JP5537087B2 - 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, for example, in the case of a stencil printing apparatus provided with a printing drum that performs printing of the first plate and a printing drum that performs printing of the second plate, the second plate is printed before the ink of the first plate is sufficiently dried. Therefore, the ink on the printing paper is transferred to a conveyance roller, a press roller, and the like on the paper passing path, and the ink is likely to be transferred again from these rollers to the printing paper. As a method for solving such a problem, in Patent Document 1, the ink transfer amount is suppressed to an optimum amount by controlling the plate making conditions such as plate making energy and dot density according to the image feature amount of a small area of the plate making image. A method has been proposed.

JP 2006-315288 A JP 2002-219849 A JP 2004-338234 A

  However, as shown in FIG. 14, when the perforations adjacent in the sheet passing direction are dense, such as ruled lines and figures continuous in the sheet passing direction, the amount of ink transfer tends to be excessive. Therefore, dirt is likely to occur. In double-sided printing, if there are ruled lines or figures that continue in the paper-passing direction as described above, dirt is likely to accumulate on the transport rollers on the paper-passing path, and the accumulated dirt retransfers to the printing paper. It becomes easy to do.

  On the other hand, since the method described in Patent Document 1 does not take into account the features such as the ruled lines and figures as described above, the ink transfer amount may not be sufficiently suppressed.

  Further, Patent Document 2 proposes a stencil printing apparatus in which printing drums are arranged on the front side and the back side of printing paper as shown in the left diagram of FIG. In order to prevent the ink from transferring from the press roller used for printing to the printing paper, a method for devising the surface shape of the press roller has been proposed. Further, in Patent Document 3, as shown in the right diagram of FIG. 15, a method of scraping dirt transferred by pressing a cleaning member against a press roller is proposed.

  However, not only the ruled lines and figures continuous in the paper passing direction as described above, but also, for example, when images are concentrated at intervals corresponding to the peripheral length of the press roller in the paper passing direction of the printing surface as shown in FIG. In addition, since the amount of ink transferred from the printing surface to the press roller is accumulated, the methods described in Patent Document 1 and Patent Document 2 cannot sufficiently suppress the ink transferred to the press roller, and the ink is still used. The stain on the printing paper due to the re-transfer cannot be suppressed.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image data generation method and apparatus and a stencil printing apparatus that can acquire a good printed matter without deteriorating the image quality of the printed matter.

  The image data generation method of the present invention accepts input of image data representing an image recorded on a recording medium conveyed in a predetermined paper feeding direction in a printing apparatus, and the above paper feeding direction for the received image data. The processed image data is generated by performing a density conversion process so that the density of image data representing an image that appears continuously in the sub-scanning direction on the image data corresponding to is reduced.

  An image data generation apparatus according to the present invention is received by an image data reception unit that receives an input of image data representing an image recorded on a recording medium that is conveyed in a predetermined sheet passing direction in the printing device, and an image data reception unit. The processed image data is generated by subjecting the image data to a density conversion process that lowers the density of the image data representing an image that appears continuously in the sub-scanning direction on the image data corresponding to the paper passing direction. And a density conversion processing unit.

  In the image data generation device of the present invention, a density information acquisition unit that acquires density information of a part of the reference region of the image data is further provided, and the density conversion processing unit is acquired by the density information acquisition unit. Based on the density information in the reference area, the image data in the reference area is subjected to density conversion processing, and the reference area is subjected to main scanning in which the length in the sub-scanning direction is orthogonal to the sub-scanning direction. The rectangular region can be longer than the length in the direction.

  Here, “the density conversion process is performed on the image data in the reference area based on the density information in the reference area acquired by the density information acquisition unit” is a partial area of the image data. This means that density conversion processing is performed on image data in the same reference area as the predetermined reference area based on the density information in the predetermined reference area.

  Further, a thin line detection unit for detecting a thin line extending in the sub-scanning direction in the image data is further provided, and the density conversion processing unit is based on the density information in the reference area and the thin line information detected by the thin line detection unit. Thus, density conversion processing can be performed.

  In addition, the density conversion processing unit may perform density conversion processing so that the density of the reference region in which the fine line is detected by the thin line detection unit is lower than the density of the reference region in which the fine line is not detected. it can.

  Further, a density information acquisition unit that acquires density information of a part of the reference region of the image data is further provided, and the density conversion processing unit is set to n times the circumference of the press roller used when the image is recorded on the recording medium. Based on the density information of a plurality of reference areas arranged in the sub-scanning direction at an interval of (n is a natural number), density conversion processing can be performed on the image data in the reference area.

  Here, based on the above-mentioned information on the density of a plurality of reference areas arranged in the sub-scanning direction at intervals of n times (n is a natural number) the circumference of the press roller used when recording an image on a recording medium. "The density conversion process is performed on the image data in the reference area" means in the sub-scanning direction at intervals of n times (n is a natural number) the perimeter of the press roller used when the image is recorded on the recording medium. This means that density conversion processing is performed on image data in the same reference area as the predetermined plurality of reference areas based on the density information of the predetermined plurality of reference areas arranged in the area.

  In addition, a density information conversion unit that converts the density information in the reference area according to the size of the density information and acquires converted density information is further provided, and the density conversion processing unit is acquired by the density information conversion unit. Based on the converted density information, the density conversion process can be performed.

  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, the density conversion curve has a characteristic that the ratio of the decrease in the density information after the conversion to the increase in the density information in the reference area gradually increases as the density information in the reference area increases and then gradually decreases. Can be.

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

  In addition, the density information conversion unit converts the density information in the reference area to acquire the thinning rate in the reference area as converted density information, and the density conversion processing unit is acquired by the density information conversion unit. Based on the thinning rate, the image data can be thinned to generate processed image data.

  The stencil printing apparatus of the present invention includes an image data generation apparatus of the present invention, a plate making unit that performs plate making processing based on processed image data generated by the image data generation device, and a plate produced in the plate making unit. A printing unit including a drum to be attached and a press roller that presses the recording medium against the drum, and a sheet conveyance unit that conveys the recording medium in the sheet direction toward the printing unit.

  Here, the “image appearing continuously in the sub-scanning direction on the image data” is not only an image appearing connected in the sub-scanning direction, but also a plurality of images arranged at predetermined intervals in the sub-scanning direction. Images. Further, it is assumed that a plurality of images arranged with a predetermined interval may be a part of a predetermined figure or character.

  According to the image data generation method and apparatus and the stencil printing apparatus of the present invention, the density conversion process that reduces the density of image data representing an image that appears continuously in the sub-scanning direction on the image data corresponding to the paper passing direction. Since the processed image data is generated by applying, it is possible to concentrate and thin out areas where ink transfer amount tends to increase, such as ruled lines and drawings continuous in the sub-scanning direction. Therefore, it is possible to obtain a good print result.

  Further, a thin line detection unit for detecting a thin line extending in the sub-scanning direction in the image data is further provided, and the density conversion processing unit is based on the density information in the reference area and the thin line information detected by the thin line detection unit. When the density conversion process is performed, the amount of ink transfer can be sufficiently suppressed even for the thin line extending in the sub-scanning direction.

  Further, density conversion processing is performed based on density information of a plurality of reference regions arranged in the sub-scanning direction at intervals of n times (n is a natural number) the circumference of the press roller used when recording an image on a recording medium. In this case, even when images are concentrated at intervals of the peripheral length of the press roller, the density of these images can be appropriately lowered, and the amount of ink transfer can be suppressed.

  In addition, when the density information in the reference area is converted according to the magnitude of the density information and the converted density information is acquired, if the density conversion curve is set in advance, the environmental conditions and user The ink transfer amount can be optimized by setting the density conversion curve according to the user's preference.

1 is an overall schematic configuration diagram of a first embodiment of a stencil printing apparatus of the present invention. The block diagram which shows the structure of the image data generation part of 1st Embodiment of the stencil printing apparatus of this invention. The flowchart for demonstrating the effect | action of 1st Embodiment of the stencil printing apparatus of this invention. The figure which shows an example of image data, a reference area, and an attention pixel The figure which shows an example of image data, a reference area, and an attention pixel Diagram showing an example of a density conversion curve The figure which shows an example of a threshold value matrix The figure which shows an example of the processed image data to which the thinning process was performed The figure which shows an example of the processed image data to which the thinning process was performed The figure which shows an example of the processed image data (edge vicinity) to which the thinning process was performed The figure which shows an example of a thin line narrower than a reference area The figure which shows an example of a thin line narrower than a reference area The figure which shows an example of a thin line narrower than a reference area Diagram showing an example of a density conversion curve for fine lines and a density conversion curve for normal use The figure for demonstrating the acquisition method of the pixel density information in 2nd Embodiment of the stencil printing apparatus of this invention. The figure which shows an example of the reference area of the reference area where the attention pixel exists, and the position away from the reference area by the press roller perimeter Diagram showing an example of a density conversion curve The figure for demonstrating the subject when there exists a continuous image in the subscanning direction. The figure for demonstrating the subject when there exists a continuous image in the subscanning direction. The figure for demonstrating the subject at the time of an image concentrating with the space | interval equivalent to the perimeter of a press roller in the paper passing direction of a printing surface.

  Hereinafter, a first embodiment of a stencil printing apparatus using an 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.

  As shown in FIG. 1, the stencil printing apparatus 1 of the present embodiment reads an image of a document and outputs image data, and the stencil sheet M is printed on the stencil sheet M based on the image data read by the image reading unit 10. The first and second plate making sections 30 and 35 to which the plate making process is performed, and the first and second plate printing sheets P1 are printed using the stencil sheet M made by the first and second plate making sections 30 and 35. The printing units 40 and 50, the paper feeding unit 20 that feeds the printing paper P1 to the first printing unit 40, and the printing paper P2 that has been printed on one side in the first printing unit 40 are temporarily stocked, and then at a predetermined timing. An intermediate stock unit 46 that feeds paper to the second printing unit 50 and a paper discharge unit 70 that discharges the printing paper P3 printed on both sides 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 35, the second plate making unit 35 has a thermal head 36, and performs the plate making process using the thermal head 36 on the stencil sheet M fed from the stencil sheet roll. 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. However, on the second printing unit 50 side, since smear due to retransfer of ink does not occur, as image data used in the second plate making unit 35, image data that has not been subjected to thinning processing in the image data generation unit 60 May be used.

  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 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 double-side printed 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 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 that sequentially feeds the finished printing paper P2 between the second printing drum 51 and the second press roller 52 at a predetermined timing.

  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 And a thinning processing unit 65 for performing thinning processing on the binary image data in the reference area based on the thinning rate thus generated and generating processed image data. The operation of each part will be described later in detail.

  Next, the operation of the stencil printing apparatus 1 according to the first embodiment of the present invention 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 the 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 received from the image reading unit 10 by the image data receiving unit 61 of the image data generating unit 60.

  The image data reception unit 61 outputs the received multi-value image data to the binarization processing unit 62, and the binarization processing unit 62 performs binarization processing on the input multi-value image data for each line. To 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.

  The binary image data 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 (S14). Specifically, as shown in FIGS. 4A and 4B, a partial area of the entire binary image data is set as a reference area, the number of black pixels in the reference area is counted, The ratio of the number of black pixels to the total number of pixels is acquired as the pixel density, and the acquired pixel density is assigned to the target pixel that is the center pixel of the reference region.

  Here, the sub-scanning direction shown in FIGS. 4A and 4B is a direction corresponding to the paper passing direction of the printing paper in the stencil printing apparatus 1, and the main scanning direction is a direction (width direction) orthogonal to the paper passing direction. 4A shows an example of a line image extending in the main scanning direction, and FIG. 4B shows an example of a line image extending in the sub-scanning direction.

  Then, in the stencil printing apparatus 1 of the present embodiment, as shown in FIGS. 4A and 4B, the density conversion process is performed so that the density of the image data representing the image that appears continuously in the sub-scanning direction is lowered. As the reference area, a rectangular area whose length in the sub-scanning direction is longer than that in the main scanning direction is set. Specifically, FIGS. 4A and 4B illustrate the range of the reference area and the position of the target pixel when 3 pixels × 7 pixels are set as the reference area.

  As shown in FIG. 4A, when the binary image data represents a line image extending in the main scanning direction, and 9 pixels out of the total number of 21 pixels in the reference region are black pixels, the pixel density is 9 pixels / 21 pixels = 0.43. On the other hand, as shown in FIG. 4B, when the binary image data represents a line image extending in the sub-scanning direction and 21 pixels out of the total number of 21 pixels in the reference area are black pixels, the pixel density Is 21 pixels / 21 pixels = 1.0.

  Then, the reference area of the rectangular area as described above is shifted by one pixel in the main scanning 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. As a result, the pixel density is assigned to all the pixels of the binary image data for each line.

  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 corresponding to the reference area necessary for calculating the pixel density as described above may be used, thereby suppressing the memory capacity. This can reduce the cost.

  Then, the pixel density information assigned to each pixel in the pixel density acquisition unit 63 is output to the density information conversion unit 64, and the density information conversion unit 64 is based on the input pixel density information of each pixel. 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 decimation rate is increased rapidly from the medium density pixel density, and the white pixel is not likely to be identified as a decimation target pixel at a high density pixel density. Instead, the decimation rate is gradually increased.

  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, when the pixel for which the thinning rate is calculated is the pixel of interest shown in FIG. 4A, the pixel density is 0.43, so 0.1 is acquired as the thinning rate,
When the pixel for which the thinning rate is to be calculated is the target pixel shown in FIG. 4B, the pixel density is 1.0, and thus 0.6 is acquired as the thinning rate. That is, a higher decimation rate is acquired for the target pixel belonging to the binary image data representing the line image extending in the sub-scanning direction than the target pixel belonging to the binary image data representing the line image extending in the main scanning direction. In this way, a thinning rate is assigned to all pixels.

  Then, the thinning rate assigned to each pixel in the density information conversion unit 64 is output to the thinning processing unit 65.

  The thinning processing unit 65 performs thinning processing on the binary image data based on the input binary image data and the thinning rate assigned to each pixel (S18). 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 thinning rate is 0.75, conversion into white pixels is performed with a probability of 75%.

  Further, instead of the method using random numbers as described above, the probability table is held as a threshold matrix as shown in FIG. 6 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 an X coordinate from 0 to 3 is assigned to the right of the threshold matrix shown in FIG. 6 and a Y coordinate is 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.

  An example of processed image data obtained by performing the above-described thinning process on the binary image data shown in FIGS. 4A and 4B is shown in FIGS. 7A and 7B. As shown in FIGS. 7A and 7B, binary image data representing a line image extending in the sub-scanning direction is thinned out more than binary image data representing a line image extending in the main scanning direction. Specifically, as described above, the pixel density of the line image extending in the main scanning direction in FIG. 4A is 9 pixels / 21 pixels = 0.43 regardless of the location of the reference region, and the thinning rate is 0 from FIG. .1. On the other hand, the pixel density of the line image extending in the sub-scanning direction in FIG. 4B is 21 pixels / 21 pixels = 1.0 at the center and 14 pixels / 21 pixels = 0.66 at the outside, and the thinning rate is 0 from FIG. .6, 0.4, and the line image extending in the sub-scanning direction has a higher thinning rate than the line image extending in the main scanning direction.

  Further, as shown in FIG. 8, since the thinning process is performed according to the size of the pixel density of the reference region as described above, the pixels in the region far from the edge have a higher pixel density, so that the number of thinned pixels increases. It has become.

  The processed image data for each line generated in the thinning processing unit 65 is sequentially output to the first plate making unit 30, and the thermal head 31 of the first plate making unit 30 is based on the processed image data for each line. The stencil sheet M is perforated by using and the stencil making process for each line is sequentially performed (S20).

  If scanning of all lines has not been completed, the reference area is shifted by one pixel in the sub-scanning direction shown in FIG. 4A (FIG. 4B), the process returns to S10 again, and the processes from S10 to S20 are repeated. (S22). Note that the processing corresponding to the image printed in the second printing unit 50 does not cause smear due to retransfer of ink, and therefore the processing of scan (S10), binarization processing (S12), and plate making (S20) You may make it perform only.

  The above-described processing from S10 to S22 is performed for each image of the document to be printed on both sides, and the processed image data corresponding to one image is input to the first plate making unit 30 as described above and the plate making processing. The processed image data corresponding to the other image is input to the second plate making unit 35 and subjected to the plate making process.

  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. The print operation is executed (S24).

  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. Is done.

  Then, when the first printing drum 41 is rotated by a predetermined angle and the single-sided stencil printing on the printing paper P1 is completed, the single-sided printing paper P2 is peeled off from the first printing drum 41 by the peeling claw 43. The single-sided printed printing paper P <b> 2 that has been removed and peeled off is conveyed to the intermediate stock unit 46 by the curved conveyance unit 44.

  The single-side printed paper P2 is once stocked in the intermediate stock section 46, and then discharged from the intermediate stock section 46 with the printing surface facing downward (the unprinted surface is the upper side), and is picked up by a pickup roller 47. And is once abutted against the timing roller 48 to form a slack and then supplied between the second printing drum 51 and the second press roller 52 by the timing roller 48 at a predetermined timing.

  Then, the non-printed surface of the single-sided printed 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, so that the single-sided printing is completed. Stencil printing is performed on the unprinted surface of the printing paper P2.

  When the second printing drum 51 rotates by a predetermined angle and the stencil printing on the unprinted surface of the single-sided printed printing paper P2 is completed, the double-sided printed printing paper P3 is removed by the peeling claw 53 by the second claw 53. The double-sided printed printing paper P3 that has been peeled off from the printing drum 51 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 double-sided stencil printing is performed on the printing paper P1 in the same manner as described above.

  In the stencil printing apparatus according to the first embodiment, as described above, the density conversion process is performed so that the density of image data representing an image appearing continuously in the Y direction (sub-scanning direction) is lowered. As a reference area, a rectangular area whose length in the sub-scanning direction is longer than that in the main-scanning direction is set, but appears continuously in the sub-scanning direction as shown in FIGS. 9A to 9C. When the image is a thin line having a width narrower than the width of the reference area in the main scanning direction, the pixel density in the reference area becomes low, and the thinning rate tends to be low.

  However, even if such a thin line is continuous in the sub-scanning direction, the amount of ink transfer tends to increase, so it is desirable that the thinning rate be equal to the target pixel shown in FIG. 4B.

  Therefore, a fine line detection unit for detecting whether or not the binary image data in the reference region represents a fine line is further provided in the density information conversion unit 64, and the fine line detection unit as shown in FIG. A fine line density conversion curve that is used when it is detected and a normal density conversion curve that is used when a thin line is not detected by the thin line detection unit may be set. The thin line density conversion curve may be set to have a higher thinning rate than the normal density conversion curve for the same pixel density.

  The fine line detection method in the fine line detection unit may be detected by primary differentiation or secondary differentiation of the density value, may be detected by pattern matching, or other known techniques can be used.

  Next, a second embodiment of the stencil printing apparatus using the image data generation apparatus of the present invention will be described in detail. The stencil printing apparatus of the second embodiment is different from the stencil printing apparatus 1 of the first embodiment described above in the operation of the pixel density acquisition unit. Since the other configuration is the same as that of the stencil printing apparatus 1 of the first embodiment, only the operation of the pixel density acquisition unit will be described below.

  As shown in FIG. 11, the pixel density acquisition unit 83 of the stencil printing apparatus according to the second embodiment is arranged at intervals corresponding to the peripheral length of the press roller in the sub-scanning direction with respect to the reference region of a predetermined target pixel. The pixel density of the predetermined pixel of interest is acquired based on the pixel densities of the plurality of reference regions. For example, when the pixel density of the target pixel shown in FIG. 11 is acquired, the pixel density of the reference region where the target pixel exists and the peripheral length of the press roller in the sub-scanning direction are separated from the reference region where the target pixel exists. And obtain the pixel density of the reference area at a position separated from the reference area where the target pixel exists by the double of the peripheral length of the press roller in the sub-scanning direction in the sub-scanning direction. An average pixel density of the pixel density of the region is obtained and assigned as information on the pixel density of the predetermined target pixel.

  In the stencil printing apparatus 1 of the first embodiment, a rectangular reference area is used. However, the stencil printing apparatus of the second embodiment is not limited to this, and for example, 5 pixels × 5 A square reference area of pixels may be used.

  In FIG. 11, the pixel density information of the target pixel is acquired based on the pixel densities of the three reference regions. However, the pixel density information of the target pixel is acquired based on the pixel densities of the two reference regions. It may be.

  Specifically, as shown in FIG. 12, the pixel density of the reference region where the pixel of interest exists, and the pixel of the reference region at a position separated from the reference region where the pixel of interest exists by the peripheral length of the press roller in the sub-scanning direction. And the average pixel density of these two pixel densities is calculated. More specifically, the pixel density of the reference area in which the target pixel exists is 15 pixels / 25 pixels = 0.6, and the pixel density of the reference area at a position separated by the peripheral length of the press roller in the sub-scanning direction is 20 Since pixels / 25 pixels = 0.8, the average pixel density is 0.7. The pixel density 0.7 is assigned as information on the pixel density of the target pixel.

  Then, as in the first embodiment, the reference area where the target pixel shown in FIG. 12 exists is shifted by one pixel in the main scanning, and the average pixel density of the target pixel in each reference area is the same as described above. Is calculated, and the average pixel density is assigned as the pixel density information of the target pixel, whereby the pixel density information is assigned to all the pixels of the binary image data for each line.

  Note that the reference region used for calculating the average pixel density is not limited to the reference region located downstream in the sub-scanning direction with respect to the reference region where the target pixel exists, as illustrated in FIGS. 11 and 12. Any reference area may be used as long as it is a reference area separated by a distance n times the circumference of the press roller (n is a natural number). For example, two reference areas sandwiching the reference area where the pixel of interest exists are used. May be.

  Then, the pixel density information assigned to each pixel in the pixel density acquisition unit 83 is output to the density information conversion unit 64, and the density information conversion unit 64 is based on the input pixel density information of each pixel. The thinning rate of each pixel corresponding to the size of the pixel density is acquired. The thinning rate acquisition method is the same as that of the stencil printing apparatus 1 of the first embodiment.

  For example, in the case of the pixel of interest shown in FIG. 12, since the pixel density information is 0.7 as described above, a thinning rate of 0.4 is acquired based on the density conversion curve shown in FIG. On the other hand, when the thinning rate is acquired only by the pixel density 0.6 in the reference region where the target pixel exists without obtaining the average pixel density as in the present embodiment, as shown in FIG. Becomes 0.3. As described above, the pixel density information assigned to the target pixel shown in FIG. 12 is influenced by the pixel density of the reference region at a position separated by the peripheral length of the press roller in the sub-scanning direction. Therefore, a thinning rate of 0.4 is assigned.

  The operation after the thinning rate is acquired for each pixel of the binary image data is the same as that of the stencil printing apparatus of the first embodiment.

  In the first and second embodiments, the entire image data is scanned in the reference area, and the thinning process is performed based on the pixel density in the reference area. It is not necessary to scan the reference area, and only a specific area in the image data may be scanned in the reference area.

  Specifically, the reference area may be scanned only within a range where the pixel value is equal to or greater than a threshold value in the image area of the image data.

  In the first and second embodiments, 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 first and second embodiments, 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 printer job is provided in the stencil printing apparatus. It may be provided in a printer controller that outputs a control signal such as.

  The stencil printing apparatus of the first and second embodiments accepts image data output from the image reading unit 10, but is not limited to this, and is an image edited and generated by a computer such as a personal computer. Data may be accepted. Further, an image data generation unit may be provided in the computer.

  The stencil printing apparatus of the first and second embodiments includes two printing drums that perform double-sided printing. However, the present invention is not limited to this, and the image data generation apparatus of the present invention can perform two-color printing. A stencil printing apparatus having two printing drums for performing printing, and a stencil printing apparatus in which one printing drum can be attached and detached, and capable of two-sided or two-color printing by passing printing paper through a printing unit twice It can also be applied to.

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 46 Middle Stock 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 83 Pixel density acquisition unit

Claims (9)

Receiving input of image data representing an image recorded on a recording medium conveyed in a predetermined paper passing direction in the printing apparatus;
A reference area of a part of the image data, wherein the length of the image data corresponding to the sheet passing direction is longer than the length of the main scanning direction perpendicular to the sub scanning direction. Get density information in the reference area,
Image data generation characterized in that, based on the acquired information on the density in the reference area, the image data in the reference area is subjected to density conversion processing for reducing the density to generate processed image data Method. An image data receiving unit that receives input of image data representing an image recorded on a recording medium conveyed in a predetermined sheet passing direction in the printing apparatus;
A reference area of a part of the image data, wherein the length of the image data corresponding to the sheet passing direction is longer than the length of the main scanning direction perpendicular to the sub scanning direction. A density information acquisition unit for acquiring density information in the reference region;
Based on the density information in the reference area acquired by the density information acquisition unit, density conversion for generating processed image data by performing density conversion processing for reducing the density of the image data in the reference area An image data generation device comprising a processing unit. A thin line detection unit for detecting a thin line extending in the sub-scanning direction in the image data;
3. The density conversion processing unit according to claim 2, wherein the density conversion processing unit performs the density conversion processing based on density information in the reference area and fine line information detected by the fine line detection unit. Image data generation device.   The density conversion processing unit performs the density conversion processing so that the density of the reference region where the thin line is detected by the thin line detection unit is lower than the density of the reference region where the thin line is not detected. The image data generating apparatus according to claim 3.   The density conversion processing unit includes a plurality of reference areas arranged in the sub-scanning direction at intervals of n times (n is a natural number) of a peripheral length of a press roller used when recording the image on the recording medium. 3. The image data generation apparatus according to claim 2, wherein the density conversion process is performed on the image data in the reference area based on density information. A density information conversion unit that converts density information in the reference area according to the size of the density information and obtains a thinning rate for the reference area;
The image data generation apparatus according to claim 2, wherein the density conversion processing unit performs the density conversion processing based on the thinning rate acquired by the density information conversion unit.   The density information conversion unit acquires the thinning rate for a predetermined pixel of interest in the reference area based on the density information in the reference area, and shifts the position of the reference area to obtain the image data. The image data generation apparatus according to claim 6, wherein the thinning-out rate for all the target pixels in the density conversion target area is acquired. A density conversion curve for converting density information in the reference region into the thinning rate is set in advance by the density information conversion unit,
The density conversion curve performs conversion such that the higher the density information in the reference area, the larger the thinning rate for the reference area, and the thinning for the increase in density information in the reference area. 8. The image data generating apparatus according to claim 6, wherein the rate of change of the rate has a characteristic of gradually decreasing after increasing as the density information in the reference region increases. An image data receiving unit that receives input of image data representing an image recorded on a recording medium conveyed in a predetermined sheet passing direction in the printing apparatus;
A density information acquisition unit that acquires density information of a part of the reference area of the image data;
Densities of the plurality of reference regions arranged in the sub-scanning direction corresponding to the paper passing direction at intervals of n times (n is a natural number) the perimeter of the press roller used when recording the image on the recording medium An image data generation apparatus comprising: a density conversion processing unit that performs density conversion processing for reducing the density of image data in the reference area based on the information of the above.

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