Abstract:
A film bridge assembly adapted to precisely position film during scanning in a digital film processing system. The film bridge assembly makes up part of a film bridge and illuminator cavity system that includes a slot for the passage of illumination light that is used to scan film at an opening of the slot. A window or cylindrical lens is provided at the opening of the slot to permit film to pass over the slot without incurring any scratching. The window or lens is effective to keep the film at a constant height, reduce debris at the image plane, and permit a maximum amount of illumination light to pass through the film.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to film scanning, and more particularly to a film bridge for use in the transportation and scanning of film in a film scanning system.  
       BACKGROUND OF THE INVENTION  
       [0002]     Color photographic film generally comprises three layers of light sensitive material that are separately sensitive to red, green, and blue light. During conventional color photographic film development, the exposed film is chemically processed to produce dyes in the three layers with color densities directly proportional to the blue, green and red spectral exposures that were recorded on the film in response to the light reflecting from the photographed scene. Yellow dye is produced in the top layer, magenta dye in the middle layer, and cyan dye in the bottom layer, the combination of the produced dyes revealing the latent image. Once the film is developed, a separate printing process can be used to record photographic prints, using the developed film and photographic paper.  
         [0003]     In contrast to conventional film development, digital film development systems, or digital film processing (DFP) systems, have been proposed. One such system involves chemically developing exposed film to form scene images comprised of silver metal particles or grains in each of the red, green, and blue recording layers of the film. Then, while the film is developing, it is scanned using electromagnetic radiation, such as light with one predominant frequency, for example, in the infrared region. In particular, as the film develops in response to chemical developer, a light source is directed to the front of the film, and/or a light source is directed to the back of the film. Grains of elemental silver developing in the top layer (e.g., the blue sensitive layer) are visible from the front of the film by light reflected from the front source; however, these grains are substantially hidden from the back of the film. Similarly, grains of elemental silver developing in the bottom layer (e.g., the red sensitive layer) are visible from the back of the film by light reflected from the back source; however these grains are substantially hidden from the front. Meanwhile, grains of elemental silver in the middle layer (e.g., the green sensitive layer) are substantially hidden from the light reflected from the front or back; however, these grains are visible by any light transmitted through the three layers, as are those grains in the other two layers. Thus, by sensing, for each pixel location, light reflected from the front of the film, light reflected from the back of the film, and light transmitted through the film, three measurements can be acquired for each pixel. The three measured numbers for each pixel can then be solved for the three colors to arrive at three color code values for each pixel, and the plurality of colored pixels can then be printed or displayed to view the image.  
         [0004]     If desired, such scanning of each frame on the film can occur at multiple times during the development of the film. Accordingly, features of the frame that may appear quickly during development can be recorded, as well as features of the frame that may not appear until later in the film development. The multiple digital image files for each frame can then be combined to form a single enhanced image file.  
         [0005]     In another such digital film processing (DFP) system, a developer solution is applied to the film and dyes form on the film. As the film is developing via the applied solution, visible light and/or infrared light are applied to one side of the film. On the opposite side of the film, a sensor detects the light passing through the film and produces a digital representation of the image developing on the film.  
         [0006]     With these and other digital film processing and scanning systems, the film can be moved across a scanning area, and the radiation can be applied to the scanning area to obtain the image data. A film bridge or similar support mechanism can be utilized to control the position of the film as it passes over the scanning area. For optimum accuracy in scanning of the film, the positioning of the film should be tightly controlled. In particular, vertical vibration and movement of the film should be avoided as such movements can jolt the film out of the focus of the optics, resulting in unfocused image data. Moreover, the film should remain substantially flat across the imaging area in order to obtain accurate results. In addition, the mechanisms used to transport and control the position of the film during scanning should avoid imparting scratches or other physical defects to the image area of the film, as such scratches and defects can result in an inferior digital image.  
         [0007]     It is further advantageous to keep the film as close to the illumination cavity as possible. This produces the maximum illumination intensity through the film.  
         [0008]     A conventional film bridge and illumination assembly or device is shown in  FIG. 1 . Illumination device  30  is in the form of an illumination cavity that includes a first member  30   a  and a second member  30   b . First and second members  30   a  and  30   b  define a slot  32  there-between for the passage of illumination light or radiation from a light source  10  to an opening  34  of slot  32 . During scanning, film  14  is slid in direction  16  over slot opening  34  while illumination  36  from light source  10  passes through film  14 . The design of  FIG. 1  has several drawbacks. First, pulling film across a metallic or plastic material tends to induce scratches that reduce scanned image quality. The debris from the scratches and other areas of the machine also tends to get trapped on an area of the trailing edge of the slot (shown in general by reference numeral  40  in  FIG. 1 ) that also causes scanning problems. This debris can eventually fall into the illumination cavity. The scratching is lessened when the film tension is reduced but this causes flatness and focus irregularities with the film that leads to poor image quality.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention relates to a method and apparatus in which the magnitude and frequency of defects that are applied to the film during film transportation and scanning are reduced. More specifically, the invention provides for a film bridge design that reduces or eliminates film scratching and reduces the susceptibility of film to debris to prevent defects to the image.  
         [0010]     The present invention further provides for a film bridge that is adapted to maintain the film in a flat state at a constant height, while at the same time permitting the application of a desired illumination intensity through the film.  
         [0011]     The present invention therefore provides for a film bridge assembly for a film scanning system which comprises: a first bridge member having a first film facing surface; a second bridge member having a second film facing surface, with the first and second bridge members being spaced from each other to define a slot there-between that provides for a passage of illumination light from an opening of the slot through film traveling across the film bridge along a film path; and a cylindrical lens provided on the opening and extending between the first film facing surface and the second film facing surface, such that the film traveling across the film bridge contacts the cylindrical lens at or near an apex of the cylindrical lens and does not contact opposing edges of the cylindrical lens on each side of the apex.  
         [0012]     The present invention further relates to a method of scanning film which comprises the steps of: locating a first bridge member having a first film facing surface and a second bridge member having a second film facing surface relative to each other so as to define a slot there-between that provides for a passage of illumination light from an opening of the slot through film traveling across the film bridge along a film path; providing a cylindrical lens on the opening so as to extend between the first film facing surface and the second film facing surface; and transporting film to be scanned across the film bridge in manner in which the film contacts the cylindrical lens at or near an apex of the cylindrical lens and does not contact opposing edges of the cylindrical lens on each side of the apex.  
         [0013]     Another embodiment of the invention is to utilize the cylindrical lens at a shoe. The cylindrical lens could be placed just before or after the illumination slot to provide a shoe which the film slides over thereby maintaining a small gap from the illumination slot to the film. The shoe concept could be applied using single shoe before of after the illumination slot or to a dual concept with each part straddling the illumination slot.  
         [0014]     The present invention therefore further relates to a film bridge assembly for a film scanning system which comprises a first bridge member having a first film-facing surface; a second bridge member having a second film facing surface, with the first and second bridge members being spaced from each other to define a slot there-between that provides for a passage of illumination light from an opening of the slot through film traveling across the film bridge along a film path; and a cylindrical part provided on one of the first or second film facing surfaces, such that the cylindrical part maintains a gap between film traveling across the cylindrical part and the opening from the slot. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a schematic view of a related illumination device and film bridge;  
         [0016]      FIG. 2  is a schematic view of a digital film processing or development system that can be used in the present invention;  
         [0017]      FIG. 3  is a view of a film bridge and illumination device in accordance with a first embodiment of the present invention;  
         [0018]      FIG. 4  is a detailed view of the film bridge of  FIG. 3 ;  
         [0019]      FIG. 5  is a view of a film bridge in accordance with a second embodiment of the present invention; and  
         [0020]      FIG. 6  is a perspective view of the film bridge and illumination device in accordance with the present invention;  
         [0021]      FIG. 7  is a view of a film bridge and illumination device in accordance with a further embodiment of the present invention;  
         [0022]      FIG. 8 a  view of a film bridge and illumination device in accordance with a still further embodiment of the present invention; and  
         [0023]      FIG. 9 a  view of a film bridge and illumination device in accordance with a still further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Referring now to the drawings, wherein like reference numerals represent identical or corresponding parts throughout the several views,  FIG. 2  shows an exemplary digital film processing system (DFP)  100 . The system operates by converting electromagnetic radiation from an image to an electronic (digital) representation of the image. The image being scanned is typically provided on a photographic film media  112  that is being developed using chemical developer. In some applications, the electromagnetic radiation used to convert the image into a digital representation is infrared light; however, visible light, microwave and other suitable types of electromagnetic radiation may also be used to produce the digitized image. The scanning system  100  generally includes a number of optic sensors  102 , which measure the intensity of electromagnetic energy passing through or reflected by the developing film  112 . The source of electromagnetic energy is typically a light source  110  that illuminates the film  112  containing the scene image  104  and  108  to be scanned, which are forming on the film during the film development. Radiation from the source  110  may be diffused or directed by additional optics such as filters or waveguides (not shown) and/or one or more lenses  106  positioned between the sensor  102  and the film  112  in order to illuminate the images  104  and  108  more uniformly.  
         [0025]     Source  110  is positioned on the side of the film  112  opposite the optic sensors  102 . This placement results in sensors  102  detecting radiation emitted from source  110  as it passes through the images  104  and  108  on the film  112 . Another radiation source  111  can be placed on the same side of the film  112  as the sensors  102 . When source  110  is activated, sensors  102  detect radiation reflected by the images  104  and  108 . The process of using two sources positioned on opposite sides of the film being scanned is referred to as duplex scanning.  
         [0026]     The optic sensors  102  are generally geometrically positioned in arrays such that the electromagnetic energy striking each optical sensor  102  corresponds to a distinct location  114  in the image  104 . Accordingly, each distinct location  114  in the scene image  104  corresponds to a distinct location, referred to as a picture element, or “pixel” for short, in a scanned image, or digital image file, which comprises a plurality of pixel data. The images  104  and  108  on film  112  can be sequentially moved, or scanned relative to the optical sensors  102 . The optical sensors  102  are typically housed in a circuit package or unit  116  which is electrically connected, such as by cable  118 , to supporting electronics for storage and digital image processing, shown together as computer  120 . Computer  120  can then process the digital image data and display it on output device  105 . Alternatively, computer  120  can be replaced with a microprocessor or controller and cable  118  replaced with an electrical connection.  
         [0027]     Optical sensors  102  may be manufactured from different materials and by different processes to detect electromagnetic radiation in varying parts and bandwidths of the electromagnetic spectrum. For instance, the optical sensor  102  can comprise a photodetector that produces an electrical signal proportional to the intensity of electromagnetic energy striking the photodetector. Accordingly, the photodetector measures the intensity of electromagnetic radiation attenuated by the images  104  and  108  on film  112 .  
         [0028]     As discussed above, in order to scan film  112 , it is preferred that film  112  travel across a film bridge A film bridge assembly for a scanning system in accordance with the present invention is shown in  FIG. 3 . More specifically, a film bridge assembly  202  which makes up part of an illumination system comprises a part, window or lens  200 , preferably in the form of a cylindrical lens or part. As illustrated in  FIG. 3 , a film bridge assembly  202  includes a first bridge member  204  having a first film facing surface  204   a , and a second bridge member  206  having a second film facing surface  206   a . The first and second bridge members ( 204 ,  206 ) are spaced from each other to define a slot or cavity  210  there-between that provides for a passage of illumination light through an opening  212  of slot  210 ; with the light thereafter passing through lens  200  and film  112  traveling across the film bridge along a film path. The illumination light is provided by light source  110  located at an entrance to slot  210 .  
         [0029]     Cylindrical lens  200  is provided on the opening  212  so as to extend between the first film facing surface  204   a  and the second film facing surface  206   a . Therefore, the film  112  traveling across the film bridge in direction  220  contacts the cylindrical lens  200  at or near an apex  224  of the cylindrical lens  200  and does not contact opposing edges  200   a ,  200   b  of the cylindrical lens  200  on each side of the apex  224 . Therefore, the contact patch or the amount of contact between the window and the film is minimized with this geometry, thus keeping the film as flat as possible, eliminating window or lens edge scratching of the film, and minimizing the accumulation of debris.  
         [0030]     It is preferred that the material for the cylindrical lens  200  be very hard in order to avoid scratching. The preferred materials are Sapphire and Diamond although any visibly clear hard material can also be used. The cylindrical lens  200  should be manufactured with minimum thickness to minimize illumination loss.  
         [0031]     As shown in  FIG. 4 , reference numeral  250  identifies a longitudinal axis that extends along the center of slot  210 . In a first feature of the present invention, lens  200  may be centered on the opening  212  relative to axis  250 . In a further option as shown in  FIG. 5 , lens  200  can be located on opening  212  in a manner in which lens  200  is offset relative to axis  250 . Locating lens  200  in an offset manner as shown in  FIG. 5  provides for an extra degree of freedom that allows an illumination pattern to be optimized for the individual scanner design. Final geometry of the window or lens depends on several factors. The window or lens thickness should be minimized for maximum illumination throughput. Additional window or lens dimensions are dependant on fabrication technique, window or lens material, film entrance and egress angles and illuminator cavity or slot size.  
         [0032]      FIG. 6  is a perspective view of film bridge assembly  202 . In a feature of the present invention, the mounting of window or lens  200  can be based on several factors. A compliant mount is dictated by the fragile nature of a thin window or lens. In addition, the mounting should address film guiding features, stray light control, and maintenance.  FIG. 6  illustrates an embodiment and method of window mounting. In the design of  FIG. 6 , cylindrical lens  200  is held down with clamps  300   a  and  300   b  provided on opposing sides of lens  200 , as well as the opposing sides of the film path for film  112 . In a feature of the invention, a compliant material  302  (foam or rubber) can be provided between each clamp  300   a ,  300   b  and the lens  200  so as to contact lens  200 . This prevents damage to the lens  200  while at the same time holding the lens  200  at the opening  212  of cavity  210 . In a further feature of the invention as shown in  FIG. 6 , clamps  300   a ,  300   b  can be accurately located by hardened dowel pins  400   a  and  400   b . Pins  400   a ,  400   b  serve as location features for the clamps  300   a ,  300   b  that hold down the lens  200 . Further, by positioning pins  400   a  and  400   b  on opposing sides of the film path as shown in  FIG. 6 , the pins  400   a ,  400   b  serve as film guides to guide film  112  along the film path.  
         [0033]     Additionally, a cylindrical lens or part  200 ′ could be used as a shoe instead of a window as shown in  FIG. 7 . Cylindrical part  200 ′ does not have to be clear or optical in this embodiment since it simply acts as a film shoe that does not scratch film and will not wear. It is desirable for cylindrical part  200 ′ to be as thin as possible to maximize the amount of light from illumination slot  210  onto the the film. The cylindrical part  200 ′ may be located prior to illumination slot  210  ( FIG. 7 ) or on the trailing side of illumination slot  210  as shown in  FIG. 8 . Additionally the film bridge assembly could utilize dual cylindrical parts  200 ′,  200 ″ as shown in  FIG. 9 . In the embodiments noted above, the cylindrical parts  200 ,  200 ′ or  200 ″ are adapted to maintain a small gap from the illumination slot to the film.  
         [0034]     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.