Two types of drive waveforms for forming are prepared. FIG. 8 shows a driving waveform used in this embodiment. The drive waveform W1 is a waveform for forming a small dot IP1, and the drive waveform W2 is a waveform for forming a medium dot IP2. As shown in FIG. 8, as the dot diameter increases, the flying speed increases. By properly using these drive waveforms, it is possible to form two types of small and medium dots from the nozzle Nz having a fixed nozzle diameter. In the printer 22 of the present embodiment, these drive waveforms are output continuously and periodically in the order of W1 and W2 as the carriage 31 moves.
[0062]
In addition, a large dot can be formed by forming a dot using both the drive waveforms W1 and W2 in FIG. This situation is shown in the lower part of FIG. The lower part of FIG. 8 shows a state from the ejection of the small and medium dot ink droplets IPs and IPm ejected from the nozzles to the paper P. When two types of small and medium dots are formed using the driving waveform of FIG. 8, the ink droplet IP is ejected vigorously because the change amount of the piezo element PE is larger in the medium dot. Due to such a difference in the flying speed of the ink, when the carriage 31 moves in the main scanning direction and the small dots and the medium dots are continuous, the scanning speed of the carriage 31 and the ejection timing of both dots are set to be different from those of the carriage 31. By adjusting the distance according to the distance between the sheets P, both ink droplets can reach the sheet P at the same timing. In this embodiment, a large dot having the largest dot diameter is thus formed from the two types of driving waveforms in the upper part of FIG.
[0063]
In this embodiment, in order to facilitate control, of the three types of dots formed in this way, two types of large and small dots are used for printing. Naturally, an image may be printed using all three types of dots.
[0064]
Next, an internal configuration of the control circuit 40 of the printer 22 will be described, and a method of driving the head 28 including a plurality of nozzles Nz shown in FIG. 6 will be described. FIG. 9 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown in FIG. 9, inside the control circuit 40, in addition to the CPU 81, the PROM 42 and the RAM 43, a PC interface 44 for exchanging data with the computer 90, the paper feed motor 23, the carriage motor 24, the operation panel 32 and the like. A peripheral input / output unit (PIO) 45 for exchanging signals with the controller, a timer 46 for measuring time, and a driving buffer 47 for outputting dot on / off signals to the heads 61 to 66 are provided. Are interconnected by a bus 48. The control circuit 40 is also provided with a transmitter 51 that outputs a drive waveform (see FIG. 8) at a predetermined frequency and a distributor 55 that distributes the output from the transmitter 51 to the heads 61 to 66 at a predetermined timing. ing. The control circuit 40 receives the dot data processed by the computer 90, temporarily stores the dot data in the RAM 43, and outputs the dot data to the driving buffer 47 at a predetermined timing.
[0065]
A mode in which the control circuit 40 outputs a signal to the heads 61 to 64 will be described. FIG. 10 is an explanatory diagram showing the connection of one nozzle row of the heads 61 to 64 as an example. One nozzle row of the heads 61 to 64 is provided in a circuit in which the driving buffer 47 is on the source side and the distribution output unit 55 is on the sink side, and each piezo element PE constituting the nozzle row has its electrode Is connected to each output terminal of the driving buffer 47, and the other is connected to the output terminal of the distribution output device 55 collectively. As shown in FIG. 10, the drive waveform of the transmitter 51 is output from the distribution output unit 55. When ON / OFF is determined for each nozzle from the CPU 81 and a signal is output to each terminal of the driving buffer 47, only the piezo element PE that has received the ON signal from the driving buffer 47 side is driven according to the driving waveform. You. As a result, the ink particles Ip are simultaneously discharged from the nozzles of the piezo element PE that have received the ON signal from the transfer buffer 47.
[0066]
As shown in FIG. 6, the heads 61 to 64 are arranged along the transport direction of the carriage 31, so that the timing at which each nozzle row reaches the same position with respect to the paper P is shifted. Therefore, the CPU 81 outputs the ON / OFF signal of each dot through the transfer buffer 47 at a necessary timing in consideration of the positional shift of each nozzle of the heads 61 to 64, and outputs the dot of each color. Has formed. Also, as shown in FIG. 6, the output of the on / off signal is controlled in consideration of the fact that each of the heads 61 to 64 also has two rows of nozzles.
[0067]
In the printer 22 having the hardware configuration described above, the carriage 31 is reciprocated by the carriage motor 24 (hereinafter, referred to as main scanning) while the paper P is transported by the paper feed motor 23 (hereinafter, referred to as sub-scanning). The piezo elements PE of the respective color heads 61 to 64 of the print head 28 are driven to discharge the respective color inks, thereby forming dots to form multi-color images on the paper P.
[0068]
In the present embodiment, as described above, the printer 22 having the head that discharges ink using the piezo element PE is used. However, a printer that discharges ink by another method may be used. For example, the present invention may be applied to a printer of a type in which a heater arranged in an ink passage is energized and ink is ejected by bubbles generated in the ink passage.
[0069]
(2) Dot formation control
Next, a control process of dot formation in this embodiment will be described. FIG. 11 shows the flow of the dot formation control processing routine. This is a process executed by the CPU 81 of the computer 90.
[0070]
When this process is started, the CPU 81 inputs image data (step S100). This image data is data passed from the application program 95 shown in FIG. 2 and includes 256 gradation values of 0 to 255 for each of the R, G, and B colors for each pixel constituting the image. Is data having The resolution of this image data changes according to the resolution of the original image data ORG and the like.
[0071]
The CPU 81 converts the resolution of the input image data into a resolution for printing by the printer 22 (step S105). If the image data is lower than the print resolution, resolution conversion is performed by generating new data between adjacent original image data by linear interpolation. Conversely, if the image data is higher than the print resolution, resolution conversion is performed by thinning out the data at a fixed rate. Note that the resolution conversion processing is not essential in the present embodiment, and printing may be executed without performing such processing.
[0072]
Next, the CPU 81 performs a color correction process (step S110). The color correction process is a process of converting image data consisting of R, G, and B tone values into tone value data of each of the C, M, Y, and K colors used by the printer 22. This processing is performed by using a color correction table LUT (see FIG. 2) storing combinations of C, M, Y, and K for expressing colors composed of respective combinations of R, G, and B on the printer 22. . Various well-known techniques can be applied to the processing itself for color correction using the color correction table LUT. For example, processing by interpolation calculation (the technique described in JP-A-4-144481) can be applied.
[0073]
The CPU 81 performs multi-value processing on the image data that has been color-corrected in this manner (step S200). Multi-value conversion means that the gradation value (256 gradations in this embodiment) of the original image data is converted into a gradation value that can be expressed by the printer 22 for each pixel. As will be described later, in the present embodiment, multi-level conversion to three gradations of “no dot formation”, “small dot formation”, and “large dot formation” is performed. May be performed. The contents of the multi-value processing in this embodiment will be described with reference to FIG.
[0074]
In the multi-value processing, the CPU 81 inputs the image data CD (step S205). The input image data CD is data that has been subjected to color correction processing (step S110 in FIG. 11) and has 256 gradations for each of C, M, Y, and K colors. The level data CDL is generated for this data (step S210).
[0075]
The setting of the level data CDL will be described with reference to FIG. FIG. 13 is a graph showing the relationship between the recording rate of each dot and the gradation value. The curve SD in FIG. 13 shows the recording rate of small dots, and the curves LD1 and LD2 show the recording rate of large dots. The curve LD3 will be described later. As will be described later, the presence / absence of formation of a large dot is determined by two types of methods, a dither method and an error diffusion method. A curve LD1 corresponds to a recording rate of a large dot by the error diffusion method, and a curve LD2 corresponds to a recording rate of the dither method. It should be noted that the dot recording rate refers to the ratio of dots formed in an area having a certain gradation value to the pixels in the area when the area is formed.
[0076]
The level data CDL refers to data obtained by converting the dot recording rate into 256 levels of 0 to 255. In step S210, level data corresponding to the gradation value is read from the curve LD2. For example, as shown in FIG. 13, when the gradation value of the image data CD is gr, the level data CDL is obtained as ld using the curve LD2. The reason why the data corresponding to the curve LD2 is read is that the dot formation is determined by the dither method based on the level data as described later. Actually, the curve LD2 is stored in the ROM 82 as a one-dimensional table, and the level data is obtained by referring to the table. In this embodiment, the level data CDL is set to be 0 when the gradation value ≤ 32 and the gradation value ≥ dp1.
[0077]
Next, the level data CDL thus set is compared with the threshold value TH (step S212). The on / off determination of the dots is performed by the so-called dither method. As the threshold value TH, a different value is set for each pixel by a so-called dither matrix. In the present embodiment, a blue noise mask type matrix in which values 0 to 255 appear evenly in 64 × 64 square pixels is used.
[0078]
FIG. 14 shows the concept of dot on / off determination by the dither method. For convenience of illustration, only some pixels are shown. As shown in FIG. 14, each pixel of the level data CDL is compared with the corresponding portion of the dither table. When the level data CDL is equal to or larger than the threshold value indicated in the dither table, the dot is turned on, and when the level data CDL is smaller, the dot is turned off. In FIG. 14, the hatched pixels indicate the pixels that turn on the dots.
[0079]
If the level data CDL is larger than the threshold value TH in step S212, the CPU 81 once determines that the large dot should be turned on, and substitutes the value 2 for the variable CDR indicating the result value (step S255). When the result value CDR is the value 2, the signal for ejecting ink is transferred to the driving buffer 47 with both the driving waveforms W1 and W2 shown in FIG. 8, and a large dot is formed accordingly. Become like By the processing described above (the processing indicated by DI in FIG. 12), ON / OFF of the formation of large dots is determined using the dither method.
[0080]
On the other hand, when the level data CDL is smaller than the threshold value TH in step S212, it is determined that a large dot should not be formed, and the process proceeds to the next process. The next process is a process indicated by ED in FIG. 12, and is a multi-value process by an error diffusion method.
[0081]
In this process, the CPU 81 generates the diffusion error correction data CDX (step S230). In the error diffusion process, an error in the gradation expression generated for the processed pixel is allocated in advance by assigning a predetermined weight to the pixels around the pixel. Therefore, in step S235, the corresponding error is read out and this is read out. From the pixel to be processed. FIG. 15 exemplifies how to assign this error to which pixel around the pixel PP of interest and how much weight is assigned to the neighboring pixels. The density error is given a predetermined weight (１ ／, ８) for several pixels in the scanning direction of the carriage 31 with respect to the target pixel PP, and for several adjacent pixels behind the paper P in the conveyance direction. , 1/16). The error diffusion processing will be described later in detail.
[0082]
The magnitude of the diffusion error correction data CDX generated in this way is compared with the first threshold value TH0 (step S235). If the data CDX is smaller than the threshold value TH0, a dot is added to the value CDR representing the multi-level quantization result. A value of 0, which means not forming, is substituted (step S240). The threshold value TH0 is a value serving as a reference for determining whether or not to form a dot as described above. This threshold value TH0 can be set to any value. In this embodiment, the threshold value TH0 is set in accordance with the density evaluation value of each dot so as to realize the dot recording rates SD and LD1 shown in FIG. Have been.
[0083]
If the correction data CDX is equal to or greater than the first threshold value TH0, then the magnitude of the correction data CDX is compared with the second threshold value TH1 (step S245). If the correction data CDX is smaller than the second threshold value TH1, a value 1 meaning the formation of a small dot is substituted for the value CDR representing the multi-value quantization result (step S250). Similar to the threshold value TH0, the threshold value TH1 is set so as to realize the dot recording rate SD shown in FIG.
[0084]
If the correction data CDX is equal to or larger than the second threshold value TH1, the determination in step S212 that a large dot should not be formed is reversed, and the value CDR representing the multi-value quantization result is a value 2 indicating the formation of a large dot. Is substituted (step S255). By the above-described processing, one of the states “dot off”, “small dot formation”, and “large dot formation” is assigned to each pixel, and ternarization is performed. As for “formation of large dots”, there are two types of cases, as described above, where the formation is determined by the dither method DI and when the formation is determined by the error diffusion method ED. “Small dot formation” can be assigned only by the error diffusion method, but a small dot may be determined by both the dither method DI and the dither method DI. In the present embodiment, the ternarization is performed by the above processing. However, when the number of types of dots that can be formed increases and it is necessary to perform more multi-level conversion, the threshold value is increased by increasing the threshold value. Can be processed.
[0085]
Next, the CPU 81 executes a process of calculating an error caused by the multi-value conversion and diffusing the error to peripheral pixels (step S260). For a large dot, the determination of ON may be made by the dither method. Even in this case, the calculation and diffusion of the error are performed in the same manner as when the determination of ON is made by the error diffusion method. Even in such a case, by calculating an error or the like, a local density error generated for a pixel that has been determined to be on by the dither method can also be eliminated by surrounding pixels. This is because an error between the density expressed based on the image and the density to be expressed based on the original image data can be minimized.
[0086]
The error refers to a value obtained by subtracting the tone value of the original image data from the evaluation value of the density represented by each dot after multi-value conversion. For example, considering a pixel having a gradation value of 255 in the original image data, the evaluation value of the density by forming a large dot is equivalent to the gradation value of 255, and the evaluation value of the density by forming small dots is equivalent to a gradation value of 128. The density evaluation value when no dot is formed is equivalent to a gradation value of 0. When it is determined that a large dot is to be formed for this pixel (CDR = 2), no error occurs because the tone value of the original image data and the density evaluation value expressed are both equal to 255. . On the other hand, when it is determined that a small dot is to be formed (CDR = 1), an error of Err = 128-255 = -127 occurs. If no dot is formed, the error Err = −255.
[0087]
The error calculated in this way is diffused to peripheral pixels at the rate shown in FIG. For example, when an error corresponding to the gradation value 4 is calculated in the pixel PP of interest, an error corresponding to the gradation value 1 which is ４ of the error is diffused to the adjacent pixel P1. Will be. Similarly, errors are diffused at other pixels in the ratio shown in FIG. The error thus diffused is reflected on the image data CD in step S230 described above, and the diffusion error correction data CDX is generated. When the processing for all pixels is completed by repeating the above (step S265), the CPU 81 once ends the multi-value processing by error diffusion, and returns to the dot formation control processing routine (FIG. 11). By the above processing, any of the values 0 to 2 is assigned to the result value CDR for each pixel.
[0088]
Next, the CPU 81 performs rasterization (step S300). This means that the data for one raster is rearranged in the order in which the data is transferred to the head of the printer 22. There are various modes in a recording method in which the printer 22 forms a raster. The simplest mode is one in which all dots of each raster are formed by one forward movement of the head. In this case, data for one raster may be output to the head in the processing order. Another mode is so-called overlap. For example, this is a recording method in which dots of each raster are formed every other dot in the first main scan, and the remaining dots are formed in the second main scan. In this case, each raster is formed by two main scans. When such a recording method is adopted, it is necessary to transfer data obtained by picking up every other dot of each raster to the head. There is a so-called bidirectional recording as another recording mode. This is to form dots not only during the forward movement of the head but also during the backward movement. When such a recording mode is adopted, it is necessary to reverse the transfer order of the data for the forward movement and the data for the backward movement. The process in step S240 creates data to be transferred to the head according to the recording method performed by the printer 22. When data that can be printed by the printer 22 is thus generated, the CPU 81 outputs the data and transfers the data to the printer 22 (step S310).
[0089]
In the image processing apparatus and the printing apparatus described above, dot formation is determined for both large dots by the dither method (the processing indicated by DI in FIG. 12) and the error diffusion method (the processing indicated by ED in FIG. 12). I do. At this time, the determination by the dither method is performed with priority. In the dither method, the dispersibility of dots can be ensured by setting the dither matrix.Therefore, the image processing device described above takes advantage of the characteristics of the error diffusion method, which has excellent image quality, while ensuring the separability of large dots. It is possible to carry out multi-value processing. As a result, very high-quality image processing can be realized as a whole. The printing apparatus according to the present embodiment prints an image based on the result of such high-quality image processing, so that high-quality printing can be performed.
[0090]
In the present embodiment, the error diffusion method that reflects the determination result in the dither method is performed. As a result, a local density error including a density error generated by the dither method can be minimized, and higher quality image processing can be realized. In particular, in the vicinity of a boundary between a region where multi-level quantization is performed mainly by the dither method and a region where multi-level quantization is performed by the error diffusion method, density errors can be appropriately eliminated, and image quality is improved. Great effect. Further, the effect of similarly improving image quality is great even in a region where the multi-value processing by the dither method and the multi-value processing by the error diffusion method are mixed at a fine cycle.
[0091]
In the present embodiment, various measures are taken in order to more appropriately obtain the above-described effects. For example, in the range of gradation values 32 to gr, the recording rate of large dots determined by the dither method (curve DL2 in FIG. 13) is the recording rate of large dots determined by the error diffusion method (curve DL1 in FIG. 13). It is set to exceed. By doing so, the ratio of the dots determined to be on by the dither method in the large dots formed by this gradation value increases, so that the dispersibility of the large dots can be more reliably secured as a whole. . As described above, the range of the gradation values that makes the dot recording rate by the dither method higher than the dot recording rate by the error diffusion method can be basically set to any range. In this embodiment, particularly, the gradation value is set so that the dispersibility of large dots affects the image quality. That is, the gradation value at which large dots begin to be sparsely formed is used. By doing so, the image quality can be effectively improved.
[0092]
In the above-described embodiment, the recording rate of the large dot (DL2 in FIG. 13) by the dither method is set to the value 0 in the range of “image data CD ≦ gradation value 32” and “image data CD ≧ gradation value dp1”. Is set to In this way, with such a gradation value, on / off determination of a large dot is performed only by the error diffusion method. Conversely, on / off determination of a large dot is performed by both the dither method and the error diffusion method in the range of “gradation value 32 <image data CD <gradation value dp1”, that is, the large dot This is a gradation value whose formation affects the image quality. In this embodiment, by limiting the area where large dot on / off determination is performed by the two multi-level converting means to gradation values having a large effect on image quality, a reduction in processing speed is prevented, and It realizes image processing that makes full use of the error diffusion characteristics that are originally excellent in image quality. Needless to say, such processing is provided in the flowchart of FIG. 12 by providing between the step S205 and the step S210 a process of determining whether or not a large dot is to be turned on / off by the dither method. However, the method of setting the recording rate of large dots to a value of 0 as in this embodiment has an advantage that the same effect can be easily obtained.
[0093]
In the present embodiment, the above-described two ideas are considered by considering the range of the gradation value of “gradation value 32 <image data CD <gradation value dp1” as the gradation value at which the dispersibility of large dots affects the image quality. However, it is needless to say that the range of the gradation value can be freely set according to the density of the large dot, the resolution of the image, and the like. Further, in the present embodiment, two types of multi-value conversion means are applied only to large dots, but it is also possible to apply both to small dots as described above. Further, three or more types of multi-value conversion means may be applied.
[0094]
On the other hand, in the present embodiment, the recording rate of large dots by the dither method can be set as a curve LD3 in FIG. The curve LD3 has the same setting as the curve LD2 in the region where the gradation value is equal to or less than the gradation value gr, and has a different setting from the curve LD2 at the gradation value equal to or larger than gr. At a tone value equal to or larger than gr, the large dots which are determined to be on by the error diffusion method in the formed large dots become dominant. As shown by the gradation values dp1 and dp2 in FIG. 13, the recording rate of the large dot for which the ON is determined by the error diffusion method causes a dip in which the recording rate sharply decreases. The curve LD3 is set so that the recording rate of large dots by the dither method is locally increased with such gradation values, so that continuity of the recording rate of large dots can be secured as a whole.
[0095]
According to the image processing apparatus and the printing apparatus that perform on / off determination of a large dot using the recording rate set as described above, the recording rate of the large dot is continuously changed according to a change in the gradation value. Can be. If the recording rate of a large dot changes suddenly, the granularity of an image printed at that gradation value changes suddenly, causing the occurrence of false contours and the like. Since the occurrence of such false contour can be prevented, the image quality can be improved. Since the dip by the error diffusion method changes according to the density evaluation value of each dot, the threshold value used for the on / off determination of each dot, and the like, the dot recording rate by the dither method (curve LD3 in FIG. 13) Is set experimentally or analytically to ensure the continuity of the recording rate of large dots.
[0096]
(3) Second embodiment
Next, an image processing apparatus and a printing apparatus according to a second embodiment of the present invention will be described. The printing apparatus of the second embodiment has the same hardware configuration as the printing apparatus of the first embodiment (see FIGS. 1 to 10). Further, the flow itself of the dot formation control processing routine is the same as that of the first embodiment (see FIG. 11). In the second embodiment, the contents of the multi-value processing are partially different from those of the first embodiment.
[0097]
The contents of the multi-value processing in the second embodiment will be described with reference to the flowchart shown in FIG. In the first embodiment, the dither method (DI in FIG. 12) and the error diffusion method (ED in FIG. 12) are used for large dot on / off determination. In the second embodiment, the error diffusion method is used instead of the dither method. Are used twice (ED1, ED2 in FIG. 16). However, they differ in the data on which the large dot is to be turned on / off. Hereinafter, the contents of the multilevel processing in the second embodiment will be sequentially described including this difference.
[0098]
When this process is started, the CPU 81 inputs the image data CD (step S205), and generates level data CDL based on the image data CD (step S210). The processing so far is the same as in the first embodiment (FIG. 12). In addition, the recording rate of the dots used for creating the level data CDL is the recording rate set by the curve DL2 in FIG. Of course, the recording rate set by the curve DL3 in FIG. 13 may be used.
[0099]
Next, diffusion error correction data CDLX is generated by performing diffusion error correction on the level data CDL (step S214). That is, in the error diffusion method ED2 in the second embodiment, on / off determination of a large dot is performed by the error diffusion method based on the level data CDL. The distribution of the diffusion error is as described above with reference to FIG.
[0100]
The magnitude of the diffusion error correction data CDLX thus generated is compared with a predetermined threshold value TH (step S216). If the correction data CDLX is greater than the threshold value TH, it is determined that a large dot should be formed, and the result value CDR is determined. (Step S220). If the value is smaller than the threshold value TH, it is once determined that a large dot should not be formed, and the value 0 is substituted into the result value CDR (Step S218). The threshold value is set such that a desired large dot recording rate (curve DL2 in FIG. 13) is secured according to the level data CDL.
[0101]
Error calculation and error diffusion are performed based on the result value CDR thus determined (step S222). The error handled here is an error relating to the level data, not an error based on the density evaluation value of the large dot. The level data is synonymous with the dot recording rate. When a large dot is recorded, that is, when the result value CDR = 2, the dot recording rate for that pixel is 100%. It will be in a corresponding state. Therefore, if the level data CDL generated in step S210 is the value ld, and a determination is made to form a large dot, the error at that time is Err = ld-255. The error calculated in this way is allocated to peripheral pixels in the distribution shown in FIG. This processing is the same as in the first embodiment.
[0102]
After the dot on / off determination is once performed on the large dot by the error diffusion method ED2, if the result value CDR is not the value 2, that is, if it is not determined that a large dot should be formed (step S224), On / off determination of each dot is performed by the error diffusion method ED1. The details of this on / off determination are the same as in the first embodiment (see FIG. 12). That is, diffusion error correction data CDX is generated for the image data CD, and ON / OFF of each dot is determined according to the magnitude relationship between the correction data CDX and the predetermined thresholds TH0 and TH1 (steps S230 to S255). . After the ON / OFF determination of each dot is completed, error calculation and error diffusion are executed (step S260).
[0103]
If it is determined by the error diffusion method ED2 that a large dot is to be formed, the error calculation and error diffusion in step S260 are performed without performing the ON / OFF determination by the error diffusion method ED1. Even when the formation of a large dot is determined by the error diffusion method ED2, the error calculation based on the density evaluation value is performed, so that the error error generated by the error diffusion method ED2 can be eliminated by the error diffusion method ED1. This is because higher quality image processing can be realized.
[0104]
According to the image processing apparatus and the printing apparatus of the second embodiment described above, similar to the first image processing apparatus, it is possible to perform high-quality image processing and image printing while ensuring dot dispersibility. . The error diffusion method is a multi-level conversion means that can sufficiently secure the dispersibility of dots when determining whether dots are on or off, that is, when performing binarization. In the above-described embodiment, since the error diffusion method ED2 for binarizing large dots on and off using the level data based on the recording rate of large dots is used, it is possible to ensure dot dispersibility. You can.
[0105]
Of course, in the multi-value processing (FIG. 16) of the second embodiment, ON / OFF of not only large dots but also small dots may be determined by the error diffusion method ED2. In addition to the level data used in the second embodiment, level data based on the recording rate of small dots is generated, and on / off of large dots and on / off of small dots are determined using the respective level data. In this case, since each determination is only a binary determination, it is possible to secure sufficient dot dispersibility even by error diffusion. The same applies to the case where the types of dots to be turned on / off are further increased.
[0106]
In the above embodiment, a printer capable of expressing three values for each pixel by forming two types of large and small dots has been described as an example. However, the present invention is applied to a multi-value printer capable of expressing more gradation values. It is also possible. For example, a printer capable of forming dots having a larger number of diameters, a printer capable of forming dots with inks having different densities, and a printer capable of forming a plurality of dots by overlapping each pixel are considered. Can be The image processing apparatus described above can be applied to an image display apparatus other than a printer as long as it is an apparatus that expresses an image by assigning dots to each pixel. Further, in the above-described embodiment, an ink jet printer having a piezo element has been described as an example. Is applicable to the printing apparatus.
[0107]
Since the image processing apparatus and the printing apparatus described above include processing by a computer, the image processing apparatus and the printing apparatus may have an embodiment as a recording medium on which a program for implementing the processing is recorded. Examples of such a recording medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a bar code is printed, and a computer internal storage device (such as a RAM or ROM). Various computer readable media are available, such as memory and external storage. Further, an embodiment as a program supply device for supplying a computer program for performing the above-described image processing and the like to a computer via a communication path is also possible.
[0108]
Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various embodiments can be implemented without departing from the gist of the present invention. For example, various control processes described in the above embodiments may be partially or entirely realized by hardware.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a printing apparatus according to the present invention.
FIG. 2 is an explanatory diagram illustrating a configuration of software.
FIG. 3 is a schematic configuration diagram of a printer of the present invention.
FIG. 4 is an explanatory diagram showing a schematic configuration of a dot recording head of the printer of the present invention.
FIG. 5 is an explanatory diagram showing a dot formation principle in the printer of the present invention.
FIG. 6 is an explanatory diagram showing an example of a nozzle arrangement in the printer of the present invention.
FIG. 7 is an enlarged view of a nozzle arrangement in the printer of the present invention and an explanatory diagram showing a relationship with a formed dot.
FIG. 8 is an explanatory diagram illustrating the principle of forming dots having different diameters by the printer of the present invention.
FIG. 9 is an explanatory diagram showing an internal configuration of a control device of the printer.
FIG. 10 is an explanatory diagram showing a nozzle driving waveform and a dot formed by the driving waveform in the printer of the present invention.
FIG. 11 is a flowchart illustrating a flow of a dot formation control routine.
FIG. 12 is a flowchart illustrating a flow of a multi-value processing according to the first embodiment.
FIG. 13 is an explanatory diagram showing the setting of the recording rate of each dot.
FIG. 14 is an explanatory diagram illustrating the concept of dot on / off determination by the dither method.
FIG. 15 is an explanatory diagram showing weights when an error is diffused.
FIG. 16 is a flowchart illustrating a flow of a multi-value processing according to the second embodiment.
FIG. 17 is an explanatory diagram showing how dots are recorded when ternarization is performed.
FIG. 18 is an explanatory diagram showing a state of printing dots that have been biased when ternarization is performed.
[Explanation of symbols]
12 ... Scanner
14 ... Keyboard
15… Flexible drive
16 ... Hard disk
18… Modem
21 ... Color display
22 ... Color printer
23 ... Paper feed motor
24 ... Carriage motor
26 ... Platen
28 ... Print head
31 ... carriage
32 Operation panel
34 ... Sliding shaft
36 ... Drive belt
38 ... Pulley
39 ... Position detection sensor
40 ... Control circuit
41 ... CPU
42 ... Programmable ROM (PROM)
43 ... RAM
44 PC interface
45: Peripheral input / output unit (PIO)
46 ... Timer
47 ... Transfer buffer
48… Bus
51… Transmitter
55 ... distribution output device
61, 62, 63, 64: ink ejection head
67… Introduction pipe
68 ... Ink passage
71: Cartridge for black ink
72 ... Color ink cartridge
80 ... Bus
81 ... CPU
82 ROM
83 ... RAM
84 input interface
85 Output interface
86 ... CRTC
87 ... Disk controller (DDC)
88: Serial input / output interface (SIO)
90 ... Personal computer
91 ... Video driver
95 ... Application program
96 ... Printer driver
97 ... Resolution conversion module
98 ... Color correction module
99 ... Halftone module
100 ... rasterizer

Claims (14)

With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. An image processing apparatus for performing
For at least some of the dots of the two or more types of dots, the dither multilevel means for determining the presence or absence of formation of each dot by a dither method,
When it is determined that any dot should not be formed by the dither multi-level converting means, the two or more types of dots including the dot which is a determination target of the formation by the dither multi-level converting means are subjected to error diffusion. Error diffusion multi-value means for determining whether or not each dot is formed,
An image processing device comprising:   The image processing device according to claim 1,
  When the gradation value of the pixel is out of the range of a specific gradation value among the gradation values that the pixel can take, the presence or absence of formation of at least some of the dots is determined by the dither multi-level conversion unit. An image processing apparatus which makes a determination by the error diffusion multi-leveling means without determining a formation. Before Symbol error diffusion multilevel means, before Symbol means for performing the multi-value conversion by an error diffusion method, which reflects also the density error generated between the results of multi-value by the dither multilevel unit and the image data The image processing device according to claim 2, wherein The image processing apparatus according to claim 2,
The range of the specific gradation value is a gradation value including a gradation value in which the dispersibility of a dot for which the presence or absence of formation is determined by the error diffusion multi-value unit has a significant effect on the image quality after multi-value conversion. in the range of the image processing apparatus. The image processing apparatus according to claim 4, wherein
At least part of the range of gray scale values within the range of the particular gradation value, among the dots whether formed by both before Symbol error diffusion multivalued means before Symbol dither multilevel means may be determined At least for some of the dot, before Symbol high image processing apparatus than the probability of formation by the dither multilevel means the probability of formation by pre Symbol error diffusion multilevel means. The image processing device according to claim 1,
The dither multi-level converting means may determine whether or not at least some of the two or more types of dots maintain continuity with respect to a change in tone value of the image data as a whole with a probability of forming the dots. in serial determination to be formed by error diffusion multilevel means it complemented the change in probability to be made probability, a dither multilevel means that obtained by determining the formation of the dots,
At least the in gradation value which dots are formed, the image processing apparatus pre-Symbol existence of formation of by Lido Tsu preparative dither multilevel means is determined.   With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. An image processing apparatus for performing
  Storage means for storing, for at least some of the two or more types of dots, the relationship between the tone value of the image data and the recording rate of the dots,
  A second image data generating unit configured to generate a second image data from the image data by obtaining a recording rate of the dot according to a gradation value of the image data with reference to the relationship;
  First error diffusion multi-valued means for multi-valued the second image data by error diffusion to determine whether or not at least some of the dots are formed;
  When the first error diffusion multi-value generating means determines that no dot should be formed, the two types including the dot subjected to the formation determination by the first error diffusion multi-value converting means are used. A second error diffusion multi-level means for multiplying the image data by error diffusion to determine whether or not each dot is formed,
  An image processing device comprising: With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. A printing apparatus that prints an image according to the image data by forming respective dots on a print medium in accordance with the result of the multi-value processing,
Image data input means for inputting the image data,
For at least some of the dots of the two or more types of dots, the dither multilevel means for determining the presence or absence of formation of each dot by a dither method,
When it is determined that any dot should not be formed by the dither multi-level converting means, the two or more types of dots including the dot which is a determination target of the formation by the dither multi-level converting means are subjected to error diffusion. Error diffusion multi-value means for determining whether or not each dot is formed,
Dot forming means for forming dots on a print medium in accordance with the determination result of the presence or absence of dot formation by the multi-value conversion means,
Ru with a printing apparatus for printing an image.   9. The printing device according to claim 8, wherein
  When the gradation value of the pixel is out of the range of a specific gradation value among the gradation values that the pixel can take, the presence or absence of formation of at least some of the dots is determined by the dither multi-level conversion unit. A printing apparatus for printing an image, wherein the determination is made by the error diffusion multi-level converting means without determining the formation.   With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. A printing apparatus that prints an image according to the image data by forming respective dots on a print medium in accordance with the result of the multi-value processing,
  Image data input means for inputting the image data,
  Storage means for storing, for at least some of the two or more types of dots, the relationship between the tone value of image data and the recording rate of the dots;
  A second image data generating unit configured to generate a second image data from the image data by obtaining a recording rate of the dot according to a gradation value of the image data with reference to the relationship;
  First error diffusion multi-valued means for multi-valued the second image data by error diffusion to determine whether or not at least some of the dots are formed;
  When the first error diffusion multi-value generating means determines that no dot should be formed, the two types including the dot subjected to the formation determination by the first error diffusion multi-value converting means are used. A second error diffusion multi-level means for multiplying the image data by error diffusion to determine whether or not each dot is formed,
  A printing device for printing an image, comprising: With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. An image processing method to be performed,
For at least some of the dots of the two or more types of dots, the dither multilevel process to determine the presence or absence of the formation of each dot by a dither method,
When it is determined that any of the dots should not be formed in the dither multi-value process, the two or more types of dots including the dot that has been determined to be formed in the dither multi-value process are subjected to error diffusion. An error diffusion multi-value process for determining whether or not each dot is formed;
An image processing method comprising:   With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. An image processing method to be performed,
  Preparing, for at least some of the two or more types of dots, storage means for storing a relationship between a tone value of image data and a recording rate of the dots;
  A second image data generating step of generating a second image data from the image data by obtaining a recording rate of the dot according to a gradation value of the image data with reference to the relationship;
  A first error-diffusion multi-value process for multi-valued the second image data by error diffusion to determine whether or not the at least some dots are formed;
  If it is determined in the first error diffusion multi-level conversion step that no dot should be formed, the two types including the dots determined to be formed in the first error diffusion multi-level conversion step A second error diffusion multi-value conversion step of determining the presence / absence of each dot by multi-valued the image data by diffusion for the above dots;
  An image processing method comprising: With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. A computer-readable recording medium for recording a program for performing,
For at least some of the dots of the two or more types of dots, the dither multivalued function to determine the presence or absence of formation of each Dots by dithering,
When it is determined that any dot should not be formed by the dither multi-level conversion function, the error diffusion is performed for the two or more types of dots including the dot that has been determined to be formed by the dither multi-level conversion function. An error diffusion multi-value function for determining whether or not each dot is formed;
Recording medium on which a program for realizing is realized.   With respect to image data having a gradation value in a predetermined range for each pixel constituting an image, it is determined whether or not two or more types of dots are formed for each pixel and multi-valued to three or more values. A computer-readable recording medium for recording a program for performing,
  For at least some of the two or more types of dots, data storing a relationship between the tone value of image data and the recording rate of the dots;
  A function of generating second image data from the image data by referring to the data and determining a recording rate of the dot according to a gradation value of the image data;
  A first multi-value function that multi-values the second image data by error diffusion to determine whether or not at least some of the dots are formed;
  When it is determined that none of the dots should be formed by the first multi-level conversion function, the two or more types of dots including the dot that has been determined to be formed by the first multi-level conversion function A second multi-level function for multi-leveling the image data by error diffusion and determining whether or not each dot is formed;
  Recording medium on which a program for realizing is realized.

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