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Digital Camera Patent Abstract
To provide a digital camera capable of causing a focus sensor to
detect a focus while outputting to an image sensor image data for
providing appropriate exposure after having adjusted an aperture
ratio of an aperture in an image capture optical system such that
appropriate exposure is achieved. A digital camera divides light
from a subject having passed through an aperture into two beams
of light; causes one of the beams to enter the image sensor to thus
cause the image sensor to capture a subject image; and causes the
other beam to enter the focus sensor to thus cause the focus sensor
to detect a focus from the other beam of light. The digital camera
adjusts an aperture ratio of the aperture such that the quantity
of the other beam reaches the minimum quantity of light at or above
which the focus sensor can detect a focus.
Digital Camera Patent Claims
1. A digital camera which divides light having come from a subject
and passed through an aperture into two beams of light; which causes
one of the divided beams of light to enter an image sensor to thereby
cause the image sensor to capture an image of a subject; and which
causes the other one of the beams of light to enter a focus sensor
to thereby cause the focus sensor to detect a focus on the basis
of the other beam of light, the camera comprising: an exposure condition
determining section for determining exposure conditions, including
an aperture ratio of the aperture, under which the image sensor
can capture an image at appropriate exposure, in accordance with
the quantity of light from the subject, wherein, when the focus
sensor cannot detect a focus on the basis of the other one of the
beams of light divided after having passed through the aperture,
at the aperture ratio determined by the exposure condition determining
section, the exposure condition determining section fixes the aperture
ratio of the aperture at a minimum aperture ratio at or above which
the focus sensor can detect a focus, thereby determining the exposure
conditions.
2. The digital camera according to claim 1, further comprising:
a focus control section for causing the focus sensor to detect a
focus while maintaining the aperture at the minimum aperture ratio
during the course of the image sensor consecutively outputting image
data on the basis of the light from the subject.
3. The digital camera according to claim 2, further comprising:
an image record control section for recording, among a plurality
of frames of image data consecutively output by the image sensor
until receipt of an image capture instruction, a frame of image
data preceding, by a predetermined time lag period, a frame of image
data captured at the time of receipt of the image capture instruction,
as an image data for storage purpose in storage memory.
4. The digital camera according to claim 2, wherein the focus control
section causes the focus sensor to detect a focus every time the
image sensor outputs a predetermined number of frames of image data.
5. The digital camera according to claim 2, wherein the focus control
section causes the focus sensor to detect a focus every time the
image sensor outputs one frame of image data.
6. The digital camera according to claim 5, further comprising:
a focus processing section for performing focus processing in response
to a result of focus detection effected by the focus sensor from
when the image sensor has completed exposure processing for one
frame until the image sensor starts exposure processing for a subsequent
one frame.
7. The digital camera according to claim 1, further comprising:
a control section for, upon receipt of an image capture stop instruction,
maintaining the aperture at the minimum aperture ratio for a predetermined
standby period from receipt of the image capture stop instruction.
8. The digital camera according to claim 7, wherein the control
section maintains the aperture at the minimum aperture ratio for
the standby period, and maintains current positions of a group of
image capture lenses provided in the digital camera.
9. The digital camera according to claim 1, wherein the digital
camera can operate in at least a normal image capture mode where
the image sensor outputs one frame of image data upon receipt of
the image capture instruction and a consecutive image capture mode
where the image sensor consecutively outputs image data until receipt
of the image capture instruction; and, when the digital camera operates
in the consecutive image capture mode and the focus sensor cannot
detect a focus at the aperture ratio determined by the exposure
condition determining section, on the basis of the other beam of
light divided after having passed through the aperture, the exposure
condition determining section fixes the aperture ratio of the aperture
at a minimum aperture ratio at or above which the focus sensor can
detect a focus, to thus determine the exposure conditions.
10. An exposure condition determining method for determining exposure
conditions, including an aperture ratio of the aperture, under which
an image sensor can capture an image at appropriate exposure, in
accordance with the quantity of light from a subject, in relation
to a digital camera which divides light having come from a subject
and passed through an aperture, into two beams of light; which causes
one of the divided beams of light to enter an image sensor to thereby
cause the image sensor to capture an image of a subject; and which
causes the other one of the beams of light to enter a focus sensor
to thereby cause the focus sensor to detect a focus on the basis
of the other beam of light, wherein, when the focus sensor cannot
detect a focus on the basis of the other one of the beams of light
divided after having passed through the aperture, at the determined
aperture ratio, the aperture ratio of the aperture is fixed at a
minimum aperture ratio at or above which the focus sensor can detect
a focus, thereby determining the exposure conditions.
Digital Camera Patent Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent Application
No. 2005-335937 filed on Nov. 21, 2005, which is incorporated herein
by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a focus sensor for detecting
a focus on the basis of light originating from a subject, as well
as to a digital camera having an image sensor for capturing an image
of a subject on the basis of light originating from the subject.
RELATED ART
[0003] Japanese Patent Laid-Open Publication No. 2002-6208 describes
a related art technique in this field. The digital camera described
in this publication has a half mirror used for dividing light, which
has originated from the subject and passed through an image capture
optical system, into two beams of light and causing one of the beams
of light to enter an image pickup element and the other one of the
beams of light to enter an AF (Auto Focus) unit of phase difference
type. By means of such a configuration, the digital camera outputs
to the image pickup element image data to be displayed in an electronic
viewfinder and, meanwhile, causes a focus sensor (an AF unit) to
detect a focus. Subsequently, after having adjusted the aperture
ratio of the aperture belonging to the image pickup optical system
in such a way that appropriate exposure is attained, the digital
camera causes the half mirror to recede from the optical axis and
also causes the image pickup element to output still image data.
[0004] However, in the patent publication, consideration is not
given to the digital camera causing the image pickup element to
output image data and, meanwhile, causing the focus sensor to detect
a focus after having adjusted the aperture ratio of the aperture
belonging to the image pickup optical system in such a way that
appropriate exposure is attained.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention provides a digital camera
capable of causing a focus sensor to detect a focus and, meanwhile,
causing an image sensor to output image data of appropriate exposure
even after having adjusted a aperture ratio of the aperture belonging
to an image pickup optical system in such a way that appropriate
exposure is attained.
[0006] The present invention provides a digital camera which divides
light having come from a subject and having passed through an aperture,
into two beams of light; which causes one of the divided beams of
light to enter an image sensor to thereby cause the image sensor
to capture an image of a subject; and which causes the other one
of the beams of light to enter a focus sensor to thereby cause the
focus sensor to detect a focus on the basis of the other beam of
light, the camera comprising:
[0007] an exposure condition determining section for determining
exposure conditions, including an aperture ratio of the aperture,
under which the image sensor can capture an image at appropriate
exposure, in accordance with the quantity of light from the subject,
wherein,
[0008] when the focus sensor cannot detect a focus on the basis
of the other one of the beams of light divided after having passed
through the aperture, at the aperture ratio determined by the exposure
condition determining section, the exposure condition determining
section fixes the aperture ratio of the aperture at a minimum aperture
ratio at or above which the focus sensor can detect a focus, thereby
determining the exposure conditions.
[0009] In one mode of the digital camera of the present invention,
the digital camera further comprises a focus control section for
causing the focus sensor to detect a focus while maintaining the
aperture at the minimum aperture ratio during the course of the
image sensor consecutively outputting image data on the basis of
the light from the subject.
[0010] The focus control section causes, for instance, the focus
sensor to detect a focus every time the image sensor outputs a predetermined
number of frames of image data.
[0011] Moreover, the focus control section causes the focus sensor
to detect a focus every time the image sensor outputs one frame
of image data. In this case, a focus processing section performs
focus processing in response to a result of focus detection effected
by the focus sensor from when the image sensor has completed exposure
processing for one frame until the image sensor starts exposure
processing for a subsequent one frame.
[0012] Further, in another mode of the digital camera of the present
invention, the digital camera further comprises a control section
for, upon receipt of an image capture stop instruction, maintaining
the aperture at the minimum aperture ratio for a predetermined standby
period from receipt of the image capture stop instruction.
[0013] According to the present invention, even after having adjusted
an aperture ratio of an aperture included in an image capture optical
system such that appropriate exposure is attained, the digital camera
can cause the focus sensor to detect a focus while outputting to
the image sensor image data for providing appropriate exposure.
[0014] The invention will be more clearly comprehended by reference
to the embodiments provided below. However, the scope of the invention
is not limited to those embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A preferred embodiment of the present invention will be
described in detail by reference to the following figures, wherein:
[0016] FIG. 1 is a view showing functional blocks of a digital
camera according to an embodiment and various modifications thereof;
FIG. 2 is a view showing functional blocks of an image processing
section according to the embodiment and the modifications thereof;
FIG. 3A is a view showing functional blocks of an image capture
section in the embodiment and the modifications thereof; FIG. 3B
is a schematic view for describing the configuration of a focus
sensor;
[0017] FIG. 4 is a view showing functional blocks of a control
section in the embodiment and the modifications thereof;
[0018] FIG. 5 is a timing chart showing image capture processing
of a conventional digital camera;
[0019] FIG. 6A is a view for describing a light detection target
area utilized for a case where a focus sensor detects a focus;
[0020] FIG. 6B is a view for describing the light detection target
area utilized for a case where a focus sensor detects a focus;
[0021] FIG. 7 is a view showing an example line drawing of a main
program referred to in the case of a normal image capture mode and
another example line drawing of a sub-program referred in the case
of a continuous image capture mode;
[0022] FIG. 8 is a flowchart showing image capture procedures of
a digital camera according to the embodiment;
[0023] FIG. 9 is a timing chart showing image capture procedures
of a digital camera according to the embodiment;
[0024] FIG. 10 is a timing chart showing image capture procedures
of a digital camera according to a first modification;
[0025] FIG. 11 is a flowchart showing the image capture procedures
of the digital camera according to a first modification;
[0026] FIG. 12 is a flowchart showing procedures of image capture
processing of the digital camera according to the first modification;
[0027] FIG. 13 is a timing chart for describing a period of movement
of a lens in the first modification; and
[0028] FIG. 14 is a flowchart showing processing procedures employed
when a digital camera of a second modification has detected release
of a shutter button from a halfway pressed state.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] A best mode for implementing the present invention (hereinafter
called an "embodiment") will be described by reference
to the drawings.
[0030] When the user usually depresses a shutter button all the
way down upon recognition of the moment in which the user desires
to capture an image, a time lag arises from when the user has visually
perceived a target until the user actually depresses the shutter
button all the way down, and there also arises an additional time
lag equal to a period of processing time during which a digital
camera captures an image. There may arise a case where, for reasons
of the time lag, the user fails to record an image of the moment
at which the user has desired to capture an image.
[0031] For these reasons, as described in Japanese Patent Laid-Open
Publication No. 2002-271673, the following digital camera has hitherto
been put forward.
[0032] When the shutter button is depressed halfway down, the digital
camera prepares for image capture operation such as AE (Automatic
Exposure)/AF (Automatic Focusing) processing. After having completed
preparation for image capture operation, the camera starts capturing
an image of a subject, and consecutively repeats image capture operation
until the shutter button is depressed all the way down. A plurality
of frames of image data acquired through image capture operation
are temporarily retained. The camera records the image data preceding,
by a predetermined time lag period, the image data captured when
the shutter button has been depressed all the way down, among the
temporarily-retained frames of image data, as image data for storage
purpose. Thus, the camera can record an image of the instant at
which the user has desired to capture.
[0033] After the digital camera has completed a preparation for
image capture operation such as AE/AF processing, there may arise
a risk of blur being induced by positional displacement of the subject
or the positional displacement of a camera main body, to thus degrade
the quality of consecutively-captured image data.
[0034] In light of the above descriptions, the present embodiment
provides a digital camera which can prevent a decrease in image
quality of captured image data even when the image data are consecutively
captured.
[0035] FIG. 1 is a view showing functional blocks of a digital
camera 1 according to the embodiment. An image capture section 10
acquires light originating from a subject and subjects the light
to photoelectric conversion, to thus output image data. A control
section 30 is a central processor for controlling the entirety of
the camera, and performs arithmetic operation and control operation
for respective circuits or the like. An image processing section
40 subjects the image data output from the image capture section
10 to predetermined image processing, to thus generate and output
image data for display purpose (hereinafter called "display
image data") or image data for storage purpose (hereinafter
called "storage image data"). The image processing section
40 detects from the image data, for example, the brightness of a
subject and the type of the light source used for illuminating the
subject. The image data are subjected to white balance adjustment
on the basis of the information about the brightness of the subject
and the information about the light source, which have been obtained
as the detection results. A display section 50 sequentially displays
the display image data on a screen, to thus serve as an electronic
viewfinder. Memory for storage purpose (hereinafter called "storage
memory") 60 records the storage image data. An operation section
70 corresponds to a user interface which includes a shutter button
and is used for operating the camera when the user captures a still
image or a motion picture by use of the camera.
[0036] The camera 1 configured as mentioned above operates in at
least two image capture modes; namely, a normal image capture mode
and a consecutive image capture mode. When the shutter button has
been depressed halfway down, the camera 1 set in the normal image
capture mode performs AE/AF processing. When the shutter button
has been depressed all the way down, the camera 1 generates image
data equivalent to one frame from the light originating from the
subject. In the meantime, the camera 1 set in the consecutive image
capture mode sequentially generates image data, from the light that
originates from the subject, in a consecutive manner at given intervals
from when the shutter button has been pressed halfway down until
when the shutter button is depressed all the way down.
[0037] FIG. 2 is a view showing more-detailed functional blocks
of the image processing section 40. In FIG. 2, a ring buffer 42
is temporary retention memory where memory areas formed from a plurality
of data buffers are logically arranged in the shape of a ring. In
the normal image capture mode, the ring buffer 42 records image
data which are output from the image capture section 10 and are
equivalent to one frame. In the meantime, in the consecutive image
capture mode, the ring buffer 42 stores the image data, which have
been consecutively output from the image capture section 10, on
a per-frame basis in chronological sequence. When the capacity of
the ring buffer 42 for storing image data has become deficient,
the ring buffer deletes the image data recorded in the past in order
of occurrence and records new image data.
[0038] A display image processing section 44 converts the image
data output from the image capture section 10 into low-resolution
image data, and subjects the low-resolution image data to predetermined
image processing for displaying the image on a screen, thereby generating
display image data. Further, the display image processing section
44 also subjects the image data stored in the ring buffer 42 to
predetermined image processing for displaying an image on the screen,
to thus generate display image data. In a normal image capture mode,
a storage image processing section 46 subjects one frame of image
data stored in the ring buffer 42 to image processing, such as white
balance adjustment, to thus generate storage image data. The thus-generated
storage image data are recorded in the storage memory 60. In the
meantime, in the consecutive image capture mode, the storage image
processing section 46 subjects, to image processing, image data--preceding,
by a preset time lag period, the image data acquired when the shutter
button has been depressed all the way down--among the image data
stored in the ring buffer 42, thereby generating storage image data.
The thus-generated storage image data are recorded in the storage
memory 60.
[0039] The image capture section 10 will be further described by
reference to the functional block diagrams shown in FIGS. 3A and
3B.
[0040] In FIG. 3A, an image capture optical system 12 corresponds
to a group of lenses comprising a zoom lens and a focus lens. In
accordance with a lens control signal from the control section 30,
a lens drive mechanism 14 actuates a group of lenses constituting
the image capture optical system 12, to thus perform zooming or
focusing operation. An aperture 16 adjusts a aperture ratio of the
aperture, thereby regulating the quantity of light having originated
from the subject and passed through the image capture optical system
12. An aperture drive mechanism 18 adjusts the aperture ratio of
the aperture 16 by means of actuating the aperture 16 in accordance
with an aperture control signal from the control section 30.
[0041] A half mirror 20 reflects a portion of the light having
passed through the aperture 16; causes the remaining portion of
light to pass through; and divides the remaining light into two
beams of light. One of the beams is guided to an image sensor 24,
and the other one of the beams is guided to a focus sensor 22. Thereby,
the light having passed through the half mirror 20 enters the image
sensor 24, and the reflected light enters the focus sensor 22.
[0042] A known sensor capable of detecting a focus from the light
originating from the subject can be used for the focus sensor 22.
For instance, a focus detection mechanism of so-called phase different
detection type can be used for the focus sensor 22.
[0043] Now, focusing procedures of the focus sensor 22 employed
when the focus detection mechanism of phase difference detection
type will be briefly described. As shown in FIG. 3B, the focus sensor
22 comprises a capacitor lens 220; a pair of separator lenses 222a,
222b; and a pair of line sensors 224a, 224b disposed at the rear
of the focus sensor. The light reflected by the half mirror 20 enters
the focus sensor 22. The light having entered the focus sensor 22
is caused to enter the respective line sensors 224 by the pair of
separator lenses 222a, 222b via the capacitor lens 220. Thereby,
an image of the subject captured by the image capture optical system
12 is formed on the respective line sensors 224. The light having
passed through the capacitor lens 220 is limited to light of specific
areas from the image capture optical system 12, which differ from
each other in terms of exit pupil, by means of the respective separator
lenses 222; and enters the respective line sensors 224. By means
of such a configuration, the positional relationship (a phase difference)
between the images of the subject formed on the respective line
sensors 224 varies in accordance with the status of a focus (a front
focus, a back focus, and a focus). Consequently, the focus sensor
22 compares the phase difference with a predetermined value, thereby
detecting whether or not the image of the subject formed on the
image sensor 24 is in focus.
[0044] The image sensor 24 is formed from an image pickup element
made from a CCD (Charge-Coupled Device) or a CMOS (Complementary
Metal Oxide Semiconductor). The image sensor 24 subjects the light,
which has passed through the image capture optical system 12, the
aperture 16, and the half mirror 20 and come from the subject, to
photoelectric conversion; and outputs a resultant image signal.
The signal processing circuit 26 subjects the image signal output
from the image sensor 24 to predetermined analog signal processing.
The signal processing circuit 26 has, e.g., a correlation double
sampling circuit (CDS) and an automatic gain control circuit (AGC).
The correlation double sampling circuit subjects the image signal
to noise reduction processing, and the automatic gain control circuit
adjusts a gain used for regulating sensitivity. Thus, the level
of the image signal is adjusted. The automatic gain control circuit
adjusts a gain on the basis of gain information output from an exposure
condition determination section 32 to be described later. An analog-to-digital
(A/D) converter circuit 27 converts an analog image signal output
from the signal processing circuit 26 into a digital signal.
[0045] The control section 30 will now be described by reference
to the functional block diagram shown in FIG. 4.
[0046] In FIG. 4, the exposure condition determination section
32 acquires subject brightness information from the image processing
section 40, and on the basis of the subject brightness information
determines the aperture ratio of the aperture 16 at which appropriate
exposure is attained, the shutter speed, and the gain (image capture
sensitivity). By reference to a program line drawing retained by
a program line drawing storage section 34, the exposure condition
determination section 32 determines the aperture ratio, the shutter
speed, and the gain in response to the brightness of the subject.
The program line drawing storage section 34 retains a standard program
line drawing (hereinafter called a "main program line drawing")
where limitations are imposed on neither the aperture nor the shutter
speed, and a sub-program line drawing where an aperture ratio to
be determined is more limited than in the case of the main program
line drawing.
[0047] In the normal image capture mode, the exposure condition
determination section 32 determines exposure conditions [a aperture
ratio, a shutter speed, and a gain (image capture sensitivity)]
corresponding to the brightness of the subject by reference to the
main program line drawing. Meanwhile, the exposure condition determination
section 32 determines, in the consecutive image capture mode, exposure
conditions corresponding to the brightness of the subject by reference
to the sub-program line drawing. The main program line drawing and
the sub-program line drawing will be described in detail later.
[0048] In accordance with the focus detection result acquired from
the focus sensor 22, the lens control section 36 outputs the lens
control signal to the lens drive mechanism 14 such that the subject
image formed on the image sensor 24 is brought into focus. The aperture
control section 38 outputs an aperture control signal to the aperture
drive mechanism 18 in such a way that the aperture ratio determined
by the exposure condition determination section 32 is achieved.
[0049] In the normal image capture mode, the thus-configured camera
1 performs AE/AF processing when the shutter button is depressed
halfway down. When the shutter button is depressed all the way down,
one frame of image data is written into the ring buffer 42. The
camera 1 reads the image data from the ring buffer 42; subjects
the thus-read image data to predetermined image processing to thus
generate storage image data from the image data; and records the
thus-generated storage image data into the storage memory 60.
[0050] In the consecutive image capture mode, the camera 1 outputs
image data from when the shutter button has been depressed halfway
down until the shutter button is depressed all the way down, and
sequentially writes the image data into the ring buffer 42. From
the groups of image data written in the ring buffer 42, the camera
1 selects one frame of image data having been recorded a preset
time lag period before the image data--having been captured when
the shutter button has been pressed all the way down--and reads
the thus-selected image data as a candidate for storage image data.
The thus-read image data are subjected to predetermined image processing
to thus generate storage image data from the image data, and the
storage image data are recorded into the storage memory 60.
[0051] Procedures of image capture processing of the camera 1 employed
during setting of the consecutive image capture mode will now be
described by reference to the drawings. The image capture mode,
such as the normal image capture mode or the consecutive image capture
mode, can be set by means of the user selecting a desired image
capture mode by operating the camera 1 before starting image capture
operation.
[0052] First, before procedures of image capture processing performed
by the camera 1 are described, procedures of image capture processing
performed by a conventional digital camera of this type will be
described by reference to the timing chart shown in FIG. 5.
[0053] In FIG. 5, upon detection of halfway-down pressing of the
shutter button (S10), the digital camera performs AF processing
in accordance with the result of a focus detected by the focus sensor
22 (S12). The digital camera adjusts the aperture so as to achieve
the aperture ratio determined by the exposure condition determination
section 32 (S14). When adjustment of the aperture is completed,
the digital camera consecutively outputs still image data to the
image sensor 24 (S16), and the thus-output image data are sequentially
written into the ring buffer 42 (S18). Subsequently, upon detection
of all-the-way-down depression of the shutter button (S20), the
digital camera selects one frame of image data having been recorded
a preset time lag period before the image data--having been captured
when the shutter button has been pressed all the way down--and reads
the thus-selected image data as a candidate for storage image data
(S22). Next, the digital camera subjects the thus-read image data
to predetermined image processing to thus generate storage image
data from the read image data, and records the generated image data
into the storage memory 60.
[0054] As has been described above, the conventional digital camera
does not adjust focusing of the group of lenses from when AF processing
has been performed as a result of halfway-down depression of the
shutter button until when the shutter button is pressed all the
way down. Consequently, for reasons of positional displacement of
the subject which arises from when the shutter button has been pressed
halfway down until the shutter button is pressed all the way down,
the image data consecutively output from the image sensor 24 are
brought out of focus, which may in turn degrade image quality.
[0055] In light of the problem, a conceivable digital camera causes
the focus sensor 22 to detect a focus during a period from when
the shutter button has been depressed halfway down until when the
shutter button is depressed all the way down, and finely adjusts
the group of lenses. However, in relation to the conventional digital
camera, no consideration is given to cause the focus sensor 22 to
detect a focus simultaneously with output of still image data from
the image sensor.
[0056] For instance, the images of the subject formed on the line
sensors 224 by means of the pair of separator lenses 222a, 222b
of the focus sensor 22 are assumed to be formed by the light having
passed through areas designated by reference numerals 102a, 102b
(hereinafter called "detection target areas") within an
exit pupil 100 of the image capture lens 12 shown in FIG. 6A. Generally,
as a distance between the detection target area 102a and the detection
target area 102b becomes larger, the accuracy of focus detection
performed by the focus sensor 22 is improved. Hence, the detection
target area 102a and the detection target area 102b are desirably
set as close as possible around the exit pupil of the image capture
lens 12. For this reason, the detection target area 102a and the
detection target area 102b are positioned so as become adjacent
to the inner radius of the exit pupil achieved when the aperture
ratio of the aperture 16 is F5.6. Thus, the positions of the detection
target areas 102a, 102b have been determined in advance. Hence,
in a case where the aperture 16 is reduced in accordance with the
output from the exposure condition determination section 32 when
the brightness of the subject is high, as shown in FIG. 6B, there
may arise a case where the detection target areas 102a, 102b come
to positions outside the exit pupil of the image capture lens, to
thus block the light of the subject that is to reach the line sensors
of the focus sensor 22.
[0057] In the present embodiment, the exposure condition determination
section 32 determines the aperture ratio of the aperture in the
consecutive image capture mode within a limited area where the focus
sensor 22 can detect a focus on the basis of incident light. Thus,
the aperture ratio of the aperture is limited to the range where
the focus sensor 22 can detect a focus. Therefore, in the present
embodiment, in addition to the main program line drawing to be referred
to in the normal image capture mode, the sub-program line drawing
to be referred to in the consecutive image capture mode is stored
in the program line drawing storage section 34. The main program
line drawing is a line drawing by means of which the aperture ratio
of the aperture is not limited to the range where the focus sensor
22 can detect a focus, when the exposure condition determination
section 32 makes a reference in order to determine exposure conditions
including the aperture ratio of the aperture. A program line drawing
analogous to a conventional one can be used. Meanwhile, the sub-program
line drawing is one by means of which the aperture ratio of the
aperture is limited to the range where the focus sensor 22 can detect
a focus, when the exposure condition detection means 32 makes a
reference in order to determine exposure conditions including an
aperture ratio of the aperture. FIG. 7 shows an example main program
line drawing and an example sub-program line drawing. In FIG. 7,
the main program line drawing is denoted by a solid line, and the
sub-program line drawing is denoted by a broken line.
[0058] In the normal image capture mode, the exposure condition
determination section 32 determines exposure conditions, including
the aperture ratio of the aperture, by reference to the main program
line drawing. In the consecutive image capture mode, the exposure
condition determination section 32 determines exposure conditions
by reference to the sub-program line drawing. At this time, when
the aperture ratio of the aperture has reached the minimum aperture
ratio at which the focus sensor 22 can detect a focus, the exposure
condition determination section 32 fixes the aperture ratio of the
aperture 16 to the minimum aperture ratio, thereby determining the
other exposure conditions. When the numeral aperture of the aperture
16 is fixed to the minimum aperture ratio, the shutter speed, which
is one of the other exposure conditions, is set so as to become
faster than the shutter speed determined on the basis of the main
program line drawing, thereby preventing occurrence of overexposure.
As mentioned above, the minimum aperture ratio is the limitation
of aperture ratio which enables appropriate entrance of light to
the respective separator lenses constituting the focus sensor 22.
The aperture ratio corresponds to a value which is determined by
the detection target area 102 determined by specifications of the
focus sensor 22.
[0059] As above, in the consecutive image capture mode, the exposure
condition determination section 32 determines the aperture ratio
of the aperture 16 so as not to fall short of the predetermined
minimum aperture ratio, whereby the focus sensor 22 can detect a
focus without fail even after adjustment of the aperture. Consequently,
during the course of the image sensor 24 outputting still image
data, the focus sensor 22 can detect a focus.
[0060] In the present embodiment, in response to setting of the
consecutive image capture mode, the focus sensor 22 detects a focus
every time the image sensor 24 outputs a predetermined number of
frames of image data from when the shutter button has been depressed
halfway down until the shutter button is depressed all the way down.
On the basis of the result of detection, the camera 1 re-adjusts
the group of lenses in such a way that that image of the subject
formed on the image sensor 24 is in focus.
[0061] In consideration of the above descriptions, image capture
procedures of the camera 1 performed at the time of setting of the
consecutive image capture mode will now be described by reference
to the drawings.
[0062] FIG. 8 is a flowchart showing image capture procedures of
the camera 1. Upon detection of halfway-down depression of the shutter
button (S100), the camera 1 performs AF processing (S102). In short,
the focus sensor 22 detects a focus, and the lens control section
36 outputs a lens control signal to the lens drive mechanism 14
on the basis of the result of detection, thereby adjusting the group
of lenses in such a way that the image of the subject formed on
the image sensor 24 is brought into focus.
[0063] The camera 1 determines the exposure conditions such that
appropriate exposure is obtained (S104). Specifically, the exposure
condition determination section 32 determines the aperture ratio
of the aperture, which leads to appropriate exposure, the shutter
speed, and the gain in accordance with the information about the
brightness of the subject by reference to the sub-program line drawing.
Subsequently, in accordance with the determined exposure conditions,
the camera 1 adjusts the aperture ratio of the aperture (S106).
[0064] Next, so long as the shutter button still remains in the
halfway-down depressed state (the result of a determination rendered
in S110 is affirmative: Y), the image sensor 24 consecutively outputs
the image data at predetermined intervals under the determined exposure
conditions. The image data are recorded on a per-frame basis in
the ring buffer 42 in chronological sequence (S108).
[0065] When the image sensor 24 does not detect all-the-way-down
depression of the shutter button during output of image data (the
result of determination rendered in S112 is negative: N), the camera
1 determines whether or not the number of frames of image data recorded
in the ring buffer 42 has reached a predetermined number of frames
(S114). When the result of determination shows that the predetermined
number of frames is achieved (the result of a determination rendered
in S114 is affirmative: Y), the lens control section 36 acquires
the result of detection of a focus performed by the focus sensor
22, and outputs the lens control signal to the lens drive mechanism
14 on the basis of the result of determination, thereby again effecting
AF adjustment (S116). In the meantime, when the result of determination
shows that the predetermined number of frames has not been attained
(the result of a determination rendered in S114 is negative: N),
the image sensor 24 continuously outputs image data without effecting
AF adjustment. Further, when a predetermined number of frames have
been attained, AF adjustment is again performed. As mentioned above,
during the course of the image sensor 24 continuously outputting
the image data, AF adjustment is performed at predetermined intervals.
As a result, even when the shutter button is held in a halfway-down
depressed state for a long period of time, less-blurred image data
can be sequentially recorded in the ring buffer 42. When the shutter
button is released from the halfway-down-depressed state (the result
of a determination rendered in S110 is negative: N), the camera
1 causes the image sensor 24 to stop outputting image data and remain
in a standby condition until the shutter button is again depressed
halfway down.
[0066] When the shutter button is depressed all the way down during
the course of the image sensor 24 outputting image data (the result
of a determination rendered in S112 is affirmative: Y), the camera
1 causes the image sensor 24 to stop outputting image data (S118).
Subsequently, the camera 1 selects image data, which will become
a candidate for storage, from among the groups of image data recorded
in the ring buffer 42 (S120). Specifically, the camera 1 selects,
from among the group of pieces of image data written in the ring
buffer 42, one frame of image data that precedes, a predetermined
time lag period, the image data captured when the shutter button
has been depressed all the way down; and reads the thus-selected
image data as a candidate for storage image data. The camera 1 subjects
the selected image data to predetermined image processing, and records
the thus-processed image data into the storage memory 60 (S122).
[0067] As mentioned above, according to the present embodiment,
the image sensor 24 performs AF adjustment as appropriate during
the course of consecutive output of image data until the shutter
button is depressed all the way down. At this time, the exposure
condition determining section 32 determines an aperture ratio of
the aperture, which is achieved during image capture operation,
so as to exceed the minimum aperture ratio that enables the focus
sensor 22 to detect a focus. Therefore, occurrence of a situation
where the aperture ratio of the aperture is too small to enable
the focus sensor 22 to detect a focus can be prevented. FIG. 9 shows
a timing chart of image capture procedures of the camera 1 of the
present embodiment achieved in the consecutive image capture mode.
As shown in FIG. 9, in the present embodiment, the focus sensor
22 can detect a focus after adjustment of the aperture, and the
image sensor 24 can perform AF adjustment as appropriate during
the course of output of still image data. Consequently, for instance,
even when the shutter button is kept in a halfway-down-depressed
state for a long period of time, the camera 1 can sequentially record
the less-blurred image data into the ring buffer 42. Consequently,
there can be diminished the probability of blurring of the image
data which are selected as a candidate for storage from the image
data recorded in the ring buffer 42.
[0068] A first modification of the present embodiment will now
be described.
[0069] FIG. 10 is a timing chart showing image capture procedures
of the camera 1 employed in the consecutive image capture mode according
to the first modification. As shown in FIG. 10, the camera 1 of
the first modification differs from the camera 1 of the embodiment,
which effects AF adjustment at intervals of a predetermined number
of frames, in that AF adjustment is sequentially performed on a
per-frame basis. The camera 1 of the first modification performs
AF adjustment from when exposure of one frame of data has been completed
until exposure of the next frame is started, thereby sequentially
performing AF adjustment on a per-frame basis. In order to realize
AF adjustment on a per-frame basis, the camera 1 of the first modification
adjusts a shutter speed, to thus adjust a timing at which exposure
of the next frame is started, thereby ensuring the time for AF adjustment.
[0070] The image capture procedures of the camera 1 of the first
modification will now be described by reference to FIGS. 11 through
13.
[0071] FIG. 11 is a flowchart showing image capture procedures
of the camera 1 of the first modification employed in the consecutive
image capture mode. As in the case of the embodiment, upon detection
of the halfway-down-depression of the shutter button, the camera
1 performs AF processing, determination of the exposure conditions,
and adjustment of the aperture (S200 to S206). Next, after completion
of adjustment of the aperture 16, the camera 1 inputs an initial
value of "1" for a variable "n" to which reference
is made during image capture processing (S208). Subsequently, when
the halfway-down-depression of the shutter button is continued (the
result of the determination rendered in S210 is affirmative: Y),
image capture processing is performed (S212). As in the case of
the above-described embodiment, when the all-the-way-down depression
of the shutter button is detected, the camera 1 selects, from the
group of image data written into the ring buffer 42, one frame of
image data that precede, a predetermined time lag period, the image
data captured when the shutter button has been depressed all the
way down; subjects the selected image data to predetermined image
processing; and records the thus-processed image data into the storage
memory 60 (S214 to S216).
[0072] Here, image capture processing pertaining to step (S212)
will be described by reference to the flowchart shown in FIG. 12
and the timing chart shown in FIG. 13.
[0073] First, the image sensor 24 starts reading the n.sup.th frame
of image (S218), and starts exposure of the (n+1).sup.th frame of
image (S219). Subsequently, after the image sensor 24 has finished
reading the n.sup.th frame of image (S220), the exposure condition
determining section 32 determines exposure conditions [the aperture
ratio F.sub.(n+2) of the aperture, a shutter speed Vf.sub.(n+2),
and a gain G.sub.(n+2)] for the (n+2).sup.th frame on the basis
of the n.sup.th frame of image data until completion of an exposure
period T.sub.E(n+1) of the (n+1).sup.th frame. In addition, the
lens control section 36 acquires a focus result output from the
focus sensor 22, and determines, from the focus result before completion
of the exposure period T.sub.E(n+1), the amount of movement of the
lens M.sub.(n+1) of the (n+1).sup.th frame of the focus lens required
for focusing (S224).
[0074] At this time, the lens control section 36 determines whether
or not the focus lens can be moved before start of exposure of the
(n+2).sup.th frame (S224). More specifically, given that the frame
period of the image sensor 24 is T.sub.F, the exposure period of
the (n+2).sup.th frame is T.sub.E(n+2), and a lens movement period
required to move the focus lens over a distance corresponding to
the amount of movement of the lens M(n+1) for the (n+1) frame is
T.sub.M(n+1), the lens control section 36 determines that the focus
lens can be moved when the following equation (1) is fulfilled.T.sub.M(n+1).ltoreq.T.sub.F-T.sub.E(n+2)
(1)
[0075] When the determination rendered in step (S224) shows that
the lens of the focus lens cannot be moved before start of exposure
of the (n+2).sup.th frame (the result of the determination rendered
in S224 is negative: N), the exposure condition determining section
32 determines exposure conditions for the (n+2).sup.th frame in
consideration of the lens movement period T.sub.M(n+1) (S226). More
specifically, the exposure condition determining section 32 adjusts
the exposure period T.sub.E(n+2) in such a way that the lens movement
period T.sub.M(n+1) fulfills Equation (1). In short, the shutter
speed Vf.sub.(n+2) included in the exposure conditions determined
in step (S226) is changed to a shutter speed V.sub.S(n+2), which
is faster than the shutter speed Vf.sub.(n+2), such that the lens
movement period T.sub.M(n+1) fulfills Equation (1). Moreover, the
exposure condition determining section 32 increases a gain used
for enhancing sensitivity (hereinafter called a "sensitivity
enhancement gain"), in order to compensate for a reduction
in the exposure period.
[0076] However, when the shutter speed V.sub.S(n+2) changed such
that the lens movement period T.sub.M(n+1) fulfills Equation (1)
is too fast, the reduction in exposure period cannot be compensated
for even when the sensitivity enhancement gain is increased. There
may also arise a case where the image sensor 24 cannot output image
data of appropriate exposure.
[0077] When the exposure condition determining section 32 has determined
the shutter speed V.sub.S(n+2), a determination is made as to whether
or not the shutter speed V.sub.S(n+2) is faster than Vf.sub.(n+2)/2
(S228). When the shutter speed V.sub.S(n+2) is determined to be
faster than Vf.sub.(n+2)/2 as a result of determination (the result
of the determination rendered in S228 is affirmative: Y), the exposure
condition determining section 32 determines that the image data
of appropriate exposure is not obtained at the shutter speed V.sub.S(n+2),
and the shutter speed is determined to be Vf.sub.(n+2)/2 (S230).
When the shutter speed V.sub.S(n+2) is Vf.sub.(n+2)/2 or less (the
result of the determination rendered in S228 is negative: N), the
exposure condition determination section 32 determines that image
data of appropriate exposure can be obtained at the shutter speed
V.sub.S(n+2), and determines the shutter speed to V.sub.S(n+2) (S232).
[0078] In the present embodiment, a determination is made as to
whether or not the shutter speed V.sub.S(n+2) is used as the exposure
conditions, on the basis of whether or not the shutter speed V.sub.S(n+2)
is faster than Vf.sub.(n+2)/2. However, the speed, which becomes
a criterion of determination, is not limited to Vf.sub.(n+2)/2.
For example, a limit shutter speed and a limit gain, at which appropriate
exposure is attained, may be computed while the gain is being changed,
and the limit shutter speed may be determined.
[0079] Subsequently, the lens control section 36 determines the
amount of movement of a lens (S234). When the shutter speed is determined
to be V.sub.S(n+2), the lens control section 36 determines the amount
of movement of the lens determined in step (S222). Meanwhile, when
the shutter speed has been determined to be Vf.sub.(n+2)/2, the
lens control section 36 again determines the amount of movement
of the lens which can be implemented during a period [T.sub.F-T.sub.E(n+2)]
before the start of exposure of the (n+2).sup.th frame, thereby
determining the thus-determined amount of movement of the lens.
[0080] So long as the all-the-way-down depression of the shutter
button is detected when exposure of the (n+1).sup.th frame performed
during an exposure period T.sub.E(n+1) is completed (S236) (the
result of the determination rendered in S238 is affirmative: Y),
image capture processing is completed. In the meantime, when the
all-the-way-down depression of the shutter button has not been detected
(the result of the determination rendered in S238 is negative: N),
the lens control section 36 outputs to the lens drive mechanism
14 the lens control signal which is based on the determined amount
of movement of the lens, thereby effecting AF adjustment (S240).
When the shutter button is in the halfway-down-depressed state,
image capture processing is further continued (S242).
[0081] In the above first modification, the camera 1 sequentially
performs AF adjustment on a per-frame basis. Consequently, the image
quality of the image data recorded in the ring buffer 42 can be
further enhanced as compared with the case where AF adjustment is
performed at predetermined frame intervals.
[0082] Since the interval at which focus information is acquired
is short, there is a high probability that the amount of offset
of focus from that achieved for the previous frame being small.
Processing is completed within a predetermined period of time if
the amount of movement of the lens is small. Hence, an accurate
focus state can be maintained.
[0083] Next, a second modification of the present embodiment will
now be described. In the second modification, after the shutter
button has been released from the halfway-down-depressed state,
the camera 1 set in the consecutive image capture mode maintains,
for a predetermined standby period, the current aperture ratio of
the aperture 16 and the positions of the group of lenses constituting
the image capture optical system 12.
[0084] In the above embodiment and the first modification, when
the shutter button is released from the halfway-down-depressed state,
the camera 1 immediately opens the aperture 16. Subsequently, when
again detecting halfway-down-depression of the shutter button, the
camera 1 again adjusts the aperture ratio of the aperture 16 and
the positions of the group of lenses. However, there is a case where
the user temporarily releases his/her finger from the shutter button
and again depresses the shutter button halfway down. In such a case,
a certain amount of time is consumed by adjustment of the aperture
ratio of the aperture 16 and the positions of the group of lenses.
Hence, a certain amount of time is consumed before the camera 1
starts capturing an image of a subject. Consequently, there is a
case where the camera 1 cannot capture an image at the user's intended
timing.
[0085] Therefore, in the second modification, after the shutter
button has been released from the halfway-down-depressed state,
the camera 1 set in the consecutive image capture mode maintains,
for a predetermined standby period, the current aperture ratio of
the aperture and the positions of the group of lenses.
[0086] FIG. 14 is a flowchart showing processing procedures employed
when the camera 1 has detected release of the shutter button from
the halfway-down-depressed state.
[0087] Upon detection of release of the shutter button from the
halfway-down-depressed state (S300), the camera 1 stops image capture
processing (S302). Specifically, the camera 1 stops writing of image
data into the ring buffer 42. Subsequently, the camera 1 sets a
timer (S304), and remains in a standby condition until the shutter
button is again depressed halfway down. During the period of a wait,
the camera 1 maintains the aperture ratio of the aperture 16 and
the positions of the group of lenses, which are achieved immediately
before release of the shutter button from the halfway-down-depressed
state, thereby monitoring the timer. The camera 1 maintains the
aperture ratio of the aperture 16 and the positions of the group
of lenses (S308) until the value of the timer exceeds a predetermined
standby period (e.g., 3.0 seconds) (the result of the determination
rendered in S306 is negative: N). In the meantime, when the value
of the timer has exceeded the predetermined standby period (e.g.,
3.0 seconds) (the result of the determination rendered in S306 is
affirmative: Y), the camera 1 releases the aperture 16 (S31O).
[0088] According to the second modification, after the shutter
button has been released from the halfway-down-depressed state,
the camera 1 maintains, for a predetermined standby period, the
current aperture ratio of the aperture and the positions of the
group of lenses. Thereby, the time required for AE/AF processing
can be shortened. Therefore, the camera 1 can capture an image at
the user's intended timing without fail. As in the case of the camera
1 of the embodiment or the second modification, the aperture ratio
of the aperture maintained by the camera 1 during a standby state
is limited to the range where the focus sensor 22 can detect a focus.
Therefore, even when the aperture ratio of the aperture 16 achieved
immediately before the shutter button is released from the halfway-down-depressed
state is maintained, the camera 1 can again effect focusing operation
on the basis of the result of focus detection performed by the focus
sensor 22 after the shutter button has again been depressed halfway
down.
[0089] The second modification has described an example where the
current aperture ratio of the aperture is maintained when the camera
1 is in a consecutive image capture mode. However, so long as the
current aperture ratio of the aperture is equal to or greater than
the minimum aperture ratio, the camera 1 can perform focusing action,
regardless of the case of the consecutive image capture mode, on
the basis of the result of focus detection performed by the focus
sensor 22 while the current aperture ratio of the aperture is maintained.
Therefore, when the camera 1 set in the normal image capture mode
has detected release of the shutter button from the halfway-down-depressed
state, a determination is made as to whether or not the current
aperture ratio of the aperture is equal to or greater than the minimum
aperture ratio. When the determination shows that the aperture ratio
of the aperture is determined to be equal to or greater than the
minimum aperture ratio, the camera 1 maintains the current aperture
ratio of the aperture and the positions of the group of lenses during
a predetermined standby period. By means of processing, even when
the camera 1 is set in the normal image capture mode, the time required
for AE/AF processing can be shortened.
Parts List:
[0090] 1 digital camera [0091] 10 image capture section [0092]
12 image capture optical system [0093] 14 lens drive mechanism [0094]
16 aperture (S310) [0095] 18 aperture drive mechanism [0096] 20
half mirror [0097] 22 focus sensor (S12) [0098] 24 image sensor
(S16) [0099] 26 signal processing circuit [0100] 27 analog-to-digital
converter [0101] 30 control section [0102] 32 exposure condition
determination section (S14) [0103] 34 line drawing storage section
[0104] 36 lens control section [0105] 38 aperture control section
[0106] 40 image processing section [0107] 42 ring buffer (S18) (S120)
[0108] 44 display image processing section [0109] 46 storage image
processing section [0110] 50 display section [0111] 60 storage memory
(S122) (S214-S216) [0112] 70 operation section [0113] 100 exit pupil
[0114] 102 detection target area [0115] 102a detection target area
[0116] 102b detection target area [0117] 220 capacitor lens [0118]
222 separator lenses [0119] 222a separator lenses [0120] 222b separator
lenses [0121] 224 line sensor [0122] 224a line sensors [0123] 224b
line sensors [0124] S10 shutter button [0125] S20 shutter button
[0126] S22 storage image data [0127] S100 shutter button [0128]
S102 AF processing [0129] S104 exposure [0130] S106 aperture ratio
[0131] S108 chronological sequence [0132] S110 half-way-down depressed
state [0133] S112 depression of shutter button [0134] S114 predetermined
number of frames [0135] S116 AF adjustment [0136] S118 stop outputting
image data [0137] S200-S206 adjustment of aperture [0138] S208 image
capture processing [0139] S210 depression of shutter button [0140]
S212 image captue processing [0141] S218 frame of image [0142] S219
frame of image [0143] S220 frame of image [0144] S222 movement of
lens [0145] S224 focus lens required for focusing [0146] S224 exposure
of the frame [0147] S226 lens movement period [0148] S228 determination
of shutter speed [0149] S230 determination of shutter speed [0150]
S232 determination of shutter speed [0151] S234 movement of lens
[0152] S236 exposure period [0153] S238 determination of exposure
period [0154] S240 AF adjustment [0155] S242 image capture processing
[0156] S300 shutter button depression state [0157] S302 image capture
processing [0158] S304 timer [0159] S306 determination of standby
period [0160] S308 group of lenses
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