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Digital Camera Patent Abstract
A digital camera, having a function for optically compensating for
camera shake, comprises: a movement detector that detects a movement
of the digital camera; a movement prediction unit that employs the
movement detected by the movement detector to predict a movement
of the digital camera after a predetermined period of time has elapsed;
an optical system moving unit that moves an optical system of the
digital camera so as to compensate for the movement of the digital
camera predicted by the movement prediction unit; and an image data
correction unit that corrects image data obtained while taking a
photograph, based on a difference between an actual movement of
the digital camera, which is detected by the movement detector while
taking the photograph, and the movement of the digital camera that
is predicted, by the movement prediction unit, to occur while taking
the photograph, so that the image data will be the same as image
data that are obtained when the optical system is moved while taking
the photograph in order to compensate for the movement of the digital
camera that is detected by the movement detector while actually
taking the photograph.
Digital Camera Patent Claims
1. A digital camera, having a function for optically compensating
for camera shake, comprising: a movement detector that detects a
movement of the digital camera; a movement prediction unit that
employs the movement detected by the movement detector to predict
a movement of the digital camera after a predetermined period of
time has elapsed; an optical system moving unit that moves an optical
system of the digital camera so as to compensate for the movement
of the digital camera predicted by the movement prediction unit;
and an image data correction unit that corrects image data obtained
while taking a photograph, based on a difference between an actual
movement of the digital camera, which is detected by the movement
detector while taking the photograph, and the movement of the digital
camera that is predicted, by the movement prediction unit, to occur
while taking the photograph, so that the image data will be the
same as image data that are obtained when the optical system is
moved while taking the photograph in order to compensate for the
movement of the digital camera that is detected by the movement
detector while actually taking the photograph.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a digital camera that has
a function for optically compensating for camera shake.
[0003] 2. Description of the Related Art
[0004] An image pickup apparatus that selectively employs the function
for optically compensating for camera shake and a function for performing
signal processing to compensate for camera shake is disclosed in
JP-A-2004-191647.
[0005] In a digital camera having an optical camera shake compensation
function, camera shake compensation is performed by moving the optical
system to counter the movement of a digital camera while taking
a photograph. However, since there is a short delay between the
detection of the movement of a digital camera and the movement of
the optical system to compensate for it, the photographic process
can be completed before the optical system can be moved to compensate
for the movement of the digital camera. Conventionally, therefore,
based on past performance, the movement of the digital camera during
the taking a photograph is predicted, and when a photograph is being
taken, the predicted movement of the digital camera is countered
by the movement of the optical system, i.e., the performance of
the camera shake compensation function.
[0006] According to the invention, however, when a difference exists
between the predicted and the actual movements of a digital camera
while taking a photograph, accurate camera shake compensation can
not be provided.
SUMMARY OF THE INVENTION
[0007] While taking the above shortcoming into account, one objective
of the present invention is to enable a digital camera having an
optical camera shake compensation function to perform accurate camera
shake compensation.
[0008] To achieve this objective, according to this invention,
a digital camera, having a function for optically compensating for
camera shake, comprises:
[0009] a movement detector that detects a movement of the digital
camera;
[0010] a movement prediction unit that employs the movement detected
by the movement detector to predict a movement of the digital camera
after a predetermined period of time has elapsed;
[0011] an optical system moving unit that moves an optical system
of the digital camera so as to compensate for the movement of the
digital camera predicted by the movement prediction unit; and
[0012] an image data correction unit that corrects image data obtained
while taking a photograph, based on a difference between an actual
movement of the digital camera, which is detected by the movement
detector while taking the photograph, and the movement of the digital
camera that is predicted, by the movement prediction unit, to occur
while taking the photograph, so that the image data will be the
same as image data that are obtained when the optical system is
moved while taking the photograph in order to compensate for the
movement of the digital camera that is detected by the movement
detector while actually taking the photograph.
[0013] With this arrangement, when there is a difference between
the movement of the digital camera that has been predicted will
occur while taking a photograph and the actual movement of the digital
camera, the same image data are generated as those obtained when
the optical system has been moved to counter the actual movement
of the digital camera. Therefore, accurate camera shake compensation
can be performed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic diagram showing the configuration
of the essential portion of a digital camera for carrying out the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] One embodiment of the present invention will now be described
while referring to a drawing.
[0016] FIG. 1 is a schematic diagram showing the configuration
of the essential portion of a digital camera according to the embodiment
of the invention.
[0017] A digital camera 100 in FIG. 1 comprises: an image pickup
unit 1, an analog front end (AFE) 2, a digital signal processor
3, a driver 4, a lens driver 5, a system controller 6, a movement
detector 7, a movement vector operation unit 8, a predicted movement
vector operation unit 9 and a differential vector generator 10.
[0018] The image pickup unit 1 employs an optical system, including
an image taking lens 1a, and an image pickup device 1b, such as
a CCD image sensor, to take a picture of an object, and outputs
an analog image signal. The optical system, for example, is movable,
vertically and horizontally, in order to optically compensate for
camera shake.
[0019] The AFE 2 performs a predetermined analog signal process
for an image pickup signal obtained by the image pickup unit 1,
and converts the obtained analog signal into a digital signal. The
AFE 2 transmits this digital signal as so-called RAW image data
to the digital signal processor 3. The RAW image data are those
obtained by digitizing the image pickup signal, without changing
the signal form received from the image pickup unit 1.
[0020] Under the control of the system controller 6, the driver
4 generates a drive signal at a predetermined timing, and based
on this drive signal, drives the image pickup device 1b and the
AFE 2.
[0021] Further, the lens driver 5, under the control of the system
controller 6, moves the optical system, which includes the image
taking lens 1a, to a predetermined position.
[0022] For the digital image data received from the AFE 2, the
digital signal processor 3 performs digital signal processing in
a designated operating mode. The processing performed by the digital
signal processor 3 includes: a camera shake compensation process,
a black level correction process (OB process), a linear matrix correction
process, a white balance control process, a gamma correction process,
a synchronization process and a Y/C conversion process. The digital
signal processor 3 is essentially a DSP device, and image data output
by the digital signal processor 3 are compressed and are recorded
on a recording medium, such as a memory card.
[0023] The movement detector 7 is a sensor for detecting the movement
of the digital camera 100, and for this, a gyro sensor or an acceleration
sensor, for example, is employed.
[0024] The movement vector operation unit 8 employs a sensor signal
output by the movement detector 7 to calculate a movement vector
that specifies the movement (the direction and the distance) of
the digital camera 100.
[0025] The predicted movement vector operation unit 9 predicts
how the digital camera 100 will be moved after a predetermined period
of time has elapsed. Specifically, the movement vectors obtained
by the movement vector operation unit 8 are accumulated, and based
on the history of the movement vectors thus accumulated, the predicted
movement vector operation unit 9 calculates a predicted movement
vector, which is a movement vector specifying the movement of the
digital camera 100 following the elapse, calculated from the current
time, of a predetermined period of time.
[0026] The system controller 6, constituted mainly by a processor
that executes commands provided by a predetermined program, controls
all the operations of the entire digital camera 100, to include
a photograph taking process. The system controller 6 moves the optical
system, through the lens driver 5, in order to cancel the predicted
movement vector previously calculated.
[0027] The predetermined period of time described above is a required
period extending from the time an optical system moving instruction,
for canceling the predicted movement vector, is issued to the lens
driver 5 by the system controller 6 to the point at which the optical
system actually starts to move. Therefore, in the period during
which a photograph is being taken, the exposure is performed, for
example, with the shutter open, and the optical system is moved
to compensate for the predicted movement of the digital camera 100.
When this prediction is correct, near precise compensation for camera
shake can be performed.
[0028] The differential vector generator 10 obtains a movement
vector, which specifies the movement of the digital camera 100 that
is detected by the movement detector 7 while a photograph was being
taken, and a predicted movement vector, which is produced by the
predicted movement vector operation unit 9 and specifies a movement
prediction for the digital camera 100 while a photograph was being
taken. Then, the differential vector generator 10 subtracts the
actual movement vector from the predicted movement vector and generates
a differential vector.
[0029] The camera shake compensation process performed by the digital
signal processor 3 will now be explained.
[0030] The camera shake compensation process is a signal process
for compensating for an error between the predicted movement of
the digital camera 100 while a photograph is being taken, and the
actual movement of the digital camera 100 at that time. The digital
signal processor 3 employs the differential vector to correct image
data obtained for a photograph, so that the image data correspond
to those obtained when the optical system was moved while the photograph
was being taken, and to thus compensate for the actual movement
of the digital camera 100 that was detected by the movement detector
7.
[0031] For example, assume that the predicted movement of the digital
camera 100 during the taking of a photograph is represented by an
upward, two-pixel vector, and that the actual movement of the digital
camera 100 at that time is represented by an upward, one-pixel vector.
In this case, image data received from the AFE 2 is shifted downward
one pixel. Since the differential vector is an upward vector for
only one pixel, the digital signal processor 3 performs the signal
processing for shifting image data, received from the AFE 2, one
pixel upward. As a result, the same image data can be generated
as are obtained when the optical system is moved to compensate for
the actual movement of the digital camera 100 during the taking
of a photograph. Accordingly, accurate camera shake compensation
is enabled.
[0032] The picture taking operation of the digital camera 100 will
now be explained.
[0033] When the digital camera 100 is set to the picture taking
mode and the camera shake compensation mode, a movement vector is
calculated in accordance with a sensor signal transmitted by the
movement detector 7. When movement vectors such as this are accumulated,
a predicted movement vector is calculated based on them, and the
optical system is moved to cancel the thus obtained predicted movement
vector. Therefore, in the camera shake compensation mode, the optical
system is always moved so as to counter the predicted movement of
the digital camera 100. It should be noted, however, that the optical
system need not always be moved, and when, for example, the digital
camera 100 has an AF function, the optical system maybe moved after
the image taking lens 1a has been moved to a focal position using
the AF function.
[0034] When a picture taking instruction is issued by a user, image
data that includes a predetermined number of pixels are output by
the AFE 2. Then, the actual movement vector of the digital camera
100, which represents the photograph taking operation performed
in accordance with the instruction, is subtracted from the predicted
movement vector of the digital camera 100, which also represents
the photograph taking operation performed in accordance with the
instruction. Thus, a differential vector is generated, and image
data output by the AFE 2 are corrected based on this differential
vector. Then a predetermined digital signal process is performed
for the corrected image data, the resultant data are compressed,
and the compressed data are recorded on a recording medium.
[0035] As described above, when there is an error between the predicted
and the actual movement of the digital camera 100 while a photograph
is being taken, this error can be corrected by performing signal
processing. Therefore, accurate camera shake compensation can be
performed.
[0036] Furthermore, since the digital signal processor 3 simply
corrects image data based on a differential vector, the processing
load imposed on the digital signal processor 3 can be reduced, compared
with when camera shake compensation is performed only by the signal
processor, without the optical system being moved.
[0037] In this embodiment, a differential vector has been generated
by subtracting the movement vector from the predicted movement vector.
However, a differential vector may also be generated by subtracting
a predicted movement vector from a movement vector, and may be employed
to correct image data.
[0038] According to the invention, for a digital camera having
an optical camera shake compensation function, accurate camera shake
compensation is enabled.
[0039] The entire disclosure of each and every foreign patent application
from which the benefit of foreign priority has been claimed in the
present application is incorporated herein by reference, as if fully
set forth. |