JP5745889B2 - Image data generation apparatus and image data generation method - Google Patents

Description

  The present invention relates to an image data generating apparatus and an image data generating method for generating image data representing an image recorded on a recording medium in a master plate making used in stencil printing, an ink jet printer, a laser printer or other printing apparatus.

  Conventionally, a stencil printing apparatus has been used as one of the printing apparatuses. In this stencil printing apparatus, binarization data is acquired by performing binarization after performing predetermined image processing and pixel value conversion processing on image data. Then, based on the acquired binarized data, a thermal head is locally heated while being brought into contact with the heat-sensitive stencil sheet to create a master. Further, the ink is transferred to the print medium through the punched portion of the created master to obtain a printed matter.

  In such a stencil printing machine, if there is a solid portion in the image data, the amount of ink transferred from the master to the printing medium increases. When the next print medium is stacked on the print medium after being discharged, the ink on the previous print medium may be transferred to the back surface of the print medium. When the ink is transferred from the other print medium to the back surface, there is a problem that the ink is seen through the surface of the print medium, so-called “show-through”, and the print quality is deteriorated.

  In order to solve such a problem, for example, there are techniques disclosed in Patent Documents 1 and 2. In the techniques disclosed in Patent Documents 1 and 2, the solid portion of the image data is recognized, and the ink amount of the solid portion is thinned out. Thereby, the occurrence of “show-through” can be reduced.

  However, in the techniques disclosed in Patent Documents 1 and 2, the thinning process is performed on the solid portion of the image data. Therefore, “character collapse” that occurs when a fine character is printed using a print medium having a large dot gain. That is, it is impossible to suppress the phenomenon that the thin lines of characters are blurred and the spaces between the thin lines are crushed.

  In particular, the occurrence of “collapsed characters” occurs when using renewed paper or kenaf paper, which is more susceptible to dot gain than high-quality paper, and whose fiber arrangement and size are not uniform and ink penetration varies widely. The tendency becomes remarkable. In particular, in the case of a kanji character having a character size of 10 points or less and a large number of strokes, there is a problem that the character reproducibility is deteriorated due to frequent character crushing of the thin character portion.

  Conventionally, a method of reducing the reading density when creating image data and a method of reducing the printing pressure at the time of printing are proposed instead of thinning out the ink amount of the solid portion of the image. Further, in the technical field such as an ink jet printer, a technique for extracting a contour portion in image data and replacing the ink droplet of the portion with a small droplet or thinning the number of droplets has been proposed (for example, Patent Document 3).

Japanese Patent Laid-Open No. 5-22582 Japanese Patent Laid-Open No. 5-22583 JP 2002-292848 A

  However, in the above-described method of reducing the reading density, if the density is uniformly reduced using a single threshold value, blurring occurs in the fine character portion. Moreover, even if the density is reduced by error diffusion processing or the like, there is an unavoidable inconvenience that blurring occurs in the fine character portion. For this reason, the method of reducing the reading density has a problem that the reproducibility of thin characters is not improved.

  Further, when the method of lowering the printing density by lowering the printing pressure on the master printing medium is adopted, the reproducibility of the fine characters is improved, but the solid portion is not filled and blurring occurs.

  Further, in the technique disclosed in Patent Document 3 described above, a contour line extending in a specific direction on a document is extracted as a feature amount. For example, a feature portion in an image is extracted to detect a contour portion, and thinning is performed. We are processing. However, in the case of image data read from a document by a scanner, for example, it is rare that the contour line in the image data itself extends in a straight line. This is because, when printing a document whose image data has been read by a scanner, the contour line of the document is rarely in a clean straight line unless image data subjected to appropriate thinning processing is used. Therefore, even if the technique of Patent Document 3 is applied to thin line thinning processing, it is difficult to expect an effective result.

  The present invention has been made in view of the above circumstances, and an object of the present invention is a print medium that is likely to cause bleeding when generating image data representing an image recorded on the recording medium in a printing apparatus such as stencil printing. Even if there is, the image data generation device can improve the reproducibility of the character by reducing the thinning of the thin line portion of the character and eliminating the collapse of the character portion without reducing the density of the solid portion. And providing an image data generation method.

In order to achieve the above object, the present invention provides:
In generating image data representing an image recorded on a recording medium in a printing apparatus,
The input image data is binarized,
A pixel in the binarized image data is sequentially selected as a target pixel, and the number of black pixels is counted among a plurality of pixels included in a reference area in a predetermined range centered on the target pixel. Calculate the pixel density of the reference region corresponding to the pixel of interest from the number of pixels of the pixel,
In the arrangement direction of the peripheral pixels for the target pixel of the reference region, in the range of higher pixel density than Jo Tokoro threshold, then reduced during discount rate higher pixel density increases, and, following pixel density the predetermined threshold value The decimation rate for each pixel is calculated based on the calculated pixel density with reference to the definition data defining the correspondence between the pixel density of the reference region and the decimation rate so that the decimation rate is lower than the range of
Performing a thinning process to reduce the density of each pixel according to the pattern according to the thinning rate;
It is characterized by that.

  In the above invention, the thinning rate of each pixel (each pixel of interest) is calculated based on the pixel density of the reference area corresponding to the pixel of interest. Therefore, from the relationship between the pixel of interest and the pixel density around it, for example, it is possible to determine the degree of thinning after determining whether the pixel of interest is a solid portion or a thin portion. Specifically, in a portion such as a solid portion where the pixel density is higher than a predetermined threshold, the thinning rate is decreased as the pixel density increases, so that the higher the density is, the more difficult it is to be thinned out. In addition, the thinning rate is set lower in a portion such as a solid portion where the pixel density is higher than a predetermined threshold than in a portion such as a thin portion where the pixel density is lower than the predetermined threshold. Thereby, even if it is a thin character part, without reducing the density | concentration of a solid part, it can be thinned out reliably, and the reproducibility of a character etc. can be improved, eliminating the crushing of a character part.

  In particular, the reference area includes a predetermined range of pixels including the target pixel, and the pixel density of the reference area is calculated based on the number of black pixels included in the reference area. For this reason, by determining the thinning rate based on the pixel density of the reference region, it is possible to change the thinning rate according to changes in the distribution of the pixel of interest and its surrounding pixels.

  For example, at a location where the pixel density is low, such as a location where the reference area reaches from the blank area to the solid area, thinning is performed at a decimation rate according to the pixel density, and the reference area is within the solid area from the outline of the solid area. The thinning rate can be changed such that the thinning rate is gradually reduced as the pixel density increases. As a result, a sharp density change does not occur even in the outline of a solid portion, and the like can be thinned out smoothly.

  Furthermore, in the above invention, since the analysis of the thinning rate is performed after binarizing the image data, the amount of data that is the target of the arithmetic processing can be reduced, and the burden on the arithmetic processing can be reduced and the speed can be increased. It is possible to reduce the size and cost of the arithmetic processing device and the memory device.

  In the above invention, when the pixel density calculation unit calculates the pixel density of the reference region corresponding to the target pixel, the pixel density calculation unit is configured to perform the reference region based on the content of the image data. It has the function to change the area or shape of the.

  In the above invention, the area and shape of the reference region are changed based on the contents of the image data. The contents of the image data include, for example, the character size, typeface, and character decoration type included in the image data. By changing the area and shape of the reference region according to these, it is possible to more accurately determine the relationship between the pixel of interest and the pixel density in the vicinity thereof, and to improve the accuracy of the thinning process.

  In general, a 5 × 5 pixel number and shape are sufficient for this reference region. However, in the case of a 10-point bold Gothic typeface, for example, there is a tendency that white pixel portions are less likely to be crushed. If the pixel density is obtained as a × 7 reference area, the ratio of the white pixel part to the reference area can be evaluated to be small, the pixel density of that part becomes high, and measures such as reducing the thinning rate as in the solid part are taken. Can be taken.

  In the above invention, the definition data is characterized in that a thinning rate at a pixel density equal to or lower than the predetermined threshold is defined as a specific upper limit value of less than 100%.

  In the above invention, for example, in a portion where the pixel density is low, such as a thin character portion, by setting an upper limit of less than 100% in the thinning rate, the character portion can be thinned out appropriately without causing character blurring, and the character portion is crushed. This eliminates the problem and improves the reproducibility of characters and the like.

  In the above invention, the specific upper limit value is 50%, and the thinning processing unit sets the pattern corresponding to the thinning rate of the specific upper limit value in a checkered pattern every other pixel.

  In the above invention, even if the reference region is located at a location such as the pixel density where the thinning rate is maximized, the specific upper limit value is set to 50%, and thinning is performed by thinning out every other pixel in a checkered pattern. It can be thinned out to such an extent that no blur is visible.

  In the above invention, the binarized data storage unit for storing the image data binarized by the binarization processing unit, the type of the recording medium is acquired, and the acquired type is a specific type set in advance. In some cases, further comprising: an image selection unit that reads out the image data stored in the binarized data storage unit and causes the thinning-out rate calculation unit to calculate the thinning-out rate of the read image data. And

  In the above-described invention, the thinning-out process can be performed only when generating image data for a recording medium that easily bleeds ink, such as reprinted paper or kenaf paper, and generates image data that matches the characteristics of the recording medium. Can do. In particular, for example, when generating image data for plain paper, the binarized image data is stored in the binarized data storage unit, and the binarized image data is recorded as a target of print processing. Depending on the type of the medium, it can be read out and used in the thinning process. Since the amount of binarized data is smaller than that of normal multilevel data, the storage area can be reduced, and the memory device can be reduced in size and cost.

  In other words, since the binarized image data is image data itself for general plain paper, when the recording medium is a type that does not require thinning processing such as plain paper, the binarized image data is binarized. The image data is used for general printing processing and master plate making processing, then stored in the binarized data storage unit, and the recording medium is of a type that requires thinning processing such as renewal or kenaf paper In addition, the stored image data can be read out and the thinning process can be performed again. As a result, not only the memory device can be reduced in size and cost but also the binarized image data can be reused, so that binarized image data is required in general printing processing and master plate making processing. In some cases, it is not necessary to perform arithmetic processing for binarizing multi-value data having a large data capacity, and the burden of arithmetic processing can be reduced and speeded up.

  According to the present invention, when generating image data representing an image to be recorded on a recording medium in a printing apparatus such as stencil printing, a location where image thinning processing is executed is appropriately selected with a simple configuration. As a result, even if the print medium is prone to bleeding, the thinned portion of the character is surely thinned out without reducing the density of the solid portion, eliminating the collapse of the character portion and improving the reproducibility of the character. Can be achieved. In addition, ink bleeding with respect to a recording medium such as a reprint paper or a kenaf paper can be reduced, and opportunities for using paper with a low environmental load can be increased.

It is a schematic sectional drawing which shows the internal structure of the stencil printing apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the module regarding the image data generation process of the arithmetic processing part of FIG. It is explanatory drawing which shows the outline | summary of the calculation of the pixel density by the pixel density calculation part of FIG. 2A is a graph showing a correspondence relationship between a pixel density and a thinning rate used for calculation of the thinning rate by the thinning rate calculation unit in FIG. 2, and FIG. 2B is used when the thinning processing unit in FIG. It is explanatory drawing which shows the structural example of a threshold value matrix. (A)-(d) is explanatory drawing which shows the structure of the threshold value matrix according to the thinning-out rate of FIG. It is a flowchart which shows the outline | summary of the image data generation method which concerns on one Embodiment of this invention. (A) is explanatory drawing which shows the digital data with a thinning process performed by the thinning-out process part of FIG. 2, (b) is a top view which shows the image screen printed with the digital data of (a) It is. (A) is explanatory drawing which shows the digital data without a thinning process which concerns on a prior art example, (b) is a top view which shows the image screen printed with the digital data of (a).

(Overall configuration of stencil printing machine)
Hereinafter, an embodiment in which an image data generation apparatus according to the present invention is applied to generation of image data for plate making in a stencil printing apparatus will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an internal configuration of the stencil printing apparatus 1 according to the present embodiment.

  As shown in FIG. 1, the stencil printing apparatus 1 of the present embodiment includes an image reading unit 10 that reads an image of a document and outputs image data, and a heat-sensitive stencil sheet based on the image data read by the image reading unit 10. The first and second plate-making units 30 and 35 for performing plate-making processing on the master 33, and the heat-sensitive stencil sheet 33 made by the first and second plate-making units 30 and 35 are used for printing paper P1. The first and second printing units 40 and 50 that perform printing, the paper feeding unit 20 that feeds the printing paper P1 to the first printing unit 40, and the single-side printed printing that is printed on one side in the first printing unit 40 The paper P2 is temporarily stocked, and then the intermediate stock unit 46 that feeds the paper P2 to the second printing unit 50 at a predetermined timing, and the double-sided printed printing paper P3 that has been printed on both sides by the second printing unit 50 are discharged. A paper discharge unit 70 That.

  The image reading unit 10 is a scanner device that includes a line image sensor that photoelectrically reads image information of a document, scans the document with the line image sensor, and outputs image data.

  The first plate making unit 30 has a thermal head unit 31 in which a plurality of heating elements are arranged in a line, and the plate making using the thermal head unit 31 is performed on the heat-sensitive stencil sheet 33 fed from the stencil sheet roll. The processing is performed. The first plate making unit 30 performs plate making processing based on processed image data output from the arithmetic processing unit 100 described later.

  Similarly to the first plate making unit 30, the second plate making unit 35 has a thermal head unit 36, and plate making processing is performed on the heat-sensitive stencil sheet 33 fed from the stencil sheet roll using the thermal head unit 36. Is what you do. The second plate making unit 35 also performs plate making processing based on processed image data output from the arithmetic processing unit 100 described later.

  The first printing unit 40 presses the printing paper P1 and the first printing drum 41 with a predetermined press pressure against the first printing drum 41 having a cylindrical shape such as a perforated metal plate or a mesh structure. A first press roller 42 and a first stripping claw 43 for stripping the single-side printed paper P2 from the first printing drum 41 are provided. A master punched in the heat-sensitive stencil sheet 33 in the first plate making unit 30 is wound around and attached to the outer periphery of the first printing drum 41. The first press roller 42 extends along the direction in which the central axis of the cylinder of the first printing drum 41 extends (the depth direction in FIG. 1).

  Similar to the first printing unit 40, the second printing unit 50 presses the cylindrical second printing drum 51 and the single-side printed printing paper P2 against the second printing drum 51 with a predetermined press pressure. A second press roller 52 and a second peeling claw 53 for peeling the double-side printed printing paper P3 from the second printing drum 51 are provided. A master punched in the second plate making section 35 is wound around and attached to the outer periphery of the second printing drum 51. Further, the second press roller 52 extends along the direction in which the central axis of the cylinder of the second printing drum 51 extends (the depth direction in the drawing of FIG. 1).

  The paper supply unit 20 includes a paper supply base 21 on which the print paper P1 is placed, and a primary paper supply roller 22 that takes out the print paper P1 one by one from the paper supply base 21 and sends it to the secondary paper supply roller 23. The leading end of the printing paper P1 that is disposed downstream of the primary paper feeding roller 22 in the carrying direction is temporarily stopped, and the printing paper P1 is transferred to the first printing drum at a predetermined timing. A secondary paper feed roller 23 is provided between 41 and the first press roller 42.

  The paper discharge unit 70 is a paper discharge feeding belt unit 72 that conveys the double-sided printed printing paper P3 to the paper discharge table 71, and a paper discharge on which the double-sided printed printing paper P3 conveyed by the paper discharge feeding belt unit 72 is stacked. A stand 71 is provided.

  Further, a curved conveyance unit 44 is installed between the first printing unit 40 and the intermediate stock unit 46. As shown in FIG. 1, the curved conveyance unit 44 includes a guide plate having a curved surface along the conveyance path. On the curved surface of the guide plate, a conveyor belt provided with a suction port for sucking the printing paper P1 sent out from the first printing unit 40 is installed. A pulley 45 that circulates and moves the transport belt is provided. The curved conveyance unit 44 sucks the single-side printed paper P2 by the suction port of the conveyance belt, and conveys the single-side printed paper P2 by the conveyance belt along the curved surface of the guide plate by rotating the pulley 45. Is.

  Further, between the intermediate stock unit 46 and the second printing unit 50, a pickup roller 47 that picks up the single-side printed printing paper P <b> 2 carried out from the intermediate stock unit 46, and single-sided printing picked up by the pickup roller 47. There is provided a timing roller 48 for sequentially sending the finished printing paper P2 between the second printing drum 51 and the second press roller 52 at a predetermined timing.

(Image data generator)
The stencil printing apparatus 1 according to this embodiment includes an arithmetic processing unit 100 that generally performs plate making processing, image processing, printing control, and control of each driving unit. In the present embodiment, the arithmetic processing unit 100 performs predetermined density conversion processing on the image data output from the image reading unit 10 and outputs the image data to the first and second plate making units 30 and 35, respectively. It has a function as a generation device. FIG. 2 is a block diagram illustrating modules related to image data generation processing of the arithmetic processing unit 100 according to the present embodiment. The “module” used in the description refers to a functional unit that is configured by hardware such as an apparatus or a device, software having the function, or a combination thereof, and achieves a predetermined operation. .

  As shown in FIG. 2, the arithmetic processing unit 100 includes a job data receiving unit 101, an operation signal acquiring unit 102, a storage unit 103, and an image formation control unit 110 as modules relating to image data generation processing. .

  The job data receiving unit 101 is an interface that receives job data that is a series of print processing units via the image reading unit 10 or the external communication interface 104, and receives data included in the received job data in the image formation control unit 110. The module to pass. The communication through the external communication interface 104 includes, for example, a short-range communication such as an infrared communication as well as a LAN such as an intranet (in-house network) or a home network based on 10BASE-T or 100BASE-TX.

  The operation signal acquisition unit 102 is connected to the operation panel 100a and a network external communication interface 104, and acquires and analyzes a user operation on the operation panel 100a or an external device of the network (for example, an information terminal such as a personal computer). It is an external interface that is input to each module in the arithmetic processing unit 100 later. Note that the user operation here includes an image mode set by the user, and this image mode includes an image mode switching signal for selecting a photographic process or a character process in the image generation process, and a master that has been made. Setting information of the type of recording medium to be used for printing processing (such as plain paper or additional paper) is included.

  The storage unit 103 (corresponding to the binarized data storage unit in the claims) is a memory device that stores and holds various data and programs. In particular, in this embodiment, binarized image data, Table data D1 (see FIG. 4A), which is definition data indicating the correspondence relationship between the pixel density and the thinning rate, pixel density threshold data, threshold matrix data M1 (see FIG. 4B), and the like are recorded and held. Yes. These stored data are read out and referred to in each process in the image formation control unit 110 described later.

  The image formation control unit 110 is an arithmetic processing unit that performs digital signal processing specialized for image processing, and is a module that performs image formation processing by converting image data necessary for printing. In particular, in the present embodiment, the image formation control unit 110 controls the driving of the thermal head units 31 and 36, and as a plate making control mechanism for controlling the entire plate making process, a photo processing unit 111, a character processing unit 112, The image selection unit 113, the pixel density calculation unit 114, the thinning rate calculation unit 115, the thinning processing unit 116, and the image output unit 117 are provided.

  The photographic processing unit 111 is a module that performs photographic processing on a photographic image in the image data, and includes a gamma conversion processing unit 111a and a binarization processing unit 111b.

  The gamma conversion processing unit 111a is a module that converts the density of each pixel in the image data into a density suitable for a halftone by gamma conversion.

  The binarization processing unit 111b is a module that binarizes pixel values of a photographic image included in gamma-converted image data. The binarization processing unit 111b converts the value of each pixel, that is, multi-value data, that is, the density or reflectance of a document into binary. The error diffusion processing unit 111c of the value processing unit 111b compares it with a predetermined threshold value, and performs halftone binarization according to the magnitude of the threshold value. The binarized data for turning on / off the energization of the thermal head is input to the image selection unit 113. In accordance with the binarized data input to the image selection unit 113, the thermal head is turned on / off to form perforations in the master (that is, to form an image on the master).

  The character processing unit 112 is a module that performs character processing on a character image in image data, and includes a binarization processing unit 112a.

  The binarization processing unit 112a is a module that binarizes the pixel value of the character part included in the image data as ON / OFF of energization of each heating element of the thermal head using a single threshold value. This binarization processing unit 112a binarizes by energizing ON if it is greater than or equal to the threshold and comparing energization OFF if less than the threshold, by comparing each pixel that is multi-value data with a single threshold. This binarized data is input to the image selection unit 113. According to the binarized data input to the image selection unit 113, the thermal head energization is turned on / off to form perforations in the master (that is, the darkness of the image is changed to thermal head energization ON / OFF instead of the time length) Then, an image is formed on the master by turning on / off the heat of the thermal head, and by setting whether or not the master is perforated.

  The image selection unit 113 is a module that selects image data subjected to character processing or photo processing according to an image mode set by the user on the operation panel 100 a and inputs the image data to the pixel density calculation unit 114. Further, the image selection unit 113 acquires the type of the recording medium that is a target of the printing process using the master that has been made, and stores the type in the storage unit 103 when the acquired type is a specific type set in advance. A function is provided for reading the read image data and causing the thinning rate calculation unit 115 to calculate the thinning rate of the read image data. The type of the recording medium is acquired from the image mode set by the user on the operation panel 100a. In the present embodiment, the image selection unit 113 selects an image after performing the photo processing and the character processing in parallel. For example, on the upstream side of the photo processing unit 111 and the character processing unit 112. An image selection unit 113 may be arranged to select a photo and a character before the binarization process and appropriately switch the input destination of the image data.

  As shown in FIG. 3, the pixel density calculation unit 114 counts the number of pixels included in a predetermined range (reference region A1) including the target pixel E1, and corresponds the number of pixels per predetermined range to the target pixel E1. This module calculates the pixel density of the reference area A1. Specifically, each pixel in the binarized image data is sequentially selected as the target pixel E1. Then, the number of black pixels is counted out of 25 pixels in the reference area A1 including each pixel of interest E1 and 24 (5 × 5-1 = 24) pixels around the pixel of interest E1. To do. By dividing the counted number of pixels (20 in the example of FIG. 3) by the total number of pixels in the reference area A1 (5 × 5 = 25), the pixel density (see FIG. In the example of 3, it is calculated as 20/25 = 0.80). The pixel density calculated by the pixel density calculation unit 114 is input to the thinning rate calculation unit 115.

  Note that the pixel density calculation unit 114 has a function of changing the area or shape of the reference area A1 according to the size, typeface, and type of character decoration included in the image data. More specifically, the pixel density calculation unit 114 uses a square area of 5 × 5 as the default area and shape of the reference area A1, but job data such as character size, typeface, character decoration type, etc. Is extracted, and the area or shape of the reference area A1 is changed. Note that the information related to the image data here is acquired from a processed character size selection signal included in the job data.

  By such a function of changing the area or shape of the reference area A1, the reference area A1 is changed to 7 × 7 in the case of a 10-point bold Gothic typeface that tends to be crushed with few white pixel portions, for example. Then, the pixel density is obtained. Accordingly, the ratio of the white pixel portion to the reference area A1 is evaluated to be small, the pixel density of the portion is increased, and the thinning rate is decreased in the same manner as the solid portion.

  The decimation rate calculation unit 115 is a module that refers to the table data D1 of the storage unit 103 based on the pixel density counted by the pixel density calculation unit 114 and calculates a decimation rate for the corresponding target pixel E1. In the present embodiment, the table data D1 is data that can represent the correspondence between the pixel density and the thinning rate with a graph as shown in FIG. 4A, and the thinning rate with respect to the pixel density in the shape of the graph. Can be set freely.

  The relationship between the pixel density and the thinning rate in the table data D1 in the present embodiment is such that the thinning rate at a pixel density equal to or higher than a predetermined threshold (pixel density threshold T1) is less than 100% (see FIG. 4A). In the example, the pixel density is set to be 50%), and the pixel density is increased in the pixel density range higher than the pixel density threshold T1 (0.36 = pixel density 36% in the example of FIG. 4A). The decimation rate is set so that the decimation rate is reduced in proportion to. Specifically, in the table data D1 here, when the pixel density is 0 to 36%, the thinning rate is almost uniformly set to 50%, and in a region where the pixel density is higher than 36%, the pixel density approaches 100%. The thinning rate is lowered as it approaches 0%. As a result, the thinning rate is reduced for a solid portion having a high pixel density, and the thinning rate is increased for a blank portion having a low pixel density.

  The thinning rate calculation unit 115 inputs the thinning rate calculated for each pixel to the thinning processing unit 116 as array data associated with the coordinate information. The thinning processing unit 116 is a module that executes thinning processing for reducing the density of each pixel according to a pattern corresponding to the thinning rate. In the thinning process, the thinning processing unit 116 uses the threshold matrix data M1 stored in the storage unit 103.

  The threshold value matrix data M1 is a filter that defines 4 × 4 16 pixels as shown in FIG. 4B as a unit pattern and repeats this to define a thinning rate threshold value for all pixels. In the threshold value matrix data M1, high threshold values and low threshold values are arranged in a Bayer array so that pixels to be thinned out are not biased.

  The thinning processing unit 116 sequentially selects 4 × 4 16 pixels so as not to overlap from the image data included in the job data. Then, the thinning process is performed on each 4 × 4 16 pixels by applying the threshold matrix data M1. Specifically, each thinning rate calculated by the selected 16 pixel thinning rate calculation unit 115 is compared with the threshold value defined in each corresponding pixel location of the threshold matrix data M1. As a result of the comparison, as shown in FIG. 5, when the thinning rate exceeds a threshold value for each pixel, the pixel is replaced with a white pixel, and when the thinning rate is equal to or less than the threshold value, thinning is performed for the pixel. Not performed. In FIG. 5, pixels to be thinned out are indicated by white, and pixels not to be thinned are indicated by hatching.

  In particular, in the present embodiment, the threshold value matrix data M1 is such that the thinning pattern when the specific upper limit value (50%) of the table data D1 is in a checkered pattern every other pixel as shown in FIG. It is configured. That is, of the threshold values in the threshold matrix data M1, 50% or more threshold values are arranged alternately every other pixel in the x-axis direction and the y-axis direction. As a result, even if the thinning rate is maximized, the pixels are thinned out uniformly without being biased.

  Further, as described above, in the range of the pixel density where the relationship between the pixel density and the thinning rate in the table data D1 is higher than the pixel density threshold T1, the thinning rate is reduced so that the thinning rate decreases in proportion to the increase in the pixel density. Is set. For this reason, as the pixel density becomes equal to or higher than the pixel density threshold T1 (36%), the thinning rate rapidly decreases to 20% (when the pixel density is 50%), and thereafter, as the pixel density becomes higher than 50%. It gradually decreases from 20% to 0% while gradually decreasing the degree of decrease. Accordingly, the thinning pattern based on the threshold matrix data M1 changes. For example, when the thinning rate becomes 35%, the thinning pattern changes to the pattern shown in FIG. 5B, and when the thinning rate becomes 25%, the thinning pattern changes to the pattern shown in FIG. Furthermore, when the thinning rate decreases to 10%, the thinning pattern changes to the pattern shown in FIG. Then, as the pixel density approaches 100%, the thinning rate approaches 0%, and when the pixel density is near 100%, the thinning rate becomes 0% and is not thinned out.

  The image output unit 117 is a module that controls the thermal head units 31 and 36 and each drive mechanism based on the image data, and controls the entire plate making mechanism. The image output unit 117 according to the present embodiment is a mode for directly making image data included in job data received by the job data receiving unit 101, and a mode for making plate making using image data thinned by the thinning processing unit 116. These modes are automatically selected according to the type of recording medium to be subjected to printing processing by the user or the master made by the plate making, and the plate making is performed based on the image data in each mode. Do.

(Image data generation method)
The image data generation method of the present invention can be implemented by operating the image data generation apparatus having the above configuration. FIG. 6 is a flowchart showing an overview of the image data generation method according to the present embodiment.

  First, when the plate making process is executed, the job data receiving unit 101 receives the job data, and inputs the image data included in the received job data to the image forming control unit 110 (step S101). The image formation control unit 110 performs photographic processing on a photographic image in image data and character processing on a character image in parallel. Specifically, in the photographic process, the density is converted to a density suitable for halftone by gamma conversion in the gamma conversion processing unit 111a (step S102), and after the binarization processing (step S103) by the binarization processing unit 111b, Error diffusion halftone processing is performed by the error diffusion processing unit 111c (step S104). On the other hand, in character processing, binarization is performed using a single threshold (step S105).

  Next, the image selection unit 113 selects image data that has been subjected to character processing or photo processing according to the image mode set by the user on the operation panel 100a, and inputs the selected image data to the pixel density calculation unit 114 (step S106). In step S106, the image selection unit 113 acquires the type of the recording medium that is the target of the printing process using the master that has been made, and stores the acquired type when the acquired type is a specific type set in advance. The image data stored in the unit 103 is read, and the read image data is input to the thinning rate calculation unit 115. Note that the type of the recording medium here is acquired from the image mode set by the user on the operation panel 100a.

  The pixel density calculation unit 114 calculates the pixel density of the target pixel E1 by counting the number of black pixels among the plurality of pixels included in the reference area A1 including the target pixel E1 from the input image data. (Step S107). Specifically, the pixel density calculation unit 114 sequentially selects the pixels in the image data binarized by each binarization processing unit 111b or 112a as the target pixel E1, and the reference region A1 centered on the target pixel E1. Among these pixels, the number of black pixels in which energization to the heat generating element of the thermal head is ON is counted. By dividing the counted number of pixels by the total number of pixels in the reference area A1 (5 × 5 = 25), the number of pixels per unit area is calculated as the pixel density.

  In step S107, the pixel density calculation unit 114 changes the area or shape of the reference area A1 according to the character size, typeface, character decoration type, and the like included in the image data. More specifically, the pixel density calculation unit 114 uses a square area of 5 × 5 as the default area and shape of the reference area A1, but job data such as character size, typeface, character decoration type, etc. The information regarding the content of the image data contained in is extracted, and the area or shape of the reference area A1 is changed.

  Thus, the pixel density calculated by the pixel density calculation unit 114 is input to the thinning rate calculation unit 115 in the form of array data associated with the coordinate information of each pixel. In the present embodiment, the process of step S107 is executed for each pixel by a loop process, and after calculation of the pixel density is completed for all pixels, the process proceeds to the next step S108.

  In step S108, based on the pixel density of each pixel, the table data D1 stored in the storage unit 103 is referred to calculate a thinning rate for each pixel. In this embodiment, the table data D1 is such that the thinning rate is lowered to almost 0 for a solid portion having a high pixel density, and the thinning rate is increased as the pixel density is lowered. However, in a portion where the pixel density is 0 to 36%, such as a blank portion where the pixel density is low, the thinning rate is uniformly set to 50%.

  Then, the thinning rate calculation unit 115 inputs the calculated thinning rate to the thinning processing unit 116 as array data associated with the coordinate information of each pixel. The thinning processing unit 116 performs pixel thinning processing according to a pattern corresponding to the thinning rate calculated by the thinning rate calculation unit 115 (step S109). Specifically, the thinning processing unit 116 uses the threshold value matrix data M1, compares the thinning rate of each pixel calculated by the thinning rate calculation unit 115 with the threshold value in the matrix corresponding to the coordinates of each pixel, and Due to the magnitude relationship, pixels below a predetermined thinning rate are replaced with white pixels.

  Thereafter, the image output unit 117 controls the driving of the thermal head units 31 and 36 based on the thinned image data, and generates a master corresponding to the image data thinned by the thinning processing unit 116. Then, an image is formed (step S110).

(Function and effect)
According to the present embodiment described above, since the thinning rate of each pixel (each target pixel) is calculated based on the pixel density of the reference area A1 corresponding to the target pixel E1, the pixel density of the target pixel E1 and its surroundings is calculated. From the relationship, for example, it is possible to determine the degree of thinning after determining whether the target pixel E1 is a solid portion or a thin portion. Accordingly, the thin character portion can be surely thinned out without reducing the density of the solid portion, and the reproducibility of characters and the like can be improved while eliminating the collapse of the character portion.

  In particular, in the present embodiment, since thinning processing is executed in accordance with the type of recording medium to be printed, image data for a recording medium that is likely to bleed ink such as renewal paper or kenaf paper is generated. Only when the above thinning process can be performed, image data matching the characteristics of the recording medium can be generated. More specifically, conventionally, when image data (digital data) as shown in FIG. 8A is printed on a recording medium that is likely to bleed ink, such as renewal paper or kenaf paper, with a character size of about 6 points, As shown in FIG. 5B, the thin character portion of a character having a large number of strokes blurs, resulting in character collapse, and the reproducibility of the thin character is lowered. On the other hand, according to the present embodiment, as shown in FIG. 7A, the image data generated by the thinning-out process is printed on a reprint or kenaf paper with a character size of about 6 points. Even so, as shown in FIG. 5B, the character collapse is improved and the reproducibility of the fine characters is improved.

  In addition, since the reference area A1 includes a predetermined number of pixels, by determining the thinning rate based on the pixel density of the reference area A1, for example, the pixel density such as a place where the reference area A1 approaches the solid part from the blank part. In a part where the pixel density is low, thinning is performed at a certain thinning rate according to the pixel density, and the reference area A1 shifts from the outline of the solid part into the solid part, and the thinning rate is lowered step by step as the pixel density increases. The decimation rate can be changed according to the change in the distribution of the pixel of interest E1 and its surrounding pixels. As a result, a sharp density change does not occur even in the outline of a solid portion, and the like can be thinned out smoothly.

  Furthermore, in the above invention, since the analysis of the thinning rate is performed after binarizing the image data, the amount of data that is the target of the arithmetic processing can be reduced, and the burden on the arithmetic processing can be reduced and the speed can be increased. It is possible to reduce the size and cost of the arithmetic processing device and the memory device.

  In the above embodiment, since the pixel density calculation unit 114 has a function of changing the area or shape of the reference area A1, the reference area depends on the size, typeface, type of character decoration, and the like included in the image data. The area and shape of A1 can be changed. Thereby, according to this embodiment, the relationship between the pixel of interest E1 and the pixel density in the vicinity thereof can be determined more accurately, and the accuracy of the thinning process can be improved.

  In the present embodiment, the relationship between the pixel density of the table data D1 and the thinning rate is set so that the thinning rate is approximately inversely proportional to the pixel density in the range of pixel density higher than a predetermined threshold. The decimation rate at the threshold is set to a specific upper limit value of less than 100%. For this reason, for example, in a portion where the pixel density is high such as a solid portion, the thinning rate is set so as to be approximately inversely proportional to the pixel density. In places, by setting an upper limit of less than 100% for the thinning rate, it is possible to thin out characters appropriately without causing blurring of characters, to eliminate crushing of character parts, and to improve the reproducibility of characters and the like. Can do.

  Furthermore, in the present embodiment, in the table data D1, the specific upper limit value is 50%, and the thinning processing unit 116 has a thinning pattern at the specific upper limit value in a checkered pattern every other pixel. As a result, even if the reference area A1 is located at a location such as the pixel density where the thinning rate is maximized, the thinning of the thin characters can be thinned out to an appropriate degree.

  In the present embodiment, for example, image data binarized when generating image data for plain paper is stored in the storage unit 103, and the binarized image data is set as a print processing target. Depending on the type of the recording medium, the data is read from the storage unit 103 and used for the thinning process. Since the amount of binarized data is smaller than that of normal multilevel data, the storage area can be reduced, and the memory device can be reduced in size and cost.

  In other words, since the binarized image data is image data itself for general plain paper, when the recording medium is a type that does not require thinning processing such as plain paper, the binarized image data is binarized. After the image data is used for general printing processing and master plate making processing, it is stored in the storage unit 103 without performing thinning processing, and the recording medium needs thinning processing such as renewal paper or kenaf paper. When the image type is different, the stored image data is read out and the thinning process is performed again. As a result, not only the memory device is reduced in size and cost, but also by reusing binarized image data, there is no need to perform arithmetic processing for binarization again, reducing the burden of arithmetic processing and increasing the speed. Can be achieved.

  As a result, according to the present embodiment, when the image data for plate making in the stencil printing apparatus is generated, the thinning portion of the character is thinned out by appropriately selecting the place where the image thinning processing is executed. While surely eliminating the collapse of the character portion, the reproducibility of the character can be improved by not performing the thinning process for the low density region portion of the image. In addition, ink bleeding with respect to a recording medium such as a reprint paper or a kenaf paper can be reduced, and opportunities for using paper with a low environmental load can be increased.

  In the present embodiment, the case where the present invention is applied to generation of image data for plate making in a stencil printing apparatus has been described. However, the present invention is not limited to this, and the present invention is not limited thereto. The present invention can be applied to all apparatuses that print on a recording medium based on image data, such as an inkjet printer, a laser printer, a thermal recording apparatus, and a thermal transfer recording apparatus.

DESCRIPTION OF SYMBOLS 1 Stencil printing apparatus 10 Image reading part 20 Paper feed part 21 Paper feed stand 22 Primary paper feed roller 23 Secondary paper feed roller 30 First plate making part 31 Thermal head unit 33 Heat-sensitive stencil sheet 35 Second plate making part 36 Thermal Head unit 40 First printing unit 41 First printing drum 42 First press roller 43 First peeling claw 44 Curved conveyance unit 45 Pulley 46 Intermediate stock unit 47 Pickup roller 48 Timing roller 50 Pixel density 50 Second Printing section 51 Second printing drum 52 Second press roller 53 Second stripping claw 70 Paper discharge section 71 Paper discharge stand 72 Belt section 100 Arithmetic processing section 100a Operation panel 101 Job data reception section 102 Operation signal acquisition section 103 Storage unit 104 External communication interface 110 Image formation control unit 111 Photo processing unit 11a gamma conversion processing unit 111b binarization processing unit 111c error diffusion processing unit 112 character processing unit 112a binarization processing unit 113 image selection unit 114 pixel density calculation unit 115 decimation rate calculation unit 116 decimation processing unit 117 image output unit A1 Reference area D1 Table data E1 Pixel of interest M1 Threshold matrix data P1 Printing paper P2 Single-sided printing paper P3 Double-sided printing paper T1 Pixel density threshold

Claims (6)

An image data generation device that generates image data representing an image recorded on a recording medium in a printing device,
A binarization processing unit that binarizes the input image data;
A pixel in the binarized image data is sequentially selected as a target pixel, and the number of black pixels is counted among a plurality of pixels included in a reference area in a predetermined range centered on the target pixel. A pixel density calculation unit that calculates the pixel density of the reference region corresponding to the target pixel from the number of pixels;
Based on the pixel density calculated by the pixel density calculation unit, with reference to definition data indicating a correspondence relationship between the pixel density of the reference region and the thinning rate, a thinning rate calculation unit that calculates a thinning rate for each pixel;
A thinning processing unit for performing a thinning process for reducing the density of each pixel according to the pattern according to the thinning rate;
Wherein the definition data, in the direction of arrangement of peripheral pixels for the target pixel of the reference region, in the range of higher pixel density than Jo Tokoro threshold, then reduced during discount rate higher pixel density increases, and the predetermined The relationship between the pixel density and the thinning rate is defined such that the thinning rate is lower than the pixel density range below the threshold value of
An image data generation apparatus characterized by the above.   The image data generation apparatus according to claim 1, wherein the pixel density calculation unit has a function of changing an area or a shape of the reference region based on the content of the image data.   3. The image data generation apparatus according to claim 1, wherein the definition data defines a thinning rate at a pixel density equal to or less than the predetermined threshold as a specific upper limit value of less than 100%.   The said specific upper limit is 50%, The said thinning-out process part makes the said pattern according to the thinning-out rate of the said specific upper limit into the checkered pattern shape every other pixel. Image data generation apparatus.   When the binarized data storage unit that stores the image data binarized by the binarization processing unit and the type of the recording medium are acquired, and the acquired type is a specific type set in advance, The image selection unit further comprising: an image selection unit that reads out image data stored in the binarized data storage unit and causes the thinning-out rate calculation unit to calculate a thinning-out rate of the read image data. The image data generation device according to 1, 2, 3, or 4. An image data generation method for generating image data representing an image recorded on a recording medium in a printing apparatus,
A binarization processing step for binarizing the input image data;
A pixel in the binarized image data is sequentially selected as a target pixel, and the number of black pixels is counted among a plurality of pixels included in a reference area in a predetermined range centered on the target pixel. A pixel density calculating step of calculating a pixel density of the reference area corresponding to the target pixel from the number of pixels;
In the arrangement direction of the peripheral pixels for the target pixel of the reference region, in the range of higher pixel density than Jo Tokoro threshold, then reduced during discount rate higher pixel density increases, and, following pixel density the predetermined threshold value With reference to the definition data that defines the correspondence between the pixel density of the reference region and the thinning rate so that the thinning rate is lower than the range of the range, the space for each pixel is calculated based on the pixel density calculated in the pixel density calculating step. A thinning-out rate calculating step for calculating a discount rate;
A thinning process step for executing a thinning process for reducing the density of each pixel according to a pattern according to the thinning ratio calculated in the thinning rate calculation step;
An image data generation method comprising: