Abstract:
An optical printer device which includes an exposure device which makes relative movements, in a predetermined direction, with respect to a photosensitive body. The optical printer also has a plurality of first, second and third light-emitting elements which emit lights of a first, second and third colors. These light-emitting elements are mounted on a first, second and third mounting substrates, independent of one another, which correspond to the first, second and third colors.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical printer device that forms color images by converting electrical signals to color optical signals. 
     2. Description of the Related Art 
     A video printer is a printer that prints images, which have been digitally processed and which are shown on a display, on a sheet. Known printing methods, which are adopted for video printers, include the thermal method, inkjet method, laser-beam scanning method and the liquid-crystal shutter method. Among such methods, the liquid-crystal shutter method is suitable for the purposes of obtaining a very small and lightweight device. 
     An optical printer device having a liquid-crystal shutter according to prior art is described below using FIGS. 7 to  9 . 
     As shown in FIG. 7, a light-source unit for this video printer comprises a pair of members  32 , which are each arranged facing one another at a predetermined interval in a horizontal direction (the X-Y direction in FIG.  7 ). A support member  31  is suspended between these members  32  such that the upper end of the hollow portion, which is formed between members  32 , is occupied by this support member  31 . 
     The lengthwise direction of support member  31  (a direction perpendicular to the surface of the paper of FIG. 7) corresponds to the direction of a single line on a photosensitive member  16 . A plurality of light-emitting elements are arranged on the lower face of support member  31 . Light-emitting diodes (hereinafter referred to as LEDs) are used for these light-emitting elements. These light-emitting elements (LEDs) are described hereinbelow by referring to FIG.  8 . 
     As shown in FIG. 8, an R light (red light) LED  30 R, B light (blue light) LED  30 B and G light (green light) LED  30 G are provided close to one another in a direction (X-Y direction) that is orthogonal to the single-line direction of photosensitive material  16 . Light-emitting element groups  33  are constituted by these LEDs  30 R,  30 G,  30 B, which are aligned to form one row in the X-Y direction of FIG. 8. A plurality of light-emitting element groups  33  are arranged at a predetermined pitch (normally on the order of about 3 mm) in the single-line direction of photosensitive material  16  (a direction perpendicular to X-Y of FIG.  8 ). 
     As shown in FIG. 7, a cylindrical lens  34  is mounted at the lower end of the above-mentioned hollow portion that is formed by the pair of members  32 . Further, below this cylindrical lens  34 , a liquid-crystal optical shutter array  36  is provided as a optical shutter array. 
     Next, control of liquid-crystal optical shutter array  36  will be described using FIG.  9 . For the sake of convenience in the description, the single line of photosensitive material  16  will be considered to correspond to one pixel column that comprises five pixels. Consequently, one liquid-crystal cell column of liquid-crystal shutter array  36  comprises five liquid-crystal cells. This liquid-crystal array  36  comprises four liquid-crystal cell columns arranged in a direction that is orthogonal (in the X-Y direction) to the single-line direction of these liquid-crystal cell columns. In other words, liquid-crystal shutter array  36  comprises twenty liquid-crystal cells, which are arranged in five columns and four rows. Hereinbelow, a liquid-crystal cell in column i (i=1 to 5) and row j (j=1 to 4) is represented by  36 SRij. Further, in FIG. 9, liquid-crystal cells  36 Sij, through which R light, which is emitted from LED 30 R, is transmitted, are distinguished using oblique lines. 
     When transportation of photosensitive material  16  begins such that the first single line is exposed, as shown in FIG.  9 ( a ), liquid-crystal cells  36 S 41 ,  36 S 43 ,  36 S 45 , which are in the fourth liquid-crystal cell column (liquid-crystal cells  36 S 41  to  36 S 45 ), are open (pattern P 1 ). Then, after this line exposure using G light and B light is complete, same having been emitted from LEDs  30 G and  30 B, respectively, a transport roller (not shown in the figure) is driven to transport photosensitive material  16  by a distance of one line in the X direction of FIG.  9 . 
     Then, when photosensitive material  16  is exposed by R light, which is emitted for a second time from LED 30 R, as shown in FIG.  9 ( b ), liquid-crystal cells  36 S 31 ,  36 S 33 ,  36 S 35  in the third liquid-crystal cell column (liquid-crystal cells  36 S 31  to  36 S 35 ) are open on the basis of a pattern P 1 , and liquid-crystal cells  36 S 42 ,  36 S 44  in the fourth liquid-crystal cell column are open on the basis of a pattern P 2 . 
     As described hereinabove, in the above-mentioned technique, R-light LEDs, B-light LEDs and G-light LEDs on support member  31  are each fixed in a predetermined column and predetermined row. As a result, when displacement occurs, of the positions of R light, B light and G light on photosensitive material  16 , from these predetermined positions, since no adjustment is possible of the corresponding mount positions of R-light LEDs, B-light LEDs and G-light LEDs on support member  31 , positions of R light, B light and G light cannot be matched with these predetermined positions. 
     In addition, due to the fact that exposure of photosensitive material  16  is performed one line at a time, there is a problem in that the image-formation speed is low. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, an optical printer of the present invention has an exposure device which makes relative movement in a predetermined direction with respect to a photosensitive body. 
     The exposure device comprises a first mounting substrate for mounting a plurality of first light-emitting elements which emit light of a first color, a second mounting substrate for mounting a plurality of second light-emitting elements which emit light of a second color, and a third mounting substrate for mounting a plurality of third light-emitting elements which emit light of a third color, in addition to a frame. 
     The exposure device further comprises an optical shutter which controls the passage of the light from the first, second and third light-emitting elements to change the amount of irradiation onto the photosensitive body. 
     The first, second and third mounting substrates are configured independent of one another, respectively, and are attached to the frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned object, and further objects and characteristics of the present invention will become evident from the description of the embodiment provided hereinbelow through reference to the attached figures, in which: 
     FIG. 1 is a perspective view that provides an overview of movement by the optical printer device according to the present invention. 
     FIG. 2 is a cross-sectional view taken along line B—B in FIG.  1 . 
     FIG. 3 is an enlarged view of the parts indicated by the circle C in FIG.  2 . 
     FIG. 4 is cross-sectional view taken along line D—D in FIG.  2 . 
     FIG. 5 is a figure illustrating a process in which a liquid-crystal shutter is used to form a color image on a photosensitive medium (stages  1  to  4  thereof). 
     FIG. 6 is a figure illustrating a process that is a continuation of the process in FIG.  5  and in which a liquid-crystal shutter is used to form a color image on a photosensitive medium (stages  6  to  8  thereof). 
     FIG. 7 is a cross-sectional view of a light-source unit in the optical printer device according to the prior art. 
     FIG. 8 is a figure showing the arrangement of LEDs provided in the light-source unit of FIG.  7 . 
     FIG. 9 is a figure illustrating control of the liquid-crystal optical shutter array provided in the light-source unit of FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The optical printer device prints an image  11   a  on the surface of a photosensitive medium  11  through exposure of a photosensitive medium  11  while an exposure device (print head)  1  is caused to move in the direction, as shown in FIG. 1, of the arrow A. 
     The structure of exposure device  1  will now be described by referring to FIG.  2 . 
     The light-source substrate  3  is mounted at the top of the inner wall of outer casing  2  of exposure device  1 . This light-source substrate  3  is of a breadth so as to cover a top portion of an inner wall face which is on the leading side with respect to the movement direction of exposure device  1 , the upper inner wall face, and also a top portion of an inner wall face which is on the trailing side with respect to the movement direction of exposure device  1 , which inner wall faces are in outer casing  2 . Further, substrates on this light-source substrate are mounted, namely: R substrate  4   a  (a first mounting substrate) on a portion that covers the inner wall face of outer casing  2  on the leading side, G substrate  4   b  (a second mounting substrate) on a portion that covers the upper inner wall face, and B substrate  4   c  (a third mounting substrate) on a portion that covers the inner wall face on the trailing side, such that the respective mount positions of these substrates are adjustable. 
     A plurality of R light-emitting elements  5   a  (first light-emitting elements), a plurality of G light-emitting elements  5   b  (second light-emitting elements) and a plurality of B light-emitting elements  5   c  (third light-emitting elements) are fixed on R substrate  4   a , G substrate  4   b  and B substrate  4   c , respectively, in a manner such that they are arranged in a direction that is orthogonal to the direction of movement of exposure device  1  (the direction indicated by arrow A in FIG.  1 ). These R light-emitting elements  5   a , G light-emitting elements  5   b  and B light-emitting elements  5   c  constitute the light source of exposure device  1 . These light-emitting elements  5   a ,  5   b ,  5   c  are LEDs (light-emitting diodes). 
     Components, which are mounted in the bottom section of the interior of outer casing  2 , are: a liquid-crystal shutter  9 , which is an optical shutter that permits and blocks the passage of light on the basis of electrical signals; and a lens array  10 , which serves to condense light, which has passed through liquid-crystal shutter  9 , such that this light is focussed on a photosensitive medium  11  (described hereinbelow). 
     A photosensitive medium  11  is disposed below exposure device  1  (outer casing  2 ). As described hereinabove, exposure device  1  causes the emission of light from a light source while moving along the upper face of photosensitive medium  11 , and prints an image on the upper face of photosensitive medium  11  by appropriate blockage, using a liquid-crystal shutter  9 , of light which is emitted by the light source. 
     The light source of exposure device  1  will now be described in detail using FIG.  3 . 
     A plurality of spherical concave lenses are juxtaposed on R substrate  4   a  in a direction that is orthogonal to the direction of movement of exposure device  1  and reflect light from R light-emitting elements  5   a  as substantially parallel beams. An R scatter member  6   a  and R lens member  7   a  are arranged at the leading face, with respect to the direction of emission, of R light-emitting elements  5   a . In addition, a reflector member  8   a  is disposed, at the leading face of R lens member  7   a , which reflects R light Lr (light of a first color) emitted by R light-emitting elements  5   a  toward photosensitive medium  11 . 
     A plurality of spherical concave lenses are juxtaposed on G substrate  4   b  in a direction that is orthogonal to the direction of movement of exposure device  1  and reflect light from G light-emitting elements  5   b  as substantially parallel beams. A G scatter member  6   b  and G lens member  7   b  are arranged at the leading face, with respect to the direction of emission, of G light-emitting elements  5   b . G light Lg (light of a second color), which has passed through G lens member  7   b , is oriented directly toward photosensitive medium  11 . 
     A plurality of spherical concave lenses are juxtaposed on B substrate  4   c  in a direction that is orthogonal to the direction of movement of exposure device  1  and reflect light from B light-emitting elements  5   c  as substantially parallel beams. A B scatter member  6   c  and B lens member  7   c  are arranged at the leading face, with respect to the direction of emission, of B light-emitting elements  5   c . In addition, a reflector member  8   c  is disposed, at the leading face of B lens member  7   c , which reflects B light Lb (light of a third color) emitted by B light-emitting elements  5   c  toward photosensitive medium  11  (described hereinbelow). 
     The liquid-crystal shutter  9  shown in FIG. 2 will now be described in detail using FIG.  4 . 
     The liquid-crystal shutter  9  is provided with two rows of R pixel shutters  9   a  in a direction that is orthogonal to the direction of movement of exposure device  1 , with tow rows of G pixel shutters  9   b  adjacent to and parallel with the R pixel shutter rows, and further with two rows of B pixel shutters  9   c  adjacent to and parallel with the G pixel shutter rows. 
     These pixel shutters  9   a ,  9   b ,  9   c  are each constituted by a first pixel shutter row, in which a plurality of microshutters are arranged in a single row at a predetermined pitch; and a second pixel shutter row, in which a plurality of microshutters are arranged in a single row at the above-mentioned predetermined pitch and in positions half a pitch behind the respective positions of the above-mentioned first pixel shutter row. 
     R pixel shutters  9   a  are irradiated with R light Lr, G pixel shutters  9   b  are irradiated with G light Lg, and B pixel shutters  9   c  are irradiated with B light Lb. 
     Should one or several of the microshutters, which constitute R pixel shutters  9   a  shown in FIG. 4, is/are not irradiated with R light Lr from R light-emitting elements  5   a  shown in FIGS. 2 and 3, the mount position of R substrate  4   a  with respect to light-source substrate  3  is adjusted so that all of the microshutters, which constitute R pixel shutters  9   a , are irradiated by R light Lr. 
     Similarly, should one or several of the plurality of microshutters, which constitute G pixel shutters  9   b  or B pixel shutters  9   c  is/are not irradiated with G light Lg or B light Lb from G light-emitting elements  5   b  or B light-emitting elements  5   c , as a result of adjustment of the mount position of G substrate  4   b  or B substrate  4   c  with respect to light-source substrate  3  is adjusted so that all of the microshutters, which constitute G pixel shutters  9   b  or B pixel shutters  9   c , are irradiated with G light Lg or B light Lb. 
     A description will now follow, using FIGS. 5 and 6, of the process of forming a color image on photosensitive medium  11  by means of liquid-crystal shutter  9 . 
     FIGS.  5 ( a ) and  6 ( a ) are figures that illustrate the process of forming an image on photosensitive medium  11  by means of liquid-crystal shutter  9 , in association with change in the state of the photosensitive medium  11 . 
     FIG.  5 ( a ) serves to show the state of image formation at each stage (stage  1  (st 1 ), stage  2  (st 2 ), stage  3  (st 3 ) and stage  4  (st 4 )) as photosensitive medium  11  is repeatedly caused to move by a distance that is equivalent to one pitch of a pixel shutter row (distance between the pixel shutter rows). FIGS.  5 ( b ),  5 ( c ),  5 ( d ), and  5 ( e ) are detailed views in which one part, of each of stages  1  through  4  shown in FIG.  5 ( a ), has been enlarged. Further, numerical value i (=1 to 9), which is shown in FIGS.  5 ( b ) to  5 ( e ), represents the ith column, which is subjected to exposure, on photosensitive medium  11 . 
     Further, FIG.  6 ( a ) serves to show the state of image formation at stage  5  (st 5 ), stage  6  (st 6 ), stage  7  (st 7 ) and stage  8  (st 8 ), which succeed stage  4  (st 4 ) of FIG.  5 ( a ). FIGS.  6 ( b ),  6 ( c ),  6 ( d ), and  6 ( e ) are detailed views in which one part, of each of stages  5  through  8  shown in FIG.  6 ( a ), has been enlarged. Further, numerical value i (=1 to 10), which is shown in FIGS.  6 ( b ) to  6 ( e ), represents the ith column, which is subjected to exposure, on photosensitive medium  11 . 
     In FIG.  5 ( a ), the number of microshutters constituting one pixel shutter row of liquid-crystal shutter  9  is nine. In actual fact, the number of microshutters constituting one pixel shutter row is greater than nine; however, here, in the interests of facilitating comprehension, a smaller number is taken. 
     As shown in FIG.  5 ( a ), the two rows of R pixel shutters  9   a , G pixel shutters  9   b  and B pixel shutters  9   c , respectively, comprise a first pixel shutter row, for which nine microshutters are arranged in a single row at a predetermined pitch; and a second pixel shutter row, for which nine microshutters are arranged in a single row at the above-mentioned predetermined pitch and in positions half a pitch behind the respective positions of the above-mentioned first pixel shutter row. 
     R pixel shutters  9   a  are irradiated with R light Lr, G pixel shutters  9   b  are irradiated with G light Lg, and B pixel shutters  9   c  are irradiated with B light Lb. 
     Stage  1  (st 1 ): R light-emitting elements  5   a , G light-emitting elements  5   b  and B light-emitting elements  5   c , which constitute the light source, emit light, and liquid-crystal shutters  9   a ,  9   b ,  9   c  transmit R light Lr, G light Lg, and B light Lb, whereby exposure of photosensitive medium  11  takes place. Specifically, here, in the interests of facilitating comprehension, when R light-emitting elements  5   a , G light-emitting elements  5   b  and B light-emitting elements  5   c  emit light, all of the respective microshutters of R-light pixel shutters  9   a , G-light pixel shutters  9   b , and B-light pixel shutters  9   c , of liquid-crystal shutter  9 , are open (in actuality, the microshutters are opened selectively in accordance with the image to be exposed). 
     As shown in FIG.  5 ( b ), in accordance with light emission by the light source, exposure of the first column and the second column is carried out with R light Lr in a manner such that the exposed points in the first column are displaced with respect to the exposed points in the second column by half a pitch in the column direction, and exposure of the third column and the fourth column is carried out with G light Lg in a manner such that the exposed points in the third column are displaced with respect to the exposed points in the fourth column by half a pitch in the column direction, and further, exposure of the fifth column and the sixth column is carried out with B light Lb in a manner such that the exposed points in the fifth column are displaced with respect to the exposed points in the sixth column by half a pitch in the column direction, 
     Stage  2  (st 2 ): After photosensitive medium  11  has been caused to move a distance d 1 , which is the same as the pitch of the pixel shutter rows, in the direction of the arrow (leftward in FIG.  5 ), similarly to stage  1  (st 1 ), R light-emitting elements  5   a , G light-emitting elements  5   b  and B light-emitting elements  5   c  emit light, and liquid-crystal shutters  9   a ,  9   b ,  9   c  transmit R light Lr, G light Lg, and B light Lb, whereby exposure of photosensitive medium  11  takes place. Here, all of the microshutters of each of liquid-crystal shutters  9   a ,  9   b ,  9   c  are open. 
     As shown in FIG.  5 ( c ), in accordance with light emission by the light source, exposure of the second column and the third column is carried out with R light Lr in a manner such that the exposed points in the second column are displaced with respect to the exposed points in the third column by half a pitch in the column direction, and exposure of the fourth column and the fifth column is carried out with G light Lg in a manner such that the exposed points in the fourth column are displaced with respect to the exposed points in the fifth column by half a pitch in the column direction. 
     Consequently, as a result of two exposures in the above-mentioned stages  1  and  2 , in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the six column in the photosensitive medium  11  assumes the form of a matrix. 
     Stage  3  (st 3 ): After photosensitive medium  11  has been caused to move a distance d 2 , which is equal to two times the pitch of the pixel shutter rows, from the position of stage  1 , in the direction of the arrow, photosensitive medium  11  is exposed in the same manner as in the previous stage. 
     Consequently, as a result of exposures in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the seven column in the photosensitive medium  11  assumes the form of a matrix, as shown in FIG.  5 ( d ). Further, exposure of the third column and the fourth column is carried out with R light Lr in a manner such that the exposed points in the third column are displaced with respect to the exposed points in the fourth column by half a pitch in the column direction, exposure of the fifth column and the sixth column is carried out with G light Lg in a manner such that the exposed points in the fifth column are displaced with respect to the exposed points in the sixth column by half a pitch in the column direction, and exposure of the seventh column and the eighth column is carried out with B light Lb in a manner such that the exposed points in the seventh column are displaced with respect to the exposed points in the eighth column by half a pitch in the column direction. 
     Locations exposed at this stage overlap locations exposed at stage  1  (st 1 ) with two rows shifted. 
     Stage  4  (st 4 ): After photosensitive medium  11  has been caused to move a distance d 3 , which is equal to three times the pitch of the pixel shutter rows, from the position of stage  1 , in the direction of the arrow, photosensitive medium  11  is exposed in the same manner as in the previous stage. 
     Consequently, as a result of exposures in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the eighth column in the photosensitive medium  11  assumes the form of a matrix, as shown in FIG.  5 ( e ). Further, exposure of the fourth column and the fifth column is carried out with R light Lr in a manner such that the exposed points in the fourth column are displaced with respect to the exposed points in the fifth column by half a pitch in the column direction, exposure of the sixth column and the seventh column is carried out with G light Lg in a manner such that the exposed points in the sixth column are displaced with respect to the exposed points in the seventh column by half a pitch in the column direction, and exposure of the eight column and the ninth column is carried out with B light Lb in a manner such that the exposed points in the eighth column are displaced with respect to the exposed points in the ninth column by half a pitch in the column direction. 
     Locations exposed at this stage overlap locations exposed at stage  2  (st 2 ) with two rows shifted. 
     Stage  5  (st 5 ): After photosensitive medium  11  has been caused to move a distance d 4 , which is equal to four times the pitch of the pixel shutter rows, from the position of stage  1 , in the direction of the arrow, photosensitive medium  11  is exposed in the same manner as in the previous stage. 
     Consequently, as a result of exposures in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the ninth column in the photosensitive medium  11  assumes the form of a matrix, as shown in FIG.  6 ( b ). Further, exposure of the fifth column and the sixth column is carried out with R light Lr in a manner such that the exposed points in the fifth column are displaced with respect to the exposed points in the sixth column by half a pitch in the column direction, exposure of the seventh column and the eighth column is carried out with G light Lg in a manner such that the exposed points in the seventh column are displaced with respect to the exposed points in the eighth column by half a pitch in the column direction, and exposure of the ninth column and the tenth column is carried out with B light Lb in a manner such that the exposed points in the ninth column are displaced with respect to the exposed points in the tenth column by half a pitch in the column direction. 
     Locations exposed at this stage overlap locations exposed at stage  3  (st 3 ) with two rows shifted. 
     Stage  6  (st 6 ): After photosensitive medium  11  has been caused to move a distance d 5 , which is equal to five times the pitch of the pixel shutter rows, from the position of stage  1 , in the direction of the arrow, photosensitive medium  11  is exposed in the same manner as in the previous stage. 
     Consequently, as a result of exposures in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the tenth column in the photosensitive medium  11  assumes the form of a matrix, as shown in FIG.  6 ( c ). Further, exposure of the sixth column and the seventh column is carried out with R light Lr in a manner such that the exposed points in the sixth column are displaced with respect to the exposed points in the seventh column by half a pitch in the column direction, exposure of the eighth column and the ninth column is carried out with G light Lg in a manner such that the exposed points in the eighth column are displaced with respect to the exposed points in the ninth column by half a pitch in the column direction, and exposure of the tenth column and the eleventh column is carried out with B light Lb in a manner such that the exposed points in the tenth column are displaced with respect to the exposed points in the eleventh column by half a pitch in the column direction. 
     Location exposed at this stage overlap locations exposed at stage  4  (st 4 ) with two rows shifted. 
     As a result of the above sequential exposures prior to this stage, the sixth column, which is indicated by the reference symbol r 1  in FIG.  6 ( c ), is an exposed region in which R light Lr, G light Lg and B light Lb have blended together. 
     Stage  7  (st 7 ): After photosensitive medium  11  has been caused to move a distance d 6 , which is equal to six times the pitch of the pixel shutter rows, from the position of stage  1 , in the direction of the arrow, photosensitive medium  11  is exposed in the same manner as in the previous stage. 
     Consequently, as a result of exposures in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the eleventh column in the photosensitive medium  11  assumes the form of a matrix, as shown in FIG.  6 ( d ). Further, exposure of the seventh column and the eighth column is carried out with R light Lr in a manner such that the exposed points in the seventh column are displaced with respect to the exposed points in the eighth column by half a pitch in the column direction, exposure of the ninth column and the tenth column is carried out with G light Lg in a manner such that the exposed points in the ninth column are displaced with respect to the exposed points in the tenth column by half a pitch in the column direction, and exposure of the eleventh column and the twelfth column is carried out with B light Lb in a manner such that the exposed points in the eleventh column are displaced with respect to the exposed points in the twelfth column by half a pitch in the column direction. 
     Locations exposed at this stage overlap locations exposed at stage  5  (st 5 ) by two rows. 
     As a result of the above sequential exposures prior to this stage, the sixth and seventh columns, which are indicated by the reference symbol r 2  in FIG.  6 ( d ), is an exposed region in which R light Lr, G light Lg and B light Lb have blended together. 
     Stage  8  (st 8 ): After photosensitive medium  11  has been caused to move a distance d 7 , which is equal to seven times the pitch of the pixel shutter rows, from the position of stage  1 , in the direction of the arrow, photosensitive medium  11  is exposed in the same manner as in the previous stage. 
     Consequently, as a result of exposures in which exposure is carried out in a manner such that the exposed points in a column are displaced with respect to the exposed points in an adjacent column by a half pitch in the column direction, exposed points ranging from the second column to the twelfth column in the photosensitive medium  11  assumes the form of a matrix, as shown in FIG.  6 ( e ). Further, exposure of the eighth column and the ninth column is carried out with R light Lr in a manner such that the exposed points in the eighth column are displaced with respect to the exposed points in the ninth column by half a pitch in the column direction, exposure of the tenth column and the eleventh column is carried out with G light Lg in a manner such that the exposed points in the tenth column are displaced with respect to the exposed points in the eleventh column by half a pitch in the column direction, and exposure of the twelfth column and the thirteenth column is carried out with B light Lb in a manner such that the exposed points in the twelfth column are displaced with respect to the exposed points in the thirteenth column by half a pitch in the column direction. 
     Location exposed locations at this stage overlap locations exposed at stage  6  (st 6 ) with two rows shifted. 
     As a result of the above sequential exposures prior to this stage, the sixth, seventh and eighth columns, which are indicated by the reference symbol r 3  in FIG.  6 ( e ), is an exposed region in which R light Lr, G light Lg and B light Lb have blended together. 
     As a result of the sequential exposure of photosensitive medium  11  in the manner described above, with the exception of the first five rows (the first row to the fifth row) and the last five rows, exposure takes place such that R light Lr, G light Lg and B light Lb blend together in the same region of photosensitive medium  11 . Consequently, by placing a mask to cover the first five rows and last five rows of photosensitive medium  11 , it is possible to perform full-color printing, for which R light, G light and B light are used, of the entire region not covered by the mask. 
     In the example above, a description was provided in which microshutters in the same pixel shutter row are all open concurrently. However, in actual fact, selective control of the opening and closure of the microshutters is performed such that only some of these microshutters are opened and the rest thereof remain closed, in accordance with the image to be formed on photosensitive medium  11 . 
     As described hereinabove, according to the present invention, an R substrate  4   a , whereon R light-emitting elements  5   a  are fixed, a G substrate  4   b , whereon G light-emitting elements  5   b  are fixed, and a B substrate  4   c , whereon B light-emitting elements  5   c  are fixed, are all mounted independently on light-source substrate  3  such that the mount position of each of these substrates is adjustable. 
     Consequently, in the event of displacement of R light with respect to R pixel shutters  9   a , the correct passage of R light through R pixel shutters  9   a , which light has been output from R light-emitting elements mounted on R substrate  4   a , can be achieved by adjustment of the mount position of R substrate  4   a  with respect to light-source substrate  3 . Similarly, in the event of displacement of G light with respect to G pixel shutters  9   b , or of B light with respect to B pixel shutters  9   c , the correct passage of G light, which has been output from G light-emitting elements mounted on G substrate  4   b , or of B light, which has been output from B light-emitting elements mounted on B substrate  4   c , through G pixel shutters  9   b  or B pixel shutters  9   c , respectively, can be achieved by adjustment of the mount position of G substrate  4   b  or B substrate  4   c , respectively, with respect to light-source substrate  3 . 
     Moreover, according to the present invention, simultaneous exposure of a photosensitive medium by R light, G light and B light is possible while exercising control of a microshutter array in which each of the pixels are arranged in positions that are mutually displaced by half a pitch in the column direction, whereby a high-density image can be printed at high speed on a photosensitive medium.