Scanning method and system being capable of registering plural reproduction images
FIELD OF THE INVENTION 
     This invention relates to a scanning method and system capable of registering plural reproduction images, particularly to such a method and system capable of rendering an actual sub-scanning position to correspond to the theoretical sub-scanning position thereof. 
     BACKGROUND OF THE INVENTION 
     When plural original pictures are to be scanned successively for use as image data for recording a photosensitive film in a desired layout pattern, reproduction images of the original pictures on the photosensitive film must be registered. 
     However in a drum scanner system, in order to vary the relative feeding speed between an input head for scanning original pictures and a recording head for exposing photosensitive films according to a desired magnification ratio, usually each head is given an individual motor individually. Because of the same reason, an input drum and a recording drum are usually given motors individually. In this arrangement, as said four motors are different in their startup characteristics, ordinarily a synthesized reproduction image of the original pictures has a shear as mentioned below. 
     FIG. 1(I)(II) show a case of image reproduction in which a reproduction image B&#39; shown in FIG. 1(II) is recorded in a window of a reproduction image A&#39; shown in FIG. 1(I). Supposing that the reproduction image A&#39; is recorded at a theoretical location on a photosensitive film by beginning a recording process from the point which is both the zero point of the sub-scanning direction factor and the -180° point of the recording drum of the main scanning direction factor, while the reproduction image B&#39; is recorded on the photosensitive film by beginning a recording operation from the point whch is both the point α of the sub-scanning direction factor and the 0° point of the recording drum of the main scanning direction factor. Thus, there exists a phase difference of 180° (time lag t 0 ) in the main scanning direction between the the reproduction images. The time lag t 0  corresponds to a shear width α as presented by the scanning line X&#39; of the image A&#39; and the scanning line x&#39; of the image B&#39;  in FIG. 1(II). Especially when four color separation images are recorded on one photosensitive film at different times, said shear becomes fatal in reproducing an image of good quality. 
     To resolve this problem, Japanese Patent Application No. 54-104323 (early opening publication No. 56-27559) discloses the following method. That is, the input (output) scanning is performed by synchronizing a sub-scanning pulse obtained from a sub-scanning pulse generator operating in connection with a scanning head with pulses obtained from the revolution of a scanning drum. 
     However, the above method has a defect. That is, for example if said pulses synchronize with each other on the Nth scanning line at a first time as shown in FIG. 2(b)  ○1 , at a second or subsequent time they don&#39;t always synchronize with each other on the Nth scanning line as shown in FIG. 2(b)  ○2 . They synchronize with each other on one of N±P (P: an integer) lines (the operation error range in the startup stage). If plural scanning processes of the input side are performed ideally (synchronously) and corresponding recording operations of the output side are performed as in the abovementioned condition, naturally the reproduction image has a shear corresponding to the difference between the two scanning line numbers. 
     SUMMARY OF THE INVENTION 
     A prime object of this invention is to improve accuracy of reproducing image by rendering an actual sub-scanning position agreeing with the corresponding theoretical sub-scanning position thereof derived from the scanning line number and the angular position of the main scanning direction factor. 
     The theory of this invention is as follows. 
     The theoretical sub-scanning position P s  is derived from an equation: ##EQU1## wherein K: a feeding path of a head in the sub-scanning direction 
     L n  : the number of a main scanning line 
     θ: an anguular position of the main scanning direction factor with respect to the angle 0° of the standard position. 
     θ m  : the maximum angular position which corresponds to the angle of 360°. 
     K o  : a shift distance of an input (output) head in the sub-scanning direction. 
     In the equation (1), K is a constant value determined by the feeding speed (having a relation with the magnification ratio) of an input (output) head. Assuming that the feeding pitch of the input side is K a  and that of the output side is K b , the magnification ratio M is M=K b  /K a , while θ m  is constant, and K 0  is the distance between the beginning point of scanning (L n  =0) and the initial position, or zero point of the head (the point where K o  =0) in the sub-scanning direction. Therefore the equation (1) becomes solvable by obtaining L n  and θ as mentioned below. As a result P s  can be found. 
     On the other hand, the actual sub-scanning point P&#39; s  of a scanning head can be found as the number of the output pulse of a rotary encoder or a linear encoder being linked to the head. 
     So, to cause the actual sub-scanning point P&#39; s  to correspond to the theoretical sub-scanning point P&#39; s , at first they are compared to each other. When P s  &gt;P&#39; s , the scanning head is fed faster. When P s  &lt;P&#39; s , the scanning head is fed slower. This synchronizing procedure must be performed on both of the input side and the output side. 
     The above and other objects and features of this invention can be appreciated more fully from the following detailed description when read with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the concept of a conventional method for reproducing plural images. 
     FIGS. 2(a) and 2(b) show (a) a relation between a sub-scanning direction position and the corresponding main scanning direction position, and (b) a relation between a sub-scanning direction position and the corresponding time. 
     FIG. 3 shows the concept of the method of this invention for reproducing plural images without producing shears. 
     FIG. 4 shows a system for embodying the method of this invention. 
     FIG. 5 shows a flow chart of a program for a situation when a CPU is used as a sub-scanning controller. 
    
    
     PREFERRED EMBODIMENT OF THE INVENTION 
     FIG. 3 shows the concept of the method of this invention in which a reproduction image B is recorded in the window of a reproduction image A. In this, the scanning line X of the reproduction image A and the scanning line x of the reproduction image B situate on an identical line to be perfectly synthesized with each other. 
     FIG. 4 shows a system for embodying the method of this invention, in which the input side (I) and the output side (II) are constructed similarly. The following explanation is based on the input side. A rotary encoder 3 a  is coaxially connected to an original picture drum 1 a , which is revolved by a motor 2 a . The rotary encoder 3 a  outputs a plurality of main scanning position pulses (n a ) every revolution of the original picture drum 1 a  to a main scanning position counter 9 a . The count number of the counter 9 a  is reset to zero on command of a reset pulse (m a ) which is output from the rotary encoder 3 a  every one revolution of the original picture drum 1 a . 
     Meanwhile, an input head 4 a  is provided against the original picture drum 1 a  and is fed in the sub-scanning direction along a feeding gear 6 a  revolved by a motor 5 a . A linear encoder 8 a  detects the position of the input head 4 a  and outputs sub-scanning position pulses (Q a ) to a sub-scanning position counter 10 a . The count number of the counter 10 a  is a reset to zero on command of a reset pulse (R a ) output from a zero position detector 7 a  which detects the return of the input head 4 a  to the zero point. 
     The counter 9 a  generates line number pulses (m a  &#39;) by using the reset pulse (m a ) and input it to a line counter 11 a  for counting the scanning line number. The count number of the line counter 11 a  is reset to zero by said reset pulse (R a ). 
     As the constitution of the output side (II) is as same as that of the input side (I) excepting for a register mark generator (mentioned later), no detailed explanation for the output side is given here. What is noticeable is that units of the input side are expressed by a combination of &#34;a number&#34; and the letter &#34;a&#34; such as &#34;1 a  &#34;, and units of the output side are expressed by a combination of &#34;a number&#34; and the letter &#34;b&#34; such as &#34;1 b  &#34;. 
     Image data of an original picture obtained by the input head 4 a  are input via an image processer 16 to a recording head 4 b . The image processer 16 comprises buffer memories to store the image data of plural scanning lines, to or from which memories the image data are written or read alternately. In this writing and reading processes, a shift amount in the main scanning direction (corresponding to the angular position θ) can be varied by controlling the writing addresses or the reading addresses of the memory (for example, the writing process is started from an advanced address). 
     By using the thus constructed system, said parameters of the equation (1) can be obtained. In the following explanation, parameters of the input side (I) are given the letter &#34;a&#34;, such as &#34;θ ma  &#34; and those of the ouput side (II) are given the letter &#34;b&#34;, such as &#34;θ mb  &#34;. That is, to a sub-scanning controller 12 a  (12 b ), there input the maximum angular position data θ ma  (θ mb ), data of the feeding pitch in the sub-scanning direction K a  (K b ) and data of the shift distance of the input (output) head in the sub-scanning direction K 0a  (K 0b ) from a data setter 14. On the other hand, data of the scanning line number L na  (L nb ) from the line counter 11 a  (11 b ), and data of the actual sub-scanning position counter 10 a  (10 b ) are also input to the sub-scanning controller 12 a  (12 b ). Then the sub-scanning controller 12 a  (12 b ) performs the following computation. In short, a motor control signal (c a ) ((c b )) obtained by comparing an actual sub-scanning position P&#39; s  to the corresponding theoretical sub-scanning position P s  thereof is used for controlling the motor 5 a  (5 b ) via a sub-scanning motor controller 13 a  (13 b ). 
     A CPU can be used as the sub-scanning controller 12 a  (12 b ). When it is used, the equation (1) is computed in a way as expressed in a flow chart of FIG. 5. 
     At first, data of a scanning start point X 1a  (X 1b ), a scanning end point X 2a  (X 2b ), a window start point X 3a  (X 3b ) and a window end point X 4a  (X 4b ) of an original picture A 0  corresponding to the reproduction image A are input to the sub-scanning controller 12 a  (12 b ) beforehand from the data setter 14 by using an input device such as a digitizer or a CRT display system. 
     Before an input (output) scanning, the input (output) head 4 a  (4 b ) is set up at the location (zero point) where the head touches the zero position detector 7 a  (7 b ). 
     Then by shifting the head 4 a  (4 b ) to the point X 1a  (X 1b ) of the original picture A 0  (the reproduction image A), the parameters of the shift distance of the head in the sub-scanning direction K 0a  (K 0b ) and the main scanning angular position θ a  (θ b ) of the point X 1a  (X 1b ) can be obtained. These parameters are input via the data setter 14 to the sub-scanning controller 12 a  (12 b ) and to the internal memory of the image processer 16. Then the head 4 a  (4 b ) is brought to an idle scanning start point. This procedure can be performed either in a conventional automatic way or in a manual way. The idle scanning can also be started from the zero point. 
     After the idle scanning is started, an interrupting pulse (I a ) ((I b )) which is output once or several times every one revolution of the original picture (recording) drum 1 a  (1 b ), is input to the sub-scanning controller 12 a  (12 b ). In between the interrupting pulses, no signals for designating other operations are accepted by the controllers 12 a  (12 b ) - - - (S 1 ). Then the sub-scanning controller 12 a  (12 b ) reads the count number L na  (L nb ) of the line counter 11 a  (11 b ) which means the corresponding scanning line number - - - (S 2 ), and reads the main scanning angular position data θ a  (θ b ) from a main scanning direction position counter 9 a  (9 b ) - - - (S 3 ). By using the above data and the parameters K a  (K b ), K 0a  (K 0b ) and θ ma  (θ mb ) of the equation (1) being input beforehand, the sub-scanning controller 12 a   (12 b ) computes the corresponding theoretical sub-scanning position number P sa  (P sb ) - - - (S 4 ). Then the sub-scanning controller 12 a  (12 b ) compares the count number P&#39; sa  (P&#39; sb ) of the sub-scanning position counter 10 a  (10 b ) to the number P sa  (P sb ) to output a correction signal (C a ) ((C b )) corresponding to the difference number between them to the sub-scanning motor controller 13 a  (13 b ) - - - (S 6 ). After finishing the abovementioned routine from (S 1 ) to (S 6 ), the sub-scanning controller 12 a  (12 b ) becomes receptive to said interrupting pulse again. Therefore by repeating the above routine several times, the actual sub-scanning position P&#39; sa  (P&#39; sb ) becomes synchronized whith the corresponding theoretical sub-scanning position P sa  (P sb ) thereof before the idle scanning comes to the actual scanning start point X 1a  (X 1b ). 
     Next, the reproduction image B is recorded in the window of the reproduction image A in the same manner. In this case, to render the scanning line Q of the reproduction image A and the scanning line q of the reproduction image B situated on an identical line, at first each parameter is determined to render a theoretical sub-scanning position of the reproduction image B corresponding to that of the reproduction image A, and then an actual sub-scanning position of the reproduction image B is rendered to agree with the corresponding theoretical sub-scanning position thereof. To perform this step, the scanning start and stop points can be designated either on the input side or on the output side. 
     Incidentally, a register mark generator 15 shown in FIG. 4 (II) operates as follows. For example, a register mark for each photosensitive film of color separation images Y (yellow), M (Magenta), C (Cyan) and K (Black) is registered into the internal register of the register mark generator 15. Then the register mark generator 15 outputs the register mark data to an identical point of each photosensitive film. By using the above method, each color separation image can be recorded on an identical position of respective photosensitive film. Although in FIG. 5 the register mark generator 15 is provided on the output side, it can also be on the input side. 
     Other from the linear encoder shown in FIG. 4, a rotary encoder connected coaxially to the feeding gear 6 a  (6 b ) can be used as a sub-scanning position detector. 
     Although the original picture drum and the recording drum are revolved individually in FIG. 4, they can also operate when connected and revolved coaxially. 
     The line counter can also be realized with soft ware using the main scanning reset pulse (m a ) ((m b )) output once per revolution of the original picture (recording) drum. 
     As mentioned above, by using the method of this invention, plural reproduction images can be recorded on an identical position of respective photosensitive films, because the method of this invention is capable of controlling the sub-scanning operation in order to render an actual sub-scanning position in agreement with the corresponding theoretical sub-scanning position thereof. When plural original pictures must be reproduced on a photosensitive film in multiple exposure processes, the method of this invention is capable of synthesizing them without producing any shears. When color separation images Y, M, C and K are recorded on a photosensitive film, a synchronous relation there between can be maintained by marking a register mark to respective places of the color separation images.