Patent Publication Number: US-7213515-B2

Title: Data creating device for a printing plates

Description:
FIELD OF THE INVENTION 
   The present invention relates to a data creating device for printing plates that optimizes image data for use in forming printing plates. 
   BACKGROUND ART 
   As illustrated in  FIG. 9 , a conventional printing unit of a digital printing press includes plate cylinder  2 , which carries printing film  1  therearound and rotates, ink feeding part  3  for feeding ink on the printing film  1  on the plate cylinder  2 , rubber cylinder (not shown) onto which ink is transferred from the printing film  1 , and an impression cylinder (not shown) for pressing and holding a printing sheet with the rubber cylinder so as to enable the ink to be transferred from the rubber cylinder to the printing sheet. 
   The printing press of  FIG. 9  is so structured that the printing film  1  having such a length as to enable several images to be formed thereon is rolled up and set to the plate cylinder  2  for easy replacement of the printing film  1 . Specifically, the plate cylinder  2  forms on its circumference recess  4 , in which a roll of the printing film  1  is mounted, and includes feed reel  5  for feeding the printing film  1  onto the circumference of the plate cylinder  2 , and rewind reel  6  for rewinding the printing film  1  by holding the leading edge  1   a  thereof so as to draw the film from the circumference of the plate cylinder  2 . 
   Once the printing film  1  is set on the plate cylinder  2 , image forming device  7 , which is secured in place with a predetermined clearance to the circumference of the plate cylinder  2 , forms an image on the printing film  1  placed on the circumference of the plate cylinder  2  so as to use the printing film  1  as a printing plate. The ink feeding part  3  feeds ink on the printing plate (the printing film  1 ) or performs any other operations so that the image is printed on the printing sheet via the rubber cylinder. 
   Subsequent to completing series of printing operations, the rewind reel  6  rewinds the printing film  1 , which was used as the printing plate, so as to draw the same from the circumference of the plate cylinder  2 , while the feed reel  5  successively feeds a new printing film  1  onto the circumference of the plate cylinder  2 . That is, in the printing press having the printing unit as illustrated in  FIG. 9 , an image can newly be formed on the printing film  1  fed from the feed reel  5  by the image forming device  7 , thereby enabling repeated printing operations without the necessity to replace the plate every time the printing operation is performed. 
   In a case where color printing (multi-color printing) is performed by using the aforesaid digital printing press, plural printing units as illustrated in  FIG. 9  are provided. The printing unit of  FIG. 9  is designed for a two-color printing, and therefore two printing units are provided to make up a digital printing press, in a case where the printing operation is performed by having four colors, namely C (cyan), M (magenta), Y (yellow) and K (black) overlapped to each other. 
   In the thus arranged digital printing press, image data (color separated, four image data) for the respective printing plates used in the printing units are created, thereby forming a printing plate in each printing unit based on each image data. 
   Image data for the respective printing plates must be prepared so as to achieve correct alignment of colors during printing. For the correct alignment of colors in printing, marks called “register marks” for the alignment are generally printed in a space near the edge of a substrate, and image data for each printing plate contains data (register mark data) for laying out register marks. This register mark data is also utilized to provide marks in sheet cutting operation in addition to an operation to adjust the alignment of colors in printing. 
     FIG. 10  respectively illustrate image data for the respective printing plates used in a digital printing press according to a conventional technique. As illustrated in  FIG. 10 , in the conventional technique, all the image data for the respective printing plates contain register mark data T 1 -T 8 . Herein,  FIGS. 10(   a ),  10 ( b ),  10 ( c ) and  10 ( d ) illustrate image data created respectively for a C plate, a M plate, a Y plate and a K plate. 
   The respective printing plates are formed based on the image data created respectively for them in  FIG. 10 .  FIG. 11  illustrates a print formed by using these printing plates. As illustrated in  FIG. 11 , print  100  containing an illustration (a logo), a color picture, text and register mark data T 1 -T 8  is made (Japanese Patent Application Laid-open No. 2002-166523). 
   The digital printing press made up of plural printing units as described above provides alignment with high accuracy and therefore there is a case where register mark data is not needed when it is presented for the purpose of adjustment of alignment of colors in printing. In such a case, it is possible to create each image data that contains no register mark data. Accordingly, in this case, the printing plates are formed based on image data without register mark data, overprinting is made by these printing plates, thereby making the print  100  as illustrated in  FIG. 11 . 
   However, according to the above conventional technique, whether register mark data are contained or not, image data created for forming the printing plates are allowed to have only a uniform size. That is, the printing film  1  for use in forming printing plates provides a uniform size for all the printing plates, regardless of presence or absence of an image to be printed, the size or the like of an image for each plate. There is a case where the size of an image to be printed is very small depending on the plate, which results in inefficient consumption of the printing film  1 . 
   For example, in each of the C plate (see  FIG. 10(   a )), the M plate (see  FIG. 10(   b )) and the Y plate (see  FIG. 10(   c )), a portion S with no data except for register marks written therein is caused. That is, if this portion S in each of the C, M and Y plates is not served to provide a register mark, which means that this portion is not used in printing by all means, the digital printing press according to the conventional technique inefficiently consumed the printing film  1 . 
   The present invention has been conceived to address a problem associated with the above conventional technique. It is an object of the present invention to provide a data creating device for printing plates that optimizes image data for printing process by using a minimum amount of a printing film. 
   SUMMARY OF THE INVENTION 
   In order to address the above problem, according to the present invention, there is provided a data creating device for printing plates that optimizes image data for use in forming printing plates, the data creating device being characterized in that a maximum position of the image data with respect to a plate transfer direction is detected; and data downstream to the maximum position with respect to the plate transfer direction is deleted, thereby creating optimized image data. 
   There is also provided a data creating device for printing plates that optimizes image data for use in forming printing plates, the data creating device being characterized in that register mark data in the image data is deleted; a maximum position of the image data with respect to a plate transfer direction is detected; and data downstream to the maximum position with respect to the plate transfer direction is deleted, thereby creating optimized image data. 
   In a data creating device for printing plates according to the present invention, color designation of 0 is preferably applied to printing plates other than a predetermined printing plate at the time of creating the register mark data, thereby deleting the register mark data. 
   In a data creating device for printing plates according to the present invention, a registration color is preferably not formed in image data for printing plates other than a predetermined printing plate by a RIP that creates image data, thereby deleting the register mark data for the printing plates other than the predetermined printing plate. 
   In a data creating device for printing plates according to the present invention, it is preferable to employ an arrangement where a RIP for creating image data creates converted data that have been converted to image data based only on data to which a registration color has been designated; XOR is calculated between the converted data and data for the printing plates other than the predetermined printing plate, thereby deleting the register mark data for the printing plates other than the predetermined printing plate. 
   According to the present invention, it is possible to produce a data creating device for printing plates that optimizes image data so as to enable printing operation by using a minimum amount of a printing film. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of an essential part of a printing unit according to one embodiment of the present invention. 
       FIG. 2  are schematic views illustrating the controlling procedures (a first case) when determining the amount of a printing film to be fed from a feed reel of the printing unit of  FIG. 1 , in which  FIG. 2(   a ) illustrates a state where an image for the first printing operation has been formed, and  FIG. 2(   b ) illustrates a state where an image for the second printing operation has been formed. 
       FIG. 3  are schematic views illustrating the controlling procedures (a second case) when determining the amount of a printing film to be fed from the feed reel of the printing unit of  FIG. 1 , in which  FIG. 3(   a ) illustrates a state where an image for the first printing operation has been formed;  FIG. 3(   b ) illustrates a state where an image for the second printing operation has been formed; and  FIG. 3(   c ) illustrates a state where an image for the third printing operation has been formed. 
       FIG. 4  is a flow chart illustrating the steps for controlling the amount of the printing film to be fed, according to this embodiment. 
       FIG. 5  is a flow chart illustrating the procedures of forming printing plates. 
       FIG. 6  is a flow chart illustrating the procedures of optimizing image data according to this embodiment. 
       FIGS. 7(   a )–( c ) show a schematic illustration of optimization process of image data according to this embodiment. 
       FIG. 8  illustrate an example of optimized image data for the respective printing plates used in a printing press according to this embodiment.  FIG. 8(   a ) illustrates optimized image data created for a C plate;  FIG. 8(   b ) illustrates optimized image data created for a M plate;  FIG. 8(   c ) illustrates optimized image data created for a Y plate; and  FIG. 8(   d ) illustrates optimized image data created for a K plate. 
       FIG. 9  is a schematic view illustrating an essential part of a printing unit according to a conventional technique. 
       FIG. 10  illustrate an example of optimized image data for the respective printing plates used in a printing press according to a conventional technique. 
       FIG. 10(   a ) illustrates optimized image data created for a C plate;  FIG. 10(   b ) illustrates optimized image data created for a M plate;  FIG. 10(   c ) illustrates optimized image data created for a Y plate; and  FIG. 10(   d ) illustrates optimized image data created for a K plate. 
       FIG. 11  is a schematic view of a print. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An example of an embodiment of the present invention will be herein described with reference to the drawings attached hereto. 
     FIG. 1  is a schematic view of a printing unit in a digital printing press according to an embodiment of the present invention. In  FIG. 1 , the same members or parts as those of the conventional printing unit of  FIG. 9  are assigned the same reference numbers. 
   The printing unit of this embodiment is for two-color printing, so that the plate cylinder  2  is structured to place two webs of the printing film  1  around the circumference. Specifically, two printing rolls  10  for feeding the respective webs of the printing film  1  are mounted at two places. For this, two sets of the feed reels  5  and the rewind reels  6  are arranged. 
   Two sets of the ink feeding parts  3 , each made up of several ink rollers, are also arranged so as to feed two colors of ink. 
   The plate cylinder  2  forms recesses  4  located on the circumference about 180 degrees opposite to one another. These recesses  4  extend in the axial direction of the plate cylinder  2 , thereby each having an overall appearance of a recessed groove. By these recesses  4 , the circumference of the plate cylinder  2  is divided into two sections, and the two webs of the printing film  1  are respectively placed around these sections. 
   The recesses  4  each are provided with the feed reel  5  for feeding a web of the printing film  1  onto a corresponding section (for one color), and the rewind reel  6  for rewinding another web of the printing film  1  on another section (for another color). The feed reel  5  and the rewind reel  6  respectively have axes extending along the axial direction of the plate cylinder  2 . In the respective recesses  4 , the rewind reels  6  are located on the downstream sides of the corresponding feed reels  5 , so that the webs of the printing film  1  are fed from the printing rolls  10  with their rear sides slidingly engaging edges  13 ,  14  of the recesses  4  of the circumference. 
   The image forming device  7  is secured in position above the plate cylinder  2  with a predetermined clearance between its bottom and the circumference of the plate cylinder  2 . On the upstream side of the image forming device  7  is provided space  8  required for setting a new web of the printing film  1  on the plate cylinder  2 . Light-shielding plate  9  is located on the upstream side of the space  8  in an upright position. 
   Wet cleaning device (plate cleaning device)  50  and dry cleaning device (not shown) are provided near the circumference of the plate cylinder  2  to clean the printing film  1  placed on the circumference of the plate cylinder  2 . The wet cleaning device  50  and the dry cleaning device are located with a predetermined clearance to the circumference of the plate cylinder  2  and designed so as to be able to be brought into contact with the printing film  1  on the circumference of the plate cylinder  2  when cleaning the printing film  1  on the circumference of the plate cylinder  2 . 
   The wet cleaning device  50  includes cleaning cloth  53  with a cleaning liquid impregnated therein, which contacts the printing film  1  on the circumference of the plate cylinder  2 , thereby cleaning the printing film  1 . Specifically, the wet cleaning device  50  includes cloth-feeding part  51  with an unused cleaning cloth  53  rolled up thereon, and cloth-collecting part  52  for winding up the cleaning cloth  53  in a roll, which was used for cleaning the printing film  1 . The cloth-feeding part  51  and the cloth-collecting part  52  respectively have rotating shafts extending parallel to the axis of the plate cylinder  2 . Inflatable member  54  having a bag-like shape is located near the circumference of the plate cylinder  2  so as to form a passage with the circumference of the plate cylinder  2 , through which the cleaning cloth  53  fed from the cloth-feeding part  51  passes and is wound up on the cloth-collecting part  52 . The inflatable member  54 , which has been inflated with air fed thereinto brings the cleaning cloth  53  into contact with the printing film  1  on the circumference of the plate cylinder  2 . The width of the cleaning cloth  53  (the length of the cleaning cloth  53  in a direction orthogonal to the winding direction) is substantially equal to the axial length of the plate cylinder  2 . Accordingly, the printing film  1 , which slidingly moves along the cleaning cloth  53  by the rotation of the plate cylinder  2 , can be cleaned. 
   The dry cleaning device (not shown) includes an elastic rotating roller made of such as rubber for scraping any foreign matters stuck on the printing film  1  on the circumference of the plate cylinder  2 , and a suction part for sucking foreign matters scraped by the rotating roller. The rotating roller is shiftable between a non-contact position at which the roller is held with a predetermined clearance to the printing film  1  on the circumference of the plate cylinder  2 , and a contacting position at which the roller contacts the printing film  1  on the circumference of the plate cylinder  2  and scraps foreign matters from the printing film  1 . Accordingly, when the rotating roller is to scrape foreign matters from the printing film  1  on the circumference of the plate cylinder  2 , it is shifted to the contact position and rotated to scrape foreign matters from the printing film  1  on the circumference of the plate cylinder  2 , while the suction part sucks scraped foreign matters. 
   When a new web of the printing film  1  is to be set in the printing unit as illustrated in  FIG. 1 , the new printing roll  10  is set to the feed reel  5 , and starting edge  1   a  of the printing roll  10  is pulled out from a corresponding recess  4 , and the plate cylinder  2  is rotated in the P direction in  FIG. 1  with pulling the starting edge  1   a , thereby applying a tension force on the printing film  1 . Thus, the printing film  1  is gradually fed on the circumference of the plate cylinder  2 . After winding up a predetermined length of the printing film  1 , the starting edge  1   a  of the printing film  1  is held by the rewind reel  6 . Through these steps, the printing roll  10  and the printing film  1  are set to the plate cylinder  2 . When the setting of the printing plate  1  on the circumference of the plate cylinder  2  has been completed, the printing operation can be performed. 
   Now, the description will be made for the printing operation. Once the printing film  1  is set on the circumference of the plate cylinder  2  after being subjected to the above steps, the image forming device  7 , which is secured in position with a predetermined clearance to the circumference of the plate cylinder  2 , forms an image on the printing film  1  placed on the circumference of the plate cylinder  2 . 
   The printing unit of  FIG. 1  is designed for a two-color printing, and therefore two printing units are provided to make up a digital printing press in a case where the printing operation is performed by having four colors, namely C (cyan), M (magenta), Y (yellow) and K (black) overlapped to each other. The printing film  1  is set in each printing unit, and the image forming device  7  forms an image on the printing film  1  set in position, based on image data optimized for each printing plate (each color) (corresponding to “optimized image data” in the present invention) (a detailed description will be made hereinafter). 
   The printing film  1  is coated thereon with a silicon layer, which is burned by laser radiated from the image forming device  7  so as to form an image on the printing film  1  based on the optimized image data. The image forming device  7  thus forms the image on the printing film  1  with a leading edge of each printing sheet to be printed positioned at the edge  13  of the rewind reel of the circumference of the plate cylinder  2 . In other words, an image formed on the printing film  1 , which is positioned at the edge  13  closer to the rewind reel  6  of the circumference of the plate cylinder  2 , is printed on the leading edge of the printing sheet. 
   Then, silicon debris or any foreign matters stuck on the printing film  1  by forming the image are removed by the wet cleaning device  50  and the dry cleaning device (not shown). 
   In this embodiment, the printing film  1  with a print formed thereon and any foreign matters removed is used as a printing plate. That is, in this embodiment, the printing film  1  with an image formed thereon based on the optimized image data created for the respective printing plates is subjected to ink feeding from the ink feeding part  3  or the like operation, and the image formed on each printing film  1  is overlapped to each printing sheet, thereby producing prints. 
   When the second printing operation has been then started, the printing film  1  is wound up and drawn from the circumference of the plate cylinder  2  by the rewind reel  6 , while it is fed from the feed reel  5 . Then, after removing foreign matters from the printing film  1  on the circumference of the plate cylinder  2  by the wet cleaning device  50 , a new image is formed on the printing film  1  by the image forming device  7  (a new image is formed according to optimized new image data), likewise to the previous printing operation. Thus, printing operation is made for printing sheets by using this image. 
   According to this embodiment, it is possible to continuously perform plural printing operations without the necessity to replace the printing plate or perform any other troublesome works as long as the current printing roll  10  remains. 
   In the thus arranged and operable printing unit, control device  20  is provided so as to control the amount of the printing film  1  fed from the recess  4  onto the circumference of the plate cylinder  2 . This control device  20  includes memory part  22  for storing optimized image data for use in forming image on the printing film  1 , and is designed to properly control the amount of the printing film  1  to be fed according to the information or the like stored in the memory part  22 . 
   Specifically, the control device  20  is capable of performing size-control for controlling the amount of the printing film  1  to be fed from the feed roll  5  based upon the size (length) of the optimized image data for use in printing operation, and circumferential-length-based feeding control for the length of the printing film  1  to be fed from the feed roll  5  based upon the circumferential length L 1  ( FIGS. 2 and 3 ) of the plate cylinder  2  between the feed reel  5  and the rewind reel  6  so that the printing film  1  is fed from the feed reel  5  by a length substantially equal to the circumferential length L 1  so as to replace a region of the printing film  1  on the circumference of the plate cylinder  2  entirely by a new region. 
   The optimized image data stored in the memory part  22  of the control device  20  comprise color separated, four (C, M, Y, K) image data for the respective printing plates for color printing, and each data subjected to optimization process such as deletion of register mark data and optimization of size. 
   The optimization process for this image data will be later described. Before that, the description will be made for the control of the feeding amount of the printing film  1  by the control device  20  with reference to  FIGS. 2 to 4 . 
   Upper parts illustrated in  FIGS. 2 and 3  each are the circumference of the plate cylinder  2  developed in plan.  FIG. 4  is a flow chart of controlling steps of controlling the amount of the printing film  1  to be fed. The description hereinafter made is based on the assumption that the information (length L and width W) relating to the optimized image data for use in forming an image. 
   In the first printing operation, an image is formed by the image forming device  7  within image forming region  30  (a cross-hatch part in  FIG. 2(   a )) of the printing film  1  on the circumference of the plate cylinder  2 , in which the image forming region  30  of the printing film  1  based on the information on the optimized image data in the memory part  22 , such as the length L 2  of the image (the length corresponding to the circumference of the plate cylinder  2 ) and the width W 2  of an image or printing sheet (Step S 401 ). At this moment, the downstream side of the image forming region  30 , that is a region closer to the feed reel  5  on the circumference of the plate cylinder  2  is designated as unused region  31  which is not used in the printing operation. In this embodiment, the printing operation is performed by using the image formed on the image forming region  30  (Step S 402 ). Thus, the first printing operation is finished. 
   When the second printing operation is to be subsequently performed (that is, for the operation when “NO” is chosen at the step S 403 ), image forming regions  32 ,  34  (cross-hatch parts in  FIGS. 2(   b ) and  3 ( b )) are determined based on the information relating to the optimized image data stored in the memory part  22 , such as the lengths L 3 , L 4  of the images, or the widths W 3 , W 4  of images or printing sheets. Accordingly, the control device  20  automatically controls the amount of the printing film  1  according to the length L 2  (e.g., the length of the image) used in the first printing operation and the lengths L 3 , L 4  (e.g., the length of the image) to be used in the second printing operation (Steps S 404 -S 407 ). 
   The printing operation will be described by taking for example the first case where when the length L 3  used in the second printing operation is longer than the length of the unused region  31  (L 1 –L 2 ), that is, when the circumferential length L 1  between a pair of the feed reel  5  and the rewind reel  6 &lt;the length L 2  used in the first printing operation+the length L 3  used in the second printing operation (that is, the case chosen by “YES” at the Step S 404 ). 
   When the printing film  1  is fed from the feed reel  5  for the second printing operation, a region of the printing film  1  positioned at the edge  14  closer to the feed reel (a boundary between the circumference and the recess, hereinafter referred to a boundary line A, see  FIG. 2(   a )) during the first printing operation is transferred on the circumference of the plate cylinder  2 . This boundary line A may be creased by a stepped portion between the circumference and the recess  4 , and therefore uneven printing may be caused if an image is formed on the creased boundary line A. Therefore, an image should not be formed on the boundary line A. Accordingly, in the first case, the printing film  1  is fed from the feed reel  5  by a length substantially equal to the circumferential length L 1  between the pair of the feed reel  5  and the rewind reel  6  so as to replace the region of the printing film  1  on the circumference of the plate cylinder  2  entirely by a new region (Step S 405 ), and an image for the second printing operation (an image formed in the image forming region  32 ) is formed on the printing film  1  fed from the feed reel  5 , as illustrated in  FIG. 2(   b ). 
   Now, another printing operation will be described by taking for example the second case where when the length L 4  used in the second printing operation is shorter than the length of the unused region  31  (L 1 –L 2 ), that is, when the circumferential length L 1  between the pair of the feed reel  5  and the rewind reel  6 &gt;the length L 2  used in the first printing operation+the length L 4  used in the second printing operation (that is, the case chosen by “NO” at the Step S 404 ), with reference to  FIG. 3 .  FIG. 3(   a ) is the same figure as  FIG. 2(   a ), illustrating the printing film  1  with the image forming region  30  on which the image for the first printing operation has been formed (Step S 401 ). 
   In the second case, the image forming region  30  for the first printing operation is rewound by the rewind reel  6 , causing the printing film  1  to be fed from the feed reel  5  by a length substantially equal to the length L 2  of the image forming region  30  (Step S 407 ), and the unused region  31  to be positioned closer to the rewind reel  6  on the circumference of the plate cylinder  2 . Then, as illustrated in  FIG. 3(   b ), the image for the second printing operation is formed on an image forming region  34  for use in the second printing operation according to the optimized image data, and thus the printing operation is performed by using this image. In this second case, another unused region  35  is caused on the downstream side of the image forming region  34 . 
   In the second case (see  FIG. 3 ), for the third printing operation, which is initiated subsequent to the finish of the second printing operation (that is, the case chosen by “NO” at the Step S 410 ), when the length L for use in the third printing operation is longer than the length of the unused region  35  (that is, the case chosen by “YES at the Step S 404 ), likewise to the first case described in  FIG. 2 , the printing film  1  is fed from the feed reel  5  by a length substantially equal to the circumferential length L 1  between the pair of the feed reel  5  and the rewind reel  6  so as to replace the region of the printing film  1  on the circumference of the plate cylinder  2  entirely by a new region, thereby preventing a creased portion from being positioned within an image forming region (Step S 405 ). 
   For the third printing operation, which is initiated from the second case, when the length L used in the third printing operation is shorter than the length of the unused region  35  (that is, the case chosen by “NO” at the Step S 404 ), this unused region  35  contains the boundary line A, as illustrated in  FIG. 3B , while the printing operation can be performed by using this unused region  35 . 
   Therefore, when the length of a portion of the unused region  35 , which portion is closer to the feed reel  5  than the boundary line A is, is longer than the length L used in the third printing operation (that is, the case chosen by “NO” at the Step S 406 ), the printing film  1  is fed from the feed reel  5  until the boundary line A is transferred to the edge  13  closer to the rewind reel  6  on the circumference of the plate cylinder  2  (Step S 407 ). Whereby, the boundary line A is not positioned within the image forming region for the third printing operation. 
   On the other hand, when the length L used in the third printing operation is longer than a portion of the length of the unused region  33 , which portion is closer to the feed reel  5  than the boundary line A is (that is, the case chosen by “YES” at the Step S 406 ), the printing film  1  is fed from the feed reel  5  by a length substantially equal to the circumferential length L 1  between the pair of the feed reel  5  and the rewind reel  6  so as to replace the region of the printing film  1  on the circumference of the plate cylinder  2  entirely by a new region (Step S 405 ). 
   Likewise to the above, when the fourth and subsequent printing operations are continuously performed, the amount of the printing film  1  to be fed from the feed reel  5  is controlled by the control device  20  according to the optimized image data in the memory part  22 , following the flow chart of  FIG. 4 . 
   Now, the description will be made for a specific method of creating optimized image data according to this embodiment. That is, the description will be made for a method of creating optimized image data for use in forming each printing plate. 
   First, a brief description will be made for a series of steps up to forming each printing plate.  FIG. 5  is a flow chart showing steps up to the formation of each printing plate. 
   As illustrated in  FIG. 5 , in this embodiment, an image forming step (Step S 501 ), an illustration forming step (Step S 502 ), an edit step (Step S 503 ), a RIP output step (Step S 504 ), a RIP processing step (Step S 505 ) and a printing-plate output step (Step S 506 ) are performed to form each printing plate. The image forming step and the illustration forming step in  FIG. 5  are sometimes skipped. 
   Specifically, after forming an image, an illustration or the like by an image forming software or an illustration forming software, data created is then read by an edit software (e.g., “EP-X” manufactured by Ryobi Ltd.), while text inputting, graphic forming or the like are made by using the edit software. Those components making up a print, such as text, graphic, illustration and image are laid out by the edit software. That is, editing such as layout, scaling and rotation of the respective components is made. 
   After finish of the layout edit, data for forming a printing plate, which is written in a page description language represented by PostScript (registered trademark), is created by the same edit software from data of the respective components subjected to the layout edit. Then, the plate forming data is transferred to a RIP, which in turn performs a RIP process (a process to raster and convert data written in a page description language to bitmap data), and then a printing plate is formed by using data subjected to the RIP process. 
   In this embodiment, when forming a printing plate (S 506 ), as described above, image data subjected to an optimization process (optimized image data) is used. Accordingly, in this embodiment, the optimization process of image data (hereinafter referred simply to “optimization process”), which will be described later, is performed prior to the printing-plate output step. 
   This optimization process may be performed in any step as long as it is performed prior to Step S 506 , and for example may be performed in the RIP processing step (S 505 ), or after the RIP processing step (between S 505  and S 506 ). This optimization process may be performed by a device that performs the RIP processing step (e.g., a computer, etc.), using a software for the optimization process or a hardware for the optimization process. That is, in this embodiment, the timing at which the optimization process is performed, a device by which the optimization process is performed and the like are not limited to specific ones. In this embodiment, the image data, to which the optimization process has been performed, is stored in the memory part  22  in  FIG. 1 , and as described above, the amount of the printing film  1  to be fed is controlled based on this optimized image data. 
     FIG. 6  is a flow chart illustrating the optimization step for image data according to this embodiment.  FIGS. 7(   a )–( c ) show a schematic illustration of an optimization process of image data according to this embodiment. In  FIGS. 7(   a )–( c ), a case where optimized image data is created by using image data for a C plate is shown. Now, the description will be made for the optimization process according to this embodiment with reference to  FIGS. 6 and 7(   a )–( c ). 
   Once the optimization process is initiated, image data (first image data  71 ) (see  FIG. 7(   a )) used for forming a printing plate according to a conventional technique is read out (Step S 601 ). This first image data  71  is one of the data groups, which were subjected to color separation for color printing (in  FIGS. 7(   a )–( c ), data for the C plate), and contains printing-sheet frame data  72  relating to printing sheets used in printing, printing-plate outputting data  73  for use in forming a printing plate (that is, data for use in forming images or the like upon receiving ink or the like), such as image data or text data (herein, image data), and register mark data T 1 -T 8 . 
   Then, the register mark data T 1 -T 8  in the first image data  71 , which have been read out, are deleted (Step S 602 ), thereby creating second image data  74  (see  FIG. 7(   b )). Deletion of the register mark data T 1 -T 8  allows the second image data  74  to contain only the printing-sheet frame data  72  and the printing-plate outputting data  73 . A method of deleting the register mark data will be later described. 
   Then, a maximum position P of the second image data  74  in a plate transfer direction is detected (Step S 603 ). That is, the detection whether an image to be actually printed is laid out is made for the second image data  74  with the register mark data T 1 -T 8  deleted therefrom in the plate transfer direction, thereby specifying a region to be kept as image data. Herein, the maximum position P is detected as an edge in the plate transfer direction for specifying the region. That is, the second image data  74  is entirely scanned in the plate transfer direction and the downstream edge of the printing plat outputting data  73  with respect to the plate transfer direction in the printing sheet frame data  72  is designated as the maximum position P. Herein, only one printing plate outputting data  73  exists in the printing-sheet frame data  72 . Where multiple printing plate outputting data  73  exist, the downstream edge of the printing plate outputting data  73  that has a most downstream edge among all the printing plate outputting data  73  with respect to the plate transfer direction is designated as the maximum position P. 
   Then, of the image data, a portion downstream to the maximum position P detected in the process of the Step S 603  is deleted (Step S 604 ). As described above, the maximum position P corresponds to the downstream edge of the printing-plate outputting data  73  with respect to the plate transfer direction. Therefore, in this Step S 604 , the printing sheet frame data  72  downstream to the maximum position P is deleted. That is, a portion S that is downstream to the maximum position P in  FIG. 7(   b ) is deleted. 
   In this embodiment, optimized image data  75  as illustrated in  FIG. 7(   c ) is created by the processes of Step S 601  Step S 604 . This optimized image data  75  contains optimized frame data  76  (length: L 0 , width: W 0 ) with a portion of the data downstream to the maximum position P deleted from the printing sheet frame data  72 , and the printing plate outputting data  73  within the optimized frame data  76 . White exists in a portion other than the printing plate outputting data  73  within the optimized frame data  76 . 
   This optimized image data  75  is memorized and stored in the memory part  22  of the control device  20  in order to form a printing plate (Step S 605 ). 
   That is, various information of the optimized image data  75  created herein (e.g., the length up to the maximum position P: L 0 , the width of a printing sheet: W 0 , etc.) is used when the amount of the printing film  1  described in  FIGS. 2–4  is automatically controlled. Specifically, as the lengths L 2 , L 3 , L 4  utilized as the information of the image forming regions  30 ,  32 ,  34  in  FIGS. 2 and 3 , the length L 0  up to the maximum position P in the optimized image data  75  is used. 
   In this embodiment, as illustrated in the flow chart of  FIG. 6 , the description was made by taking for example the case where the optimized image data is created by reading out image data (first image data) and then deleting the register mark data. This optimization process may be made for all the plates (C, M, Y, K), or may not be made for a predetermined plate, according to needs and circumstances. That is, since there is a case where register marks must be left in final prints such as for cutting, the optimization process may be made in such a manner to leave register mark data for a predetermined plate in such a case. 
   Specifically, where a step of determining “whether register marks must be left on a plate”, is provided and performed prior to Step S 601 , processing immediately transfers to Step S 605  and its subsequent steps when it is determined that the plate must keep the register marks thereon. Thus, the optimization process for this plate is finished. 
   For example, where “register marks are to be left in image data for a K plate”, a step of determining “whether the data is for the K plate” is performed just after the start of the optimization process, so that where the data is for the K plate, processing immediately transfers to Step S 605  and its subsequent steps, and otherwise, processes of Step S 601  and its subsequent steps are performed. 
   The deletion of the register mark data in Step S 602  may be made by any method, which is not necessarily limited to a specific one. 
   For example, according to one method, where the designation of “registration colors” outputted for every plate at the time of creating the register mark data in an editing step may be made in such a manner as: C=0, Y=0, M=0, K=100. This designation allows the register mark data to be left only in the image data for the K plate, while being deleted from the image data for the other plates. 
   According to another method, the designation of registration colors may be made in a RIP process for creating image data, so that an image is formed only on the K plate (corresponding to “a predetermined plate” in the present invention). This method also allows the register mark data to be left only in the image data for the K plate, while being deleted from the image data for the other plates. 
   According to still another method, data (corresponding to “converted data” in the present invention), which has been converted to image data, is created based on only data to which registration colors have been designated in a RIP process for creating image data; XOR is calculated over the respective bits of this converted data and the image data for each of the C, M and Y plates (corresponding to “plates other than a predetermined plate” in the present invention); and the calculated result is stored as data for each plate. According to this method, the data, for which XOR has been calculated, corresponds to data in which images of the register mark data designated by registration colors are deleted, and therefore the register mark data is created only in image data for the K plate, while the register mark data is deleted from the image data for the other plates. 
     FIG. 8  illustrate an example of image data (optimized image data) for the respective printing plates created through the optimization process according to this embodiment. That is, these Figures illustrate an example of the optimized image data for the respective printing plates created by the methods described with reference to such as  FIGS. 6 and 7 . 
     FIG. 8(   a ) illustrates optimized image data  75 C created for the C plate;  FIG. 8(   b ) illustrates optimized image data  75 M created for the M plate;  FIG. 8(   c ) illustrates optimized image data  75 Y created for the Y plate; and  FIG. 8(   d ) illustrates optimized image data  75 K created for the K plate. Herein, a case is presented, in which the register mark data are deleted from the optimized image data  75 C,  75 M,  75 Y for the C, M, Y plates, while the register mark data is left in the optimized image data  75 K for the K plate. 
   In this embodiment, the respective printing plates are formed by using the thus created optimized image data  75 C,  75 M,  75 Y,  75 K, thereby processing printing by using the respective printing plates. Thus, print  100  as illustrated in  FIG. 11  can be produced. 
   That is, according to the digital printing press of this embodiment, it is not necessary to provide register mark data for the purpose of the adjustment in alignment of colors to be printed, thanks to its highly accurate alignment capability. Therefore, it is possible to produce print  100  (see  FIG. 11 ) without misalignment or the like even by using the data  75 C,  75 M,  75 Y,  75 K (data without the register mark data) for the respective plates as illustrated in  FIG. 8 . 
   Thus, the optimized image data without the register mark data has less data amount as compared with conventionally used data, which contains the register mark data. This allows the memory capacity of the memory part  22  in the control device  20  to be small in this embodiment, and it is possible to shorten the time to transfer the data. 
   According to this embodiment, a printing image region (the maximum position P) generated in each plate is detected; the size of image data is optimized based on the detected result; and a printing late is formed by using this optimized image data. In forming each printing plate, the amount of the printing film  1  to be fed is automatically controlled, as described with reference to  FIGS. 2–4 . In this control, image data used is preferably created as small as possible, so that the printing film  1  can more efficiently be consumed. 
   Therefore, in this embodiment, an image is formed based on the optimized image data by using the image forming device  7  so as to consume the printing film  1  only for a printing region to which printing is performed at each printing unit. This allows reduction in the amount of the printing film  1  to be consumed, as well as reduction in running cost of the digital printing press. That is, since the amount of the printing film  1  used corresponding to the printed range is optimized based on the image to be printed, it is possible to significantly reduce the cost as compared with a conventional case where the printing film is consumed corresponding to the entire plate size (printing sheet size or the like). 
   Further, in this embodiment, as described above, it is possible to leave the register mark data only in a predetermined plate (e.g., the K plate). Accordingly, it is possible to perform deletion of the register mark data and optimization of the image data for the plates other than the predetermined plate, while allowing production of print  100  having the register mark data for use in cutting or other operation. 
   It is to be noted that the present invention is not limited to the above embodiment. It is possible to carry out various modifications other than those described above, as long as they fall within the scope of the present invention. 
   For example, in this embodiment, the description was made by taking for example the case where the register mark data is left in the image data for the K plate. The present invention is not limited to this case. It is possible to employ an arrangement where the register mark data is left in image data for a plate other than the K plate.