Abstract:
The present invention provides an image pick up apparatus having means for cumulatively adding image signals and storing the image signals in memory, which is capable of preventing cumulative addition of image signals for which camera-shake correction is insufficient and improving picture quality of image signals stored in memory.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an image pickup apparatus and method, and more particularly, an image pickup apparatus and method for preventing cumulative addition of image signals for which camera-shake correction is insufficient, and for improving picture quality of image signals stored in memory. 
   2. Description of the Related Art 
   Various forms of camera-shake prevention technologies for preventing blurring of images resulting from vibration due to movement of a camera operator and preventing degrading (blurring, dislocating) of recording images have been proposed for image pickup apparatus such as digital still cameras and video cameras capable of taking and recording images in the related art. 
   For example, an image pickup apparatus that detects an amount of dislocation in the event of taking a picture from an image (still image) captured over a prescribed period or prescribed number of times and then records images (still images) for which the dislocation amount is the smallest has been proposed, and described in, for example, Japanese Patent Application Publication No. Hei. 11-317904 (at page 11-12, FIG. 1, FIG. 26). 
   However, as shown in  FIG. 7A , it is preferable for image pickup apparatus that cumulatively add picked up image signals for storage in memory to ensure a sufficient maximum value (herein after referred as maximum correction amount) for the correction amount in order to correct camera-shake completely so as to enable cumulative addition. However, in reality, as shown in  FIG. 7B , cumulative addition only achieves camera-shake correction up to the maximum correction value for image signals which exceed the maximum correction amount, and blurred and overlapping (dislocated) images are therefore stored in memory. 
   Further, as the recording size of image signal (hereafter referred to as recording image size) is set in advance, when recording image size is set to be large against the range for which pictures can be taken by the image pickup element (hereafter referred to as possible image size), the range in which camera-shake correction is possible (hereafter referred to as correction range) becomes small, and the ends of the correction range are reached even for comparatively small camera-shake vibrations. 
   As an image signal corrected at the ends (hereinafter, correction ends) of the correction range is an image signal corresponding to the straight line parts of  FIG. 7B , so the camera-shake correction processing is insufficient, when an image signal corrected at the correction ends in this manner is cumulatively added, images in a blurred or overlapping (dislocated) state are stored in memory. 
   Therefore, there is the problem to be resolved for image pickup apparatus having means for cumulatively adding image signals and storing the image signals in memory, with respect to preventing cumulative addition of image signals for which camera-shake correction is insufficient, and improving picture quality of image signals stored in memory. 
   SUMMARY OF THE INVENTION 
   In order to resolve the aforementioned problems, the image pickup apparatus of the present invention is configured in the following manner. 
   (1) An image pickup apparatus having means for cumulatively adding image signals picked up by an image pickup section for storage in memory, characterized by: camera-shake detection means for detecting an amount of vibration due to hand-shaking of the image pickup section and outputting a camera-shake signal according to the detected camera-shake vibration amount, camera-shake correction means for correcting the image signal photographed by the image pickup section based on a camera-shake correction amount calculated according to the camera-shake signal outputted by the camera-shake detection means, recording image size setting means for setting recording image size in the event of recording the image signal, maximum correction amount calculating means for calculating a maximum value for a camera-shake correction amount for correcting camera-shake of the image signal based on recording image size set using the recording image size setting means and a possible image size constituting a range for which imaging is possible at the image pickup element of the image pickup section, image discrimination means for comparing the camera-shake correction amount calculated by the camera-shake correction means and the maximum value for the camera-shake correction amount calculated by the maximum value correction amount calculating means and performing discrimination processing on an image signal cumulatively added to the memory, and cumulative addition control means for controlling cumulative addition processing of the image signal corrected by the camera-shake correction means in accordance with the image discrimination means. 
   (2) An image pickup apparatus having means for cumulatively adding image signals picked up by an image pickup section for storage in memory, characterized by: camera-shake detection means for detecting an amount of vibration due to hand-shaking of the image pickup section and outputting a camera-shake signal according to the detected camera-shake vibration amount, camera-shake correction means for correcting the image signal picked up by the image pickup section based on a camera-shake correction amount calculated according to the camera-shake signal outputted by the camera-shake detection means, recording image size setting means for setting recording image size in the event of recording the image signal, maximum correction amount calculating means for calculating a maximum value for a camera-shake correction amount for correcting camera-shake of the image signal based on recording image size set using the recording image size setting means and a possible image size constituting a range for which imaging is possible at the image pickup element of the image pickup section, image discrimination means for comparing the camera-shake correction amount calculated by the camera-shake correction means and the maximum value for the camera-shake correction amount calculated by the maximum value correction amount calculating means and performing discrimination processing on an image signal cumulatively added to the memory, cumulative addition control means for controlling cumulative addition processing of the image signal corrected by the camera-shake correction means in accordance with the image discrimination means, and image output means for multiplying a coefficient value calculated according to the number of times of cumulative addition processing by the cumulative addition control means and an image signal cumulatively added and then stored and outputted. 
   With an image pickup apparatus of this configuration, a maximum value for a camera-shake correction amount calculated based on recording image size set by the recording image size setting means and actual image size constituting a range where imaging is possible of the image pickup element of the image pickup section and a camera-shake correction amount calculated by the camera-shake correction means are compared, and cumulative addition processing of the image signal corrected by the camera-shake correction means is controlled. It is therefore possible to only cumulatively add and store to memory image signals appropriately corrected within the range where camera-shake correction is possible. 
   EFFECTS OF THE INVENTION  
   By comparing a maximum value (hereinafter, maximum correction value) for a camera-shake correction amount calculated based on the predetermined recording image size and possible image size constituted by the range of the image pickup element of the image pickup section for which imaging is possible and a camera-shake correction amount calculated based on camera-shake vibration amount of the image pickup section and then cumulatively adding and storing in memory only image signals corrected using camera-shake correction amounts smaller than the maximum correction amount, image signals for which correction processing is insufficient (those reaching the correction ends, image signals correction-processed using the maximum correction amounts) are not subjected to cumulative addition, and only image signals that have been appropriately corrected are cumulatively added. This means that superior results can be obtained where the picture quality (S/N ratio) of image signals stored in memory is improved. 
   Further, the maximum correction amount is calculated based on the predetermined recording image size. Therefore, even when with respect to the possible image size the recording image size is large, i.e. the camera-shake correction range is small, since only appropriately corrected image signals are cumulatively added, superior results that the picture quality (S/N ratio) of the image signals stored in memory is improved, can be obtained. 
   Moreover, the aforementioned image signal stored in memory is multiplied by a coefficient value corresponding to the number of times of cumulative addition and outputted. It is therefore possible to record image signals (still images) of superior picture quality (S/N ratio) to recording media and recording devices. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block view showing a simplified configuration for the essential parts of the image device of the present invention. 
       FIG. 2  is a block view showing a simplified internal configuration for the cumulative addition circuit shown in  FIG. 1 . 
       FIG. 3  is a view illustrating a method for calculating a maximum value (maximum correction amount) for a camera-shake correction amount. 
       FIG. 4  is an view illustrating operation of the camera-shake detector shown in  FIG. 1 . 
       FIG. 5  is a flowchart of the operation of the image pickup apparatus shown in  FIG. 1 . 
       FIG. 6  is a view illustrating the relationship between a correction amount for an image signal and a cumulatively added image signal for the image pickup apparatus shown in  FIG. 1 . 
       FIG. 7A and 7B  are views illustrating the relationship between a correction amount for an image signal and a cumulatively added image signal for the image pickup apparatus of the related art. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The following is a description with reference to the drawings of a preferred embodiment of an image pickup apparatus of the present invention. However, the drawings are provided for the purpose of description, and in no way limit the technological scope of the present invention. 
   Embodiments  
     FIG. 1  is a block view showing a simplified configuration of the essential parts of an image pickup apparatus of the present invention, comprised of an image pickup section  110 , correction circuit  120 , cumulative addition circuit  130 , multiplier  140 , recording section  150 , microcomputer  160 , camera-shake detector  170 , and UI (user interface)  180 , etc. 
   The image pickup section  110  is equipped with an image pickup element such as a lens and CCD (Charge Coupled Device) etc. and a signal processing circuit etc., and converts light from a subject inputted via the lens to an image signal using an image pickup element. This image signal is then subjected to prescribed signal processing at a signal processing circuit and is then sent to the correction circuit  120 . 
   The correction circuit  120  corrects image signals transmitted from the image pickup section  110  based on correction vector data specified by the microcomputer  160  and transmits these image signals to the cumulative addition circuit  130 . 
   As shown in  FIG. 2 , the cumulative addition circuit  130  is comprised of an adder  131 , memory  132 , and switch  133 . Image signals sent from the correction circuit  120  are then cumulatively added in the time axis direction and stored in the memory  132  every time a capture is performed under the control of the microcomputer  160 . 
   The adder  131  of the cumulative addition circuit  130  adds and outputs the image signal outputted from the correction circuit  120  and the image signal stored in the memory  132 . When the switch  133 is on, the memory  132  stores image signals outputted from the adder  131  and sends image signals to the adder  131  when image signals are inputted from the correction circuit  120 . Further, the switch  133  is turned on and off according to the camera-shake signal of the camera-shake detector  170  in accordance with the control of the microcomputer  160 , and the output (image signal) of the adder  131  is sent to the memory  132  when the switch  133  is on. 
   The multiplier  140  subjects image signals outputted from the cumulative addition circuit  130  to multiplication processing under the control of the microcomputer  160  based on coefficient values specified by the microcomputer  160  and outputs the image signals to the recording section  150 . 
   The recording section  150  records image signals outputted from the multiplier  140  under the control of the microcomputer  160 . For example, image signals are recorded on a recording medium such as a hard disc device, memory card, magnetic tape, or optical disc etc. 
   The microcomputer  160  controls each section within the image pickup apparatus and each circuit based on pre-stored programs and data etc. 
   For example, camera-shake correction amounts and correction vector data for correcting camera-shake are calculated based on a camera-shake signal detected by the camera-shake detector  170  and are sent to the correction circuit  120 . 
   Further, a maximum value for the camera-shake correction amount (hereinafter, maximum correction amount) is calculated based on the size of the range for which photographing is possible using the image pickup element of the image pickup section  110  and the recording image size set by the UI section  180 , and the cumulative addition circuit  130  is controlled based on the calculated maximum correction amount and the camera-shake correction amount. 
   Further, calculation of coefficient values for the multiplier  140  and transmission of these coefficient values to the multiplier  140 , control of timing in the event of recording image signals to the recording section  150 , etc. are carried out. 
   The camera-shake detector  170  detects the amount of vibration due to camera-shake of the image pickup section  110  and sends the detected vibration amount to the microcomputer  160  as a camera-shake signal. Detection of the camera-shake signal is carried out by utilizing a gyro sensor and image recognition technology etc., a value that is the integral of the amount of vibration due to the camera-shake, being detected as a camera-shake signal and sent to the microcomputer  160  every time an image signal is captured. 
   For example, with the integrator expressing the complete integral shown in  FIG. 3 , in the case of taking input signal X(z) and output signal Y(z), the camera-shake signal can be expressed by the following equation.
 
 Y ( z )=1/((1 −z   −1 )/ X ( z ))
 
   The UI (user interface) section  180  transmits control signals so that prescribed setting/operations are executed at the microcomputer  160  according to user operations. 
   A description is now given with reference to  FIG. 4  of a method of calculating a maximum correction amount. 
     FIG. 4  shows the relationship between a possible image area (possible image size) showing the range in which photographing is possible using the image pickup element of the image pickup section  110  and an actual image area (recording image size) showing image size in the event of recording to the recording section  150 . 
   When the length of the possible image area is taken to be bh in the vertical direction and bw in the horizontal direction, and the length of the actual image area is taken to be ah in the vertical direction and aw in the horizontal direction, for example, in a state where camera-shake correction is not carried out, the actual image area is positioned at the center of the possible image area. The maximum correction amount in this state can then be calculated using the following equation. 
   Correction amount in vertical direction:
 
 Sw =( bh−ah )/2
 
Correction amount in horizontal direction:
 
 Sw =( bw−aw )/2 where  bh≧ah, bw≧aw. 
 
   A description is given of the operation flow occurring at the image pickup apparatus of this configuration with reference to the flowchart of  FIG. 5 . 
   When imaging commences, first, the microcomputer  160  determines whether or not the value of a capture counter (hereinafter referred to as CC) counting the number of image signals captured (hereinafter referred to as capture number) is “0” (ST 110 ). 
   When CC is “0”, the microcomputer  160  clears the correction amount for the correction circuit  120  to “0” (ST 111 ). 
   Switch  133  of the cumulative addition circuit  130  is then turned on, and image signals taken by the image pickup section  110  are captured, cumulatively added, and stored in the memory  132  (ST 112 , ST 113 ). 
   As a result, the first image signal taken as a reference is stored in memory  132  of the cumulative addition circuit  130 . This is to say that the correction amount for the image signal is first cleared to “0”, and the maximum correction amount is not exceeded, so that an image signal is prevented from not being captured at all in cases where for image signals captured thereafter the camera-shake correction amount exceeds the maximum correction amount. 
   The microcomputer  160  then increases the value of CC by 1 and increases the value of the time counter (hereinafter referred to as TC) by 1, so that processing is complete (ST 114 ,ST 115 →END) 
   On the other hand, when CC is not “0”, then a captured signal is being cumulatively added at the cumulative addition circuit  130 , and the microcomputer  160  then determines whether or not the value of CC is greater than or equal to the maximum value (hereinafter referred to as CCmax) of the capture number set in advance (ST 110 →ST 120 ). 
   When the value of CC is greater than or equal to the maximum value CCmax (CC≧CCmax), processing for recording the image signal to the recording section  150  is advanced to (ST 120 →ST 130 → . . . ). 
   On the other hand, in the event that the value of CC is smaller than the maximum value CCmax (CC&lt;CCmax), the microcomputer  160  determines whether or not the value of TC is greater than or equal to a prescribed set time (hereinafter referred to as TCmax) (ST 120 →ST 121 ). 
   When the value of TC is greater than or equal to the set time TCmax (TC≧TCmax), processing for recording the image signal to the recording section  150  is advanced to (ST 121 →ST 130 → . . . ). 
   On the other hand, in the event that the value of TC is smaller than the set time TCmax (TC&lt;TCmax), the microcomputer  160  calculates the camera-shake correction amount based on the camera-shake signal from the camera-shake detector  170  and calculates correction vector data for transmission to the correction circuit  120  based on this camera-shake correction amount. At the correction circuit  120 , the image signal sent from the image pickup section  110  is corrected based on the correction vector data (ST 121 →ST 122 ). 
   Continuing on, the microcomputer  160  compares the absolute value of the calculated camera-shake correction amount and the maximum correction amount calculated based on the image pickup element size and the recording image size set by the UI section  180  (ST 122 →ST 123 ) 
   When the absolute value of the camera-shake correction amount is less than the maximum correction amount, the switch  133  of the cumulative addition circuit  130  is turned on, and the image signal from the correction circuit  120  is cumulatively added and stored in the memory  132  (ST 123 →ST 112 , ST 113 ) 
   Next, the microcomputer  160  increases the value of CC by 1 and increases the value of the time counter (hereinafter referred to as TC) by 1, so that processing is complete (ST 114 , ST 115 →END) 
   On the other hand, when the absolute value of the camera-shake correction amount exceeds the maximum correction value, the value of TC is increased by 1 and processing ends (ST 123 →ST 115 →END). 
   Further, in step S 120  above, in the event that the value of CC is greater than or equal to CCmax (CC≧CCmax), or in step S 121  above, in the event that the value of TC is greater than or equal to TCmax (TC≧TCmax), processing commences to record the image signal stored in the cumulative addition circuit  130  to the recording section  150 . 
   First, the microcomputer  160  provides the reciprocal of the value of CC to the multiplier  140  as a prescribed coefficient (ST 120 →ST 130 , or ST 121 →ST 130 ) 
   Next, the multiplier  140  multiplies the prescribed coefficient provided by the microcomputer  160  and the image signal cumulatively added at the cumulative addition circuit  130  and outputs this to the recording section  150 , and the recording section  150  records the image signal outputted from the multiplier  140  on a prescribed recording medium (recording device) (ST 131 ). 
   When the image signal is recorded in the recording section  150 , the microcomputer  160  clears the value of CC, clears the value of TC, and ends processing (ST 132 →ST 133 →END). 
     FIG. 6  is a graph showing an outline of the relationship camera-shake correction amount calculated based on a camera-shake signal and a cumulatively added image signal for an image pickup apparatus operating according to the operation flow of  FIG. 5  above. 
   In the graph of  FIG. 6 , the image signal corrected by a camera-shake correction amount of less than the maximum correction amount corresponds to a solid line, and the image signal corrected by a correction amount greater than or equal to the maximum correction amount corresponds to a dotted line. Image signals corrected at the correction ends, i.e. image signals corrected using a correction amount greater than or equal to the maximum correction amount (the image signal corresponding to the straight line section of  FIG. 7B ) are not subjected to cumulative addition, and only images signals corrected by less than the maximum correction amount are subjected to cumulative addition and stored in memory.