System, image forming apparatus, information processing method, and program

Abstract

To reduce an amount of data to be transferred, while maintaining the number of gradations and graininess.SOLUTION: An information processing apparatus acquires a first image with first resolution, creates a second image with second resolution on the basis of the first image with first resolution, wherein the gradation value of one pixel of the second image indicates the number of dots when an area of the first image corresponding to one pixel is converted to have third resolution higher than the first resolution and the second resolution and is binarized by using a first threshold matrix according to the third resolution, and transmits the second image to an image forming apparatus. The image forming apparatus converts the received second image into a third image that is a binarized image with the third resolution, and creates the third image according to information indicating an arrangement of dots in the third image corresponding to the gradation value for one pixel of the second image, wherein the arrangement of dots corresponding to one pixel of the third image is determined on the basis of a relationship between magnitudes of thresholds in an area corresponding to one pixel in the first threshold matrix.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a system, an image forming apparatus, an information processing method, and a program. [Background technology]

[0002] Inkjet image forming devices form images on inkjet paper, a print medium, by converting image data input at an input resolution into dot arrangement (dot formation or non-formation) data at an output resolution, which is the resolution of the ejection ports. In such image forming devices, the image formation data that determines the dot arrangement for forming an image is generally generated by quantizing image data input in multi-value (e.g., 8 bits). Here, the quantization process for image data is performed by converting the image data into binary data for each pixel, in which dot formation (tone value 1) or non-formation (tone value 0) is determined. This quantization process is also called area modulation, because it allows multi-value representation by combining the dot formation / non-formation arrangements across multiple pixels of a certain unit area. For example, if the input image has 8 bits and 256 gradations, a unit area of ​​16 x 16 dots can achieve the same gradation values ​​of 0 to 255 for dot formation / non-formation.

[0003] In recent years, with the advancement of inkjet image quality, inkjet image formation has become applicable to the field of conventional commercial offset printing, and there is a growing demand for inkjet image formation to achieve higher image quality and resolution.

[0004] To achieve this high-quality, high-resolution image formation, high-density recording heads have been used, which have a higher integration density of image-forming elements in the recording head, including the ejection ports. The resolution of the image formed by these high-density recording heads can be higher than the resolution of the general image data input (e.g., 300 dpi or 600 dpi). High-density recording heads, which can achieve a higher resolution during image formation than the resolution of the input image, are devices suitable for area modulation.

[0005] There are three image quality elements that are realized by the resolution of the input and output images and the quantization process: resolution (jaggies), number of gradations, and graininess. Resolution (jaggies) is an image quality element related to the jaggedness of the image and depends on the input resolution of the input image data. Number of gradations represents the ability of area modulation. This number of gradations is the number of gradations that can be reproduced per pixel of a certain resolution and depends greatly on the relationship between the resolutions of the input and output images. Graininess is an image quality element related to the roughness of the image and depends greatly on the dot arrangement when the image is formed.

[0006] The quantization method described in Patent Document 1 uses dot arrangement patterns stored in a table memory, making it possible to realize a number of gradations while suppressing the amount of data transfer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 09-046522 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when high-resolution quantization is performed to match the resolution of a high-density recording head in order to reduce graininess, the amount of data in the quantized image data becomes enormous. Also, with the technology described in Patent Document 1, after multi-value quantization at the input resolution, multiple dot arrangement patterns stored in a table memory are assigned in order, so dot arrangement control cannot be performed at the resolution used for image formation, and graininess can become more visible.

[0009] The present invention aims to reduce the amount of data transfer while maintaining the number of gradations and granularity. [Means for solving the problem]

[0010] In order to achieve the object of the present invention, for example, a system according to one embodiment has the following arrangement. That is, a system comprising an information processing device and an image forming device, wherein the information processing device comprises an acquisition means for acquiring a first image of a first resolution, and a first conversion means for generating a second image of a second resolution based on the first image of the first resolution, wherein the gradation value of one pixel of the second image indicates the number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first and second resolutions and then binarized using a first threshold matrix according to the third resolution, and a transmission means for transmitting the second image to the image forming device, and the image forming device comprises a reception means for receiving the second image, and a second conversion means for converting the second image into a third image which is a binary image of the third resolution, wherein the third image is generated in accordance with information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, and the dot arrangement corresponding to the one pixel of the third image is determined based on the magnitude relationship of each threshold value in the first threshold matrix in the area corresponding to the one pixel. [Effects of the Invention]

[0011] To reduce the amount of data transfer while maintaining the number of gradations and granularity. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing an example of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of a recording head according to the first embodiment. [Figure 3] FIG. 1 is a block diagram showing an example of the hardware configuration of a system according to a first embodiment. [Figure 4] 5 is a flowchart showing an example of image processing according to the first embodiment. [Figure 5] FIG. 1 is a diagram showing an example of the functional configuration of a system according to a first embodiment. [Figure 6] FIG. 10 is a diagram showing an example of multiple types of image data generated by the system. [Figure 7] FIG. 10 is a diagram showing an example of a matrix generated by the system. [Figure 8] 4 is a flowchart showing an example of information processing by the system according to the first embodiment. [Figure 9] FIG. 10 is a diagram for explaining processing in the prior art. [Figure 10] 10 is a diagram for comparing the amount of data transferred with other examples. [Figure 11] A diagram for comparing the frequency characteristics of images. [Figure 12] A diagram for comparing the graininess of images. [Figure 13] FIG. 10 is a diagram showing an example of the functional configuration of a system according to a second embodiment. [Figure 14] 10 is a flowchart showing an example of information processing by the system according to the second embodiment. [Figure 15] FIG. 10 is a diagram showing an example of the functional configuration of a system according to a third embodiment. [Figure 16] 11 is a flowchart showing an example of information processing by the system according to the third embodiment. [Figure 17] FIG. 10 is a diagram showing an example of the functional configuration of a system according to a fourth embodiment. [Figure 18] 10 is a flowchart showing an example of information processing by the system according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0014] [Term definition] The terms used in each embodiment will be defined below.

[0015] [Input resolution] In the following, "input resolution" refers to the resolution of input image data input by a user in the image forming system according to each embodiment. In the following, the input resolution will be described as XxY being 600 dpi x 600 dpi, but this is not particularly limited as long as the relationship (input resolution) < (output resolution) holds.

[0016] Output resolution In the following, "output resolution" refers to the resolution of an image formed by an inkjet printhead used in a system according to each embodiment. The direction along the main scanning direction, shown as the Y direction in FIG. 1 (described later), coincides with the nozzle pitch of the inkjet printhead used, and has a resolution of 1200 dpi. In each embodiment, the same resolution is also used in the sub-scanning direction, and the explanation will be given assuming that XxY is 1200 dpi x 1200 dpi, but this is not particularly limited as long as the relationship (input resolution) < (output resolution) holds. The output resolution can be any value, such as 2400 dpi or 4800 dpi, depending on the user's desired conditions and environment.

[0017] [Pixels] In the following, the term "pixel" refers to one section, the smallest unit at each resolution.

[0018] [pixel] Subpixel In the following, "pixel" refers to a picture element in the input resolution unit. Also, in the following, "subpixel" refers to a picture element in the output resolution unit. For example, if the input resolution is 600 dpi x 600 dpi and the output resolution is 1200 dpi x 1200 dpi, 2 x 2 subpixels correspond to 1 pixel (= picture element) of the input resolution. In the following, 600 dpi x 600 dpi and 1200 dpi x 1200 dpi may be simply referred to as 600 dpi and 1200 dpi, respectively.

[0019] [Threshold matrix] In the following, the term "threshold matrix" refers to a matrix that represents threshold values ​​for dither processing. A specific example of a threshold matrix will be described later with reference to FIG. 7. The threshold matrix may also be referred to as a "threshold MTX" or a "dither pattern."

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0021] [Embodiment 1] [Image formation system] 1 is a perspective view showing an outline of an image forming unit in a serial inkjet image forming apparatus 300, which is employed in a system (image forming system) according to this embodiment and is capable of applying image data quantization processing and dot expansion processing. Hereinafter, this system may be referred to as an inkjet image forming system, or simply as an image forming system. Hereinafter, the inkjet image forming apparatus 300 will be referred to simply as the image forming apparatus 300.

[0022] The printing medium P fed to the image forming section is transported in the direction of arrow Y (sub-scanning direction) in the figure by a nip section including a transport roller 101 arranged on the transport path and a pinch roller 102 driven by it, as the transport roller 101 rotates.

[0023] The platen 103 is provided at an image formation position facing the surface (discharge surface) of the inkjet recording head 303 on which ejection ports are formed, and supports the back surface of the printing medium P from below, thereby maintaining a constant distance between the front surface of the printing medium P and the ejection surface of the recording head 303. The printing medium P in the area on the platen 103 where the image has been formed is nipped between the discharge roller 105 and a spur 106 driven by the discharge roller 105, transported in the Y direction as the discharge roller 105 rotates, and discharged onto a paper output tray 107. The discharge roller 105 and the spur 106 form components of a second transport means located downstream in the printing medium transport direction.

[0024] The recording head 303 is detachably mounted on the carriage 108 with its ejection port surface facing the platen 103 or the printing medium P. The carriage 108 is moved back and forth in the X direction along two guide rails 109 and 110 by the driving force of a carriage motor, and during this movement the recording head 303 performs an ejection operation in accordance with an image formation signal.

[0025] The X direction in which the carriage 108 moves is perpendicular to the Y direction in which the print medium is transported, and is referred to here as the main scanning direction. In contrast, the Y direction in which the print medium is transported is referred to as the sub-scanning direction. An image is formed in stages on the print medium P by alternating between main scanning (movement accompanying image formation) of the carriage 108 and recording head 303 and transport of the print medium (sub-scanning).

[0026] FIG. 2 is a schematic diagram of a print head 303 as viewed from the nozzle formation surface. The print head 303 according to this embodiment includes a cyan image-forming element array 21, a magenta image-forming element array 22, a yellow image-forming element array 23, and a black image-forming element array 24. As described above, the print head 303 according to this embodiment forms images using four colors: CMYK. However, the colors and the number of colors are not particularly limited. For example, the print head 303 may use similar colors with different densities, such as light cyan, light magenta, or gray. If the print head 303 has special colors such as red, green, and blue, it may perform processing using the same number of planes as the number of those colors. As shown in FIG. 2, the image-forming element arrays of the print head 303 according to this embodiment are aligned in the X direction. Furthermore, the nozzle arrays of these image-forming elements have 128 nozzles for ejecting ink arranged at a regular pitch in the Y direction.

[0027] In this embodiment, the width of each nozzle array in the Y direction of the print head 303 is approximately 21 μm, which corresponds to one pixel at 1200 dpi, and a single scan can form an image approximately 21 μm wide. An image-forming element (not shown) is installed directly below each nozzle. When the image-forming element is driven, thermal energy is generated, causing the ink directly below to bubble, thereby ejecting the ink from the nozzle. In the following description, the term "image-forming element array" refers to an array of multiple image-forming elements formed directly below multiple nozzles that form an array ejecting the same color and amount of ink. The print head configuration shown in FIG. 2 is merely an example, and any of those included in known image-forming devices can be adopted.

[0028] 3 is a block diagram showing an example of the hardware configuration of each device in an inkjet image forming system including an information processing device according to this embodiment. The inkjet image forming system according to this embodiment includes an information processing device 316 and an inkjet image forming device 300 (hereinafter also simply referred to as an image forming device).

[0029] The image forming apparatus 300 according to this embodiment includes a control unit 301, an image buffer 302, a printhead 303, a motor control unit 304, an I / F 305, and a data buffer 306. In FIG. 3, the control unit 301 controls the entire image forming apparatus 300 and is composed of a control device such as a CPU and storage devices such as a ROM and RAM. The image buffer 302 stores image data as raster data before transferring it to the printhead 303. The printhead 303 is an inkjet printhead having multiple image forming elements capable of ejecting ink droplets, and each image forming element ejects ink according to the image data stored in the image buffer 302. The motor control unit 304 controls the operation of the motors included in the image forming apparatus 300, thereby controlling the transport of the print medium and the feeding and ejection of paper. The interface (I / F) 305 exchanges data signals with an information processing device 316.

[0030] The I / F signal line 313 connects the image forming apparatus 300 and the information processing device 316 so that they can communicate with each other. The I / F signal line 313 may be a wired connection, such as a USB cable, or a wireless connection, such as a wireless communication network using a wireless access point, Wi-Fi Direct (registered trademark), or a local area network. By using the I / F signal line 313 in this manner, it is possible to install the information processing device 316 in a location remote from the image forming apparatus 300 or to deploy it as a cloud server. The I / F signal line 313 may also be used as a system bus. In this case, the image forming apparatus 300 and the information processing device 316 may be mounted on the same board or the same system chip.

[0031] A data buffer 306 temporarily stores image data received from the information processing device 316. A system bus 307 connects the various functional units of the image forming device 300 together.

[0032] The information processing device 316 according to this embodiment includes a control unit 308, an I / F 309, a display unit 310, an operation unit 311, and a connection I / F 314. The control unit 308 controls various processes in the information processing device 316, such as image creation and image data control, and is composed of a control device such as a CPU and storage devices such as a ROM and RAM. The I / F 309 exchanges data signals with the image forming device. The connection I / F 314 receives image data (for example, input by a user) from an image supply device 315 and supplies the received image data to the information processing device 316 as a data signal via a system bus 312.

[0033] The display unit 310 is, for example, a display, and displays various processing results to the user. The display unit 310 may be a liquid crystal display (LCD) or the like when the information processing device 316 is a personal computer (PC), or may be a touch panel liquid crystal display when the information processing device 316 is an integrated device with the image forming device 300. The operation unit 311 is, for example, a keyboard and mouse, or a touch panel, and accepts operations from the user. The operation unit 311 may be a keyboard and mouse when the information processing device is a PC, or may be a touch panel or mechanical switches such as push buttons when the information processing device is an integrated device with the image forming device. The system bus 312 connects the various functional units included in the information processing device 316.

[0034] Note that information processing device 316 may be a PC, a mobile terminal such as a smartphone, or a server device, and is not particularly limited to that type as long as it is capable of performing similar processing. Furthermore, although information processing device 316 is illustrated in the example of Fig. 3 as a device separate from image forming device 300, it may also be a device integrated with the image forming device, for example, built into image forming device 300.

[0035] The image supply device 315 supplies image data to the information processing device 316 according to this embodiment. The image supply device 315 according to this embodiment transmits image data selected by a user to the information processing device 316, for example, in response to a user operation. However, for example, the image supply device 315 may be an imaging device with an imaging function, and transmit the captured image to the information processing device 316. Furthermore, for example, the image supply device 315 may be a storage medium capable of storing image data, such as a USB memory or a DVD disc, which is referenced by the information processing device 316 and from which the image data is read.

[0036] Fig. 4 is a flowchart showing an example of image data processing performed by the information processing device 316 of this embodiment. The processing in Fig. 4 is started when image data is input to the information processing device 316, with the image data being the processing target.

[0037] In S401, the information processing device 316 performs color correction on the image data. In this embodiment, the following description will be given assuming that the input image data is 600 dpi RGB data. In color correction, brightness data expressed as values ​​from 0 to 255 for each of the R (red), G (green), and B (blue) elements is corrected, thereby converting the data into brightness data in a color space specific to the image forming device 300 (here, RGB 8-bit). Here, the signal values ​​can be converted using any known conversion method, such as by referencing a lookup table (LUT) stored in advance in memory.

[0038] In S402, the information processing device 316 separates the corrected RGB data into 8-bit density data for the four colors of C (cyan), M (magenta), Y (yellow), and K (black), which are the ink colors of the image forming device 300. In S402, single-channel gray images for each color are generated for four planes (four colors). As with the color correction process of S401, the ink color separation process in S402 can employ any known method, such as referencing a lookup table (LUT) stored in advance in memory.

[0039] In S403, the information processing device 316 performs correction to adjust the number of dots actually formed for each of the multi-value color signal data CMYK that has been subjected to ink color separation processing. Generally, there is no linear relationship between the number of dots formed on a print medium and the optical density achieved on the print medium by that number of dots. Therefore, to make this relationship linear, the information processing device 316 adjusts the number of dots formed on the print medium by linearly converting the multi-value color signal data CMYK. Specifically, the information processing device 316 converts CMYK colors into C'M'Y'K' colors by referencing one-dimensional lookup tables prepared for each ink color.

[0040] In S404, the information processing device 316 performs quantization processing on each plane of the ink color separated density data using a dither method to reduce the number of gradations.

[0041] In S405, the information processing device 316 can perform dot expansion on the quantized data. Dot expansion will be described later with reference to FIG. 8. In S405, the image is converted into 1-bit binary data. In S405 according to this embodiment, the information processing device 316 generates binary data that specifies ink formation (1) or non-formation (0) for each element according to the value of the quantized data.

[0042] In this embodiment, an image forming apparatus 300 having an output resolution of 1200 dpi for the ejection ports is used. Hereinafter, a case where, in accordance with the use of such an image forming apparatus 300, dots are expanded to 1200 dpi x 1200 dpi image data, where the resolution in the X direction in FIG. 1 is 1200 dpi and the resolution in the Y direction is 1200 dpi, will be described. Details of the dithering process, threshold matrix, and dot expansion process will be described later. In this embodiment, RGB data, which is the original image data, is converted into binary data that can be formed by the print head 303 for each of the ink colors CMYK. The converted image data is output to the image forming apparatus 300.

[0043] 4 is executed in the image forming system according to this embodiment. For example, the information processing device 316 may perform S401 to S404 (processing up to quantization), and the image forming device 300 may perform the dot expansion process of S405. The quantized data generated in S404 is transferred to the image forming device 300, and the control unit 301 of the image forming device 300 performs dot expansion by referring to the data buffer 306. In this case, if the information processing device 316 performs the processes up to quantization, the quantized data is transferred to the image forming device 300, and the main control unit 301 of the image forming device 300 performs dot expansion by referring to the data buffer 306, and controls image formation.

[0044] The number of bits of input and output data used in each process is not limited to the above-mentioned number of bits. For example, the number of bits of output data may be set higher than that of input data in order to maintain accuracy.

[0045] The quantization process and dot expansion process performed in the system according to this embodiment will be described in detail below. First, the image quality elements realized in the image formation process according to this embodiment will be described.

[0046] [Image quality elements achieved by input / output resolution and quantization processing] In this embodiment, we will explain the resolution (jaggies), number of gradations, and graininess as image quality elements realized by input / output resolution and quantization processing. Resolution is an image quality element related to image jaggedness, i.e., jaggies, and depends on the input resolution of the input image data. Number of gradations represents the ability of area modulation. Here, number of gradations is the number of gradations that can be reproduced per pixel at a certain resolution and is greatly dependent on the relationship between input and output resolutions. Graininess is an image quality element related to image roughness and is greatly dependent on the dot arrangement during image formation, i.e., the dispersion of dots at the output resolution. For example, if the input resolution is 600 dpi and the output resolution is 1200 dpi, one input pixel corresponds to 2 x 2 pixels at the output resolution. Therefore, with regard to number of gradations, four output gradations can be realized for one input pixel.

[0047] To utilize the potential of a 1200 dpi high-density print head to reduce graininess and ensure dispersibility at the output resolution, one possible approach is to perform dithering at 1200 dpi, the print head's output resolution. This is because performing dithering at 1200 dpi makes it possible to use a blue noise dither matrix that takes into account dot dispersibility in 1200 dpi increments, thereby achieving dot dispersibility at the output resolution.

[0048] However, if high-resolution quantization is performed to match the resolution of the high-density print head in order to maintain the number of gradations and reduce graininess, the amount of image data after quantization will be enormous. Therefore, in the system according to this embodiment, processing is performed to reduce the amount of image data sent and received between devices while ensuring dot dispersion in units of 1200 dpi, which is the output resolution.

[0049] [Dithering, Threshold Matrix (MTX), and Dot Expansion Processing in This Embodiment] 5 is a block diagram showing an example of the functional units of the image forming apparatus 300 and the information processing apparatus 316, for explaining the dithering process, threshold matrix (MTX), and dot expansion process according to this embodiment. First, the processing flow in the system according to this embodiment will be explained with reference to this block diagram.

[0050] The information processing device 316 according to this embodiment includes a data acquisition unit 501, a resolution conversion unit 502, a quantization processing unit 503, a conversion processing unit 504, and a data transfer unit 506. The image forming device 300 according to this embodiment includes a data reception unit 507, a dot development unit 508, and an MTX generation unit 509. Each functional unit shown in Fig. 5 performs the processes from S404 to S405 in Fig. 4.

[0051] The data acquisition unit 501 acquires an input image with a first resolution (for example, from the image supply device 315). The first resolution according to this embodiment is a resolution lower than the output resolution of the image forming device 300, and in this description it is assumed to be 600 dpi. The processing shown in FIG. 4 is started when the data acquisition unit 501 acquires the input image. Note that in the following description, it is assumed that the data acquisition unit 501 acquires image data after gradation correction (here, 600 dpi x 600 dpi, 8-bit data for each color of C'M'Y'K') after S401 to S403 as the input image to be used in the processing described below. Furthermore, although processing is performed for each of the colors C'M'Y'K', the processing is similar, so the processing for the color K' will be described.

[0052] The information processing device 316 according to this embodiment generates a multi-valued image with a resolution lower than the output resolution based on the image acquired by the data acquisition unit 501, and transmits the image to the image forming device 300. This multi-valued image is, for example, the image shown in (I5) of FIG. 6 (described later), and has the same resolution as the input image. This multi-valued image may also be generated so that the gradation value of one pixel indicates the number of dots when the area of ​​the input image corresponding to that pixel is converted to the output resolution and then binarized using a first threshold matrix (described later). Note that, hereinafter, the resolution at which image data (multi-valued image) is transmitted to the image forming device 300 in this manner will be referred to as the transfer resolution. The process of generating such a multi-valued image will be described below.

[0053] The resolution conversion unit 502 converts the resolution of the input image (8-bit image data) into 8-bit image data with an output resolution of 1200 dpi. The resolution conversion unit 502 can convert the input image to a higher resolution using a known interpolation method such as nearest neighbor.

[0054] The quantization processing unit 503 dithers the resolution-converted 1200 dpi, 8-bit (gradation values ​​0 to 255) image using a binary dither using a first threshold matrix. Here, the binarization process using the first threshold matrix reduces the number of gradations to 1200 dpi, 1-bit (binary, gradation values ​​0 or 1) image data, in which each element of the image is 1 (dot formation) or 0 (dot non-formation). Note that the first threshold matrix used here is, for example, a 1200 dpi, 8-bit threshold matrix (M1) (described below) that conforms to the output resolution.

[0055] In order to compress the amount of data transfer, the conversion processing unit 504 converts the 1200 dpi 1 bit (binary) image data into a multi-valued image of the transfer resolution (here, 600 dpi 3 bit (5-valued, gradation values ​​0 to 4)). The conversion processing performed by the conversion processing unit 504 will be described later with reference to FIG. 6. The data transfer unit 506 transfers the multi-valued image converted by the conversion processing unit 504 from the information processing device 316 to the image forming device 300.

[0056] The data receiving unit 507 receives the 600 dpi 3 bit image data (multi-value image) transferred by the data transferring unit 506.

[0057] The dot expansion unit 508 converts the image data received by the data receiving unit 507 into a dot image, which is a binary image at the output resolution, and reduces the gradation values ​​to 1200 dpi 1-bit (binary) (gradation values ​​0 to 1) data. Here, the dot expansion unit 508 converts one pixel of the multi-valued image at the transfer resolution into a dot image in accordance with information indicating the dot arrangement in the multi-valued image, which corresponds to the gradation value of the pixel. This information indicating the dot arrangement in the multi-valued image is determined based on the magnitude relationship between the threshold values ​​in the area of ​​the threshold matrix corresponding to the one pixel. In this embodiment, the information indicating the dot arrangement is represented by a sub-pixel threshold order matrix (hereinafter referred to as threshold order matrix) M2, which will be described later; the process of generating the threshold order matrix (M2) will be described later.

[0058] The MTX generation unit 509 receives the threshold matrix (M1) as input, orders the thresholds within the 2x2 sub-pixels, and generates a threshold order matrix M2. The processing performed by the MTX generation unit 509 will be described later.

[0059] Hereinafter, the processes performed by the information processing device 316 and the image forming device 300 will be described with reference to FIGS.

[0060] FIG. 6 shows an example of multiple types of image data generated by conversion processing by the information processing device 316, and image data generated by the dot expansion unit 508. The squares shown in FIG. 6 represent one pixel, the smallest unit in the image data. Two square sizes are shown here, with the large square representing one pixel at 600 dpi and the small square representing one pixel at 1200 dpi. In other words, the large square is equivalent to 2x2 small squares. Image sizes are arbitrary, but for the sake of explanation, FIG. 6 illustrates processing on data of 4x4 pixels at 600 dpi and 8x8 pixels at 1200 dpi.

[0061] FIG. 7 is a diagram illustrating the threshold matrix used in this embodiment. Each square in FIG. 7 represents one pixel of the dither pattern. Two square sizes are shown here, with the large square representing one pixel at 600 dpi and the small square representing one pixel at 1200 dpi. In other words, the large square is equivalent to 2x2 small squares. The dither pattern may be any size, but for the sake of explanation, FIG. 7 illustrates processing of 4x4 pixel data at 600 dpi and 8x8 pixel data at 1200 dpi.

[0062] In reality, to express 256 gradations in 8 bits, it is necessary to print dots ranging from 0 to 255, requiring at least 16x16 pixels. Therefore, all numbers from 0 to 255 should appear as thresholds in a dither pattern of at least 16x16 pixels. However, for the sake of explanation, the illustration is simplified and the thresholds shown are discrete values. Therefore, when implementing this embodiment, it is preferable to use a threshold matrix of 16x16 pixels or larger.

[0063] 8 is a flowchart showing an example of information processing including dither processing, threshold matrix (MTX), and dot expansion processing performed by the information processing device 316 and image forming device 300 according to this embodiment. In FIG. 8, steps S801 to S808 are processes performed by the information processing device 316, and steps S809 to S818 are processes performed by the image forming device 300.

[0064] In S801, the data acquisition unit 501 acquires an input image of the input resolution. The following description will be given assuming that the input data is, for example, image data of 4x4 pixels at 600 dpi, with a total pixel count of K'=128, as shown in (I1) of FIG.

[0065] In S802, the resolution conversion unit 502 converts the acquired input image (600 dpi, 8 bit (tone values ​​0 to 255)) to a resolution of 1200 dpi, which is the output resolution, using a known resolution conversion process such as nearest neighbor. As a result, 8x8 pixel data of 1200 dpi is obtained, as shown in (I2) of FIG. 6. The single pixel in the upper left corner indicated by the thick solid line in (I1) of FIG. 6 is converted into 2x2 pixels represented by the thick solid line frame in the upper left corner of (I2) of FIG. 6 through this conversion.

[0066] In S803, the quantization processing unit 503 reads out a threshold matrix (M1) according to the output resolution to be used in the next step S804. The threshold matrix read out here is an 8x8 size matrix with an output resolution of 1200 dpi, and is (M1) in FIG.

[0067] In S804, the quantization processing unit 503 performs binary quantization (binarization) on the resolution-converted 1200 dpi 8-bit image data using the threshold matrix (M1) read in S803, thereby reducing the gradation value. Here, binary quantization of the image data is performed by, for example, comparing the pixel value at a corresponding position in the image data and threshold matrix with a threshold, and assigning a gradation value of 1 (dot formation) if the pixel value exceeds the threshold, and a gradation value of 0 (dot non-formation) if it does not. Here, the pixel value at the upper left corner of the resolution-converted input image (I2) shown in FIG. 6 is 128, and the threshold value at the upper left corner of the threshold matrix (M1) shown in FIG. 7 is 166. Comparing these values ​​reveals that the pixel value is equal to or less than the threshold, so the value at that position in the binarized image becomes 0 (dot non-formation).

[0068] The binary image (I3) in Figure 6 is generated by performing the same binary quantization process on all pixels of the input image (I2). In the binary image (I3) in Figure 6, pixels that form dots (value is 1) are marked with a black circle. For example, it can be seen that the pixel in the upper left corner of (I3) does not form a dot. This process results in a 1200 dpi 1 bit binary image (dot image).

[0069] In S805, the conversion processing unit 504 performs multi-value low-resolution conversion processing to convert the 1200 dpi 1-bit image data into a multi-value image expressed as 600 dpi 3-bit data in order to compress the amount of data transfer. S805, which is the multi-value low-resolution conversion processing according to this embodiment, includes two steps, S806 and S807.

[0070] In S806, the conversion processing unit 504 performs dot counting on the binary image in pixel units of the transfer resolution. Here, dot counting refers to the process of counting the number of dots in the binarized image as described above in areas that satisfy certain conditions. Here, the transfer resolution is 600 dpi, the same as the input resolution, and the conversion processing unit 504 counts the number of dots in the binary image for each area corresponding to one pixel at this resolution. In the example of FIG. 6, first, the 1200 dpi, 1-bit binary image (I3) is divided into 600 dpi units. (I4) in FIG. 6 shows the binary image (I3) divided into 600 dpi units (2x2 subpixels), with the 600 dpi units depicted by bold lines. The dot counting process counts the number of dots in each 2x2 subpixel, and the resulting number of dots becomes the gradation value for each pixel of the multi-value image. That is, a multi-valued image at the transfer resolution has, as the gradation value of one pixel, the number of dots in the area corresponding to that one pixel of the binarized image.

[0071] The number of gradations that can be expressed by a 2x2 subpixel is equivalent to the number of dots that can be formed in that subpixel. Since 0 to 4 dots can be placed in a 2x2 subpixel, the number of gradations is 5, and gradation values ​​0 to 4 can be expressed. By transmitting the dot count information for the 2x2 subpixel to the image forming device 300 as the gradation value of the multi-valued image, the number of gradations can be maintained even after data transfer. The resulting multi-valued image with an input resolution of 600 dpi (5-value) (gradation values ​​0 to 4) is shown in Figure 6 (I5). Looking within the bold line at the top left of Figure 6 (I4), two dots are present in the 2x2 pixel. Therefore, when viewed at a transfer resolution of 600 dpi, two dots should be formed at the corresponding pixel position. The top left pixel of the multi-valued image (I5) has a gradation value of "2," corresponding to the total number of dots in this 2x2 subpixel, "2." In S807, the conversion processing unit 504 similarly obtains the gradation value for each pixel of the multi-valued image, and obtains the multi-valued image (I5).

[0072] In S808, the data transfer unit 506 transmits the generated 600 dpi 3 bit multi-valued image to the image forming apparatus 300.

[0073] In S809, the data receiving unit 507 receives the multi-valued image transmitted by the data transferring unit 506. In S810, the dot expansion unit 508 reads out a threshold matrix to be used for dot expansion. Here, the threshold matrix (M1) in FIG. 7 is read out.

[0074] In S811, the dot expansion section 508 and MTX generation section 509 perform dot expansion processing by using the read threshold matrix. S811, which is the dot expansion processing according to this embodiment, includes seven processes from S812 to S818.

[0075] In S812, the MTX generation unit 509 generates a threshold order matrix to be used in the dot expansion process based on the threshold matrix. The threshold order matrix is ​​a matrix that indicates the magnitude relationship of the thresholds in an area of ​​the threshold matrix that corresponds to one pixel of a multi-value image (here, within 2x2 sub-pixels). In the threshold order matrix, the threshold numbers within the sub-pixels are sorted in ascending order, and each sort order number is indicated for each element within the sub-pixel. Below, 2x2 sub-pixels will be referred to as an example of an area that corresponds to one pixel of a multi-value image.

[0076] For example, consider the 2x2 subpixel at the top left of the threshold matrix (M1) in Figure 7. When viewed at an output resolution of 1200 dpi, the order in which dots are most likely to be placed within this subpixel is the order of lowest threshold. Here, when an image at transfer resolution is converted to the output resolution, all four 2x2 pixels have the same pixel value. Therefore, when forming one dot in a 2x2 subpixel, the position corresponding to the smallest threshold becomes the formation pixel. Similarly, when forming two dots, the pixels corresponding to the first and second smallest thresholds become the formation pixels. Similarly, when forming three dots, the first through third smallest pixels become the formation pixels. The thresholds for the 2x2 subpixel at the top left of the threshold matrix (M1) are 166 (top left), 231 (top right), 36 (bottom left), and 117 (bottom right). Sorting them in ascending order is 36 → 117 → 166 → 231. By listing the order of the threshold values ​​in the corresponding 2x2 sub-pixels for the entire threshold matrix (M1), the threshold order matrix (M2) shown in FIG. 7 is generated.

[0077] The processes from S813 to S818 are repeatedly looped and performed for each pixel of all pixels of the multi-value image input to the image forming apparatus 300. Here, the explanation will be given assuming that the input multi-value image is 4x4 pixels as shown in (I5) of FIG. 6, so repeated processing is performed for 16 pixels. In S813, the dot development unit 508 selects one of the pixels of the multi-value image as the processing target. Here, in the first loop processing, the pixel at the top left corner of the multi-value image is assumed to be the processing target.

[0078] The processes from S814 to S817 are repeated for each pixel in the 2x2 subpixels (a total of four loops in this case). In S814, the dot expansion unit 508 selects one of the subpixels of one pixel as the processing target. In the first loop, the upper left subpixel of the 2x2 is selected as the processing target.

[0079] In S815, the dot expansion unit 508 compares the gradation value of the multi-value image (I5) with the threshold value of the subpixel to be processed in the threshold order matrix (M2). If the gradation value is equal to or greater than the threshold value (Yes), the process proceeds to S816; if not (No), the process proceeds to S817, assuming that a dot will not be formed in the subpixel to be processed. In S816, the dot expansion unit 508 sets the subpixel to be processed as one in which a dot will be formed, and the process proceeds to S817. In S817, the dot expansion unit 508 determines whether all subpixels have been processed; if not, the process returns to S814; if yes, the process proceeds to S818.

[0080] Here, a specific example will be used to explain the first loop processing from S814. First, in FIG. 6, the gradation value at the top left of the multi-value image (I5) is 2, and in FIG. 7, the threshold value for the top left subpixel to be processed within the 2x2 thick-lined box at the top left is 3. Because the gradation value is smaller than the threshold, the result is "No," and no dot is formed for the subpixel to be processed. In this case, processing returns from S817 to S814, and loop processing is performed on the next subpixel to be processed. Here, the threshold value for the top right of the 2x2 thick-lined box at the top left of the threshold ordering matrix (M2) is 4. A comparison of the gradation value 2 with the threshold value 4 results in the gradation value being smaller than the threshold, so the result is "No," and no dot is formed for the subpixel to be processed. Next, processing returns from S817 to S814, and the next subpixel is processed. The threshold value for the bottom left of the 2x2 thick-lined box at the top left of the threshold ordering matrix (M2) is 1. As a result of comparing the gradation value 2 with the threshold value 1, the gradation value is greater than or equal to the threshold, so the result is "Yes," and in S816, a setting is made such that a dot will be formed in the subpixel being processed. Then, the process returns again from S817 to S814, and loop processing is performed with the last subpixel being processed. The threshold value at the bottom right of the 2x2 box with the thick line frame at the top left of the threshold order matrix (M2) is 2. As a result of comparing the gradation value 2 with the threshold value 2, the gradation value is greater than or equal to the threshold, so the result is "Yes," and in S816, a setting is made such that a dot will be formed in the subpixel being processed. Next, in S817, the dot expansion unit 508 has determined that all 2x2 subpixels of the pixel being processed will be processed, so the process proceeds to S818.

[0081] In S818, the dot expansion unit 508 determines whether all pixels of the multi-value image have been processed in S813, and if so, ends the processing of Figure 8, and if not, returns to S813.

[0082] By this process, the dot expansion result generated as a result of performing dot expansion processing on all sub-pixels of all pixels is shown, for example, as expansion result (I6) in Figure 6. Looking at the expansion result (I6), it can be seen that it matches the binarized image (I3), which is the binary quantization result of the output resolution generated before the data transfer process S808.

[0083] With this type of processing, even if image data with a resolution lower than the output resolution (here 600 dpi) is sent when transferring the data, the binary quantization result of the output resolution can be realized after transfer, and the dot dispersion of the output resolution can be realized.

[0084] In the following, the effects of the processing according to this embodiment on image quality elements such as data volume and graininess will be described in comparison with a comparative example, which will be described with reference to FIG.

[0085] [Comparative Example] In the following, as a comparative example, a process will be described in which, after multi-level quantization (quasi-halftone processing), dot expansion processing is performed using a dot pattern that is not related to the dither matrix used during multi-level quantization.

[0086] 9 is a diagram for explaining the dot expansion process of the comparative example. Here, the explanation will be given assuming that the process of the comparative example is performed by the information processing device 316 and the image forming device 300. The process of the comparative example can be performed by the method described in Patent Document 1, and a detailed explanation will be omitted here.

[0087] 9(a) is a block diagram showing an example of the functional configuration of an information processing device 316 and an image forming device 300 that execute the method described in Literature 1. The information processing device 316 according to the comparative example has a configuration similar to that shown in FIG. 5 and is capable of performing similar processing, except that it has a quantization processing unit 901 instead of the resolution conversion unit 502, the quantization processing unit 503, and the conversion processing unit 504. Furthermore, the image forming device 300 according to the comparative example has a configuration similar to that shown in FIG. 5 and is capable of performing similar processing, except that it has a pattern expansion unit 902 instead of the dot expansion unit 508 and the MTX generation unit 509.

[0088] The quantization processing unit 901 according to the comparative example performs multi-value error diffusion processing to obtain multi-value quantized data with an input resolution of 600 dpi and 3 bits per 5 value as a multi-value image. Here, the quantization processing unit 901 refers to an error diffusion coefficient M9.

[0089] In this comparative example, dot patterns corresponding to multi-value output values ​​(index numbers) are stored in a table memory, and a pattern expansion unit 902 performs dot expansion by using this index pattern according to the method described in Patent Document 1.

[0090] The pattern expansion unit 902 performs dot expansion by referring to the index pattern J1. Here, the index patterns shown in FIGS. 9(c) to 9(f) are stored in the index pattern J1. FIG. 9(c) is the pattern for index level (tone value) 1. As shown in FIG. 9(c), there are four 2x2 sections, and each section has one formed dot (black circle). If the same dot arrangement occurs multiple times, texture will appear in the image, so these four patterns are applied in order or randomly. FIG. 9(d) corresponds to level 2, and the number of formed dots is two in each case. FIG. 9(e) corresponds to level 3, and FIG. 9(f) corresponds to level 4.

[0091] In the comparative example, the multi-valued image generated by the quantization processing unit 901 is the multi-valued image (I5) in Fig. 6. Next, the process of index development from the multi-valued image (I5) by the pattern development unit 902 will be described.

[0092] The gradation value of the pixel at the top left of the multi-value image (I5) is level 2. For this position, the pattern expansion unit 902 assigns the dot pattern at the left end of the four sections in FIG. 9(d) that corresponds to level 2 as the corresponding pattern. The pattern expansion unit 902 can perform dot expansion from the multi-value image by assigning the four patterns for each level in turn in the order in which each level appears. Here, the expansion result generated by the dot expansion process by the pattern expansion unit 902 is shown in FIG. 9(g). When compared to the binarized image (I3), the expansion result shown in FIG. 9(g) maintains the number of gradations (number of dots) per pixel of the multi-value image, but the dot arrangement is not.

[0093] [Data volume comparison] FIG. 10 is a diagram for explaining a comparison between the data amount of a multi-valued image transmitted to the image forming apparatus 300 by the information processing apparatus according to this embodiment and the data amount of a multi-valued image generated by a method of the comparative example.

[0094] Figure 10(a) shows the image size assumed for the calculation. Figure 10(b) shows the data volume of the input image, the case where the image is left as is after binarization, the multi-valued image (conventional) generated by the method of the comparative example, and the multi-valued image generated by the method of this embodiment. The data volume of the input image is 1049 MB, and the data volume after binarization processing at 1200 dpi binary is 699 MB. On the other hand, the multi-valued images generated by the method of the comparative example and the method of this embodiment are transferred as multi-valued data with a resolution of 600 dpi, so the image data volume is kept to 524 MB.

[0095] [Graininess] [Method of measuring graininess] Next, an example of a method for measuring graininess will be explained. Here, digital dot image data that has been image-processed, or dot image data scanned using a scanner, is prepared as the object of measurement. This dot image data is subjected to a well-known two-dimensional Fourier transform (FFT). This yields a two-dimensional complex number, and to obtain characteristics for each frequency, the amplitude for each radial frequency is calculated. This amplitude for each radial frequency is the average value obtained by taking the sum of the squares of amplitude components equidistant from the origin (DC component). An example of the amplitude (power spectrum) obtained in this way is shown in Figure 11.

[0096] Graininess is the roughness perceived by the human eye. Therefore, in order to reflect the characteristics of human vision, the spatial frequency characteristics (VTF) of human vision are reflected in the graininess. Specifically, the graininess is determined by multiplying the obtained power spectrum by the spatial frequency characteristics (VTF) of human vision for each spatial frequency and integrating the result.

[0097] FIG. 11 illustrates the frequency characteristics of image data obtained by the method of this embodiment and the comparative example. In FIG. 11, the dashed line indicates the spatial frequency characteristic (VTF) of human vision at a clear viewing distance of 250 mm. In FIG. 11, the horizontal axis represents frequency (radial frequency) [cycles / mm], and the vertical axis represents the power spectrum. The left side of the graph indicates lower frequencies, and the right side indicates higher frequencies, with the vertical axis representing the intensity (power) at the frequency. The VTF characteristic of human vision is highly sensitive to low frequencies and less sensitive to high frequencies. Therefore, low-frequency components are easily noticeable, but high-frequency components are less noticeable. Blue noise characteristics are based on the above-mentioned visual characteristics, and have almost no power in the low-frequency region where visual sensitivity is high (easily visible), and have power in the high-frequency region where sensitivity is low (hardly visible). Therefore, frequency components are barely visible, resulting in a comfortable image with low graininess.

[0098] In Fig. 11, the graph indicated by x marks shows the frequency characteristics of image data obtained by the method of the comparative example, and the graph indicated by a thick solid line shows the frequency characteristics of image data obtained by the method of this embodiment. Referring to Fig. 11, in the spatial frequency range of 3 to 7 [cycles / mm], where VTF is also sensitive, the method of the comparative example has greater power than the method of this embodiment. Therefore, it can be seen that the processing according to this embodiment reduces graininess more than the method of the comparative example.

[0099] FIG. 12 is a diagram illustrating the graininess of image data obtained by the methods of this embodiment and the comparative example. FIG. 12 is a graph showing the VTF and power integrated over all frequencies, as described in FIG. 11, representing the graininess perceived by human vision. The information processing device 316 and image forming device 300 according to this embodiment are thus capable of evaluating the graininess of an image. As shown in FIG. 12, the processing according to this embodiment reduces the graininess compared to the method of the comparative example. Note that the granularity is not limited to the above definition; RMS granularity, as defined by the ANSI (American National Standards Institute) standard, can also be used. Note that in this embodiment, each process may be performed so that the difference in graininess evaluated as described above between the binary image (I3) and the expansion result (I6) obtained by the dot expansion process of the image forming device 300 is within a predetermined range. Here, by generating a multi-valued image and performing dot expansion processing so that the graininess of these images is approximately the same, it is possible to maintain sufficient graininess.

[0100] [Embodiment 2] In the first embodiment, the dot expansion unit 508 performs dot expansion processing by comparing a multi-valued image with a threshold value by referencing the threshold order matrix (M2), thereby generating a dot image. The image forming apparatus 300 according to the second embodiment performs dot expansion processing by referencing a dot pattern that has been previously expanded, instead of this comparison processing. The dot expansion processing performed by the image forming apparatus according to this embodiment will be described below. The same reference numerals are used for configurations and processing similar to those of the first embodiment, and duplicated descriptions will be omitted.

[0101] 13 is a block diagram showing an example of the functional units of the image forming apparatus 300 and the information processing apparatus 316, for explaining the dithering process, threshold matrix (MTX), and dot expansion process according to this embodiment. The system according to this embodiment has the same configuration as that shown in FIG. 5, except that the image forming apparatus 300 has a pattern expansion unit 1301 instead of the dot expansion unit 508, and further has an additional table generation unit 1302, and therefore redundant explanations will be omitted.

[0102] The pattern development unit 1301 performs dot development from the multi-value image by referring to a dot pattern table that indicates a dot arrangement according to the gradation values ​​of the multi-value image. The pattern development unit 1301 according to this embodiment performs dot development from the image data (multi-value image) received by the data receiving unit 507 based on dot pattern tables (M41 to M44) prepared in advance. In this embodiment, the dot pattern tables (M41 to M44) are generated by the table generation unit 1302 based on a threshold order matrix (M2).

[0103] The dot pattern tables (M41 to M44) according to this embodiment are associated with the threshold matrix (M1), and can achieve the same dot arrangement as when dots are expanded using the threshold matrix (M1). The dot pattern tables (M41 to M44) are shown in FIG.

[0104] Fig. 14 is a flowchart showing an example of information processing including dithering, a threshold matrix (MTX), and dot pattern expansion processing performed by the information processing device 316 and image forming device 300 according to this embodiment. The processing shown in Fig. 14 is performed in the same manner as the processing shown in Fig. 8, except that S1401 is performed instead of S811. In S1401, the pattern expansion unit 1301 performs dot pattern expansion processing. S1401, which is the dot pattern expansion processing according to this embodiment, includes S812 and three processes, S1402 to S1403.

[0105] In S812, the MTX generation unit 509 generates a threshold order matrix (here, (M2)) to be used in the dot expansion process.

[0106] In S1402, the table generation unit 1302 references this threshold order matrix and generates a dot pattern table for each level. The dot pattern table for level 1 corresponds to the case where one dot is placed on a 2x2 subpixel. Similarly, level 2 corresponds to two dots, level 3 corresponds to three dots, and level 4 corresponds to four dots. Therefore, in the case of level 1, it can be seen that which subpixels will become neglected dots by looking at subpixels with a value of 1 in the threshold order matrix. Similarly, in the case of level 2, subpixels with a value of 1 and 2 in the threshold order matrix correspond to formed dots. In the case of level 3, subpixels with a value of 1, 2, and 3 in the threshold order matrix correspond to formed dots. In the case of level 4, subpixels with a value of 1, 2, 3, and 4 in the threshold order matrix correspond to formed dots.

[0107] The level 1 dot pattern table obtained in this way is shown as table (M41) in Figure 7. In table (M41), it can be seen that positions corresponding to 1 in the threshold order matrix (M2) are formed dots (black circles). Similarly, the level 2 dot pattern table is table (M42), the level 3 dot pattern table is table (M43), and the level 4 dot pattern table is table (M44).

[0108] In S1403, the pattern expansion unit 1301 expands dots using the obtained dot pattern table for each level. The pattern expansion unit 1301 reads the gradation value of each pixel from the multi-value image (I5), and performs dot expansion using the pattern at the same pixel position in the dot pattern table for the corresponding level value (gradation value). For example, the gradation value at the top left corner of the multi-value image (I5) is 2, and the 2x2 pattern at the top left corner in the dot pattern table (M42) corresponding to level 2 is used as the dot pattern to be expanded. In this way, it is possible to realize a dot pattern that is the same as the 2x2 pixels at the top left corner of the expansion result (I6).

[0109] This type of processing allows for dot expansion to be performed using dot patterns prepared according to the gradation values ​​of a multi-value image, eliminating the need for repeated comparison calculations in the dot expansion processing of the first embodiment, and enabling high-speed processing without changing the final dot expansion result.

[0110] [Embodiment 3] The quantization processing unit 503 according to the first embodiment performs binarization processing on pixels of an output resolution of 1200 dpi x 1200 dpi. In the third embodiment, instead of the binary quantization of the output resolution, multi-value quantization is performed on the input image of the input resolution.

[0111] Furthermore, the dot expansion unit 508 according to the first embodiment performs dot expansion processing by comparing the multi-valued image (I5) at the input resolution with the threshold order matrix (M2). On the other hand, the dot expansion unit 508 according to this embodiment performs dither processing instead of dot expansion processing based on such comparison processing.

[0112] 15 is a block diagram showing an example of the functional units of the image forming apparatus 300 and the information processing apparatus 316 for explaining the dithering process, threshold matrix (MTX), and dot expansion process according to this embodiment. The information processing apparatus 316 according to this embodiment has the same configuration as that shown in FIG. 5 except that it has a quantization processing unit 1501 and an MTX generation unit 1504 instead of the resolution conversion unit 502, quantization processing unit 503, and conversion processing unit 504, so a duplicated description will be omitted. Also, the image forming apparatus 300 according to this embodiment has the same configuration as that shown in FIG. 5 except that it has a resolution conversion unit 1502 and a quantization processing unit 1503 instead of the dot expansion unit 508, so a duplicated description will be omitted.

[0113] [Quantization processing] The quantization processing unit 1501 generates a 600 dpi 3-bit (5-value) multi-value image by directly performing multi-value dithering on the input image (here, 600 dpi 8-bit image data) acquired by the data acquisition unit 501. The quantization processing unit 1501 according to this embodiment can generate a multi-value image from the input image using threshold matrices (M31 to M34) for each level. Also, here, the MTX generation unit 1504 generates the threshold matrices (M31 to M34) for each level based on the threshold matrix (M1).

[0114] A resolution conversion unit 1502 converts the resolution of the multi-valued image received by the data receiving unit 507 into an output resolution (1200 dpi in this case) using a known resolution conversion process such as nearest neighbor. A quantization processing unit 1503 performs binarization processing on the 1200 dpi 3-bit 5-value input data generated by the conversion process of the resolution conversion unit 1502, thereby generating a dot image.

[0115] Fig. 16 is a flowchart showing an example of information processing including dithering, threshold matrix (MTX), and dot expansion processing performed by the information processing device 316 and image forming device 300 according to this embodiment. The processing shown in Fig. 16 is performed in the same manner as the processing shown in Fig. 8, except that S802 is not performed, S1601 to S1604 are performed instead of S804 to S805, and S1610 to S1611 are performed instead of S810 to S811.

[0116] In S1601, the MTX generation unit 1504 generates a threshold ordering matrix (M2). This is the same processing as in S810.

[0117] In S1602, the MTX generation unit 1504 generates a threshold matrix for each level. For example, the MTX generation unit 1504 can generate threshold matrices (M31 to M34) according to the transfer resolution for each gradation value of a multi-value image. Here, by examining the correspondence between each element of the threshold matrix (M1) and the threshold order matrix (M2) shown in FIG. 7, it is possible to determine which threshold in the threshold matrix (M1) is referenced at each level. For example, the upper left corner of the threshold matrix (M1) is 166, and by examining the threshold order matrix (M2), it is possible to determine that this is the threshold referenced at level 3. Similarly, by examining the second threshold from the top left corner of the threshold matrix (M1), it is determined that the threshold is 36. By examining the threshold order matrix (M2), it is possible to determine that this is the threshold referenced at level 1. In this way, the thresholds corresponding to level 1 are collected to form the threshold matrix (M31) for level 1 shown in FIG. 7. Similarly, the threshold matrix (M32) corresponds to level 2, the threshold matrix (M33) corresponds to level 3, and the threshold matrix (M34) corresponds to level 4. After S1602, the process proceeds to S1604.

[0118] In S1604, the quantization processing unit 1501 performs input resolution multi-value quantization processing. S1604 includes S1605 to S1609.

[0119] The processes from S1605 to S1608 are repeatedly performed in a loop for each pixel of the input image. In S1605, the quantization processing unit 1501 sets one pixel of the input image that has not yet been processed as a processing target.

[0120] In S1606, the quantization processing unit 1501 initializes the level Lv to 1 and the dot Dt to 0. In S1607, the quantization processing unit 1501 compares the input image data with the threshold value at the corresponding position in the threshold matrix for the level indicated by Lv, and determines whether the corresponding input image value is equal to or greater than the threshold value. If it is determined that the value is equal to or greater than the threshold value (Yes), the process proceeds to S1609; if not (No), the process proceeds to S1608.

[0121] In S1609, the quantization processing unit 1501 increments the level Lv and the dot Dt by 1, and returns the process to S1607. In S1608, the quantization processing unit 1501 determines whether or not all pixels were processed in S1605, and if so, proceeds to S808, and if not, returns the process to S1605.

[0122] For example, the value at the top left corner of the input image (I1) is 128. Here, since Lv=1, the threshold value to be referenced is the threshold value 36 at the top left corner of the threshold matrix (M31). Therefore, since the input data is equal to or greater than the threshold value, the process proceeds to S1609, where Lv=2 and Dt=1. Next, in S1607, since Lv=2, the quantization processing unit 1501 compares the input data with the threshold value 117 at the top left corner of the threshold matrix (M32). Since the input data is equal to or greater than the threshold value, the process proceeds to S1609, where Lv=3 and Dt=2. Next, in S1607, since Lv=3, the quantization processing unit 1501 compares the input data with the threshold value 166 at the top left corner of the threshold matrix (M33). Since the input data does not exceed the threshold value, Dt=2 is determined, and the process proceeds to S1608. 6, it can be seen that the number of dots indicated by the number at the top left corner is indeed 2. Processing continues in the same manner, and the flow returns from S1608 to S1605, where loop processing is executed for each pixel of the input pixels.

[0123] This process limits the number of pixels to be compared to the input resolution of 600 dpi, and once the threshold is no longer exceeded, the process moves on to the next pixel, reducing the number of comparisons with the threshold. Furthermore, there is no need for a buffer for the output resolution required for binary development, which also saves memory.

[0124] [Dot Expansion]

[0125] In S1610 following S809, the resolution conversion unit 1502 converts the resolution of the multi-valued image (I5) received in S809 to the output resolution (1200 dpi in this case) by a known resolution conversion process such as nearest neighbor. The multi-valued image with the output resolution thus obtained is shown in FIG. 6 as multi-valued image (I7).

[0126] In S1611, the quantization processing unit 1503 performs binary quantization processing at the output resolution on the multi-valued image at this output resolution. S1611 includes S810, S812, and S1612.

[0127] In S1612, binary quantization processing is performed on the multi-value image (I7) using the threshold order matrix (M2). Here, the quantization processing unit 1503 takes the value 2 at the top left corner of the multi-value image (I7) as input data and compares it with the threshold value 3 at the top left corner of the threshold order matrix (M2). Here, because the input data is not equal to or greater than the threshold, a dot is not formed at this position. Referring to the expansion result (I6), it is clear that a dot is not formed at that position. Next, the value 2 at the second pixel from the top left corner of the multi-value image (I7) is used as input data and compared with the threshold value 1 at the second pixel from the top left corner of the threshold order matrix (M2). Here, because the input data is equal to or greater than the threshold, a dot is formed at that position. Referring to the expansion result (I6), it is clear that a dot is formed (marked with a black circle) in the multi-value image (I7) across the entire field of view.

[0128] Although this type of processing does not use an 8-bit pixel range, quantization can be performed using normal binarization processing. This makes it possible to use a general-purpose dither processing circuit, thereby reducing the circuit size.

[0129] [Embodiment 4] The conversion processing unit 504 according to the first embodiment converts a 1200 dpi 1-bit binary image into a multi-value image with an input resolution of 600 dpi, which is used during data transfer, assuming that the transfer resolution is equal to the input resolution. The conversion processing unit 504 according to the present embodiment sets the transfer resolution to a value different from the input resolution. The following describes a case where the input resolution is 600 dpi and the transfer resolution is 400 × 400 dpi (hereinafter simply referred to as 400 dpi).

[0130] 17 is a block diagram showing an example of the functional units of the image forming apparatus 300 and the information processing apparatus 316 for explaining the dithering process, threshold matrix (MTX), and dot expansion process according to this embodiment. The system according to this embodiment has the same configuration as that shown in FIG. 5, except that the information processing apparatus 316 has a conversion processing unit 1704 instead of the conversion processing unit 504, and therefore a duplicated description will be omitted.

[0131] In the process according to the third embodiment, the transfer resolution is different from that in the first embodiment, and accordingly, the process by the conversion processing unit 1704 and the threshold order matrix (M2') referenced by the dot expansion unit 508 are different.

[0132] [Multi-value low-resolution conversion processing] The conversion processing unit 1704 according to this embodiment converts the resolution of the binary quantized 1200 dpi 1 bit binary image data (gradation values ​​0 to 1) to match the resolution at the time of data transfer. Here, as described above, the transfer resolution is assumed to be 400 dpi.

[0133] Fig. 18 is a flowchart showing an example of information processing including dither processing, threshold matrix (MTX), and dot expansion processing performed by the information processing device 316 and image forming device 300 according to this embodiment. The processing in Fig. 18 is performed in the same manner as the processing shown in Fig. 8, except that S1800 is performed instead of S805, and S1804 is performed instead of S811, and therefore a duplicated description will be omitted.

[0134] In S1800, the conversion processing unit 1704 performs multi-value low-resolution conversion processing to convert the resolution of the image data of 1200 dpi 1 bit (binary) to the transfer resolution (400 dpi) in order to compress the amount of data transfer.

[0135] When a 1200dpi x 1200dpi binary image is viewed at a resolution of 400dpi x 400dpi, one 400dpi x 400dpi pixel contains 9 pixels (3 x 3) in 1200dpi units. 3 x 3 pixels can represent 0 to 9 pixels, and gradation values ​​0 to 9, so there are 10 gradations, and 4 bits are required to represent this number of gradations. Therefore, data transfer here will be performed at 400dpi, 4bit, 10 values.

[0136] S1800 includes three processes: S1801, S1802, and S1803. In S1801, the conversion processing unit 1704 sets the transfer resolution. In this embodiment, the transfer resolution is set to 400 dpi, but this is not particularly limited. This transfer resolution is not particularly limited as long as it is lower than the output resolution, and may be set to any value by the user. Also, for example, the transfer resolution may be set according to the output resolution (for example, so that it is a resolution of a predetermined size relative to the output resolution). Also, this transfer resolution may be determined based on the balance between the amount of data transfer and the amount of calculation in the image forming system.

[0137] In S1802, the conversion processing unit 1704 counts the number of dots in the binary image in pixel units of the transfer resolution, as in S806. Here, the 1200 dpi 1 bit binary image (I3) is divided into 400 dpi units.

[0138] The binary image (I4') shown in Figure 6 is a diagram in which the 1200 dpi 1-bit binary image (I3) is divided into 400 dpi increments, with the 400 dpi increments depicted in bold. Note that the binary image (I4') is illustrated as 9x9 pixel image data so that it can be divided into 3x3 pixel increments. Note that although dots actually exist in the binary image (I4'), they are not used for the purpose of explanation and are therefore not shown in some places.

[0139] By counting the number of dots in the 3x3 subpixels indicated by the thick lines, the counted value becomes the number of dots to be formed at 400 dpi. The conversion processing unit 1704 sets the number of dots counted in this way as the gradation value of the corresponding multi-value image to be transmitted to the image forming apparatus 300. The multi-value image with a transfer resolution of 400 dpi obtained in this way is shown as multi-value image (I5') in FIG. 6. Looking within the thick line in the upper left corner of the binary image (I4'), four dots are formed in 3x3 pixels. Therefore, when viewed at a transfer resolution of 400 dpi, four dots should be formed at the corresponding pixel position, and the value of that pixel in the multi-value image becomes 4. In S1803, the conversion processing unit 1704 performs similar processing on each pixel of the multi-value image obtained in this way, thereby obtaining multi-value image (I5').

[0140] In S808, the data transfer unit 506 transmits a 400 dpi 4 bit (10-level) multi-valued image to the image forming apparatus 300.

[0141] [Dot Expansion] In S1804, the dot expansion unit 508 performs dot expansion processing by using the read threshold matrix. The dot expansion processing in S1804 is the same processing as S811 in Fig. 8, except that S1805 is performed instead of S812.

[0142] In S1805, the dot expansion unit 508 generates a threshold order matrix to be used in the dot expansion process. Here, the threshold order matrix is ​​a matrix (arranged in ascending order) that indicates the magnitude relationship between thresholds within a 3x3 subpixel at a binary quantization resolution of 1200 dpi, which corresponds to one pixel at a transfer resolution of 400 dpi. Here, FIG. 7 shows a threshold order matrix (M1') in which 3x3 subpixel divisions are added with bold lines to the threshold matrix (M1). Note that the threshold order matrix (M1') in FIG. 7 is shown as 9x9 pixel data so that it can be divided into 3x3 pixel units. Note that while thresholds do actually exist in the threshold order matrix (M1'), they are not used for explanatory purposes and are therefore not shown in some places. When viewed at an output resolution of 1200 dpi, dots are more likely to be placed within these subpixels in ascending order of threshold value.

[0143] In this example, when a multi-valued image at the transfer resolution is converted to the output resolution, all nine 3x3 pixels have the same pixel value. Therefore, when forming one dot in a 3x3 subpixel, the position corresponding to the smallest threshold value becomes the formed pixel. Similarly, when forming two dots, the pixels corresponding to the first and second smallest threshold values ​​become the formed pixels. Similarly, when forming three dots, the first through third smallest pixels become the formed pixels. Similarly, by recording the order of the corresponding 3x3 subpixels for the entire threshold matrix, the threshold order matrix (M2') shown in Figure 7 is generated. Determining this threshold order requires sorting the threshold number string. When the target subpixel is a 2x2 pixel, this requires sorting four numbers, but when it is a 3x3 pixel, this requires sorting nine numbers. However, setting such a low transfer resolution reduces the amount of data to be transferred. Referring to Figure 10(b), the data transfer volume at a transfer resolution of 400 dpi is reduced to 310 MB compared to 524 MB at 600 dpi, thereby reducing the amount of data transfer.

[0144] By using this process, a transfer resolution different from the input resolution can be set, and the binary quantization result of the output resolution can be realized after transfer, thereby realizing the dot dispersion of the output resolution.

[0145] The disclosure of this specification includes the following system, image forming apparatus, information processing method, and program.

[0146] (Item 1) A system including an information processing device and an image forming device, The information processing device includes: acquisition means for acquiring a first image at a first resolution; a first conversion means for generating a second image of a second resolution based on a first image of the first resolution, wherein the gradation value of one pixel of the second image indicates the number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first and second resolutions and then binarized using a first threshold matrix according to the third resolution; a transmitting means for transmitting the second image to an image forming device, the image forming apparatus, receiving means for receiving the second image; a second conversion means for converting the second image into a third image which is a binary image of the third resolution, the second conversion means generating the third image in accordance with information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, the dot arrangement corresponding to the one pixel of the third image being determined based on the magnitude relationship of the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; A system comprising: (Item 2) 2. The system according to claim 1, wherein the second conversion means converts the second image into the third image using a second threshold matrix according to the third resolution. (Item 3) The system described in item 2, characterized in that the magnitude relationship of each threshold value in the area corresponding to the one pixel in the second threshold matrix is ​​equal to the magnitude relationship of each threshold value in the area corresponding to the one pixel in the first threshold matrix. (Item 4) 4. The system according to claim 3, wherein the second threshold matrix is ​​the same matrix as the first threshold matrix. (Item 5) The system described in any one of items 1 to 4, characterized in that the dot arrangement corresponding to the one pixel of the third image is determined based on the magnitude relationship of each threshold value in the area of ​​the first threshold matrix corresponding to the one pixel and the gradation value of the one pixel of the second image. (Item 6) Item 6. The system according to item 5, characterized in that the dot arrangement corresponding to the first pixel of the third image is determined so that in the area corresponding to the first pixel of the third image, dots are formed at pixel positions equal to the gradation value of the one pixel of the second image in ascending order of the threshold value in the area corresponding to the one pixel in the first threshold matrix. (Item 7) 7. The system according to any one of items 1 to 6, wherein the first resolution and the second resolution are the same. (Item 8) 7. The system of any one of items 1 to 6, wherein the second resolution is lower than the first resolution. (Item 9) a third conversion means for converting the resolution of the first image into the third resolution; a fourth conversion means for converting the first image having the third resolution into a fourth image binarized using the first threshold matrix; The system described in any one of items 1 to 8, characterized in that the first conversion means sets the gradation value of one pixel of the third image to the number of dots contained in the area corresponding to the one pixel of the fourth image. (Item 10) further comprising an evaluation means for evaluating the graininess of the binary image, 10. The system according to item 9, wherein the difference in the evaluation of graininess between the fourth image and the third image falls within a predetermined range. (Item 11) a generating means for generating a plurality of second threshold matrices according to a second resolution, each of which corresponds to a tone value of the second image, based on the first threshold matrix; 11. The system according to any one of items 1 to 10, wherein the first conversion means generates the second image based on the first image and a plurality of the second threshold matrices. (Item 12) a receiving means for receiving a second image of a second resolution generated based on a first image of a first resolution, wherein the gradation value of one pixel of the second image indicates the number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first and second resolutions and then binarized using a first threshold matrix according to the third resolution; a second conversion means for converting the second image into a third image which is a binary image of the third resolution, the second conversion means generating the third image in accordance with information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, the dot arrangement corresponding to the one pixel of the third image being determined based on the magnitude relationship of the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; An image forming apparatus comprising: (Item 13) acquiring a first image at a first resolution; a step of generating a second image of a second resolution based on a first image of the first resolution, wherein the gradation value of one pixel of the second image indicates the number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first and second resolutions and then binarized using a first threshold matrix according to the third resolution; transmitting the second image to an image forming device; receiving the second image; a step of converting the second image into a third image which is a binary image of the third resolution, wherein the third image is generated in accordance with information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, and the dot arrangement corresponding to the one pixel of the third image is determined based on the magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; An information processing method comprising: (Item 14) receiving a second image of a second resolution generated based on a first image of a first resolution, wherein the gradation value of one pixel of the second image indicates the number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first and second resolutions and then binarized using a first threshold matrix according to the third resolution; a step of converting the second image into a third image which is a binary image of the third resolution, wherein the third image is generated in accordance with information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, and the dot arrangement corresponding to the one pixel of the third image is determined based on the magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; An information processing method comprising: (Item 15) A program for causing a computer to function as each means of the system according to any one of items 1 to 11 or the image forming apparatus according to item 12.

[0147] (Other Examples) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0148] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0149] 300: Image forming device, 315: Image supply device, 316: Information processing device

Claims

1. A system including an information processing device and an image forming device, The information processing device includes: acquiring means for acquiring a first image having a first resolution; a first conversion means for generating a second image having a second resolution based on a first image having the first resolution, wherein a gradation value of one pixel of the second image indicates a number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first resolution and the second resolution and then binarized using a first threshold matrix according to the third resolution; a transmitting means for transmitting the second image to an image forming device, The image forming apparatus includes: a receiving means for receiving the second image; a second conversion means for converting the second image into a third image which is a binary image of the third resolution, the second conversion means generating the third image according to information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, the dot arrangement corresponding to the one pixel of the third image being determined based on a magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; A system comprising:

2. 2. The system of claim 1, wherein the second conversion means converts the second image into the third image using a second threshold matrix according to the third resolution.

3. 3. The system according to claim 2, wherein the second threshold matrix has a magnitude relationship between the thresholds in the region corresponding to the one pixel that is equal to a magnitude relationship between the thresholds in the first threshold matrix in the region corresponding to the one pixel.

4. 4. The system of claim 3, wherein the second threshold matrix is ​​the same matrix as the first threshold matrix.

5. 2. The system according to claim 1, wherein a dot arrangement corresponding to the one pixel of the third image is determined based on a magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel and a gradation value of the one pixel of the second image.

6. 6. The system according to claim 5, wherein a dot arrangement corresponding to the first pixel of the third image is determined so that, in an area corresponding to the first pixel of the third image, dots are formed at pixel positions equal in number to the gradation value of the one pixel of the second image in ascending order of threshold values ​​in the area corresponding to the one pixel in the first threshold matrix.

7. 2. The system of claim 1, wherein the first resolution and the second resolution are the same.

8. 2. The system of claim 1, wherein the second resolution is lower than the first resolution.

9. a third conversion means for converting a resolution of the first image to the third resolution; a fourth conversion means for converting the first image having the third resolution into a fourth image binarized by using the first threshold matrix, 2. The system according to claim 1, wherein the first conversion means converts a gradation value of one pixel of the third image into the number of dots contained in an area of ​​the fourth image corresponding to the one pixel.

10. Further comprising an evaluation means for evaluating the graininess of the binary image, 10. The system according to claim 9, wherein a difference in the evaluation of graininess between the fourth image and the third image falls within a predetermined range.

11. a generating unit configured to generate a plurality of second threshold matrices according to a second resolution, each of which corresponds to a tone value of the second image, based on the first threshold matrix; 2. The system of claim 1, wherein the first conversion means generates the second image based on the first image and a plurality of the second threshold matrices.

12. a receiving means for receiving a second image of a second resolution generated based on a first image of a first resolution, wherein a gradation value of one pixel of the second image indicates a number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first resolution and the second resolution and then binarized using a first threshold matrix according to the third resolution; a second conversion means for converting the second image into a third image which is a binary image of the third resolution, the second conversion means generating the third image according to information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, the dot arrangement corresponding to the one pixel of the third image being determined based on a magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; An image forming apparatus comprising:

13. acquiring a first image at a first resolution; a step of generating a second image of a second resolution based on a first image of the first resolution, wherein a gradation value of one pixel of the second image indicates a number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first resolution and the second resolution, and then binarized using a first threshold matrix according to the third resolution; transmitting the second image to an image forming device; receiving the second image; a step of converting the second image into a third image which is a binary image of the third resolution, generating the third image according to information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, the dot arrangement corresponding to the one pixel of the third image being determined based on a magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; An information processing method comprising:

14. receiving a second image of a second resolution generated based on a first image of a first resolution, wherein a gradation value of one pixel of the second image indicates a number of dots when an area of ​​the first image corresponding to the one pixel is converted to a third resolution higher than the first resolution and the second resolution, and then binarized using a first threshold matrix according to the third resolution; a step of converting the second image into a third image which is a binary image of the third resolution, generating the third image according to information indicating a dot arrangement in the third image corresponding to the gradation value for one pixel of the second image, the dot arrangement corresponding to the one pixel of the third image being determined based on a magnitude relationship between the threshold values ​​in an area of ​​the first threshold matrix corresponding to the one pixel; An information processing method comprising:

15. A program for causing a computer to function as each of the units of the system according to any one of claims 1 to 11 or the image forming apparatus according to claim 12.

Images