1. Field of the Invention
The present invention relates to an image pickup device such as a digital still camera, a digital video camera, or the like which obtains image data corresponding to a photographed image, and in particular, relates to a camera shaking correcting method of an image pickup device equipped with an optical-type camera shaking correcting function, and to a camera shaking correcting device and an image pickup device.
2. Description of the Related Art
Of course among digital video cameras, digital still cameras, and the like, and among silver salt photographic cameras and the like as well, there are cameras equipped with a camera shaking correcting function which corrects blurring of a photographed image due to so-called camera shaking. The provision of a camera shaking correcting function is becoming standard in higher-end cameras.
Camera shaking correcting functions include electronic-type blurring correction in which, in accordance with shaking which is detected by using the correlation with an image, the data reading position from an image pickup element such as a CCD or from image data expanded in a memory is controlled, so that blurring caused by camera shaking does not arise in the photographed image. In addition, there is optical-type blurring correction in which, by using a sensor (e.g., a gyro sensor) detecting the acceleration, angular acceleration, angular velocity or the like of the device main body, the center of the lens is shifted along a direction orthogonal to the optical axis on the basis of an output signal from the sensor, and by correcting the offset of the optical axis by changing the inclination of the incident light within the lens, the effects of shaking which appear on the image pickup element due to camera shaking are compensated (offset).
An optical-type camera shaking correcting mechanism uses a gyro sensor which works semi-independently of a signal processing system, and from output of the gyro sensor which is sampled at an arbitrary period, computes an amount of movement of the image caused by blurring, determines a shift amount of the lens, and controls an actuator so as to thereby shift the optical axis.
At this time, shaking which arises due to rotation of the overall device is detected as a time-series change in the rotational velocity at a predetermined sampling interval by an angle sensor. Because this time-series information is the rotational velocity at each sampling time, correction angle information is obtained by carrying out integration processing using the sampling period as the time unit, by cumulative integration (successive addition).
Further, by sending this integrated value to a driving circuit as information specifying the lens position, the driving circuit moves a predetermined lens on the basis of this integrated value. In this way, shaking of the image of the subject of photographing, which is imaged on the image pickup element, i.e., the generation of changes in the imaging position, is suppressed (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 63-8628 and 8-101418).
Because optical-type blurring correction compensates changes in the image angle of the device main body by optical axis rotation, if there is a time delay (time lag) from the detection of the shaking of the main body to the lens control, shaking amount corresponding to that delay time will appear as blurring of the image which is imaged at the image pickup element, and the quality of the photographed image will deteriorate.
Because it is difficult to eliminate the delay time, there have been proposals to make the effects of a delay time substantially not be manifested, by carrying out correction processing using optimal parameters corresponding to the shaking, by judging the shaking frequency and switching parameters which are set for each shaking frequency (see, for example, JP-A No. 6-98246).
Further, there have also been proposals to make blurring not arise in a photographed image by judging a shaking waveform from time-series information, estimating a shaking amount at a prescribed time in the future, and carrying out shaking correction on the basis of the results of estimation (see, for example, JP-A Nos. 5-204013 and 5-204014).
However, in these methods, there is the need to analyze the shaking frequency components, or carry out computation processing by the method of least squares or the like such that the time-series data of the camera shaking vibrations approximates a high-order regression curve line, and judge the main frequency of the shaking. To this end, complicated computation processing utilizing a large amount of data is necessary, and a system having a high computational capacity must be used or a long computing time is required.
This therefore leads to an increase in the size of and an increase in the cost of the pickup device, and substantial elimination of blurring is difficult.
On the other hand, an angular velocity sensor which is used in detecting shaking utilizes a method of sensing the torsional force of the vibrating object. Therefore, the detection sensitivity is low. Accordingly, when the torsional force is extracted as time-series information of the rotational velocity, it must be amplified. Thus, it is easy for fluctuations in output to arise due to affects such as noise or drift of the DC or the like due to the temperature characteristic or the like, and as a result, it is easy for the shaking correcting device to function erroneously.
A general output circuit 202 using angular velocity sensors 200A, 200B is shown in FIG. 19A. An HPF (High-Pass Filter) 206 using a large-capacity capacitor 204 is structured in this output circuit 202. By the HPF 206, the DC components of the angular velocity sensors 200A, 200B are cut-off, and a predetermined bias voltage is applied at an amplifying circuit 208. In this way, signals (a PITCH signal and a YAW signal), in which the occurrence of errors due to drift and the DC component are suppressed, are outputted.
On the other hand, low frequency components of around 1 Hz also are included in the frequency components of the shaking. Therefore, if the DC component removal by the HPF 206 is made to be great, the low frequency camera shaking components are damped, and a sufficient camera shaking correcting effect cannot be obtained.
In order to prevent this, the time constant at the HPF 206 must be made to be long (e.g., greater than or equal to 10 sec), but, by doing this, the effect of reducing the drift deteriorates. Namely, it is difficult to simultaneously achieve both drift reduction and precise shaking detection of low frequencies at the output circuit of the angular velocity sensor.
As a method of overcoming this problem, drift reduction is aimed for as follows: a reference value which follows fluctuations in input is determined by using a cyclic filter of a long period on the numerical data obtained by A/D converting and sampling the sensor output (the output of the output circuit) with the time constant of the HPF being made to be 10 sec or more, and this reference value is subtracted from the input signal.
FIG. 19B shows the schematic structure of a general cyclic filter 210. In this cyclic filter 210, given that a transfer coefficient of a register 212 is n, an input signal is Sin, and an output signal (reference value) is Sout, the reference value Sout is:Sout=Sin×(1−n)+Sout×n and the drift component is extracted as a difference between the reference value Sout and the input signal Sin.
However, drift following which uses such a cyclic filter has a high band pass limiting (LPF) characteristic with respect to the input signal. Therefore, with respect to high-frequency shaking, the correction value is damped. Further, a detection signal in which the high-frequency components are damped has an HPF characteristic in which the higher the frequency, the greater the amplitude, which is opposite of the reference value which is the output of the cyclic filter.
In this way, the level of the correction value obtained by integrating the detection value differs in accordance with the frequency, and the problem arises that an optimal correction level can be obtained only with respect to vibrations of specific frequencies.