JP7468005B2 - Image forming apparatus, image forming method and program - Google Patents

Description

The present invention relates to an image forming apparatus, an image forming method, and a program, and in particular to technology that is applied when forming an image on fabric.

Image forming devices such as inkjet printers that print on fabric have been developed. By using an inkjet printer to print on fabric, processes such as plate making that were previously necessary when printing on fabric are no longer necessary, and printing on fabric can be done quickly, easily, and at low cost.

However, in the case of inkjet image forming devices, the amount of ink ejected can only be controlled to a limited number of levels, so when printing image data with continuous gradations, it is necessary to perform halftone processing to convert the image data into the number of gradations that can be recorded by the inkjet head.
For example, in dither matrix processing, which is known as a type of halftone processing, the inkjet head selects dots from which to eject ink in block units of, for example, 256 pixels x 256 pixels, depending on the number of gradations of the original image, so that the original number of gradations is reproduced.
Another type of halftone processing is error diffusion, which adds tone errors to adjacent areas.

Patent document 1 describes a technology that performs processing to make moire patterns less noticeable when printed on fabric using an inkjet printer, which are caused by interference between a noticeable image and the periodic structure of the fabric.

Japanese Patent Application Laid-Open No. 10-290366

As described in Patent Document 1, it is known that when printing on fabric, the periodic structure of the woven fabric interferes with the periodic structure of the image to be printed, resulting in a pattern known as a moiré pattern, which reduces the quality of the printed image.
In the technology of Patent Document 1, a unit (extended matrix) is prepared by combining multiple basic sizes (basic matrix sizes) as a matrix size for performing threshold matrix processing, and a unit (sub-matrix) smaller than the basic matrix size is used. By using this sub-matrix, threshold matrix processing is performed with a periodicity larger than that of the basic matrix, and moire patterns are not visible to the human eye.

However, simply increasing the size of the threshold matrix used for dithering increases the amount of computation required during halftone processing, which converts input image data into gradation data for printing, and increases the amount of memory required for computation, which is undesirable.

The present invention aims to provide an image forming device, an image forming method, and a program that can perform image processing such as a dither matrix to print on a medium such as cloth, without causing image degradation such as moire.

The image forming apparatus of the present invention is an image forming apparatus that prints by ejecting ink onto fabric using an ink ejection head, and includes a medium characteristic acquisition unit that acquires spatial frequencies as periodic characteristics of the fabric when no image is printed, a control unit that selects a print mode in which an image is printed using a dither matrix having a spatial frequency peak in a portion of the spatial frequency of the fabric acquired by the medium characteristic acquisition unit excluding spatial frequency bands exceeding a predetermined intensity, and determines print parameters for printing the image, and a head drive unit that prints the image on a recording medium using the print parameters by operating the ink ejection head based on image data under the control of the control unit , and the medium characteristic acquisition unit frequency analyzes an image obtained by scanning the fabric to calculate the spatial frequency as a periodic structure, and when acquiring the periodic structure from the image obtained by scanning the fabric, if abnormal values are detected in any of the following areas, such as surface dirt, fabric seams, or remaining moisture, the areas where the abnormal values are detected are excluded from the areas to be frequency analyzed.

The image forming method of the present invention is an image forming method for printing an image by ejecting ink onto a fabric using an ink ejection head, and includes a medium characteristic acquisition process for acquiring a spatial frequency as a periodic feature of the fabric when no image is printed, a control process for selecting a print mode for printing an image using a dither matrix having a spatial frequency peak in a portion of the spatial frequency of the fabric acquired by the medium characteristic acquisition process excluding a spatial frequency band exceeding a predetermined intensity, and determining print parameters for forming the image, and an image forming process for printing an image on the fabric using the print parameters by selectively operating the ink ejection head based on the image data . In the medium characteristic acquisition process, an image obtained by scanning the fabric is frequency analyzed to calculate the spatial frequency as a periodic structure, and when acquiring the periodic structure from the image obtained by scanning the fabric, if any abnormal value of surface dirt, fabric seams, or remaining moisture is detected, the location where the abnormal value is detected is excluded from the locations to be frequency analyzed.

The program of the present invention also proceduralizes each process of the image forming method described above and causes a computer to execute it.

According to the present invention, by acquiring periodic characteristics of a recording medium, such as the spatial frequency of the weave of a cloth, and determining printing parameters, it becomes possible to set appropriate printing parameters, and it is possible to effectively prevent image degradation such as moire that depends on the structure specific to the recording medium.

1 is a block diagram showing an example of the configuration of an image forming apparatus according to a first embodiment of the present invention; 1 is a perspective view showing an example of the configuration of an external shape of an image forming apparatus according to a first embodiment of the present invention; 1 is a block diagram showing an example of a hardware configuration of an image forming apparatus according to a first embodiment of the present invention; FIG. 2 is a perspective view showing a configuration example of a scanning unit according to the first embodiment of the present invention; 1 is an enlarged view showing a surface of an example of a recording medium on which an image is printed by an image forming apparatus according to a first embodiment of the present invention; 4 is a flowchart showing a flow of an image forming process according to the first embodiment of the present invention. 5 is a characteristic diagram showing an example of the spatial frequency of a recording medium and the spatial frequency of a dither matrix according to the first embodiment of the present invention. FIG. 3A to 3C are diagrams showing examples of dot patterns of a dither matrix according to the first embodiment of the present invention; 11 is a characteristic diagram showing an example in which input tone and density characteristics change depending on the type of recording medium (fabric). 10 is a flowchart showing a flow of an image forming process according to a second embodiment of the present invention. FIG. 11 is a diagram showing an example of a fabric type selection screen according to the second embodiment of the present invention.

First embodiment
A first embodiment of the present invention will now be described with reference to FIGS. 1 to 9. FIG.

[Configuration of Image Forming Apparatus]
First, the overall configuration of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG.
The image forming apparatus 100 prints an image by means of an inkjet head on a recording medium 104 such as a piece of cloth whose surface structure has periodic characteristics.
A recording medium 104 supplied to the image forming apparatus 100 is transported by an endless belt 103 stretched between rollers 101 and 102. In Fig. 2, the recording medium 104 is transported in the direction indicated by an arrow M from the upper left to the lower right. The recording medium 104 has a width of, for example, about several meters. The transport of the recording medium 104 is performed in conjunction with printing onto the recording medium 104 by the image forming apparatus 100.
In the following description, the width direction of the recording medium 104 is defined as the X direction, and the conveying direction perpendicular to the X direction is defined as the Y direction.

On the recording medium 104 transported by the belt 103, a pre-processing unit 110, a first head unit 120, a second head unit 130, a third head unit 140, a fourth head unit 150, and a post-processing unit 160 are arranged in the order of transport.

The pre-processing unit 110 is provided with a scanning unit 111 (Figure 1). The scanning unit 111 performs a process of reading the surface of the recording medium 104 before printing. The scanning unit 111 performs the process of reading the surface of the recording medium 104 not only for inspection purposes to determine whether the recording medium 104 is defective, but also for processing to detect periodic characteristics of the recording medium 104, which will be described later.

The first head unit 120, the second head unit 130, the third head unit 140, and the fourth head unit 150 are respectively provided with ink ejection heads 121, 131, 141, and 151 (FIG. 1) of different colors. That is, the first head unit 120 is provided with an ink ejection head 121 for cyan (C), and the second head unit 130 is provided with an ink ejection head 131 for magenta (M). The third head unit 140 is provided with an ink ejection head 141 for yellow (Y), and the fourth head unit 150 is provided with an ink ejection head 151 for black (K). For example, an inkjet type head is used for the ink ejection heads 121, 131, 141, and 151 of each color.

Each ink ejection head 121, 131, 141, 151 has multiple nozzles arranged in a predetermined pattern, and ejects ink droplets from the openings of the multiple nozzles at appropriate timing to print across almost the entire width of the recording medium 104. Alternatively, the ink ejection heads 121, 131, 141, 151 may be movable in the X direction within each head unit 120-150, and may be made to be shorter than the width of the recording medium 104.

A scanning section (not shown) is arranged in the post-processing unit 160. Images read by the scanning section of this post-processing unit 160 are used to perform an inspection process to determine whether the images printed on the recording medium 104 by ink ejection from each of the head units 120 to 150 are of good quality.

The image forming apparatus 100 also includes a control unit 170. The control unit 170 includes an operation panel 180, and displays the printing status and issues various operational instructions. The configuration of the control unit 170 will be described with reference to FIG.
The control unit 170 may be configured as one unit with any of the units 110 to 160. The color configurations of the head units 120 to 150 described above are merely examples, and other color combinations or only head units of one of the colors may be arranged.

FIG. 1 is a functional block diagram showing the internal configuration of an image forming apparatus 100. As shown in FIG.
The control unit 170 of the image forming apparatus 100 includes an image data input unit 171, an input image processing unit 172, a halftone processing unit 173, a head driving unit 174, a print control unit 175, a medium characteristic acquisition unit 176, a frequency analysis unit 177, a print mode selection unit 178, and an operation panel 180.

Image data to be printed on the recording medium 104 is input from the outside to the image data input unit 171 .
The input image processing unit 172 performs an input process of converting the image data input to the image data input unit 171 into image data for printing. For example, when the number of gradations of the image data input to the image data input unit 171 is different from the number of gradations expressed by printing in the image forming apparatus 100, a process of converting the number of gradations into the number of gradations expressed by printing in the image forming apparatus 100 is performed.

The halftone processing unit 173 performs halftone processing to express the image data with the number of gradations input and processed by the input image processing unit 172 using the ink ejection amount from the ink ejection heads 121 to 151. That is, the ink ejection heads 121 to 151 are limited in the amount of ejection when ejecting droplets from the nozzles to a limited number of steps, such as one or two steps per dot. For this reason, the halftone processing unit 173 performs halftone processing using a certain amount of printing area (area of multiple dots) to express multiple gradations, such as 256 gradations. In this halftone processing, a dither matrix method that expresses gradations using a dither matrix of a fixed size, or an error diffusion method that transmits gradation errors to adjacent areas, are used. Here, as an example, the halftone processing is performed using the dither matrix method.

When the halftone processing unit 173 performs halftone processing, a print mode is selected by the print mode selection unit 178, which will be described later. For example, when the halftone processing unit 173 performs halftone processing using a dither matrix method, multiple matrices with different spatial frequencies are prepared as dither matrix patterns to be selected for each gradation value. The print mode selection unit 178 then selects one of the multiple prepared matrices of spatial frequency patterns. The relationship between the dither matrix pattern and the spatial frequency will be described in detail later.

The head driving unit 174 controls the driving of the ink ejection heads 121 , 131 , 141 , and 151 of each color so that the ink ejection amount from the ink ejection heads 121 , 131 , 141 , and 151 of each color corresponds to the ink ejection amount for each dot determined by the halftone processing unit 173 .
The halftone processing in the halftone processing unit 173 and the driving of the ink ejection heads 121 , 131 , 141 , and 151 by the head driving unit 174 are performed under the control of a print control unit 175 .

The medium characteristics acquisition unit 176 acquires image data read by the scanning unit 111 disposed in the pre-processing unit 110 (FIG. 2). The scanning unit 111 performs a process of reading the surface of the recording medium 104 before printing is performed.

The medium characteristic acquisition unit 176 performs a medium characteristic acquisition process to acquire characteristics of the recording medium 104 from the image data acquired by the scan unit 111. That is, in the case of this embodiment, since the recording medium 104 is cloth, the medium characteristic acquisition unit 176 acquires the weave components of the cloth from the image data acquired by the scan unit 111.
The frequency analysis unit 177 performs frequency analysis on the fabric weave components acquired by the medium characteristic acquisition unit 176 to acquire the spatial frequency of the fabric weave components.
The print mode selection unit 178 selects a print mode when the halftone processing unit 173 performs halftone processing, based on the spatial frequency acquired by the frequency analysis unit 177 .

The print control unit 175 controls the entire printing operation on the recording medium 104 in the image forming device 100. This print control unit 175 controls the start and stop of the printing operation based on the operation reception at the operation unit 181 of the operation panel 180. The print control unit 175 also causes the display unit 182 of the operation panel 180 to display the operating status of the image forming device 100. Note that the operation unit 181 and display unit 182 of the operation panel 180 may be integrated, for example, by configuring them as a touch panel.

The print control unit 175 also issues instructions to the medium transport unit 105 to transport the recording medium 104 in conjunction with the ink ejection control of each head 121 to 151 by the head drive unit 174. The medium transport unit 105 transports the recording medium 104 using the belt 103 (Figure 2).

[Example of Hardware Configuration of Image Forming Apparatus]
FIG. 3 shows an example of a hardware configuration in which the control unit 170 of the image forming apparatus 100 is configured by a computer.
The control unit 170 includes a CPU (Central Processing Unit) 191, a ROM (Read Only Memory) 192, a RAM (Random Access Memory) 193, a non-volatile storage 194, and a network interface 195, which are connected via a bus line so as to be capable of transferring data. An operation unit 181 and a display unit 182 constituting an operation panel 180 (FIG. 1) are also connected to the CPU 191 and the like via the bus line so as to be capable of transferring data.

The CPU 191 is an arithmetic processing unit that reads out from the ROM 192 or the like and executes program code of software that realizes the functions of performing processing operations in each part of the control unit 170 .
The ROM 192 stores program codes for executing various functions of the image forming apparatus 100 .
The RAM 193 is a work memory in which variables, parameters, etc. generated during the arithmetic processing are temporarily written.
In addition to program code, the non-volatile storage 194 stores image data for printing, various setting data, and the like.

The network interface 195 is used for data transfer between the control unit 170 and the outside. For example, the input processing of image data for printing in the image data input unit 171 is performed via the network interface 195.

The display on the display unit 182 is also executed under the control of the CPU 191. The CPU 191 also determines input operations on the operation unit 181, such as touch operations on the screen being displayed, and controls the image forming device 100 to enter an operating state corresponding to the input operation.

Note that the control unit 170 of the image forming device 100 configured as a computer as shown in FIG. 3 is just one example, and other configurations are also possible. For example, some or all of the functions of the control unit 170 may be realized by dedicated hardware such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[Example of scanning unit configuration]
FIG. 4 shows an example of the configuration of the scanning section 111 included in the pre-processing unit 110. As shown in FIG.
Here, two examples are shown: a first configuration example (FIG. 4(a)) and a second configuration example (FIG. 4(b)).
4A shows a first configuration example in which the longitudinal direction of the scanning unit 111 is arranged in the Y direction, which coincides with the transport direction M of the recording medium 104, within the pre-processing unit 110 installed so as to straddle the surface of the recording medium 104. That is, the scanning unit 111 is configured with a relatively short line sensor having a length of about several centimeters to several tens of centimeters, and is arranged in the pre-processing unit 110 in a state of extending in the Y direction. The pre-processing unit 110 includes a drive unit (not shown) and moves the scanning unit 111 arranged so as to extend in the Y direction, in the X direction, which is the width direction of the recording medium 104.

By moving the scanning unit 111 in the Y direction in this manner, the scanning unit 111 can scan the entire width of the surface of the recording medium 104. Note that the operation of moving the scanning unit 111 in the X direction and the operation of transporting the recording medium 104 are executed under the control of the printing control unit 175.

4B shows a second configuration example in which the longitudinal direction of the scanning unit 111 is arranged in the X direction, which is the width direction of the recording medium 104, within the pre-processing unit 110 installed so as to straddle the surface of the recording medium 104. In other words, the scanning unit 111 is composed of a line sensor whose length is approximately the same as the width of the recording medium 104, and is arranged in the pre-processing unit 110 while extending in the X direction.
In this case, multiple line sensors may be combined to have a length approximately equal to the width of the recording medium 104. Alternatively, a driving unit (not shown) may be provided that moves a line sensor having a length of about several tens of centimeters in the X direction, and scanning by the line sensor and driving may be alternated to scan the entire width of the recording medium 104.

[Examples of the structure of the recording medium]
FIG. 5 is an example of an image obtained by photographing the surface of the recording medium 104 on which the image forming apparatus 100 performs printing processing.
As already described, in this embodiment, a woven cloth (fabric) is used as the recording medium 104. Fig. 5 shows an enlarged view of a portion 104a of the recording medium 104 made of the cloth.
The recording medium 104 made of cloth has a structure in which the weaving or knitting of the cloth is repeated periodically in a specific pattern, and when enlarged as shown in Fig. 5, the weaving or knitting structure becomes visible as a pattern. The period of the weaving or knitting structure is determined by the type of weaving and the type of color, and exists in various periods.
Here, the medium characteristic acquisition unit 176 included in the image forming apparatus 100 acquires the components of the weave or knit structure of the recording medium 104 as shown in FIG. 5 from the image scanned by the scanning unit 111 .
The frequency analysis unit 177 then performs frequency analysis on the structural components of the recording medium 104, such as weaving or knitting, to obtain a spatial frequency that indicates the period of the weaving or knitting of the fabric.
The image forming apparatus 100 of this embodiment acquires the spatial frequency of the recording medium 104, and selects the print mode for performing halftone processing in accordance with the spatial frequency.

[Printing process flow]
FIG. 6 is a flow chart showing a flow of a printing process on the recording medium 104 by the image forming apparatus 100. As shown in FIG.
First, the scanning section 111 in the pre-processing unit 110 of the image forming apparatus 100 scans the conveyed recording medium 104 and obtains an image of the surface of the recording medium 104 (step S11).
The image of the recording medium 104 obtained by the scanning unit 111 is supplied to the medium characteristic acquisition unit 176, which acquires components that indicate the structure of the recording medium 104. An example of a component that indicates the structure of the medium is the brightness component of the image data. At this time, the medium characteristic acquisition unit 176 performs a process of removing abnormal values contained in the components that indicate the structure of the recording medium 104 (step S12). The abnormal values here include dirt on the surface of the cloth, seams between pieces of cloth, and moisture remaining when the belt 103 is washed.

Then, the frequency analysis unit 177 performs frequency analysis on the components that indicate the structure of the medium from which the abnormal values have been removed by the medium characteristic acquisition unit 176, and calculates the spatial frequency of the weave of the recording medium (fabric) 104 (step S13). Note that although it depends on the type of fabric used as the recording medium 104, the spatial frequency calculated here usually includes multiple frequency components.

Next, the print mode selection unit 178 performs a control process to select a print mode in which, among the spatial frequencies calculated by the frequency analysis unit 177, a frequency band that exceeds a predetermined intensity does not overlap with the spatial frequency of the dither matrix when the halftone processing unit 173 performs halftone processing (step S14).
Then, the halftone processing unit 173 performs halftone processing on the image data for printing to express gradation values using a dither matrix in the print mode selected in step S14 (step S15). The halftone processing unit 173 supplies the image data that has been halftone processed in step S15 to the head driving unit 174.
The head driving unit 174 controls the driving of the ink ejection heads 121, 131, 141, and 151 of each color based on the supplied image data, and prints on the recording medium 104 by ejecting ink from the ink ejection heads 121, 131, 141, and 151 of each color (step S16).

In the flowchart in FIG. 6, steps S11 to S16 are described as one flow, but in reality, the processes from steps S11 to S14 need to be performed only once at the beginning when printing on one type of fabric. On the other hand, the halftone process in step S15 and the printing process in step S16 are performed continuously while printing continues.

Figure 7 shows an example of the spatial frequency characteristic T when the recording medium is cloth, and an example of the spatial frequency of the dither matrix in two print modes when performing halftone processing. Figure 7 shows the first print mode Pa and the second print mode Pb. The horizontal axis of Figure 7 shows spatial frequency, and the vertical axis shows intensity.

As shown in FIG. 7, the spatial frequency characteristic T of the weave structure of the recording medium (cloth) in this example has three intensity peaks Ta, Tb, and Tc.
Here, it is assumed that the print mode selection unit 178 has determined that two peaks Ta and Tb have intensities higher than a threshold value TH indicated by a dashed line. In this case, the spatial frequency characteristics in the first print mode Pa have a frequency band that almost overlaps with one of the peaks Tb and has a high intensity. On the other hand, the spatial frequency characteristics in the second print mode Pb have a frequency band with a high intensity that is higher than the peaks Ta, Tb, and Tc and does not overlap with the peak of the spatial frequency characteristics T of the weave structure of the recording medium (cloth).
Therefore, when the spatial frequency characteristic T of the recording medium shown in FIG. 7 is acquired, the print mode selection unit 178 selects the second print mode Pb.

FIG. 8 shows an example of the spatial frequency of the dither matrix in each print mode.
The two dither matrices shown in Figure 8 show examples of the same gradation value but different spatial frequencies, in which ink is ejected onto 16 dots (black areas) out of a 64-pixel area of 8 dots x 8 dots, and ink is not ejected onto the other dots (white areas).
Here, in the case of the dot pattern of the first print mode Pa shown in Fig. 8(a), the locations where ink is ejected are in a relatively concentrated state, and the spatial frequency is relatively low. On the other hand, in the case of the dot pattern of the second print mode Pb shown in Fig. 8(b), the locations where ink is ejected are in a relatively dispersed state, and the spatial frequency is relatively high.

In this way, by preparing multiple modes with different spatial frequencies of the dither matrix when performing halftone processing and selecting the print mode when performing halftone processing based on the spatial frequency characteristics of the structure of the recording medium 104, it is possible to prevent moire from occurring in the printed image. In other words, the main cause of moire when printing on a recording medium such as cloth is the overlap between the spatial frequency of the weave structure of the recording medium 104 and the spatial frequency of the dither matrix during halftone processing, and it is possible to appropriately prevent the occurrence of moire by selecting the print mode.

[Example of differences depending on the type of fabric]
When cloth is used as the recording medium 104, there is a difference between the input gradation expressed by the image data and the printed gradation when printed on the cloth, and during processing in the input image processing unit 172 or halftone processing unit 173, corrections may be made according to the type of cloth.
FIG. 9 shows input gradation (horizontal axis) and printed gradation (vertical axis) with characteristics T1, T2, and T3 of three types of fabric.
As shown by the characteristics T1, T2, and T3 of the three fabrics, there are differences in the gradation characteristics expressed in the printed image. By correcting these differences during processing in the input image processing unit 172 and the halftone processing unit 173, it is possible to print with better image quality.

Second embodiment
Next, a second embodiment of the present invention will be described with reference to FIGS.
In the second embodiment, the configuration of the image forming apparatus 100 is the same as that of the image forming apparatus 100 described in the first embodiment.
In the second embodiment, the process of setting the print mode during print processing differs from the process shown in the flowchart of FIG. 6 described in the first embodiment.

[Printing process flow]
FIG. 10 is a flow chart showing a flow of a printing process performed on the recording medium 104 by the image forming apparatus 100 in the second embodiment.
First, the print control unit 175 judges whether the type of fabric as the recording medium 104 to be used for printing has already been registered (step S21). If the type of fabric (fabric) has not been registered in step S21 (NO in step S21), the print control unit 175 displays a fabric type registration screen on the display unit 182 of the operation panel 180, and the printing operator operates the operation unit 181 to register the fabric type according to the instructions on the registration screen (step S22). An example of the fabric type registration screen will be described later (FIG. 11).

After the registration operation in step S22 is performed, or if it is determined in step S21 that the type of fabric has already been registered (YES in step S21), the print control unit 175 selects the specified type of fabric (step S23). Then, the print control unit 175 calculates the spatial frequency of the recording medium 104 to be used for printing from the selected type of fabric (step S24).

Then, the print mode selection unit 178 performs a control process to select a print mode in which, among the spatial frequencies calculated by the print control unit 175, a frequency band that exceeds a predetermined intensity does not overlap with the spatial frequency of the dither matrix when the halftone processing unit 173 performs halftone processing (step S25).
Then, the halftone processing unit 173 performs halftone processing on the image data for printing to express gradation values using a dither matrix in the print mode selected in step S25 (step S26). The halftone processing unit 173 supplies the image data that has been halftone processed in step S26 to the head driving unit 174.
The head driving unit 174 controls the driving of the ink ejection heads 121, 131, 141, and 151 of each color based on the supplied image data, and prints on the recording medium 104 by ejecting ink from the ink ejection heads 121, 131, 141, and 151 of each color (step S27).

Note that the halftone process in step S26 and the printing process in step S27 are performed continuously while printing continues.

[Example of fabric type registration screen]
FIG. 11 shows an example of a registration screen displayed on the display unit 182 when the type of fabric is registered in step S22 of the flowchart in FIG.
The registration screen shown in FIG. 11 has the following items: fabric type, warp density, weft density, warp diameter, weft diameter, weaving type, and print mode.

The item of fabric type displays an identification name for distinguishing each fabric. The fabric type may be automatically set by the image forming apparatus 100, or the operator may set it by inputting the name of the fabric type on the registration screen.
The items "warp density" and "weft density" display the density of the warp threads (vertical threads) and weft threads (horizontal threads) that make up the fabric. The operator inputs these warp and weft densities. In the example of Fig. 11, the number of threads per inch is displayed as the warp and weft densities.
The warp diameter and weft diameter items display the diameters of the warp and weft threads that make up the fabric. These warp diameter and weft diameter are input by the operator. In the example of Fig. 11, the warp diameter and weft diameter are displayed in denier units.
The weave type item displays the weave type of the fabric, such as twill weave, plain weave, etc. This weave type is also input by the operator.

The print mode item displays the print mode to be selected from among the prepared print modes.
In the example of Fig. 11, three print modes, mode A, mode B, and mode C, are displayed, and the print mode selected among the three is displayed with a check mark. Also, in the example of Fig. 11, mode A is displayed as for low density, and mode C is displayed as for high density. In other words, the three print modes have different spatial frequencies set for the dither matrix during halftone processing, and mode A is suitable for low density fabrics, mode B is suitable for normal density fabrics, and mode C is suitable for high density fabrics.

The image forming apparatus 100 calculates the spatial frequency of the weave of the fabric by selecting the warp density, weft density, warp diameter, weft diameter, and weave type, and automatically selects and displays a print mode that does not overlap with the spatial frequency of the weave. This print mode selection process corresponds to the process in step S25 of the flowchart in FIG. 10. The image forming apparatus 100 calculates the spatial frequency of the fabric from the items of warp density, weft density, warp diameter, weft diameter, and weave type by calculation using a formula based on the values of each item. Alternatively, the image forming apparatus 100 may store in advance a database showing the correspondence between the values and types of warp density, weft density, warp diameter, weft diameter, and weave type and the spatial frequency, and acquire the spatial frequency by referring to the database.
However, the print mode automatically selected based on the spatial frequency of the fabric can also be changed by the operator's operation on the registration screen.

In the registration screen shown in FIG. 11, the operator may freely input numerical values for the warp density, weft density, warp diameter, weft diameter, and weaving type, or candidate numerical values may be displayed on the screen and the operator may select a value or type from the candidates.

As in this embodiment, the spatial frequency is obtained from the density, diameter, and weave type of the threads in the fabric, and a print mode is automatically selected that uses a spatial frequency of a dither matrix that does not overlap with that spatial frequency, making it possible to prevent degradation of image quality, such as the occurrence of moire, as in the first embodiment.

<Modification>
The present invention is not limited to the above-described embodiments, and modifications and variations are possible without departing from the spirit and scope of the present invention.
For example, in each of the above-mentioned embodiments, an example has been described in which cloth is used as a recording medium on which the image forming apparatus 100 prints. In contrast, when printing on a recording medium such as paper, if a pattern or some other design is formed on the surface of the recording medium, the same processing can be used to prevent image quality degradation such as the occurrence of moire. For example, when performing printing processing using a recording medium on which ruled lines or grids are formed at regular intervals on the surface of paper, a printing mode using a spatial frequency of a dither matrix that does not overlap with the spatial frequency of the ruled lines or grids may be selected.

In addition, in each of the above-described embodiments, the print mode in which the image forming device 100 prints on the recording medium is a mode in which the spatial frequency of the dither matrix during halftone processing is changed. In contrast, when performing other halftone processing, multiple print modes that change the spatial frequency, etc. may be prepared, and the print mode may be controlled so as not to overlap with the spatial frequency of the recording medium.

In addition, in each of the above-described embodiments, the image forming device 100 is an inkjet type. However, the present invention can also be applied to image forming devices that perform printing processing on a recording medium by ejecting ink using other methods.

In addition, in the configuration shown in FIG. 2, the image forming apparatus 100 has a scanning unit 111 disposed in the pre-processing unit 110 disposed upstream of each of the head units 120 to 150, and the scanning unit 111 scans the recording medium before printing. Alternatively, the scanning unit 111 may be disposed in the head unit 120, and scanning may be performed immediately before printing. Alternatively, a scanning device or camera separate from the image forming apparatus 100 shown in FIG. 2 may be used to photograph the surface of the recording medium and input the photographed image.

Furthermore, when performing the processing of each embodiment using image forming apparatus 100, this can be achieved by, for example, configuring control unit 170 of image forming apparatus 100 as a computer, and implementing a program (software) and various data for executing the image formation processing method described in the flowchart of FIG. 6 in control unit 170.
In this case, the programs and data can be stored in a storage medium such as a semiconductor memory or various disks and implemented in the control unit 170 .

100...image forming apparatus, 101, 102...rollers, 103...belt, 104...recording medium, 105...medium transport section, 110...pre-processing unit, 111...scanning section, 120...first head unit, 121...ink ejection head (for C), 130...second head unit, 131...ink ejection head (for M), 140...third head unit, 141...ink ejection head (for Y), 150...fourth head unit, 151...ink ejection head (for K), 160...rear Processing unit, 170...control unit, 171...image data input unit, 172...input image processing unit, 173...halftone processing unit, 174...head driving unit, 175...print control unit, 176...medium characteristics acquisition unit, 177...frequency analysis unit, 178...print mode selection unit, 180...operation panel, 181...operation unit, 182...display unit, 191...CPU, 192...ROM, 193...RAM, 194...non-volatile storage, 195...network interface

Claims (8)

An image forming apparatus that performs printing by ejecting ink onto a fabric using an ink ejection head,
a medium characteristic acquisition unit that acquires a spatial frequency as a periodic characteristic of the fabric in a state where no image is printed;
a control unit that selects a print mode in which an image is printed using a dither matrix having a spatial frequency peak in a portion of the spatial frequency of the fabric acquired by the medium characteristic acquisition unit excluding a spatial frequency band exceeding a predetermined intensity, and determines print parameters for printing the image;
a head driving unit that operates the ink ejection head based on image data under the control of the control unit, thereby printing an image on the fabric using the printing parameters ;
The medium characteristic acquisition unit performs frequency analysis on the scanned image of the fabric to calculate a spatial frequency as a periodic structure, and, when acquiring the periodic structure from the scanned image of the fabric, if any abnormal value of surface dirt, seams of the fabric, or remaining moisture is detected, the portion where the abnormal value is detected is excluded from the portion to be subjected to the frequency analysis.
Image forming device. The image forming apparatus according to claim 1 , wherein the print mode is determined by the control unit based on an operation received through an operation panel. The image forming apparatus according to claim 1 , wherein the control unit determines a dither matrix to be used when the head driving unit performs printing, based on a periodic structure that is a periodic feature of the fabric . The medium characteristic acquisition unit acquires a spatial frequency as a periodic structure of the fabric ,
The image forming apparatus according to claim 3 , wherein the control unit determines a dither matrix so that a spatial frequency peak is present in a portion excluding a spatial frequency band exceeding a predetermined intensity among the spatial frequencies acquired by the medium characteristic acquisition unit. The image forming device according to claim 4 , wherein the control unit controls the dither matrix so that the dither matrix has a spatial frequency peak in a portion of the spatial frequencies acquired by the medium characteristic acquisition unit excluding spatial frequency bands exceeding a predetermined intensity. The image forming apparatus according to claim 1 , wherein the head driving section determines an amount of liquid to be applied during printing based on a periodic structure that is a periodic feature of the fabric. An image forming method for printing an image by ejecting ink onto a fabric using an ink ejection head, comprising the steps of:
A medium characteristic acquisition process for acquiring a spatial frequency as a periodic characteristic of the fabric in a state where no image is printed;
a control process for selecting a print mode for printing an image using a dither matrix having a spatial frequency peak in a portion excluding a spatial frequency band exceeding a predetermined intensity among the spatial frequencies of the fabric acquired by the medium characteristic acquisition process, and determining print parameters for forming an image;
an image forming process for printing an image on the fabric using the printing parameters by selectively operating the ink ejection head based on image data ;
In the medium characteristic acquisition process, the image obtained by scanning the fabric is frequency analyzed to calculate the spatial frequency as a periodic structure, and when an abnormal value of any of surface stains, seams of the fabric, and remaining moisture is detected in acquiring the periodic structure from the image obtained by scanning the fabric, the portion where the abnormal value is detected is excluded from the portion to be subjected to the frequency analysis.
Imaging method. A program for causing a computer to execute a process for printing an image on a fabric by an image forming device,
a medium characteristic acquisition step of acquiring a spatial frequency as a periodic characteristic of the fabric in a state where no image is printed;
a control step of selecting a print mode for printing an image using a dither matrix having a spatial frequency peak in a portion excluding a spatial frequency band exceeding a predetermined intensity among the spatial frequencies of the fabric acquired in the medium characteristic acquisition step, and determining print parameters for forming an image;
an image forming procedure for printing an image on the fabric using the printing parameters by operating an ink ejection head that ejects ink onto the fabric based on image data,
In the medium characteristic acquisition step, the image obtained by scanning the fabric is frequency analyzed to calculate the spatial frequency as a periodic structure, and when an abnormal value of any of the surface stains, the seam of the fabric, and the remaining moisture is detected in acquiring the periodic structure from the image obtained by scanning the fabric, the portion where the abnormal value is detected is excluded from the portion to be subjected to the frequency analysis.
program.

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