Television – Camera – system and detail – Camera image stabilization
Reexamination Certificate
1996-08-01
2002-05-14
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Camera image stabilization
C348S352000
Reexamination Certificate
active
06388705
ABSTRACT:
BACKGROUND OF THE INVENTION
Present invention relates to an apparatus for preventing undesired effects to an image due to vibrations of an image sensing apparatus.
Development has been made conventionally in a video camera for automated-functioning and multiple-functioning in various ways, such as AE (auto exposure), AF (auto focus) and the like, so that it is possible to sense images in good quality without difficulty.
Along with the recent miniaturization of a video camera and high-magnification of an optical system, vibrations of a camera have become the major cause in deteriorating quality of a sensed image. In view of this problem, various image sensing apparatuses having a vibration cancellation feature for canceling vibrations of a camera have been suggested.
FIG. 1
shows an example of a main structure of a conventional image sensing apparatus featured with vibration cancellation function.
In
FIG. 1
, an angular velocity detector
1
is incorporated in the image sensing apparatus, for example, has an angular velocity sensor such as a vibration gyro. A DC cutting-off filter
2
cuts off a direct-current component of the angular velocity signal outputted by the angular velocity detector
1
and passes the alternating component only. Note that the DC cutting-off filter
2
may be substituted with a high-pass filter (hereinafter referred to as HPF) which cuts off signal frequency component lower than a predetermined frequency. An amplifier
3
amplifies the angular velocity signal outputted by the DC cutting-off filter
2
to an appropriate level (a level in which necessary detection sensitivity can be obtained). An A/D converter
4
converts the angular velocity signal outputted by the amplifier
3
into a digital signal. A high-pass filter (HPF)
5
cuts off the low frequency component of the output of the A/D converter
4
. Note that the HPF
5
can alter the cut-off characteristic in arbitrary frequency regions. An integrator
6
integrates the output signal (angular velocity signal AV) of the HPF
5
and outputs a signal indicating an angle displacement amount AD. The integrator
6
also includes a function which can alter the characteristic in arbitrary frequency ranges.
A decision circuit
7
decides whether or not the image sensing apparatus is intentionally panned or tilted by a user, in accordance with the angular velocity signal AV detected by the high-pass filter (HPF)
5
and an integrated signal (indicative of angle displacement amount) of the angular velocity signal outputted by the integrator
6
, that is, the angle displacement amount signal AD. “Panning and tilting control” (i.e. suppression control of vibration cancellation which will be described later) is performed in accordance with a decision made by the decision circuit
7
.
A D/A converter
8
converts the angle displacement amount signal AD outputted by the integrator
6
into an analog signal to apply to a driving circuit
9
.
The A/D converter
4
, HPF
5
, integrator
6
, decision circuit
7
, D/A converter
8
are constituted by, for instance, a microcomputer (hereinafter referred to as “COM”) which is not shown in the figure.
The driving circuit
9
suppresses vibrations by driving a unit
10
for optically canceling image vibrations which will be described later, based upon the angle displacement amount signal AD outputted from the COM. The cancellation unit
10
drives an optical system (not shown), in other words, optically alters an optical axis of the system, to cancel the vibrations of the image sensing apparatus. A VAP (variable angle prism) is used as the vibration cancellation unit
10
.
FIG. 2
shows a structure of the VAP which is conventionally utilized.
In
FIG. 2
, the VAP is configured with two pieces of glass plates
21
and
22
, bellows
23
and
24
which connect the two pieces of glass plates
21
and
22
, and liquid
25
having a high refractive index which fills the area enclosed with the two pieces of glass plates
21
and
22
and the bellows
23
and
24
. The glass plates
21
and
22
comprise rotation axles
26
and
27
respectively.
An incident light flux
28
when the glass plate
21
is rotated by &dgr; upon the rotation axle
26
, deflects by &phgr; because of the principle similar to that of a wedge prism. Similarly, the other glass plate
22
rotates upon the rotation axle
27
and the incident light flux
28
is deflected.
In other words, by simultaneously controlling the two pieces of glass plates
21
and
22
, vibrations of a subject image is corrected and canceled.
Next will be described the decision circuit
7
, which decides whether vibrations are caused by panning and tilting movement.
Movement of panning and tilting may be misinterpreted as vibrations of an image sensing apparatus caused by unstable movement of user's hands. If the vibration cancellation unit
10
is actuated while the user performs panning or tilting operation, the variance in an image angle, which should be generated by the panning or tilting operation, is suppressed. In other words, an improper compensation which would be made by the cancellation unit
10
and which is not intended by a user is performed. The decision circuit
7
detects the panning or tilting operation performed by the user. When such operation is detected, the decision circuit
7
performs suppression control of vibration cancellation so that the vibration cancellation mechanism is not actuated. The suppression control is performed onto the HPF
5
and the integrator
6
, as shown in FIG.
1
. An operation of the decision circuit
7
will be described.
The decision circuit
7
inputs an angular velocity signal AV and an angle displacement amount signal AD; and when the angular velocity signal AV is more than a predetermined threshold value TH
1
(i.e. when an image sensing apparatus makes fast movement), or even if the angular velocity signal is less than the predetermined threshold value TH
1
, when the angle displacement amount signal AD is more than a predetermined threshold value TH
2
(i.e. when an image sensing apparatus makes a large movement), the decision circuit
7
concludes that a user is currently performing panning or tilting operation. When it is decided that panning or tilting operation is currently performed, a low cut-off frequency f
c
of the HPF
5
is shifted to a higher frequency value, thereby increasing the signals to be cut off by the HPF
5
. By virtue of this, the magnitude of a control signal inputted to the driving circuit
9
is reduced and vibration cancellation control is suppressed. More specifically, for panning operation or tilting operation recognized as vibrations having low frequency, the driving circuit
9
and the image vibration cancellation unit
10
will not respond, in other words, vibration cancellation will not be performed.
Note that when panning or tilting operation is detected, the COM reduces a time constant of the integrator
6
, in order to gradually move the angular position of the VAP to the center position of the movable range of the VAP, along with shifting the cut-off frequency f
c
of the HPF
5
. Reducing the time constant has a value accumulated in the integrator
6
as a reference value (a feasible value when vibrations are not detected).
In the present specification, the control operation, which suppresses vibration cancellation when it is detected that a user is performing panning or tilting operation, is hereinafter referred to as “vibration cancellation suppression control” or “panning-tilting control.”
Note that the angular velocity signal AV as well as angle displacement amount signal AD are detected even during the foregoing suppression control. When the panning or tilting operation is detected to terminate, the reduced cut-off frequency f
c
is restored to enlarge the vibration cancellation range and the panning-tilting control is canceled.
The above described operation will be explained with reference to the flowchart in FIG.
3
. The COM repeats steps S
2
-S
11
shown in
FIG. 3
in a predetermined time period.
Step S
2
: Angular vel
Kawahara Hideo
Kudo Toshimichi
Ho Tuan
Morgan & Finnegan , LLP
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