JP5543153B2 - Image data generation method and apparatus, and stencil printing apparatus - Google Patents

Description

  The present invention relates to an image data generation method and apparatus that accepts input of image data and performs density conversion processing on the image data, and a stencil printing apparatus.

  Conventionally, a thermal head or the like is driven based on image data read from a document by a scanner or the like, and a stencil sheet is melted and perforated to create a plate, and the created plate is wound around a printing drum. Various stencil printing apparatuses that perform printing by supplying ink from the inside of the printing drum and transferring the ink to printing paper using rollers or the like have been proposed.

  As the stencil printing apparatus as described above, for example, one that performs double-sided printing or one that performs two-color printing has been proposed.

  Here, in the stencil printing apparatus as described above, for example, when the ink is excessively transferred to the printing paper, a problem of smearing of the printed matter due to so-called back-through, back-off, ink re-transfer, and the like occurs. In particular, in a stencil printing apparatus that performs two-color printing, since the second plate is printed before the first plate ink is sufficiently dried, the printing range between the first plate and the printing range of the second plate Since the amount of transferred ink further increases at the overlapping position, the above problem is likely to occur.

  As a method for solving such a problem, a method for suppressing the ink transfer amount by suppressing the press pressure has been proposed.

  Japanese Patent Application Laid-Open No. 2004-228561 proposes a method of suppressing the ink transfer amount to an optimum amount by controlling plate making conditions such as plate making energy and dot density in accordance with the image feature amount of a small area of the plate making image.

JP 2006-315288 A

  However, in the method of suppressing the press pressure as described above, the ink transfer amount can be suppressed if the press pressure is too low, but there is a problem that the density stability is impaired and the image quality is deteriorated.

  Further, in the method described in Patent Document 1, no consideration is given to an increase in the amount of ink transferred at the overlapping position in two-color printing, so that optimal ink transfer is achieved only by controlling the plate-making conditions as described above. The amount cannot be controlled, and problems such as behind-the-scenes and set-offs occur.

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an image data generation method and apparatus, and stencil capable of suppressing image deterioration such as smearing or fading of printed matter due to back-through, set-off, ink re-transfer, etc. in multi-color stencil printing. An object of the present invention is to provide a printing apparatus.

  The image data generation method of the present invention accepts input of a plurality of image data representing a plurality of images recorded on the same surface of a recording medium, and the density in a reference region of a part of each received image data. Information is acquired, and based on the density information of the reference area corresponding to each image data, the density information in the reference area of each image data is converted to obtain converted density information, respectively, Based on the converted density information corresponding to the image data, processed image data corresponding to each image data is generated.

  An image data generation device according to the present invention includes an image data receiving unit that receives input of a plurality of image data representing a plurality of images recorded on the same surface of a recording medium, and each image data received by the image data receiving unit. Based on the density information acquisition unit that acquires the density information in a part of the reference area and the density information of the reference area corresponding to each image data, the density information in the reference area of each image data is converted A density information conversion unit for acquiring converted density information, and converted image data corresponding to each image data based on the converted density information corresponding to each image data acquired by the density information conversion unit, respectively. And a density conversion processing unit to be generated.

  Further, in the image data generation device of the present invention, the density information conversion unit acquires a correction amount according to the information on the plurality of densities based on the density information of the reference area corresponding to each image data, Based on the acquired correction amount, the density information in the reference area of each image data is converted to acquire converted density information.

  Further, the density information conversion unit calculates the thinning rate of the image data in each reference area based on the density information of each reference area for each reference area corresponding to each image data, The corrected thinning rate can be acquired as converted density information based on the thinning rate and the correction amount.

  Further, it is assumed that the density information conversion unit has a density conversion curve set in advance, and as the density conversion curve, the density information in the reference area is converted into lower density information as the density information in the reference area is higher. Things can be used.

  Further, as a density conversion curve, the ratio of the decrease in density information after conversion to the increase in density information in the reference area gradually increases as the density information in the reference area increases, and then gradually decreases. Things can be used.

  Further, the density information acquisition unit may acquire the pixel density as density information in the reference area.

  The stencil printing apparatus of the present invention includes the image data generation apparatus of the present invention, a plate making unit that performs plate making processing based on each processed image data corresponding to each image data generated in the image data generation device, and a plate making unit And a printing section having a drum around which the plate produced in (1) is wound.

  According to the image data generation method and apparatus and the stencil printing apparatus of the present invention, the density information in some reference areas of a plurality of image data representing a plurality of images recorded on the same surface of the recording medium, respectively. Obtained and converted density information by converting the density information in the reference area of each image data based on the density information of the reference area corresponding to each image data, and each obtained image data Since the processed image data corresponding to each image data is generated based on the converted density information corresponding to the image data, the density conversion is performed by converting the density according to the local density at the overlapping position of each image data. Ink transfer at an excessive position can be suppressed, and a good printing result can be obtained.

  Also, when converting the density information in the reference area to obtain the converted density information, if the density conversion curve is set in advance, the density conversion curve is set according to the environmental conditions and user preferences. By doing so, the ink transfer amount can be optimized.

1 is an overall schematic configuration diagram of an embodiment of a stencil printing apparatus according to the present invention. The block diagram which shows the structure of the image data generation part of one Embodiment of the stencil printing apparatus of this invention The flowchart for demonstrating the effect | action of one Embodiment of the stencil printing apparatus of this invention. The figure which shows an example of the image data of 1st edition, a reference area, and an attention pixel The figure which shows an example of the image data of 2nd edition, a reference area, and an attention pixel Diagram showing an example of a density conversion curve Diagram for explaining calculation of average pixel density The figure which shows an example of the correction function which matched average pixel density and correction amount The figure which shows an example of a threshold value matrix The figure which shows an example of the processed image data of the 1st plate in which the thinning process was performed The figure which shows an example of the processed image data of the 2nd edition in which the thinning process was performed Schematic diagram when the processed image data of the first edition and the processed image data of the second edition are viewed globally

  Hereinafter, an embodiment of a stencil printing apparatus using the image data generation apparatus of the present invention will be described in detail with reference to the drawings. The stencil printing apparatus according to the present embodiment is characterized by a method for generating image data. First, the schematic configuration will be described. FIG. 1 is a schematic configuration diagram of the stencil printing apparatus of the present embodiment.

  The stencil printing apparatus 1 according to the present embodiment is a stencil printing apparatus that performs two-color printing. As shown in FIG. 1, an image reading unit 10 that reads an image of a document and outputs image data reads the image. Printing paper using the stencil sheet M made in the first and second plate making sections 30 and 35, which performs the plate making process on the stencil sheet M based on the obtained image data First and second printing units 40 and 50 that perform printing on P1, a paper feeding unit 20 that feeds printing paper P1 to the first printing unit 40, and a print in which the first color is printed on the first printing unit 40 A transport belt unit 44 that transports the paper P2 toward the second printing unit 50 and a paper discharge unit 70 that discharges the printing paper P3 on which the second color is printed by the second printing unit 50 are provided.

  The image reading unit 10 includes a line image sensor that photoelectrically reads image information of an original, scans the original with the line image sensor, and outputs image data.

  The first plate making unit 30 has a thermal head 31 in which a plurality of heating elements are arranged in a line, and performs a plate making process on the stencil sheet M fed from a stencil sheet roll using the thermal head 31. Is. The first plate making unit 30 performs plate making processing based on processed image data output from an image data generation unit 60 described later.

  Similarly to the first plate making unit 30, the second plate making unit 35 has a thermal head 36, and performs the plate making process on the stencil sheet M fed from the stencil sheet roll using the thermal head 36. is there. The second plate making unit 35 also performs plate making processing based on processed image data output from an image data generation unit 60 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 that strips the one-color printed printing paper P2 from the first printing drum 41 are provided. A pre-made stencil sheet M perforated 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 thickness direction in FIG. 1).

  Similarly to the first printing unit 40, the second printing unit 50 is configured to press the cylindrical second printing drum 51 and the printing paper P2 against the second printing drum 51 with a predetermined press pressure. A press roller 52 and a second peeling claw 53 for peeling the two-color printed printing paper P3 from the second printing drum 51 are provided. A pre-made stencil sheet M perforated in the second plate making unit 35 is wound around and attached to the outer periphery of the second printing drum 51. 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 thickness direction in 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 loaded with a paper discharge feed belt unit 72 that conveys the two-color printed print paper P3 to the paper discharge stand 71, and a two-color printed print paper P3 conveyed by the paper discharge feed belt unit 72. A paper discharge table 71 is provided.

  Further, the stencil printing apparatus 1 of the present embodiment performs a predetermined density conversion process on the image data output from the image reading unit 10 and outputs images to the first and second plate making units 30 and 35, respectively. A data generation unit 60 is provided.

  Specifically, as shown in FIG. 2, the image data generating unit 60 includes an image data receiving unit 61 that receives input of image data output from the image reading unit 10, and an image received by the image data receiving unit 61. The binarization processing unit 62 that performs binarization processing on the data, and the pixel density in a part of the reference area of the binary image data that has been binarized by the binarization processing unit 62 are acquired. Based on the pixel density acquisition unit 63, the density information conversion unit 64 that acquires the thinning rate of the binary image data in the reference area based on the pixel density acquired by the pixel density acquisition unit 63, and the density information conversion unit 64 The corrected thinning rate is corrected based on the pixel density of the binary image data of the two plates to obtain a corrected thinning rate, and the binary image data in the reference area is thinned based on the corrected thinning rate The And a thinning processing unit 65 for generating to processed image data. The operation of each part will be described later in detail.

  Next, the operation of the stencil printing apparatus 1 of the present embodiment will be described. First, the operation of the image data generation unit 60 will be described with reference to the flowchart shown in FIG.

  First, a document is placed on a document table of the image reading unit 10 and scanned by a line image sensor while being pressed by a pressing plate to read image data (S10). Then, multi-value image data representing an image recorded on the document is sequentially acquired for each line, and the multi-value image data is subjected to color separation processing to generate two-value multi-value image data. It is received by 60 image data receiving units 61. In FIG. 2, a separation processing unit for performing the separation processing is not shown. In this embodiment, the multivalued image data is subjected to the color separation process to obtain the second version of the multivalued image data. However, the present invention is not limited to this. Multi-value image data for a plate may be acquired.

  The image data receiving unit 61 outputs the received two-version multi-value image data to the binarization processing unit 62, and the binarization processing unit 62 applies 2 to each of the input two-version multi-value image data. A binarization process is performed and converted into binary image data (S12). As the binarization process, a known binarization process such as a simple binarization process, an error diffusion method, and a halftone dot binarization method can be used.

  Then, the binary image data of the second version converted by the binarization processing unit 62 is output to the pixel density acquisition unit 63 and the thinning processing unit 65.

  The pixel density acquisition unit 63 acquires the pixel density as the density information based on the input binary image data of the second version (S14). Specifically, as shown in FIG. 4A (first-version binary image data) and FIG. 4B (second-version binary image data), a part of the entire binary image data is referred to. As a region, the number of black pixels in the reference region is counted, and the ratio of the number of black pixels to the total number of pixels in the reference region is obtained as the pixel density. Then, the acquired pixel density is assigned to the target pixel which is the center pixel of the reference region. 4A and 4B show the range of the reference area and the position of the target pixel when 5 pixels × 5 pixels are set as the reference area.

  As shown in FIG. 4A, when 12 pixels out of the total number of 25 pixels in the reference area are black pixels, the pixel density is 12 pixels / 25 pixels = 0.48. On the other hand, as shown in FIG. 4B, when 20 pixels out of the total number of 25 pixels in the reference area are black pixels, the pixel density is 20 pixels / 25 pixels = 0.8.

  Then, the reference area is shifted one pixel at a time in the X direction shown in FIGS. 4A and 4B, the pixel density is acquired in each reference area, and the pixel density is assigned to the target pixel, so that two versions for each line are obtained. Pixel density is assigned to all the pixels of the binary image data.

  Note that when the set reference area is large, the time required for counting the number of black pixels becomes long and the processing speed becomes slow. Therefore, each time the reference area is shifted by one pixel, the number of black pixels may be calculated by counting only the increase / decrease in the number of black pixels in the difference area between the previous reference area and the current reference area.

  Further, as a memory for storing binary image data, a line buffer memory (see FIGS. 4A and 4B) corresponding to a reference area necessary for calculation of the pixel density as described above may be used. As a result, the capacity of the memory can be suppressed, and the cost can be reduced.

  Then, the pixel density information assigned to each pixel of the binary image data of the second version in the pixel density acquisition unit 63 is output to the density information conversion unit 64, and the density information conversion unit 64 receives the information of each input pixel. Based on the pixel density information, the thinning rate of each pixel corresponding to the size of the pixel density is acquired (S16). Specifically, the density information conversion unit 64 is set with a density conversion curve in which the pixel density and the thinning rate are associated with each other as shown in FIG.

  Here, as shown in FIG. 5, the density conversion curve is such that the higher the pixel density assigned to the pixels, the higher the thinning rate. Further, the rate (inclination) of the increase in the thinning rate with respect to the increase in the pixel density has a characteristic that gradually increases as the pixel density increases and then gradually decreases. Note that the characteristics of the density conversion curve may be automatically changed according to environmental conditions such as air temperature, or may be changed according to preference by the operator.

  Here, the reason why the thinning rate with respect to the pixel density has the characteristics as shown in FIG. 5 will be described below.

  First, in the present embodiment, as described above, a thinning rate corresponding to the pixel density of the reference region is assigned to the target pixel of the reference region, and the thinning rate is set for each black pixel in the reference region. Not assigned.

  For example, if the thinning rate is assigned to each black pixel in the reference area, the number of black pixels after actual thinning in the reference area is counted. This is because it is necessary to specify the black pixel, which increases the mounting cost. Also, when shifting the reference area from left to right and from top to bottom, the lower right half of the reference area is not thinned out, so it is necessary to predict the thinning result. This is because it is necessary to prepare.

  On the other hand, if the method of this embodiment is employ | adopted, a structure can be simplified.

  However, when the method of the present embodiment is employed, the white pixel also becomes a pixel to be thinned out depending on the surrounding density.

  Therefore, it is necessary to calculate by adding a thinning rate slightly more than when assigning a thinning rate to black pixels.

  Therefore, the thinning rate is increased rapidly from the pixel density 0.5, which is a medium density, and since it is unlikely that a white pixel is identified as a thinning target pixel at a high density pixel density, The decimation rate is gradually increased without adding.

  For low density pixel density, there is no need for thinning because no ink retransfer occurs in the first place. However, a thinning rate is assigned in consideration of density continuity after thinning processing.

  Then, the density information conversion unit 64 calculates the thinning rate of each pixel based on the density conversion curve and the pixel density of each pixel. For example, if the pixel for which the thinning rate is to be calculated is the target pixel shown in FIG. 4A, the pixel density is 0.48, so 0.2 is acquired as the thinning rate. For example, when the pixel for which the thinning rate is to be calculated is the target pixel shown in FIG. 4B, the pixel density is 0.8, and thus 0.5 is acquired as the thinning rate. In this way, a thinning rate is assigned to each pixel of the binary image data of the second version.

  Next, the density information conversion unit 64 corrects the thinning rate of each pixel of the input binary image data of the second version and acquires the corrected thinning rate (S18).

  Here, as shown in FIG. 6, the density information conversion unit 64 converts the target pixel in a predetermined reference area of the first version of the binary image data and the second version of the binary image data corresponding to the target pixel. Based on the average pixel density with the target pixel in the reference area, the thinning rate of the target pixel corresponding to each other is corrected.

  More specifically, for example, the target pixel in a predetermined reference area of the first version of the binary image data is the target pixel shown in FIG. 4A, and the second version of the binary image data corresponding to the target pixel When the target pixel in the reference region is the target pixel shown in FIG. 4B, as described above, the pixel density of the target pixel in FIG. 4A is 0.48, and the pixel density of the target pixel in FIG. 4B is 0.8. Therefore, the average pixel density of these pixel densities is (0.48 + 0.8) = 0.64.

  The density information conversion unit 64 is set with a correction function that associates the average pixel density and the correction amount as shown in the graph of FIG. 7, and this correction function and the average pixel calculated as described above are set. A correction amount is calculated based on the density, and the correction amount and the thinning rate are multiplied to calculate a correction thinning rate. As the correction function, specifically, a function that increases the correction amount at a predetermined increase rate according to the increase in the average pixel density is used. As a correction function, as shown in the graph of FIG. 7, the correction amount is increased at a predetermined increase rate until the average pixel density 0.5, at which the ink transfer amount increases, is 0.5 or more. In this range, it is desirable to increase the correction amount at an increase rate smaller than the predetermined increase rate.

  As described above, when the average pixel density is 0.64, the correction amount 1.4 is calculated from the correction function shown in FIG. 7, and the correction amount and the thinning rate are multiplied to calculate the correction thinning rate. The Since the thinning rate of the target pixel in FIG. 4A is 0.2, the correction thinning rate is 0.2 × 1.4 = 0.28, and the thinning rate of the target pixel in FIG. Is 0.5 × 1.4 = 0.7.

  As described above, the correction thinning rate is calculated and assigned to all the pixels of the binary image data of the second version.

  Then, the correction thinning rate assigned to each pixel of the binary image data of the second version in the density information conversion unit 64 is output to the thinning processing unit 65, and the thinning processing unit 65 receives the input binary image data of the second version. On the basis of the correction thinning rate assigned to each pixel of the binary image data of the second version, a thinning process is performed on the binary image data of the second version (S20). Specifically, for example, in the case where the thinning process is performed stochastically based on a random number, black is determined when the value determined by the random number between 0 and 1 is smaller than the thinning rate assigned to each pixel. A pixel may be converted into a white pixel. For example, when the correction thinning rate is 0.28, it is converted to white pixels with a probability of 28%, and when the correction thinning rate is 0.7, it is converted to white pixels with a probability of 70%. become.

  Further, instead of the method using random numbers as described above, a probability table is held as a threshold matrix as shown in FIG. 8, and the threshold matrix value corresponding to the coordinates of each pixel is assigned to the target pixel. If smaller than this, the black pixels may be converted into white pixels.

  The following method may be employed as a method of acquiring the threshold matrix value T (X, Y) corresponding to each pixel. For example, when X coordinates from 0 to 3 are assigned in the right direction of the threshold matrix shown in FIG. 7 and Y coordinates are assigned from 0 to 3 in the upward direction, the threshold matrix assigned to a predetermined pixel (x, y). The coordinates of the value of X are x = x% 4 and Y = y% 4. Note that% is an operator that returns a remainder obtained by dividing x or y by 4.

  FIG. 9A shows an example of processed image data obtained by performing the above-described thinning process on the first version of binary image data shown in FIG. 4A. FIG. 9B shows an example of processed image data obtained by performing the above-described thinning process on the second version of binary image data shown in FIG. 4B. As shown in FIGS. 9A and 9B, the pixels in the left area closer to the edge have a lower pixel density because the pixel density is lower, and the pixels in the right area away from the edge have a higher pixel density. There are many more pixels.

  Further, FIG. 10 shows an example when the two-processed image data subjected to the thinning process and the binary image data obtained by superimposing these images are viewed globally. As shown in FIG. 10, the overlapping area between the binary image data of the first plate and the binary image data of the second plate is thinned more than other regions.

  Then, the processed image data of two plates for each line generated in the thinning processing unit 65 is sequentially output to the first plate making unit 30 and the second plate making unit 35, respectively, and processed for each line of the first plate. The stencil sheet M is punched using the thermal head 31 of the first plate making unit 30 based on the image data, and the second plate making unit based on the processed image data for each line of the second plate. The stencil sheet M is perforated using the thermal head 36 of 35, and the plate making process for each line is performed (S22).

  If the scanning of the reference areas for all the lines has not been completed, the reference area is shifted by one pixel in the Y direction shown in FIG. 4A (B), the process returns to S12 again, and the processes from S12 to S22 are repeated. (S24).

  The plate subjected to the plate making process in the first plate making unit 30 is wound around the first printing drum 41, and the plate subjected to the plate making process in the second plate making unit 35 is used as the second printing drum. 51, the printing operation is executed (S26).

  Specifically, ink is supplied to the inside of the first and second printing drums 41 and 51 by an ink supply pump (not shown), and the first and second printing drums 41 and 51 are rotationally driven. Then, the printing paper P1 is fed out from the paper feed tray 21 by the primary paper feed roller 22 at a predetermined timing in synchronization with the rotation of the first and second print drums 41 and 51, and once the secondary paper feed roller 23 is reached. 1 is formed by the secondary paper feed roller 23 from the left to the right in FIG. 1 at a predetermined timing, and is supplied between the first printing drum 41 and the first press roller 42. The Then, the printing paper P1 is pressed against the printing paper P1 by the first press roller 42 against the stencil stencil sheet M wound around the outer peripheral surface of the first printing drum 41, whereby the first color stencil is printed on the printing paper P1. Printing is performed.

  When the first printing drum 41 rotates by a predetermined angle and the first stencil printing on the printing paper P1 is completed, the one-color printed printing paper P2 is removed by the peeling claw 43 from the first printing drum. The one-color-printed printing paper P2 peeled off from the paper 41 is transported to the second printing section 50 by the transport belt section 44, and the second printing drum 51 and the second press at a predetermined timing. Supplied between the rollers 52.

  Then, the printing surface of the one-color printed printing paper P2 is pressed against the stencil stencil sheet M wound around the outer peripheral surface of the second printing drum 51 by the second press roller 52 to perform one-color printing. The second color stencil printing is performed on the printing surface of the finished printing paper P2.

  When the second printing drum 51 is rotated by a predetermined angle and the second color stencil printing on the printing surface of the one-color printed printing paper P2 is completed, the two-color printed printing paper P3 is peeled off by the nail 53. Is peeled off from the second printing drum 51, and the two-color printed printing paper P <b> 3 that has been peeled off is transported to the paper discharge tray 71 by the paper discharge feed belt 72 and stacked on the paper discharge tray 71.

  Then, the printing paper P1 is again fed out from the paper feed tray 21, and two-color stencil printing is performed on the printing paper P1 in the same manner as described above.

  Note that the stencil printing apparatus of the above embodiment is a stencil printing apparatus having two printing drums, and after obtaining both binary image data of the first color and the second color, density information of these binary image data is acquired. The correction amount is acquired on the basis of, for example, a case where a separated original is scanned to acquire multi-value image data for two plates, or a monochromatic stencil printing apparatus having a printing drum In a stencil printing apparatus that performs two-color printing by exchanging the image, there are cases where binary image data for the second plate cannot be acquired at the time of plate making based on the binary image data for the first plate. In such a case, with respect to the binary image data of the first plate, the thinning rate is not corrected based on the average pixel density as described above, and the thinning processing is performed based on the thinning rate before correction. By retaining the binary image data of the first version only for the binary image data of the eye, the thinning rate is corrected based on the average pixel density, and the thinning process is performed based on the corrected thinning rate. It may be. Further, after performing the thinning process on the first version of the binary image data based on the thinning rate before correction, the first version of the binary image data and the second version of the binary image data The correction amount may be obtained based on the average pixel density of the second image, and the thinning process may be performed on the second-level binary image data based on the correction thinning rate. However, in this case, since the first binary image data after the thinning process is used when obtaining the correction amount, the correction amount is obtained using the first binary image data before the thinning process. It is also desirable to increase the correction amount.

  In the above embodiment, the entire two image data are respectively scanned in the reference area, and the correction of the thinning rate and the thinning process are performed based on the pixel density in the corresponding reference area. It is not necessary to scan the reference area for the entire image data, and only a part of specific areas in the two image data may be scanned with the reference area.

  Specifically, the reference area may be scanned only within a range in which the image areas of the two image data overlap each other. Further, the reference area may be scanned only within a range where the pixel value of at least one of the image areas is equal to or greater than a threshold value in a range where the image areas overlap each other.

  In the above-described embodiment, the reference area has a size of 5 pixels × 5 pixels. However, the size is not limited to this, and may be other sizes. When the image area to be subjected to density conversion is smaller than the size of the reference area, it is not always necessary to scan the reference area as in the above embodiment, and the density information in the reference areas corresponding to each other is not necessary. Based on this, the density conversion in the reference area may be performed.

  In the above-described embodiment, the image data generation unit is provided in the stencil printing apparatus. However, the apparatus provided with the image data generation unit is not limited to this. For example, a control signal such as a printer job is output to the stencil printing apparatus. It may be provided in the printer controller.

  Further, the stencil printing apparatus of the above-described embodiment accepts image data output from the image reading unit 10, but is not limited thereto, and may accept image data edited and generated by a computer such as a personal computer. Good. Further, an image data generation unit may be provided in the computer.

DESCRIPTION OF SYMBOLS 1 Stencil printing apparatus 10 Image reading part 20 Paper feed part 30 1st plate making part 31 Thermal head 35 2nd plate making part 36 Thermal head 40 1st printing part 41 1st printing drum 42 1st press roller 44 Conveyance Belt unit 50 Second printing unit 51 Second printing drum 52 Second press roller 60 Image data generation unit 61 Image data reception unit 62 Binarization processing unit 63 Pixel density acquisition unit 64 Density information conversion unit 65 Thinning processing unit 70 Paper discharge unit

Claims (4)

Receiving input of a plurality of image data representing a plurality of images recorded on the same surface of the recording medium,
A binarization process is performed on each of the received plurality of image data to convert it into a plurality of binarized image data,
A partial area of the binarized image data is set as a reference area, density information is acquired in each reference area while shifting the position of the reference area, and the density information is stored in the reference area. Assigned to the pixel of interest,
Assigning a thinning rate to each pixel of interest based on the assigned density information of each pixel of interest and a density conversion curve that associates the density information with the thinning rate;
The correction amount is calculated based on the density information of the target pixel in the predetermined reference area of the predetermined binary image data and the density information of the target pixel in the reference area of the other binary image data corresponding to the target pixel. , Multiplying the correction amount by the thinning rate and assigning a correction thinning rate to all the pixels of the binary image data,
For each of the binary image data, generate processed image data by performing a thinning process based on the correction thinning rate assigned to each pixel,
The density conversion curve has a characteristic that the rate of change of the thinning rate with respect to the increase in density information in the reference region gradually increases as the density information in the reference region increases and then gradually decreases. An image data generation method characterized by the above . An image data receiving unit for receiving input of a plurality of image data representing a plurality of images recorded on the same surface of the recording medium;
A binarization processing unit that performs binarization processing on each of the plurality of image data received by the image data reception unit and converts the image data into a plurality of binary image data;
A partial area of the binarized image data is set as a reference area, density information is acquired in each reference area while shifting the position of the reference area, and the density information is stored in the reference area. A density information acquisition unit assigned to the pixel of interest;
Based on the density information of each pixel of interest assigned by the density information acquisition unit and the density conversion curve in which the density information and the thinning rate are associated with each other, a thinning rate is assigned to each pixel of interest. A correction amount is calculated based on the density information of the target pixel in the predetermined reference area of the binary image data and the density information of the target pixel in the reference area of the other binary image data corresponding to the target pixel; A density information converter that multiplies the correction amount by the thinning rate and assigns the correction thinning rate to all the pixels of the binary image data;
A thinning processing unit that generates processed image data by performing a thinning process based on the correction thinning rate assigned to each pixel for each of the binary image data;
The density conversion curve has a characteristic that a rate of change of the thinning rate with respect to an increase in density information in the reference area gradually increases after the density information in the reference area increases and then gradually decreases. An image data generation device characterized by the above.   The image data generation apparatus according to claim 2, wherein the density information acquisition unit acquires a pixel density as density information in the reference area. The image data generation device according to claim 2 or 3,
A plate making unit that performs plate making processing based on each processed image data corresponding to each image data generated in the image data generation device;
A stencil printing apparatus comprising: a printing unit having a drum around which a plate produced in the plate making unit is wound.

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