Abstract:
A digital camera having an image reader which reads an optical image projected thereon and generates image signals by scanning the projected optical image, an optical unit which projects the optical image on the image reader at various ratios, and a controller which determines a range of the scanning operation performed by the image reader in accordance with the ratios employed by the optical unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to a digital camera, and more particularly, to a digital camera that performs photo-taking of a two dimensional image by means of a line sensor. 
     2. Description of the Related Art 
     A digital camera that performs photo-taking using a combination of a line sensor and a scanning mechanism, such as a mirror rotation mechanism, has been conventionally proposed (Japanese Laid-Open Patent Application No. 62-47278). This type of digital camera is called a line sensor camera. A line sensor camera has the advantage of being able to perform higher-resolution photo-taking than a digital camera that employs an area sensor. For example, photo-taking of an entire A4-sized sheet of paper may be performed such that regular-sized characters on the page may be read. 
     By incorporating into the line sensor camera a zoom unit as a lens system to perform magnification, the amount of freedom in framing the photo may be increased, improving user convenience. 
     However, in a line sensor camera having a construction in which the optical axis of the lens system moves relative to the photo object in conjunction with secondary scanning, e.g., in a line sensor camera in which a mirror to perform secondary scanning is located on the front side of the lens system, when the lens system focal length changes during the zooming operation (that is, when the image magnification changes), a problem occurs that the aspect ratio of the object image (photo image) on the image pickup surface of the line sensor also changes. 
     SUMMARY OF THE INVENTION 
     In view of the situation described above, the object of the present invention is to provide an improved digital camera. 
     Another object of the present invention is to provide a line sensor camera in which the aspect ratio of the object image on the image pickup surface does not change when the image magnification changes. 
     These and other objects are achieved by providing a digital camera equipped with the following components: 
     an image reader which reads an optical image projected thereon and generates image signals by scanning the projected optical image; 
     an optical unit which projects the optical image on the image reader at various ratios; and 
     a controller which determines a range of the scanning operation performed by the image reader in accordance with the ratios employed by the optical unit. 
     The photo-taking range in the direction of main scanning (i.e., the direction of alignment of the image pickup elements of the line sensor) depends on the focal length. On the other hand, the photo-taking range in the direction of secondary scanning depends on the angle of rotation of the scanning mechanism during photo-taking. Therefore, if the angle of rotation in the direction of secondary scanning used for photo-taking is increased or decreased in response to a change in the focal length (i.e., a change in the magnification), the aspect ratio of the object image on the image pickup surface may be made constant. 
     These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a summary construction of a digital camera in which the line sensor of the present invention is employed. 
     FIG. 2 is a drawing showing the construction of the scanning mechanism of the digital camera of FIG.  1 . 
     FIG. 3 is a block diagram of the control circuit of the digital camera. 
     FIGS. 4A and 4B are drawings showing the angle of view of the digital camera in the direction of main scanning. 
     FIGS. 5A and 5B are drawings showing the photo-taking angle range of the digital camera in the direction of secondary scanning. 
     FIGS. 6A,  6 B and  6 C are graphs to explain the operations of three photo-taking modes. 
     FIG. 7 is a flow chart showing the control sequence of the digital camera. 
     FIG. 8 is a flow chart showing the specific sequence of the parameter setting subroutine of FIG.  7 . 
     FIG. 9 is a drawing showing another example of the scanning mechanism. 
     In the following description, like parts are designated by like reference numbers throughout the several drawings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This application is based on application No. 8-45128 filed in Japan, the content of which is incorporated hereinto by reference. 
     FIG. 1 is a drawing showing the construction of a digital camera  1  employing the line sensor in which the present invention is applied, and FIG. 2 is a simplified drawing showing the elements of a scanning mechanism  13 . 
     The camera  1  is a compact and lightweight line sensor camera. A window opening  56  which permits light from the photo object into the camera is located on the front surface of housing a protective glass  10 A is embedded in the window opening  56 . A mirror  14  which performs secondary scanning is located behind the window  56 . Light from the photo object that is reflected off mirror  14  is projected onto a line sensor  11  by means of a projecting lens system  17 . By having the mirror  14  located in front of (on the object side of) the projecting lens system  17  in this way, the thickness the housing  10  may be reduced. 
     The line sensor  11  is an image pickup device comprising multiple image pickup elements such as CCDs arranged in a line, and is fixed at a position at which the object image is formed. The image pickup elements of line sensor  11  are aligned in a vertical direction in the drawing. A different image pickup device (such as a MOS-type image pickup device) may be used for line sensor  11  instead of a CCD-based device. 
     The mirror  14  is attached to the rotation shaft of a scan motor  15 . This rotation shaft is parallel to the direction of pixel alignment of line sensor  11  (the direction of main scanning). The photo object image moves on the light receiving surface of the line sensor  11  as the mirror  14  rotates. In other words, the photo object image is scanned over the line sensor  11  in a direction perpendicular to the direction of main scanning (i.e., the direction of secondary scanning). A rotation sensor which detects the angle and speed of rotation is attached to the scan motor  15 . The line scanning mechanism  13  comprises the mirror  14 , the scan motor  15  and the rotation sensor  55 . As shown in FIG. 2, photo-taking range (angle of view) H in the direction of secondary scanning depends on the angle of rotation (amount of rotational movement) of mirror  14  during photo-taking. 
     The projecting lens system  17  is an internal focusing zoom unit, and a portion of the incident light is used for autofocusing. An actuator  18  performs electric powered zooming is attached to the projecting lens system  17 . The actuator  18  has a built-in encoder that indicates the position of the zoom lens. A finder  19  of camera  1  is an optical finder. 
     A release switch  63 , a mode switch  68  and two zoom switches  66  and  67  are located on the top surface of the housing  10 . Each time the user presses the mode switch  68 , the photo-taking mode alternates in a repeating cycle. When the user presses the wide angle zoom switch  66 , zooming in the wide-angle direction is carried out, and when the user presses the telephoto zoom switch  67 , zooming in the telephoto direction is carried out. The mode switch  68  and the zoom switches  66  and  67  cannot be operated during photo-taking. 
     FIG. 3 is a block diagram of the control circuit of the camera  1 . 
     The construction of the control circuit centers around a microcomputer  101  (hereinafter CPU  101 ) that is responsible for overall control of the camera. Signals output from various switches described above and rotation sensor  55  are input to the CPU  101 . The CPU  101  detects the angle and speed of rotation of scan motor  15  based on a signal output from rotation sensor  55  and sends an appropriate instruction to a scan motor drive circuit  16  such that the photo object image is scanned at a prescribed speed. In addition, the CPU  101  performs a routine to adjust photo-taking range H in the direction of secondary scanning in response to changes in the projection magnification in order to maintain the aspect ratio of the photo image at a constant level regardless of zooming. Specifically, it determines the angular position of the mirror  14  which is necessary to begin photo-taking, and then sets control parameters such as the scan time for one line (line cycle ΔT), rotation speed ω of the mirror  14  and number of the scanning lines N. A RAM  102  is a work area for the CPU  101  to execute programs, and is used as a temporary memory for focal length data Df that changes as a result of zooming. 
     An image pickup control circuit  12  begins control of the line sensor  11  in response to a START signal from the CPU  101 , and outputs to the line sensor  11  a shift gate signal that regulates the time period of integration (charge accumulation) of the CCD. The line sensor  11  latches photoelectric conversion signals for each of the image pickup elements (pixels) in response to the shift gate signal, and outputs them to an A/D converter  110  in the order of pixel arrangement. This main scanning is repeated N times for each line cycle ΔT. 
     The A/D converter  110  converts the photoelectric conversion signals from the line sensor  11  into image pickup data D 1  having a prescribed number of bits (for example, eight bits) per pixel in synchronization with the pixel clock. After image pickup data D 1  is stored once in an image buffer  111  as actual photo object information recorded by the camera  1 , it is transferred to an image correcting member  130 . After subjecting image pickup data D 1  to necessary processing such as image quality improvement, the image correcting circuit  130  outputs post-processing image data D 2 . The image data D 2  output from the image correcting member  130  is then transferred to an image memory  140  via an interface  135 , and then stored as image information for one frame. It is then sent out at an appropriate time from the image memory  140  to a printer  150  or a display  160  and used to perform either printing or display. 
     FIGS. 4A and 4B are drawings showing the angle of view in the direction of main scanning. 
     The photo-taking range in the direction of main scanning changes depending on the projection magnification (image magnification) after zooming. As shown in FIG. 4A, in the telephoto condition where the focal length of the projecting lens system  17  is increased by zooming, the angle of view Θ T  is small and the image magnification is large. Conversely, in the wide-angle condition in FIG. 4B, the angle of view Θ W  is large and the image magnification is small. The length of mirror  14  in the direction of main scanning is selected to be the length at which a sufficient amount of light from the photo object may be led to the line sensor  11  when the projecting lens system  17  is at the shortest focal length. 
     FIGS. 5A and 5B are drawings showing the photo-taking angle in the secondary scanning direction. 
     As is obvious from a comparison of FIGS. 5A and 5B, the scan angles Θ T  and Θ W , which are the angle of rotation of the optical axis during scanning for one frame, are changed depending on the degree of zooming. In other words, the scan angle Θ W  in the wide-angle condition is set to a larger value than the scan angle Θ T  in the telephoto condition. 
     In order to increase or decrease the scan angles Θ T  and Θ W  without changing the direction of the central axis of the angle that defines the photo-taking range, the timing of the beginning and ending of scanning should be adjusted appropriately. As shown in FIG. 5A, in the telephoto condition, photo-taking is begun when the rotational position of the mirror  14  reaches the position at which the amount of displacement from the reference position is an angle (photo-taking commencement angle) α T , and photo-taking is completed when the rotational position of the mirror  14  reaches the position at which the amount of displacement from the reference position is an angle (photo-taking completion angle) β T . As shown in FIG. 5B, in the wide-angle condition, photo-taking is begun when the rotational position of mirror  14  reaches the position at which the amount of displacement from the reference position is an angle α W , which is smaller than angle α T , and photo-taking is completed when the rotational position of the mirror  14  reaches the position at which the amount of displacement from the reference position is an angle β W , which is larger than the angle β T . Angles α T , α W , β T  and β W  have the following interrelationships: 
     
       
         α W &lt;α T &lt;β T &lt;β W . 
       
     
     As described above, in order to increase or decrease angle Θ T  or angle Θ W , at least one of the three control parameters (line cycle ΔT, rotation speed ω, number of lines N) must be changed. 
     Camera  1  has three photo-taking modes that are defined by different setting possibilities for the three control parameters, as shown in the table below. 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                 Photo-taking mode 
                 ΔT 
                 ω 
                 N 
               
               
                   
               
             
             
               
                 {circle around (1)} Exposure control priority 
                 Variable 
                 Fixed 
                 Fixed 
               
               
                 mode 
               
               
                 {circle around (2)} Blur prevention priority 
                 Fixed 
                 Variable 
                 Fixed 
               
               
                 mode 
               
               
                 {circle around (3)} Number of lines priority 
                 Fixed 
                 Fixed 
                 Variable 
               
               
                 mode 
               
               
                   
               
             
          
         
       
     
     FIGS. 6A,  6 B and  6 C are graphs to explain the operations of the three photo-taking modes. The horizontal axis represents period of time t required for photo-taking, while the vertical axis represents the scan angle Θ. 
     Here, variations in the values of the parameters are explained using the hypothetical case of zooming from the telephoto condition to the wide-angle condition, i.e., of increasing the value of scan angle Θ, for the sake of convenience. The subscript character ‘T’ following each parameter indicates the telephoto condition, while the subscript character ‘W’ following each parameter indicates the wide-angle condition. 
     Where exposure control for line sensor  11  is concerned, it is preferable for line cycle ΔT to be long rather than short. This permits the charge accumulation time set for the CCD to be sufficiently long, allowing insufficient exposure to be avoided. 
     As shown in FIG. 6A, in exposure control priority mode, when the scan angle is increased from Θ T  to Θ W (Θ T &lt;Θ W ), the line cycle is increased from ΔT T  to ΔT W (ΔT T &lt;ΔT W ). Rotation speed ω and number of lines N are fixed. Therefore, the exposure time for one frame (i.e., the scan time for number of lines N) is longer in the wide-angle condition than in the telephoto condition. 
     When the exposure period is longer, the probability of blurring of the photo image due to camera shake during photo-taking increases. As shown in FIG. 6B, in blur prevention priority mode, when scan angle Θ is increased, rotation speed ω is increased from ω T  to ω W (ω T &lt;ω W ) without changing line cycle ΔT. Consequently, the exposure time for one frame becomes fixed regardless of zooming, and the probability that blurring will occur does not increase. 
     As shown in FIG. 6C, in number of lines priority mode, when scan angle Θ is increased, number of lines N is increased from N T  to N W (N T &lt;N W ). Consequently, the resolution in the direction of secondary scanning becomes fixed regardless of zooming. Because line cycle ΔT and rotation speed ω are fixed, the exposure time in the wide-angle condition (=ΔT×N W ) is longer than the exposure time in the telephoto condition (=ΔT×N T ). 
     FIG. 7 is a flow chart showing the control sequence for the operation of the camera performed by CPU  101 . 
     When a battery is housed in the camera, the control power supply is activated and the main switch is ON, the CPU  101  performs processing in response to the operation of switches. When the zoom switches  66  and  67  are pressed (# 100 ), drive control of the actuator  18  is performed (# 101 ), and focal length data Df corresponding to the most recent position of the movable part of the projecting lens system  17  is stored in memory (# 102 ). 
     When the release switch  63  is pressed (# 103 ), a release operation is performed in which parameters α, β, ΔT, ω and N are set based on focal length data Df residing in RAM  102  (# 104 ), and the photo object image is then converted into image data D 2  and is stored in image memory  140  (# 105 ). 
     When mode switch  68  is pressed (# 106 ), the photo-taking mode alternates in a repeating cycle as described above (# 107 ). Until the main switch is turned OFF, the existence of any change in the status of each switch is monitored (# 108 , # 100 ). 
     FIG. 8 is a flow chart showing the specific sequence of the parameter setting subroutine of step # 104  in FIG.  7 . 
     First, as a process to increase or decrease scan angle Θ during photo-taking in response to the focal length (image magnification) so as to keep the aspect ratio of the photo image constant, focal length data Df is taken in and photo-taking commencement angle a and photo-taking completion angle β are calculated (# 201 , # 202 ). 
     Parameter values appropriate to focal length data Df are then calculated in accordance with the photo-taking mode (# 203 -# 207 ). The parameter values for the release operation for the current exposure are set and the subroutine returns to the main routine (# 208 ). The parameter values appropriate to focal length data Df may be stored beforehand in a ROM, etc., and said values may then be read out in steps # 203  through # 207 . 
     While the embodiment described above performs line scanning by the rotating mirror  14 , the present invention may also be applied in a line sensor camera having a construction in which the optical axis moves relative to the photo object during secondary scanning, e.g., a construction in which image pickup unit  170  comprising a lens system  17   a  and the line sensor  11  integrated as a single unit is rotated within a prescribed angular range, as shown in FIG.  9 . In the example shown in FIG. 9, the center of rotation is located between the lens system  17   a  and the line sensor  11 , but the position of the center of rotation may be in front of the lens system  17   a  or behind the line sensor  11 . 
     By shifting photo-taking commencement angle α and photo-taking completion angle β to photo-taking commencement angle α′ and photo taking completion angle β′, respectively, when performing photo-taking using a prescribed scan angle Θ(Θ=β−α=β′−α′), the same effect as panning may be attained while the aspect ratio of the photo image is maintained at a constant level. By increasing scan angle Θ in the telephoto condition in the same manner as in the wide-angle condition, the aspect ratio of the photo-taking frame may be changed while the aspect ratio of the photo image is maintained at a constant level, realizing a horizontally wide (panorama) photo. In addition, while the embodiments described above involved configurations using the zoom units (lens systems)  17  and  17   a , the present invention may also be applied in a configuration in which the focal length is changed by changing the photo-taking lens. 
     In addition, while the embodiments described above involved configurations rotating the mirror for a predetermined angle to take an image, the present invention may also be applied in a configuration in which the image data is extracted by changing a range of sampling image data generated from a line sensor. 
     Moreover, the present invention may also be applied in an image reading scanner which moves relative to a sensor with respect to an original object. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.