Abstract:
There is provided a microfilm scanner which easily eliminate a search mark provided to each frame of a strip-shaped microfilm to precisely read only a range (image photographed range) including the frame. The microfilm scanner comprising: a film-edge detector for a width edge of the microfilm in each main scanning line in response to an output of a line sensor; and reading-range setter for setting an image reading range in each main scanning line by referring the detected edge of the microfilm. In a case that a width of the film is known in advance, start and end points of the image reading range may be determined from the first edge detected along a main scanning direction of the film-edge detector. A control method for the microfilm scanner is also provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a microfilm scanner which searches or retrieves a target frame from a strip-shaped microfilm, reads an image in the target frame using a line sensor, and outputs data representing the read image to a CRT or a printer. The present invention also relates a control method for this microfilm scanner. 
     2. Description of the Prior Art 
     There is a known microfilm scanner, which searches or retrieves a target frame from a strip of microfilm such as a roll film and reads an image projected from the target frame using a line sensor. There is also proposed a microfilm reader which uses the above microfilm scanner in combination with an output device such as a CRT display or a printer. 
     The use of the line sensor to read an image makes it easier to process the image as digital image signals, to display it onto a CRT or a liquid crystal display panel, or to output it to a printer. This also makes it easier to store data representing the read image into a memory such as a magneto-optical disk or to transfer the image data to other image processor. Therefore, the read image can be widely used. 
     In a microfilm formed in a band, tape, ribbon or long strip shape, such as a roll film, search or retrieval marks such as blips are generally provided or recorded within a given range of an edge side. Therefore, the given range from each edge of the film is defined as a region for search marks and an image is photographed on the remaining range between both edge-side regions. Thus photographed image constitutes a frame containing an original or document image. 
     When reading an image in a target frame using such a microfilm scanner, it may be appreciated that the entire area except the search-mark regions scanned with high density, that is, it will be desirable to be able to read only image signals in the image photographed region with high density for use as image data to be output. It is therefore necessary to correctly discriminate a range occupied by photographed image frames from a range occupied by search marks. In the conventional microfilm scanner, however, the operation procedure such as for discriminating therebetween is made complicated. 
     For example, when the image photographed on the microfilm is a negative image, the background portion in each original image is blackened and white frame region surrounds each original image. When a negative image is reversed to make it a positive image, the above mentioned white frame region turns to the blackened frame region. In this specification, such portions other than the original image region in the frame are called a black frame. On the other hand, search marks or blips are typically black spots or markers on the edge of the negative-positive reversed film, one spot or marker for each frame. Therefore, the black frames and the search marks are often confused with each other. As a result, the detection accuracy of the microfilm scanner is lowered and thereby a range including the target frame may not be detected. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances as aforementioned, and a first object thereof is to provide a microfilm scanner which easily eliminates search marks on a strip of microfilm so that only a range including a target frame (image photographed range) can be scanned precisely. 
     Also, a second object of the present invention is to provide a control method for a microfilm scanner, in which search marks on a strip of microfilm are easily eliminated so that only a range including a target frame (image photographed range) can be scanned precisely. 
     The first object of the present invention is attained by the provision of a microfilm scanner having a line sensor for reading an image photographed or recorded on a frame of a strip-shaped microfilm, comprising: 
     (a) film-edge detecting means for receiving an output of said line sensor obtained by scanning the microfilm in the main scanning direction perpendicular to the lengthwise direction of the microfilm and for detecting a width edge of the microfilm in each main scanning line; and 
     (b) reading-range setting means for setting a range of an image to be read in each main scanning line by referring to the detected edge of the microfilm. 
     The second object of the present invention is attained by the provision of a control method for a microfilm scanner, in which an image photographed or recorded on a frame of a strip-shaped microfilm is read by a line sensor, comprising steps of: 
     detecting a width edge of the microfilm by using an output of the line sensor; and 
     setting a range of an image to be read in each main scanning line by referring to the detected edge. 
     If a width of the microfilm is known in advance, start and end points of the image reading range can be set by referring to the first-detected film edge in the main scanning direction of the line sensor. 
     Among from outputs of the line sensor, which have been used for detecting the edges of the film, only image signals contained in the image reading range are selected so that the image in the image reading range represented by the selected image signals can be used as an output image. Alternatively, the line sensor may perform two types of scanning; the one is first or preliminary scanning for detecting width edges of the film, and the other is second or real scanning. 
     After the image reading range is set through the preliminary scanning with low density, the second or real scanning may be performed with high density. Image signals contained in the image reading range set by preliminary scanning are selected from the entire image signals obtained by the second scanning operation. With such a operation, an image represented by the selected image signals can be read for use as an output image. 
     The line sensor may perform preliminary scanning for detecting a black frame of a target frame and its inclination angle, then may perform real scanning for reading the original image with high density. In such a case, the line sensor can scan the entire range (image reading range) except the search mark region by referring to the edges of the film, during the preliminarily scanning, before the black frame and its inclination angle are detected. 
     Referring now to FIGS. 6 and 7, an outline of the present invention will be described. In FIG. 6, there is shown a portion of a roll of microfilm  200 . In the film  200 , each of given ranges a, b from both edges  202 ,  204  has been set to be a region where a search mark or blip  206  should be provided to each frame. Accordingly, an image in each frame has been photographed in a range c between the ranges a and b. The range c is thus set to be an image photographed range including an image in each frame. 
     Although a line sensor  208  is to read a enlarged image projected from the film  200 , it is conceptually or schematically illustrated over the film  200  in FIG. 6 for easy understanding of the present invention. The line sensor  208  is arranged in a direction substantially perpendicular to a length-wise direction of the film  200  to relatively move in the length-wise direction of the film  200  (a direction indicated by an arrow in FIG.  6 ). 
     The line sensor  208  scans or reads an image in a main scanning direction, for example, from the lower side to the upper side in FIG.  6 . Outputs of the line sensor  208  are supplied to film-edge detecting means  210  in which the first edge  202  of the film  200  is detected. After detecting the first edge  202 , reading-range setting means  212  determines coordinates of an end point of the range a, where the blip  206  has been provided to each frame, and coordinates of an end point of the image photographed range c. In other words, the reading-range setting means  212  determines coordinates of the start and end points of the image photographed range (image reading range) c. 
     The outputs of the line sensor  208  are also supplied to image reading means  214 . In the image reading means  214 , image signals in the reading range c determined by the reading-range setting means  212  are selected from among the outputs of the line sensor  208  so that only an image represented by the selected image signals can be read. Therefore, it permits the line sensor  208  to scan the entire image range c except a region where the blip  206  has been provided to each frame. 
     The read image is processed in appropriate image processing by image processing means  216  and output to an output device such as a printer  218 . It should be noted that the image signals obtained from the image area c and input to the image processing means  216  contain both an original image in a target frame and a black frame surrounding the original image. It is therefore preferable to detect and erase the black frame, or to detect and correct an inclination angle of the target frame. 
     When reading images, the film  200  is fixed between panels of glass. However, the film  200  is fed with any play in the width-wise direction and thereby the fixed position of the film  200  somewhat changes. For example, it may move up and down or is tilted at an angle. 
     In FIG. 7, the solid line indicates that the film  200  is slightly tilted while the virtual line or double-dot-and-dash line indicates that the film  200  is put in a correct position. Even if the film  200  is tilted as shown by the solid line in FIG. 7, the line sensor  208  can determine an image reading range c in each main scanning line by referring to the edge  202  independently of the inclination angle of the film  200 . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages and further description will now be discussed in connection with the drawings, in which: 
     FIG. 1 is a diagram showing an image reading and processing apparatus which incorporates a microfilm scanner of an embodiment according to the invention; 
     FIG. 2 is a perspective view illustrating the interior of a scanner used in the embodiment of FIG. 1; 
     FIG. 3 is a side view illustrating an arrangement of main parts of the scanner in FIGS. 1 and 2; 
     FIG. 4 is a perspective view illustrating a line sensor driving unit of the scanner in FIG. 3; 
     FIG. 5 is a schematic block diagram illustrating a control system of the scanner; 
     FIG. 6 is a diagram explaining an flow of operation according to the present invention; and 
     FIG. 7 is a diagram explaining the outline of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment will be described below with reference to the drawings. 
     Referring now to FIG. 1, there is shown a computer body  10 , a display device  12  such as a CRT or a liquid crystal display panel, a keyboard  14  used for user&#39;s manual operation, a scanner  18 , and a printer  20 . The display device  12  and the keyboard  14  are put on a desk  16 , the scanner  18  is put under the desk  16  and a printer  20  is placed at the side of the desk  16 . 
     The scanner  18  has a cartridge loading port  22  in the upper portion of the front panel, and serves to read an image on a microfilm  26  with low density (preliminary scanning), the microfilm  26  being contained in a cartridge  24  (see FIGS. 2 and 3) which has been inserted into the cartridge loading port  22 . During the preliminary scanning, the first edge of the film  26  are detected, as previously described, to determine an image reading area c (see FIGS. 6 and 7) by referring to the detected edge. Therefore, the scanner  18  reads only the image in the image reading range c. The read image with low density is processed in predetermined image processing by a CPU or the like incorporated in the scanner  18 . The processed image is then displayed on the display device  12 . 
     After checking the low-density image on the display device  12 , if it is required to output the image data to the printer  20 , the scanner  18  reads the image in this frame with high density (real scanning). After the real scanning, a black frame region is erased from the read image of high density while an inclination of the original image in this frame is corrected, as described in detail later. The read image is then processed in predetermined image processing and output to the printer  20 , stored in a memory such as a magneto-optical disk, or transferred to other external processor. 
     The inner arrangement of the scanner  18  will now be described. The scanner  18  has a longitudinal cabinet  28 , in which a feed reel driving unit  30  and a take-up reel driving unit  32  are arranged in the upper front portion and the lower front portion, respectively. When the cartridge  24  is inserted into the cartridge loading port  22 , the feed reel driving unit  30  moves the cartridge  24  automatically and engages a reel  24 A with a rotating shaft of the feed reel driving unit  30 . Then, the feed reel driving unit  30  pulls out the head lead of the roll film  26  from the cartridge  24  and feeds it downward to guide it to a take-up reel  32 A in the take-up reel driving unit  32 . 
     When viewing the scanner  18  in FIGS. 2 and 3, the film  26  passes through the rear side of the empty space between the reel driving units  30 ,  32 , that is, the film  26  passes through at the inner back side viewed from the front of the cabinet  28 . Referring to FIG. 3, there are shown guide rollers  34 ,  34 ,  36  and  36  for guiding the film  26 . Accordingly, a space  38  is formed by a gap between the reel driving units  30 ,  32  and a front panel  28 A of the cabinet  28 , and a light source  52 , described later, is housed in this space. 
     The take-up reel driving unit  32  has a drive belt  40  which runs in contact with the reel  32 A as shown in FIG.  3 . The drive belt  40  is wound around guide rollers  42  and  44 , a driving roller  46 , an encoder  48  and a tension roller  50 , and it is driven by the driving roller  46  to run in a film take-up direction (indicated by an arrow in FIG.  3 ). 
     The light source  52  is housed in the space  38  between the above-described two reel driving units  30  and  32 , which includes a lamp  54 , a reflector  56 , a condenser lens  58 , and an appropriate filter. In FIG. 2, there are illustrated a power supply circuit  60  and a power control circuit  62  for controlling an actuator such as a motor. 
     A line sensor driving unit  64  will next be described. The line sensor driving unit  64  is integrated with a projection lens  66 . More specifically, as shown in FIGS. 3 and 4, a cylindrical section  70  for holding the projection lens  66  is integrally formed with a frame (rotatable frame)  68  of the line sensor driving unit  64 . The projection lens  66  mounted in the cylindrical section  70  is a fixed focus lens with a magnifying power of approx. 2. The cylindrical section  70  is held rotatably in a frame (fixed frame)  72  fixed to the cabinet  28  so that an inclination of an image to be read can be corrected. Thus, the cylindrical section  70  rotates along a light axis  74  perpendicular to the surface of the film  26 . 
     A belt  78  is wound around the cylindrical section  70  and a pulley  76 A of a servo motor  76  mounted on the fixed frame  72 . Therefore, the rotary frame  68  can be rotated around the light axis  74  by the rotation of the motor  76 . 
     On the rotary frame  68 , a movable plate  80  is provided on the side opposite to the cylindrical section  70  as shown in FIG.  4 . In details, the movable plate  80  is slidably held by a pair of guide rods  82 ,  82  to permit the movable plate  80  to reciprocate, along a plane which perpendicularly intersects to the optical axis  74 , around the opening of the cylindrical section  70 . 
     In the rotary frame  68 , a belt  86  wound around pulleys  84 ,  84  is provided in a direction parallel to the up-and-down moving direction of the movable plate  80 , and one side of the movable plate  80  is fixed to the belt  86 . To one pulley  84 , the rotation of the servo motor  88  is transmitted through a belt  90 . As a result, the movable plate  80  can be moved up and down on a plane perpendicular to the light axis  74  by rotating the servo motor  88  in a forward or inverse direction. 
     On the movable plate  80 , an elongated window (narrow slit)  92  is formed in a direction perpendicular to the guide rods  82 ,  82 , that is, perpendicular to the up-and-down moving direction of the movable plate  80 . The elongated window  92  has its longitudinal center through which the light axis  74  passes. In the rear side of the movable plate  80 , that is, in the side opposite to the cylindrical section  70 , a printed circuit board  94  is fixed perpendicularly to the light axis  74 . 
     A longitudinal CCD arrayed line sensor  96  is fixed to the printed circuit board  94  to face the window  92  (FIG.  3 ). A preamplifier for amplifying an output of the line sensor  96  is also mounted on the printed circuit board  94 . The position of the light-receiving surface of the CCD line sensor  96  must correspond to a plane on which a projected image from the projection lens  66  is focused. 
     The CPU  100  incorporated in the scanner  18  serves as a controller for controlling the whole operation of the scanner  18  and has various functions as shown in FIG.  5 . Although these functions are provided by software, FIG. 5 shows them by using block diagram for convenience sake. 
     In FIG. 5, a search control means  102  detects a target frame from the film  26  by using a search blip mark (labeled by reference numeral  206  in FIG. 6) which is previously provided to each frame of the film  26 . Specifically, a pair of blip sensors consisting of a light-emitting element  104   a  and a light-receiving element  104   b  are arranged on both sides through a running path of the film  26  for counting outputs of the blip sensor  104   b.  While counting the outputs of the blip sensor  104   b,  the target frame is discriminated by controlling a motor  106  of the take-up reel driving unit  32  and a motor (not shown) of the feed reel driving unit  30 . 
     A scan control means  108  outputs an operating signal to actuate the line sensor driving unit  64  when the target frame comes in at a predetermined position within a projection range including the optical axis  74 . More specifically, the motor  88  is actuated to move the line sensor  96  in parallel on the image-focused plane for reading or scanning the projected image. 
     The line sensor  96  moves at a high speed when reading the image with low density for displaying it on the CRT display device  12  (low-density real scanning), whereas it moves at a low speed when reading the image of high density for outputting it to the printer  20  (high-density real scanning). The lamp  54  of the light source  52  is turned on only at a scanning time. It is therefore possible to save the power. 
     When using a halogen lamp as the lamp  54 , it takes about 100 msec to make the intensity of the halogen lamp stable after turning on the lamp  54 . It is therefore necessary to turn on the lamp  54  about 150 msec before the scanning is started. However, an electric current with the strength of 1/3 may be applied to the lamp  54  even at a non-scanning time to make the intensity of the lamp  54  stable more quickly. 
     As shown in FIG. 5, a circuit changing switch  110  is used for connection to Side A at the first or preliminary scanning and for connection to Side B at the second or real scanning. An edge detecting means  112  detects the first edge  202  (see FIG. 6) of the film  26  during the main scanning by the line sensor  96 . A reading-range setting means  114  sets a reading range c (see FIGS. 6 and 7) by referring to the detected edge  202 . A black-frame detecting means  116  detects a black frame from output signals representing the reading range c to be read by the line sensor  96 . 
     This black frame is a peripheral portion of an original, that is, a portion which appears in the external area of the original image when printed. There are various known types of algorithm for detecting the black frame. For example, when the scanning line runs from black frame to an original image area, a predetermined number or more contiguous black pixels turns to a series of continuous white pixels on the scanning line, so that a boundary between a black frame and an original image can be detected. 
     After the black frame is detected, an inclination detecting means  114  detects or determines an inclination angle of the projected and read image of the original by detecting the inclination angle of the image frame of the rectangular projected image. An inclination correcting means  120  actuates a motor  76  to correct the inclination of the image frame. As a result, the entire line sensor driving unit  64  rotates to set the line sensor  96  parallel to one side of the projected image. 
     When the circuit changing switch  110  is connected to Side B for the main or real scanning, an image processing means  122  receives outputs of the line sensor  96  and performs predetermined or desired image processing. 
     The real scanning contains two types of scanning; the one is to read an image with low density for displaying it on the CRT, and the other is to read an image in a target frame with high density for printing it out. The line sensor  96  performs the real scanning of the image to be displayed faster than the real scanning of the image to be printed out. 
     As mentioned above, the image processing means  122  performs predetermined image processing such as image enhancement, image inversion, image expansion or reduction, spatial filtering, trimming, or masking. The image data processed by the image processing means  122  is displayed on the CRT display device  12 . 
     While viewing the image on the CRT display device  12 , the user or operator can instruct the image processing means  122  to print out the currently-displayed image. In accordance with the instructions from the operator, the image processing means  122  actuates the scan control means  108  to read the image with high density (main or real scanning). The read image of high density is processed in predetermined image processing and the processed image data is printed out. When the line sensor  96  is used for the real scanning, the image processing means  122  serves as an image reading means according to the present invention. 
     In reading the image, the moving speed of the line sensor  96  in the subsidiary scanning direction may be changed according to the magnification ratio. When the magnification ratio is set higher than a reference magnification, for example, where all pixels of the line sensor  96  can be output without intermittently deleting nor interpolating, the moving or feeding speed of the line sensor  96  is lowered. On the other hand, when the magnification ratio is set lower than the reference magnification, the feeding speed of the line sensor  96  is made higher. It should be noted that the feeding speed of the line sensor  96  is in inverse proportion to the ratio of the set magnification (scale factor) to the reference magnification. 
     The light exposure may be controlled or adjusted automatically such that the output level of the line sensor  96  falls into a predetermined range during the preliminary scanning or real scanning. In this case, storage time for which each pixel of the CCD line sensor  96  stores a data piece representative of a corresponding portion of the read image is changed by changing the frequency of the clock signal applied to the line sensor  96  so that the amount of light reception can be controlled. It is also possible to change the amount of light reception of the line sensor  96  by changing light intensity of the lamp  54  of the light source  52 . 
     Operation procedures of this embodiment are now described. When the cartridge  24  is inserted into the cartridge loading port  22  and loaded in the feed reel driving unit  30 , a head lead of the film  26  is pulled out downward. The head lead of the film  26  is guided to the take-up reel driving unit  32  by the guide rollers  34 ,  34 ,  36 ,  36 . Then, the head lead of the film  26  is put between the reel  32 A and the drive belt  40  and wound on the reel  32 A. 
     The CPU  100  executes preliminary processing prior to real scanning, including target-frame retrieval, preliminary scanning, and inclination-angle correction. A search-blip mark is provided to each frame of the film  26  in advance, and the blip is detected by the blip sensor  104   b  (FIG. 5) such as a phototransistor while the film  26  is running. 
     The frame of a retrieval or search target is discriminated by counting blips in the search means  102 . When a target frame is detected, it is positioned within a projection range (frame) including the light axis  74  and feeding of the film  26  is stopped. Then, reading an image of this frame (preliminary scanning) and preliminary processing are started. 
     In this first image reading, the edges of the film  26  are detected to determine the image reading range c, as previously described with reference to FIGS. 6 and 7. The line sensor  96  then scans the image reading range c. This scanning is performed as preliminary processing to determine an inclination of the read image or for automatic exposure control, and therefore it is referred to as preliminary scanning. 
     In this preliminary scanning, the scan control means  108  changes the circuit changing switch  110  to Side A to turn on the lamp  54  of the light source  52 . Consequently, an image in the target frame is expanded approximately two-fold by the projection lens  66  and projected on the movable plate  80 . 
     The movable plate  80  is driven by the motor  88  such that the line sensor  96  moves from one side to the other side of the entire projection range of the projected image. During this moving operation, the line sensor  96  reads the projected image on the image-formed plane. While the line sensor  96  performs this scanning (preliminary scanning), outputs of the line sensor  96  are amplified by the preamplifier disposed on the circuit board  94  and sent to the CPU  100  incorporated in the scanner  18 . 
     The CPU  100  uses image signals derived from the line sensor  96  during this preliminary scanning to perform automatic exposure (AE) control or adjustment in a light-exposure control means. For example, if the output levels of the image signals exceed a predetermined setting range, the clock frequency of the line sensor  96  will be raised to reduce the storage time of each pixel of the line sensor  96 , thereby reducing the amount of light reception. Otherwise, the clock frequency of the line sensor  96  is lowered so as to increase the amount of incident light. 
     The CPU  100  then makes correction for eliminating the effect of uneven or different characteristics of pixels of the line sensor  96  (CCD pixel correction). In other words, uneven output levels of respective pixels are prestored or memorized in advance, so that the CPU  100  corrects the output level of each pixel when reading the projected image. 
     The edge detecting means  112  determines an edge of the film  26  in response to the image signals the output levels of which have been corrected in a manner previously described. The reading-range setting means  114  sets the reading range c by referring to the detected edge of the film  26 . The black frame detecting means  116  detects or determines a black frame region surrounding the original image region which is included in a projected and read image within the reading range c. The inclination detecting means  118  then determines an inclination angle of the projected image from the black frame. 
     The inclination angle can be determined by detecting the rectangular black frame which appears in a circumference of the original image. After determining the inclination angle of the projected image, the rotary frame  68  is rotated by the servo motor  88  so that the inclination angle becomes zero. In other words, a side in the length-wise direction of the line sensor  96  is matched with a side of the black frame. 
     After end operation of the preliminary processing discussed above, real scanning is performed. The above preliminary scanning operations are preliminary for frame retrieval or matching between the inclination of the projected image and the inclination of the line sensor  96 . Therefore, the real and main scanning for reading the original image to be printed out is performed after the preliminary scanning. 
     The real scanning contains two types of scanning; the one is to read an image with low density for displaying it on the CRT (real scanning for display), and the other is to read an image with high density for printing it out (real scanning for printing). It should be noted that both real scanning operations are not basically different from each other except in the scanning speed. 
     In this real scanning, the circuit changing switch  110  is changed to Side B (FIG.  5 ). The line sensor  96  determines a scanning speed for reading the image with low density enough to display the read image on the CRT. This scanning speed is also set to corresponds to the set magnification ratio. Then, the line sensor  96  is moved at the scanning speed to read or scan the original image with the low density. 
     The image read by the line sensor  96  is output to the image processing means  122  (FIG. 5) and processed in predetermined processing. In this image processing, the image processing means  122  performs predetermined or desired image processing such as output level correction for correcting uneven output levels of pixels of the line sensor  96 , image expansion or reduction, image inversion, negative-positive inversion, image enhancement with an unsharped masking (USM) technique, or processing for binarization, dithering or multinarization. After end operation of the predetermined image processing, the processed image is displayed on the CRT display device  12 . 
     While viewing the image on the CRT display device  12 , if the user or operator wishes to print out the image, he or she can give printing instructions using a manual operation means such as a keyboard  14  or a mouse  14 A so that the printer  20  will start printing. 
     In accordance with the printing instructions from the operator, the image processing means  122  sends a command to the scan control means  108  so that the image in the currently-displayed frame will be read with high density. The read image is then processed and printed out. 
     In a conventional microfilm scanner or projector, the light source  52  and the projection lens  66  are usually arranged in the horizontally-reverse direction to those of the embodiment shown in FIG.  3 . Accordingly, if a microfilm such as used for a conventional device is used in this embodiment, the projected image will be reversed to be mirror image. In such a case, it can be electrically converted to a correct image through an appropriate image processing and this kind of processing is easy. 
     Also, when the film  26  used in the embodiment is a negative film, the projected image to be read by the line sensor  96  is a negative image. If such a negative image is displayed on the CRT display device  12  without performing any image processing, it will exhibit reverse black-and-white (light-and-shade) tones. In such a case, the most significant bit and the least significant bit in the black-and-white tone data are replaced with each other, then subsequent bits are exchanged in due order. Accordingly, the polarity of the read image can be reversed to be positive image. 
     Further, when a binary (black and white) density image needs to be output to the printer  20 , a multi-valued density or multi-tone image output from the line sensor  96  may be binarized by referring to a predetermined threshold value, then each bit of the binarized image is changed between a logical  1  and a logical  0 . Thus, the multi-tone image photographed or recorded on a negative film can be displayed or printed as a binarized positive image. 
     In this embodiment, since the line sensor  96  performs the real scanning after the preliminary scanning, an image in a target frame must be scanned by the line sensor  96  plural times. To reduce the processing time, the line sensor  96  may perform the preliminary scanning in a direction and the real scanning in a reverse direction to that of the preliminary scanning. With such arrangement, the line sensor  96  does not needs to be returned to the home position as it scans one line, and this permits the line sensor  96  to read an image continuously. 
     If only a subsidiary or vertical scanning direction (moving direction) of the line sensor  96  is reversed with a fixed main scanning direction, the scanned image will be reversed to be mirror image. In such a case, it can be specularly converted to a correct image through an appropriate image processing. In printing out an image onto a given paper, it may be desirable to change the orientation of the image according to the aspect ratio of the frame determined from the detected black frame region. In this case, it is preferable to input image data to a memory while rotating the image 90 deg each time the line sensor  96  reads the image. 
     In the conventional, two image memories are provided for writing image data from one memory to the other memory while rotating the image data 90 deg, and therefore a problem arises that a large storage capacity is required and thereby the processing time increases. Accordingly, if an output of the line sensor  96  is directly written to a memory while rotating it 90 deg, as discussed above, a required storage capacity of the memory will be reduced to about one-half the storage capacity in the conventional to decrease the processing time by several 100 μsec. 
     Although the projection lens  66  of the scanner is a fixed focus lens in the above embodiment, the present invention is not limited by the embodiment. For example, an automatic focus mechanism may be provided in the scanner. In this case, the automatic focusing processing can be performed as one of preliminary processing. 
     The display device  12  is also not limited by the CRT display device, and other display device may be used instead of the CRT display device, such as a liquid crystal panel or a plasma display. Similarly, the output device is not limited by the printer  20 . For example, images read and processed by the microfilm scanner according to the present invention may be output to an external memory such as a magneto-optical disk or transferred to other image processor. 
     In the embodiment, if the lamp  54  is turned on only when the line sensor  96  performs scanning, it will reduce the amount of heating of the lamp  54  as well as the power consumption. Accordingly, a cooling system of the lamp  54  can be simplified. The lamp  54  may be turned on by loading the cartridge  24  into the scanner  18  and turned off by pulling out the cartridge  25  from the scanner  18 . 
     As described in detail above, according to the present invention, the line sensor detects an edge of the microfilm and sets an image reading range in each main scanning line by referring to the detected edge. Therefore, even if a search mark such as a blip is provided to each frame of the microfilm, it can not affect the scanning operation and permits the line sensor to read or scan the entire correct image except the mark. 
     The image reading range can be set by referring to the first edge detected along the main scanning direction of the line sensor, that is, it can be set to a given range starting from a point at a predetermined distance away from the first edge detected along the main scanning direction. If the image area is detected by preliminary scanning, a black frame of the original image in each frame and an inclination angle of the black frame can be detected from the image reading range determined by referring to the first-detected edge to correct the inclination angle of the projected image prior to real scanning.