Abstract:
A method and apparatus for taking digital pictures. A film camera having a standard back panel, a shutter, and a primary lens is provided. An image sensing array is disposed within the camera in an area normally occupied by film so as to be in optical communication with the primary lens when the shutter is open. A read-out circuit is packaged to reside in a cavity normally occupied by film when the camera is employed to take standard pictures. The read-out circuit is coupled to the image sensing array and reads out an image captured by the image sensing array. A memory is coupled to a read-out circuit to store images read from the image sensing array. The memory is packaged to also reside in a cavity vacated in the absence of film. In one embodiment, the read-out circuit and the memory occupy the same cavity. In another embodiment, the read-out circuit and the memory occupy different cavities.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to digital photography. More specifically, the invention relates to providing an industry standard film camera the capacity to take digital pictures. 
     (2) Related Art 
     Film cameras have been around for decades. Among the typical cameras available are 35mm, 110, and 660. In the case of 35mm, a film canister is placed inside the cavity within the camera. The film leader is extended across an aperture which is in optical communication with a lens when a shutter is opened. The leader engages a take-up reel. The take-up reel is a core of a second cavity within the camera. As pictures are taken and the film advanced, the film is retained on the take-up reel. Some cameras initially advance all the film onto the take-up reel and then rewind frame by frame as pictures are taken. In either case, upon completion of the roll of film, the film is rewound off the take-up reel back within the canister. The canister must then be sent for processing before the pictures are available. Other varieties of cameras such as 110 and 660 are similar except they use a self-contained film cartridge with a built-in take-up reel. The whole cartridge is sent in for developing. 
     More recently, digital cameras have proliferated in the marketplace. A typical digital camera employs an electronic image sensing array, such as a charge coupled device (CCD) or CMOS image sensing array, which communicates with the lens of the camera. When a picture is taken, the shutter opens and exposes an image sensing array to light. The image sensing array thereby captures the image which is then retrieved from the array and stored in a memory. The camera can be coupled to a laptop computer or a desktop computer to download the images stored in memory. In that way, the picture is immediately available for on-screen viewing. 
     Some attempts have been made to provide film cameras with the ability to take digital pictures. These efforts have generally involved construction of a large relatively heavy replacement back panel for the camera which contains the necessary electronics required to take digital pictures. This does not facilitate the ready transition between film and digital pictures as the camera back must be interchanged depending on the medium in which the pictures are to be taken. Changing the camera back is difficult, time consuming and, in many cases, requires the service of a camera technician. 
     In view of the foregoing, it would be desirable to have a device which permits existing film cameras to take one or more digital pictures without excessive cost. It would also be desirable if the camera could be easily switched between taking digital pictures and taking film pictures by the user without requiring any service department assistance. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and apparatus for taking digital pictures is disclosed. A film camera having a standard back panel, a shutter, and a primary lens is provided. An image sensing array is disposed within the camera in an area normally occupied by film so as to be in optical communication with the primary lens when the shutter is open. A read-out circuit is packaged to reside in a cavity normally occupied by film when the camera is employed to take standard pictures. The read-out circuit is coupled to the image sensing array and reads out an image captured by the image sensing array. A memory is coupled to a read-out circuit to store images read from the image sensing array. The memory is packaged to also reside in a cavity vacated in the absence of film. In one embodiment, the read-out circuit and the memory occupy the same cavity. In another embodiment, the read-out circuit and the memory occupy different cavities. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a camera for use with one embodiment of the invention. 
     FIG. 2 is a back perspective view diagram of one embodiment of the invention. 
     FIG. 3 is a top view of the memory housing of one embodiment of the invention. 
     FIGS. 4-6 is a block diagram of one embodiment of the invention. 
     FIG. 7 is a top view of an alternative embodiment of the invention. 
     FIG. 8 is a perspective rear view of the alternative embodiment of the invention of FIG.  7 . 
     FIG. 9 is a top view of a second alternative embodiment of the invention. 
     FIG. 10 is a cross-section view of one mechanical stop for use in the embodiment of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a perspective view of a camera for use with one embodiment of the invention. The 35mm camera  10  has a standard back panel  1  with a spring-loaded pressure plate  2  coupled thereto. When used with conventional film, the film canister resides in cavity  3  and engages return post  6 . The film is disposed over cavity  8  so that when shutter  9  is open, the film is in optical communication with a primary lens not shown on the other side of shutter  9 . Drive gear  7  engages perforations in the edge of the film to advance the film on to take-up reel  4 . As more pictures are taken, more and more film is advanced onto take-up reel  4  and fills more and more of cavity  5  which surrounds take-up reel  4 . The pressure plate  2  holds the film against the edges  11  of cavity  8 , thereby defining the frame size of each exposure. When used with the invention to take digital pictures, the requisite electronics and memory are disposed in one or both of film canister cavity  3  and take-up reel cavity  5 , while the image sensing array resides over cavity  8 . In one embodiment, a secondary lens  20  is inserted into cavity  8  to focus the light entering shutter  9  onto a smaller area. Secondary lens  20  may engage the sides of cavity  8  or may be coupled to the carrier for an image sensing array (ISA) as discussed further below. This permits a smaller ISA to be used and, therefore, reduces the cost of the array. 
     FIG. 2 is a back perspective view diagram of one embodiment of the invention. A cylindrical image processing canister  30  shaped like a traditional film canister is provided to house image processing electronics discussed below in connection with FIGS. 4-7. Disposed on canister  30  is an image quality switch  32  which permits selection between resolution versus number of pictures which can be stored in the memory. The higher the resolution, the greater the memory required to store each picture. In some situations, a user may wish to give up some resolution in favor of more pictures before reloading. Switch  32  provides that capability. In one embodiment, it is a four-position switch. In another embodiment, one switch controls resolution, and a second switch controls color depth. A programmable film speed indicator  31  is disposed on the cylinder to be read like the film speed indicators on conventional film to indicate the speed at which the camera can operate with the ISA  35  that is being used. This permits different ISAs to be used with the same image processing canister  30 . When installed, canister  30  is disposed over return post  6  (of FIG.  1 ). Accordingly, canister  30  may be provided with a hollow area so as not to engage return post  6  such that the return post  6  is free to rotate unimpeded and without effecting the positioning of canister  30 . Alternatively, canister  30  may engage return post  6  and be provided with a controlled friction wind mechanism to cause the camera to believe that the film has been successfully rewound or not as desired. 
     One problem faced in 35 mm cameras which does not exist in 110 or 660 cameras is that the center-to-center distance  42  between the center of the film canister when installed and the take-up reel is variable. Both the distance  43  between the film canister and the aperture and the distance  44  between the aperture and the take-up reel are themselves variable. Thus, to accommodate variable distance  43 , canister  30  has connector  33  coupled thereto. Connector  33  provides a relatively long connector surface for any incoming signal lines. Accordingly, if the variable distance is short, the signal lines can be inserted deeper into connector  33 , and if the variable distance is long, the signal lines can be inserted less deeply into connector  33  while still insuring appropriate contact 
     An ISA  35  is mounted so that the sensing surface may be disposed in optical communication with the camera lens when the shutter is open. ISA  35  can typically be mounted on a carrier such as a circuit board. Cameras typically accommodate at least 2-3 millimeters between pressure plate  2  (referring to FIG. 1) and the top edge  11  of cavity  8  within the space that the ISD mounted on the circuit board will be disposed. Therefore, it is important that the thickness of the ISA/carrier combination not exceed 2-3mm if the combination is intended to be used in a broad spectrum of existing cameras. Using existing techniques, it is possible to get an ISA/circuit board combination of two millimeters in thickness. Moreover, ISAs come in a range of sizes such that a single ISA may be used in one embodiment. In another embodiment, smaller edge buttable ISAs are used to produce a single ISA of larger size. In still another embodiment alluded to above and discussed below, a smaller ISA is used in conjunction with secondary lens  20  to provide a lower cost solution. 
     ISA  35  is coupled to the canister  30  at connector  33  by image access lines  34 . Memory housing  39  having data port  40  is to be disposed in cavity  5  about take-up reel  4  (take-up reel  4 , while shown in FIG. 2, does not form a part of this invention). A film wind detector  41  engages take-up reel  4  and senses when a film advance has been initiated. Connector  37  is like connector  33 , but will provide connection points for different signal lines. Significantly, this allows detachment and removal of the memory housing unit  39  from the ISA  35 . Thus, memory units may be switched in and out, not unlike a regular roll of film. Memory access lines  36  couple canister  30  to memory housing  39 . It is also anticipated that memory housing  39 , in addition to housing the memory, will house a power supply which is a battery. In one embodiment, memory housing  39  is a half cylinder hollowed to accommodate the take-up reel  4 . 
     In one embodiment, a tape backing  45  provides a backing for the image sense array  35  and the signal lines exiting therefrom. The tape backing  45  may be mylar or any other suitable material. The tape backing is prepared to engage connectors  33  and  37  so that tension is maintained and proper positioning of the image sensing array can be effected. Space  38  is provided in tape  45  to avoid interference with film drive gear  7 . 
     Because of the variable distance issue discussed above, and the fact that the ISA is unlike regular 35mm film which has no pre-defined frames, steps must be taken to ensure that a user will properly position the ISA. To that end, it is desirable that there be some marking or gradation on the, e.g., tape backing to delineate by type of camera the depth of insertion appropriate. As one example, this may take the form of color bands and a package insert that advises the user which color band corresponds to which model of cameras. 
     FIG. 3 is a top view of the memory housing  39  of one embodiment of the invention. The film wind detector  41  is shown engaging take-up reel  4  which are both shown in phantom lines. Connector  37  is shown engaging tape backing  45 . 
     FIGS. 4-6 show a block diagram of one embodiment of the invention. A battery  100  provides power supply for the rest of the electronic components of the invention. A clock  101  is coupled to a clock division circuit  102 . Clock  101  may be a suitable frequency crystal. The clock division circuit  102  converts the clock signal from the clock  101  into three clock signals, a bit clock  108 , a pixel clock  107 , and a scan clock  106 . The frequency of the scan clock is determined by the time the clock must be asserted to read a scan line from the ISA  139 . The pixel clock is the number of pixels in a scan line times faster than the scan clock, and the bit clock is at least the number of bits in a pixel line faster than the pixel clock. For example, assuming eight pixels in a scan line and eight bits in a pixel and that the scan clock has a frequency of one, the pixel clock and bit clock would have a frequency of eight and at least sixty-four, respectively. Switch  142  in this embodiment is a four-position quality select switch which generates two-bit quality select signal  103 . Similarly, wind detection unit  143  generates a spool state signal  104 . 
     A scan address counter  105  is responsive to scan clock  106  and addresses the ISA  139  along scan address lines  114 . ISA  139  is responsive to pixel clock  107 . Parallel pixel output  115  of the ISA  139  is fed into the capture start logic 110, along with the ISA pixel ready signal  111  and an addressing complete signal  134  generated by scan address counter  105 . When the addressing complete signal  134  is asserted and the ISA pixel ready signal  115  is asserted, the capture start logic  110  determines from the parallel output  115  of the ISA  139  whether a picture has been taken. Effectively, the amount of light captured by the scan line indicates whether a picture has been taken, i.e., if the output light level exceeds a predetermined threshold, a picture has been taken. In one embodiment, an additional sensor is added to determine if the camera back is open. Opening the camera back would otherwise be interpreted as a picture taken because the ISA would exceed the light threshold. This sensor is particularly useful where it is desired to change the quality select setting “during the roll.” For example, as the memory is filled up, a user may decide they want, e.g., three low resolution shots rather than a single additional high resolution shot. If opening the camera back results in a “picture,” memory would be wasted defeating the benefit of changing the quality settings. 
     If a picture has been taken, the capture start logic asserts a capture active signal  133  at both capture start gate  109  and the scan address counter. This enables the count of the scan address counter  105 . When capture active is not asserted, the scan address counter  105  merely repeatedly asserts one predetermined scan address. Usually, the scan line is in the middle of the ISA. This scan line forms a basis for the capture start logic determination of a picture taken. The capture start gate  109  is responsive to both the ISA pixel ready signal  111  and the capture active signal  112 . When both are asserted, capture start gate asserts pixel ready signal  113  to the input pixel compressor shown in FIG.  5 . In one embodiment, to improve power efficiency, the capture active signal  133  is used to disable all downstream units when it is deasserted. 
     While compression is not essential to the invention, because memory space is limited, compression will often be desirable. Input pixel compressor  117  is responsive to bit clock  108 , a spool state signal  104 , a quality select signal  103 , and the pixel ready signal  111 . The spool state signal  104  indicates the beginning of a new frame which should be tagged in memory to simplify downloading the frames from the memory at a later time. The quality select signals  103  contribute to the tag by defining the space that will be required to store the frame. The pixel ready signal  113  is used to signal the compressor  117  that a new image pixel is available on the parallel ISA pixel output signal lines  115 . The compressor  117  also receives the parallel ISA pixel output signal lines  115 . The input pixel compressor  117  compresses the parallel ISA pixel output as parallel compressor output  116 , and it serves a compressed data ready signal  118  at input multiplexor  119 . Input multiplexor  119  is also responsive to the bit clock  108  and serializes the parallel compressor output  116  as serial compressor output  121 . It is important that the bit clock be sufficiently fast to permit the compressor to compress the incoming data on the parallel pixel output lines  115 . The bit clock  108  should also be an integral multiple of the pixel clock  107 . Input multiplexor  119  also asserts a bit ready signal  120 . Both the bit ready signal  120  and the serial compressor output  121  are provided to the output decoder  122  which transforms the serial bit stream into parallel compressed data and asserts the storage data ready signal  124 . The parallel compressed data is transmitted on parallel compress storage data lines  123  to static memory  132  (shown in FIG.  6 ). 
     A storage clock selection unit  128  senses connection to the data port  40  through the data port connects signal  125 . When the data port  40  is connected, the external clock signal is provided as data port clock  126 . The data storage clock selection unit  128  selects between the data port clock  126  and the data storage ready signal  124  to assert as the storage address clock  127 . Storage address counter  130  addresses the memory  132  via memory address lines  131 , and also generates an address ready signal  150 . A read/write signal  129  is provided by the data port with a default to a write signal. The data port  40  receives the data stored in the memory along parallel output pixel storage data lines  136  and also asserts a data valid signal  137  to advise a downloading computer (not shown) whether the output data is valid. 
     FIG. 7 is a top view of an alternative embodiment of the invention. In this embodiment, a single canister  200  has memory distributed around an outer cylinder  201 . The memory may be, for example, flash memory. The hollow center core of the cylinder is constructed to accept a non-proprietary three-volt battery to power the memory and other required electronics. Connector  205  connects the carrier  204  which carries an image processing chip  203  and a JPEG compression chip  202 . The image processing chip  203  retrieves captured images from image sensor array  206 . Auto winds sprocket treadmill  207  is attached to the carrier  204  and engages winding gears and a camera to simulate film. 
     FIG. 8 is a back perspective view of the alternative embodiment of the invention of FIG.  7 . In this figure, data port  210  is shown disposed on canister  200 . A wind sensor  208  for detecting a rewind condition is also disposed on canister  200 . Programmable speed indicators  211  are on the canister to be read by the camera in the conventional manner. A data port  210  is provided to allow easy downloading of images stored in the memory. Additionally, a liquid crystal display (LCD)  209  is disposed on the canister  200  so as to be readable through a window provided in many camera back panels. The LCD  209  may, e.g., display the number of shots remaining at the current resolution level. The treadmill  207  is also shown. The treadmill  207  advances similar to regular film so that the camera believes it has advanced regular film. There are a number of ways an “end of roll” condition can be handled. In one embodiment, operation of the treadmill  207  is constant as between any two pictures. In this embodiment, the user must recognize by, e.g., the LCD  209  display that a maximum number of shots has been taken. Other signaling mechanisms / such as an audible tone may be used to indicate the memory is full. The user must then take steps to empty the memory. It is desirable to ensure that the memory will not overwrite itself if the number of pictures taken exceeds the capacity of the memory. 
     In an alternative embodiment, a mechanical stop mechanism prevents advancement of the treadmill  207  after a last shot is taken. FIG. 10 is a cross-sectional view of one such mechanical stop. When a last picture is taken, pin  220  is triggered to engage sprockets  222  of a treadmill axle  221 . Pin  210  engages the sprockets  222  so as to prevent advancement, but permits auto rewind to occur unhampered. Once auto rewind begins, pin  10  is reset to a disengaged position. Other ways of increasing treadmill tension to simulate the “end of roll” condition will occur to those of ordinary skill in the art and are within the scope and contemplation of the invention. 
     FIG. 9 is a top view of a second alternative embodiment of the invention. This embodiment is similar in most respects to the embodiment of FIG.  7 . However, the secondary lens  220  extends from carrier  204  to focus light entering the camera onto ISA  219  which has a smaller area than a typical film frame. Secondary lens  220  should be affixed to carrier  204  to ensure that the appropriate focal length between the secondary lens  220  and the ISA  219  is maintained. This embodiment will only be suitable for cameras in which the shutter is set significantly forward of the film plane such as the camera shown in FIG.  1 . It is expected that the smaller ISA  219  will significantly reduce the cost of the overall apparatus. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Therefore, the scope of the invention should be limited only by the appended claims.