Abstract:
A small image-pickup apparatus generating image signals representing subject light based on the subject light coming through an image-taking optical system, has: an image-pickup device generating image signals representing a subject image formed by the subject light focused on a surface thereof; a light reflecting mechanism leading the subject light to the image-pickup device as the subject light coming through the image-taking optical system is reflected in sequence by multiple reflector sections placed apart from each other; a rotation sensor sensing rotation of the image-pickup apparatus in a place along a surface of the image-pickup device; and a rotating mechanism reducing displacement of the subject image resulting from the rotation sensed by the rotation sensor, by rotating at least one of the multiple reflector sections around an axis along an optical path among the multiple reflector sections, whereby preventing camera shake.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an image pickup apparatus which forms subject light and generates image signals to represent subject light.  
         [0003]     2. Description of the Related Art  
         [0004]     Image pickup apparatus which shoot subjects and generate image data have been downsized and it has become common practice to incorporate such an image pickup apparatus in small equipment such as cell phones and PDAs (Personal Digital Assistants). By incorporating an image pickup apparatus in small equipment carried on a routine basis, it is possible to photograph readily any time without the trouble of carrying a digital camera or video camera. Also, such small equipment generally has a wireless or infrared data communications function and provides the advantage of being able to transfer a taken image to another cell phone, personal computer, or the like on the instant.  
         [0005]     When shooting with a small digital camera or cell phone, the camera is liable to move as a release switch is pressed, causing problems such as camera shake which can result in blurring of a taken image. Recently, it has been a common practice for a photographer to take a picture including the photographer, for example, by one-hand operation. This practice is prone to camera shake.  
         [0006]      FIG. 1  is a diagram illustrating camera shake.  
         [0007]     Broken lines in  FIG. 1  indicate positions of a camera  10  when the camera  10  is focused on a subject and solid lines indicate positions of the camera  10  when a photographer presses a release button  11 .  
         [0008]     Part (A) of  FIG. 1  is a top view of the camera  10 . When shooting with the camera  10  held in one hand, the front face of the camera  10  may rotate in such a direction (direction of arrow A) as to deviate in the right-and-left direction from the front of the subject. The direction of arrow A corresponds to an azimuth direction with respect to the camera  10  placed horizontally to shoot a horizontally oriented picture, and thus it will be referred to as the azimuth direction hereinafter.  
         [0009]     Part (B) of  FIG. 1  is a lateral view of the camera  10 . In the case of the small camera  10 , when pressing the release button  11 , the wrist may bend vertically, causing the front face of the camera  10  to rotate in such a direction (direction of arrow B) as to deviate in the up-and-down direction from the front of the subject. Some cell phones have their release button  11  installed on their front face, making them prone to rotation especially in the direction of arrow B. The direction of arrow B corresponds to an elevation direction with respect to the camera  10  placed horizontally to shoot a horizontally oriented picture, and thus it will be referred to as the elevation direction hereinafter.  
         [0010]     Part (C) of  FIG. 1  is a front view of the camera  10 . When shooting with the camera  10  which has its release button  11  installed near its flank, if the camera  10  is held in one hand, it may rotate in a clockwise/counterclockwise direction, as viewed from the subject, when the release button  11  is pressed. The direction of arrow C corresponds to a tumble direction of the camera  10  placed horizontally to shoot a horizontally oriented picture, and thus it will be referred to as the tumble direction hereinafter.  
         [0011]     Other than the movements shown in  FIG. 1 , the camera may make, for example, up-and-down movements, right-and-left movements, back-and-forth movements, or combinations thereof with its front face looking straight ahead at the subject. Although a horizontal movement of the camera looking straight ahead at the subject causes only a small amount of displacement in the image forming position of subject light on an image pickup element, rotational movements in the elevation direction, azimuth direction, and tumble direction cause large amounts of displacement in the image forming position, resulting in blurring of a taken image.  
         [0012]     Techniques for preventing camera shake in the rotational directions have been proposed, including a technique for preventing image blur by tilting part of the lenses in a direction normal to an optical axis and thereby decentering it according to movements of the camera (see, for example, Japanese Patent Laid-Open No. 7-301839) and a technique for installing a prism on an optical path and changing its vertical angle according to movements of the camera (see, for example, Japanese Patent Laid-Open Nos. 5-134285, 5-181094, and 8-6087).  
         [0013]     However, the camera shake prevention techniques described above cannot correct camera shake in the tumble direction shown in part (C) of  FIG. 1  although they can correct camera shake in the elevation direction and azimuth direction shown in parts (A) and (B) of  FIG. 1 .  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention has been made in view of the above circumstances and provides a small image pickup apparatus which can reliably prevent camera shake in the tumble direction.  
         [0015]     The present invention provides an image pickup apparatus which generates an image signal to represent subject light based on the subject light coming through an image-taking optical system, having:  
         [0016]     an image pickup device which generates image signals to represent a subject image formed by the subject light focused on a surface thereof;  
         [0017]     a light reflecting mechanism which leads the subject light to the image pickup device as the subject light coming through the image-taking optical system is reflected in sequence by a plurality of reflector sections placed apart from each other;  
         [0018]     a rotation sensor which senses rotation of the image pickup apparatus in a place along a surface of the image pickup device; and  
         [0019]     a rotating mechanism which reduces displacement of the subject image resulting from the rotation sensed by the rotation sensor, by rotating at least one of the plurality of reflector sections around an axis along an optical path among the plurality of reflector sections.  
         [0020]     The image pickup device according to the present invention means a CCD or CMOS sensor containing multiple light-sensitive elements which receive light and generate photoelectric signals.  
         [0021]     With the image pickup apparatus according to the present invention, when the rotation sensor senses rotation in the tumble direction, for example, as shown in part (C) of  FIG. 1 , at least one of the multiple reflector sections is rotated around an axis along an optical path among the multiple reflector sections. Consequently, the subject light is rotated in the opposite direction to the rotation sensed by the rotation sensor and the subject image is formed in the correct direction on the image pickup device. Thus, the image pickup apparatus according to the present invention can reduce blurring of taken images using multiple reflector sections of a conventional image pickup apparatus as they are.  
         [0022]     Preferably, the image pickup apparatus according to the present invention has a correction section which corrects the displacement of the subject image which occurs as the optical path leading from the light reflecting mechanism to the image pickup device is displaced in the direction in which the reflector sections are rotated by the rotating mechanism.  
         [0023]     When the reflector sections are rotated by the rotating mechanism, the subject image is formed in the correct direction on the image pickup device, but the image forming position is displaced in the same direction as the rotation of the reflector sections. The image pickup apparatus according to a preferred embodiment of the present invention corrects the displacement of the subject image due to the rotation, making it possible to obtain a taken image of higher quality.  
         [0024]     The present invention provides a small image pickup apparatus which can reliably prevent camera shake in the tumble direction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a diagram illustrating camera shake;  
         [0026]      FIG. 2  is an external perspective view of a digital camera according to an embodiment of the present invention, as viewed obliquely from the upper front;  
         [0027]      FIG. 3  is a schematic block diagram of the digital camera shown in  FIG. 2 ;  
         [0028]      FIG. 4  is a diagram showing two mirrors;  
         [0029]      FIG. 5  is a diagram showing a state of the lower mirror when it is rotated, from its position in  FIG. 4 , around an optical path of light passing between the two mirrors;  
         [0030]      FIG. 6  is a diagram showing the lower mirror rotated further from its position in  FIG. 5 ; and  
         [0031]      FIG. 7  is a schematic block diagram of components around a CCD in a digital camera according to a second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     Embodiments of the present invention will be described below with reference to the drawings.  
         [0033]      FIG. 2  is an external perspective view of a digital camera according to an embodiment of the present invention. In the following description, a state in which the digital camera  100  is placed horizontally to shoot a horizontally oriented picture as shown in  FIG. 2  is assumed to be a normal state. Also, it is assumed that the top side, bottom side, near side, and far side of  FIG. 2  correspond to the top, bottom, front, and rear of the digital camera  100 , respectively.  
         [0034]     At the center in the front face of the digital camera  100 , there is a taking lens  101 . Also, on an upper front part of the digital camera  100 , there are an optical finder&#39;s objective window  102  and a fill-flash section  103 . Furthermore, on the top face of the digital camera  100 , there are a slide-type power switch  104  and a release switch  150 .  
         [0035]      FIG. 3  is a schematic block diagram of the digital camera  100  shown in  FIG. 2 .  
         [0036]     As shown in  FIG. 3 , the digital camera  100  largely consists of an image-taking optical system  110 , various components which lead subject light passing through the image-taking optical system  110  to a CCD  134 , and a signal processing section  120 . Besides, the digital camera  100  is equipped with an image display section  180  for use to display taken images; an external recording medium  200  for use to record image signals obtained by image taking; a zoom switch  170 , a shooting mode switch  160 , and the release switch  150  for use to make the digital camera  100  perform various processes for shooting; and movement sensors  140  which sense movements of the digital camera  100 .  
         [0037]     First, a configuration of the image-taking optical system  110  will be described with reference to  FIG. 3 .  
         [0038]     Subject light enters the digital camera  100  from the left side of  FIG. 3  through a zoom lens  115  and focus lens  114  and passes through an iris  113  which adjusts quantity of the subject light. When a shutter  112  is open, the subject light has its optical path bent by mirrors  131  and  132 , and then forms an image on the CCD  134  placed behind. Essentially, the image-taking optical system contains multiple lenses, at least one of which plays a major role in focus adjustment while relative positions among the lenses affect focal length. In  FIG. 3 , the lenses concerned with changing the focal length are schematically shown as the zoom lens  115  while the lenses concerned with the focus adjustment are schematically shown as the focus lens  114 .  
         [0039]     The zoom lens  115 , focus lens  114 , iris  113 , and shutter  112  are driven by a zoom motor  115   a , focus motor  114   a , iris motor  113   a , and shutter motor  112   a , respectively. Instructions to operate the zoom motor  115   a , focus motor  114   a , iris motor  113   a , and shutter motor  112   a  are transmitted from a digital signal processing section  120   b  of a signal processing section  120  via a motor driver  120   c.    
         [0040]     The zoom lens  115  is moved along the optical axis (forward/backward direction) by the zoom motor  115   a . As the zoom lens  115  is moved to a position specified by a signal from the signal processing section  120 , the focal length is changed and photographic magnification is determined.  
         [0041]     The focus lens  114  implements a TTLAF (Through The Lens Auto Focus) function. The TTLAF function moves the focus lens along the optical axis, makes an AF/AE computing section  126  of the signal processing section  120  detect contrast of an image signal obtained by the CCD  134 , and moves the focus lens  114  into focus position which corresponds to the lens position that gives a peak contrast. The TTLAF function makes it possible to take a shot by automatically focusing on the subject which gives the peak contrast.  
         [0042]     The iris  113  adjusts the quantity of subject light, being driven based on instructions from a system controller  121  of the digital signal processing section  120   b.    
         [0043]     With the digital camera  100  according to this embodiment, subject light passing through the image-taking optical system  110  is bent by the mirrors  131  and  132  before entering the CCD  134 , and thus the optical path of the subject light is longer than the case where the subject light enters the CCD  134  directly from the image-taking optical system  110 . This reduces amounts of forward/backward movements of the zoom lens  115  and focus lens  114  needed to implement a zoom function and focus function, resulting in reduced thickness of the digital camera  100 .  
         [0044]     The above explains the configuration of the image-taking optical system  110 .  
         [0045]     The CCD  134  and various elements related to it will be described next.  
         [0046]     The subject light passing through the image-taking optical system  110  is reflected by the two mirrors  131  and  132  placed one above the other with a clearance between them, passes through a relay lens  133 , and forms an image on the CCD  134 , which generates image signals representing the subject light. The mirrors  131  and  132  are an example of multiple reflector sections according to the present invention and the CCD  134  is an example of the image pickup device according to the present invention.  
         [0047]     The digital camera  100  is equipped with the movement sensors  140  which sense movements of the digital camera  100 . The movement sensors  140  are composed of an elevation velocity sensor  141  which measures angular velocity in the elevation direction (direction of arrow B in  FIG. 1 ) of the digital camera  100 , azimuth velocity sensor  142  which measures angular velocity in the azimuth direction (direction of arrow A in  FIG. 1 ) of the digital camera  100 , and rotational velocity sensor  143  which measures angular velocity in the tumble direction (direction of arrow C in  FIG. 1 ) of the digital camera  100  around the optical axis. The rotational velocity sensor  143  is an example of the rotation sensor according to the present invention. Measurement results of the elevation velocity sensor  141 , azimuth velocity sensor  142 , and rotational velocity sensor  143  are converted into digital measurement values by an analog processing (A/D) section  120   a  and the digital measurement values are transmitted to an angle computing section  129 . Upon acquiring the measurement values in the azimuth direction, elevation direction, and tumble direction, the angle computing section  129  calculates the amounts of movement of the lower mirror  132  and CCD  134  based on the measurement values in order to correct the displacement of the subject image on the CCD  134  due to movements of the digital camera  100 . The movements of the lower mirror  132  and CCD  134  will be described in detail later. The calculated amounts of movement are transmitted to the motor driver  120   c  via the system controller  121  and then the motor driver  120   c  transmits operation commands to a mirror motor  132   a  and CCD motor  134   a . Upon receiving the operation commands from the motor driver  120   c , the mirror motor  132   a  moves the lower mirror  132  according to results of sensing by the movement sensors  140 . The CCD motor  134   a  moves the CCD  134  according to results of sensing by the movement sensors  140 . The mirror motor  132   a  is an example of the rotating mechanism according to the present invention and the CCD motor  134   a  is an example of the correction section according to the present invention.  
         [0048]     Next, a configuration of the signal processing section  120  will be described. The subject image formed on the CCD  134  in the image-taking optical system  110  is read out as image signals by the analog processing (A/D) section  120   a , which converts the analog signals into digital signals, which are then supplied to the digital signal processing section  120   b . The digital signal processing section  120   b  is equipped with the system controller  121 . Signal processing in the digital signal processing section  120   b  is performed according to a program which describes operating procedures in the system controller  121 . The system controller  121  exchanges data with an image signal processing section  122 , image display control section  123 , image compression section  124 , media controller  125 , AF/AE computing section  126 , key controller  127 , buffer memory  128 , and angle computing section  129  via a bus  1200 . When data is exchanged via the bus  1200 , an internal memory  1201  serves as a buffer. Data which serve as variables are written as needed into the internal memory  1201  according to progress of processes in various parts, and the system controller  121 , image signal processing section  122 , image display control section  123 , image compression section  124 , media controller  125 , AF/AE computing section  126 , key controller  127 , and angle computing section  129  perform appropriate processes based on these data. That is, instructions from the system controller  121  are transmitted to the various parts via the bus  1200  to start up the processes in the various parts. The data in the internal memory  1201  are updated according to the progress of the processes and referred to by the system controller  121  to control the various parts. In other words, upon power-up, the processes in the various parts are started according to the procedures of the program in the system controller  121 . For example, if the release switch  150 , zoom switch  170 , or shooting mode switch  160  is manipulated, information about the manipulation is transmitted to the system controller  121  via the key controller  127  and a process corresponding to the manipulation is performed according to the procedures of the program in the system controller  121 .  
         [0049]     When the shutter is released, the image data read out of the CCD  134  are converted from analog signals into digital signals by the analog processing (A/D) section  120   a  and the digitized image data are stored temporarily in the buffer memory  128  of the digital signal processing section  120   b . RGB signals of the digitized image data are converted by the image signal processing section  122  into YC signals, which are then compressed into an image file in JPEG format by the image compression section  124 . The resulting image file is recorded on the external recording medium  200  via the media controller  125 . The image data recorded in the image file are played back in the image display section  180  via the image display control section  123 . During this process, the AF/AE computing section  126  detects contrast in the RGB signals according to subject distance to adjust focus. Based on the detection results, focus is adjusted by the focus lens  114 . The AF/AE computing section extracts luminance signals from the RGB signals and detects field luminance from the luminance signal. Based on the detected field luminance, the iris  113  adjusts exposure so that an appropriate quantity of subject light will fall on the CCD  134 .  
         [0050]     The digital camera  100  is basically configured as described above.  
         [0051]     Movements of the mirror  132  and CCD  134  will be described in detail below.  
         [0052]     First, description will be given of a relationship between the rotation of the mirror  132  and subject image formed on the CCD  134 .  
         [0053]      FIG. 4  shows the two mirrors  131  and  132  also shown in  FIG. 3 .  
         [0054]     Part (A) of  FIG. 4  is a top view of the mirrors  131  and  132  shown in  FIG. 3 . Here, the two mirrors  131  and  132  completely overlap vertically.  
         [0055]     Part (B) of  FIG. 4  is a side view of the mirrors  131  and  132 . The two mirrors  131  and  132  are arranged in parallel. Subject light reflected by the mirrors  131  and  132  forms a subject image which points in the same direction as the incident subject light.  
         [0056]      FIG. 5  is a diagram showing a state of the lower mirror  132  when it is rotated, from its position in  FIG. 4 , around the optical path of light passing between the two mirrors  131  and  132 .  
         [0057]     As shown in part (A) of  FIG. 5 , the two mirrors  131  and  132  are displaced with respect to each other as the lower mirror  132  is rotated in the direction of arrow D. When the two mirrors  131  and  132  are arranged in parallel, light L 0  incident on the upper mirror  131  from the front is led to the rear by the lower mirror  132 . On the other hand, when the mirrors  131  and  132  are displaced with respect to each other, the light L 0  incident on the upper mirror  131  is led by the lower mirror  132  to a location displaced from the rear in the direction of arrow D, i.e., in the direction of rotation.  
         [0058]     Also, as shown in part (B) of  FIG. 5 , the subject image formed with the arrangement of the mirrors  131  and  132  shown in  FIG. 4 , is tilted in the counterclockwise direction as viewed from the incident side of the subject light.  
         [0059]      FIG. 6  is a diagram showing the lower mirror  132  rotated further from its position in  FIG. 5 .  
         [0060]     As shown in part (A) of  FIG. 6 , when the lower mirror  132  is rotated further for a total of 180 degrees from its position in  FIG. 4 , the two mirrors  131  and  132  completely overlap vertically again. At this time, as shown in part (B) of  FIG. 6 , the subject light reflected by the two mirrors  131  and  132  is formed on the same side as the subject light, 180 degrees opposite to the side shown in part (B) of  FIG. 4 . With the arrangement of the mirrors  131  and  132  shown in  FIG. 6 , the subject light forms an image rotated 180 degrees.  
         [0061]     In this way, when the lower mirror  132  is rotated, in the direction of arrow D, around the optical path of the light passing between the two mirrors  131  and  132 , the optical path of the subject light rotates in the same direction as the rotation of the mirror  132  and the subject image rotates in the counterclockwise direction as viewed from the incident side of the subject light. Incidentally, in this example, the optical path of the subject light moves in the azimuth direction as the mirror  132  is rotated. The digital camera  100  according to this embodiment prevents camera shake in the tumble direction (direction of arrow C in  FIG. 1 ) of the digital camera  100  using this feature of the mirrors  131  and  132 . A method for preventing camera shake of the digital camera  100  will be described below.  
         [0062]     As the photographer presses the release button  104  (shown in  FIG. 2 ) with the digital camera  100  directed at the subject; the elevation velocity sensor  141  (shown in  FIG. 3 ) measures the angular velocity in the elevation direction of the digital camera  100 , azimuth velocity sensor  142  measures the angular velocity in the azimuth direction of the digital camera  100 , and rotational velocity sensor  143  measures the angular velocity in the tumble direction of the digital camera  100 . The measurement values are converted into digital values by the analog processing section  120   a  and transmitted to the angle computing section  129 .  
         [0063]     The angle computing section  129  calculates the amount of vertical movement of the image in the up-and-down direction of the digital camera  100  based on the angular velocity in the elevation direction, the amount of lateral movement of the image in the right-and-left direction of the digital camera  100  based on the angular velocity in the azimuth direction, and the angle of tumble movement of the image in the tumble direction of the digital camera  100  based on the angular velocity in the tumble direction (direction of arrow C in  FIG. 1 ).  
         [0064]     Also, the angle computing section  129  calculates the amount of displacement of the subject image caused by changes in the optical path of the subject light as the lower mirror  132  is rotated around the optical axis of light passing between the two mirrors  131  and  132 . In this example, since the optical path of the subject light moves in the azimuth direction as the mirror  132  is rotated, the calculated amount of displacement is added to the amount of lateral movement in the right-and-left direction of the digital camera  100  to calculate a new corrected amount of lateral movement. The calculated values (the amount of vertical movement in the up-and-down direction, corrected amount of lateral movement in the right-and-left direction, and angle of tumble movement in the tumble direction) are transmitted to the motor driver  120   c  via the system controller  121 .  
         [0065]     Based on the values transmitted from the angle computing section  129 , the motor driver  120   c  drives the mirror motor  132   a  and CCD motor  134   a . Consequently, the lower mirror  132  is rotated by the angle of the tumble movement around the optical axis of the light passing between the two mirrors  131  and  132  while the CCD  134  is moved by the corrected amount of movement in the right-and-left direction and by the amount of vertical movement in the up-and-down direction.  
         [0066]     After the mirror  132  and CCD  134  are moved, the subject image formed on the CCD  134  is read out as image signals by the analog processing section  120   a  to start an exposure process. At this time, the subject light passing through the image-taking optical system  110  is received at the correct position, reducing displacement of the subject image formed on the CCD  134 . Thus, the digital camera  100  according to this embodiment makes it possible to obtain a taken image of higher quality with reduced image blur even if the digital camera  100  moves during shooting.  
         [0067]     This concludes description of the first embodiment of the present invention and a second embodiment of the present invention will be described next. The second embodiment has almost the same configuration as the first embodiment except for the components which leads the subject light passing through the image-taking optical system  110  to the CCD  134 . Thus, components in common with the first embodiment will be denoted by the same reference numerals as the corresponding components of the first embodiment, omitting description thereof, and only the differences from the first embodiment will be described below.  
         [0068]      FIG. 7  is a schematic block diagram of components around a CCD in a digital camera according to the second embodiment of the present invention.  
         [0069]     Unlike the digital camera  100  according to the first embodiment, the digital camera according to the second embodiment has an image-taking optical system motor  110   a  which moves the image-taking optical system  110  in the up-and-down direction and right-and-left direction as well as a relay lens motor  133   a  which moves the relay lens  133  in the up-and-down direction and right-and-left direction. Also, instead of the two mirrors  131  and  132  and mirror motor  132   a  mounted on the digital camera  100  according to the first embodiment, this embodiment has two prisms  301  and  302  placed one above the other with a clearance between them as well as a prism motor  302   a  which rotates the lower prism  302  around the optical axis of the light passing between the two prisms  301  and  302 .  
         [0070]     As in the case of the first embodiment, with the digital camera according to this embodiment, the amount of vertical movement in the up-and-down direction, corrected amount of movement in the right-and-left direction, and angle of tumble movement in the tumble direction are calculated by the angle computing section  129  and the calculated values are transmitted to the motor driver  120   c  via the system controller  121 .  
         [0071]     Based on the values transmitted from the angle computing section  129 , the motor driver  120   c  drives the image-taking optical system motor  110   a , relay lens motor  133   a , and prism motor  302   a . Consequently, the image-taking optical system  110  and relay lens  133  are moved by the corrected amount in the right-and-left direction and by the amount of vertical movement in the up-and-down direction while the lower prism  302  is rotated by the angle of tumble movement around the optical axis of the light passing between the two prisms  301  and  302 .  
         [0072]     In this way, camera shake can also be prevented by using prisms instead of mirrors and moving the image-taking optical system and relay lens instead of the CCD.  
         [0073]     Although an example of the velocity sensor which senses the angular velocity in the tumble direction has been described above, the rotation sensor according to the present invention may be an angle sensor which detects the angle of movement in the tumble direction.  
         [0074]     Also, a rotating mechanism which moves the lower one of two reflector sections placed one above the other has been described above as an example of the rotating mechanism according to the present invention. However, the rotating mechanism according to the present invention may move all or the top one of multiple reflector sections.  
         [0075]     Also, although a correction section which corrects displacement of a subject image by moving the CCD has been described above as an example of the correction section according to the present invention, the correction section according to the present invention may correct displacement of a subject image by image processing.