Digital Camera Patent Abstract
In a digital camera, when flash shooting is performed, a maximum
distance at which a subject can be illuminated to appropriate brightness
is calculated based on the guide number of a flash and the open
aperture value of an aperture stop, and the distance to the subject
measured is compared with the maximum distance. If the distance
to the subject is equal to or shorter than the maximum distance,
the exposure time is set at a predetermined value, and the amount
of the flash light emitted is controlled based on the amount of
the light reflected from the subject, and white balance of the taken
image is adjusted in accordance with the color characteristics of
the flash light. If the distance to the subject is greater than
the maximum distance, the exposure time is set to be longer than
the predetermined value in order to use a larger amount of ambient
light to illuminate the subject, and white balance of the taken
image is adjusted in accordance with the color characteristics of
the ambient light. Digital Camera Patent Claims
What is claimed is:
1. A digital camera comprising: a photoelectric conversion device
for sensing light from a subject to generate image data of the subject;
a flash for emitting light to illuminate the subject; and a time
setter for setting, when shooting is performed using the light emitted
by the flash, a photoelectric conversion time for which the photoelectric
conversion device performs photoelectric conversion in accordance
with a distance to the subject, wherein the time setter sets the
photoelectric conversion time to be equal to a predetermined length
of time when the distance to the subject is equal to or shorter
than a predetermined distance.
2. A digital camera as claimed in claim 1, wherein the time setter
sets the photoelectric conversion time to be longer than the predetermined
length of time when the distance to the subject is longer than the
predetermined distance.
3. A digital camera as claimed in claim 1, wherein the predetermined
length of time is determined based on a guide number of the flash.
4. A digital camera as claimed in claim 1, further comprising:
a balance adjuster for performing white balance adjustment on the
image data generated by the photoelectric conversion device.
5. A digital camera as claimed in claim 4, wherein the balance
adjuster performs white balance adjustment based on color characteristics
of the light emitted by the flash when the distance to the subject
is equal to or shorter than a predetermined distance.
6. A digital camera as claimed in claim 5, wherein the balance
adjuster performs white balance adjustment based on color characteristics
of ambient light when the distance to the subject is longer than
the predetermined distance.
7. A digital camera as claimed in claim 1, wherein, whether shooting
is performed using light emitted by the flash, ambient light, or
a combination thereof, the predetermined length of time is a maximum
handshake-free period, wherein the maximum hand-shake-free period
is a maximum photoelectric conversion time that does not allow a
shake of a hand to cause a substantially noticeable distortion of
the subject image data.
8. A digital camera as claimed in claim 1, further comprising:
a checker for checking an exposure condition of the subject image
data; an amplification circuit; and a gain setter for setting a
gain of the amplification circuit, wherein when the checker recognizes
an under exposure condition, the gain and the photoelectric conversion
time are respectively set in such a way that the photoelectric conversion
time multiplied by the gain remains constant.
9. A digital camera comprising: a photoelectric conversion device
for sensing light from a subject to generate image data of the subject;
a flash for emitting light to illuminate the subject; a first time
setter for setting, when shooting is performed using the light emitted
by the flash, a photoelectric conversion time for which the photoelectric
conversion device performs photoelectric conversion to be equal
to a predetermined length of time when a distance to the subject
is equal to or shorter than a predetermined distance that corresponds
to a guide number of the flash; a second time setter for setting,
when shooting is performed using the light emitted by the flash,
the photoelectric conversion time for which the photoelectric conversion
device performs photoelectric conversion to be longer than the predetermined
length of time when the distance to the subject is longer than the
predetermined distance; a first balance adjuster for performing
white balance adjustment on the image data generated by the photoelectric
conversion device based on color characteristics of the light emitted
by the flash when the distance to the subject is equal to or shorter
than the predetermined distance; and a second balance adjuster for
performing white balance adjustment on the image data generated
by the photoelectric conversion device based on color characteristics
of ambient light when the distance to the subject is longer than
the predetermined distance.
10. A digital camera that shoots an image by means of a photoelectric
conversion device and that is capable of performing flash shooting
by emitting flash light to illuminate a subject, during photoelectric
conversion, wherein, in flash shooting, when the subject lies within
a distance range in which the flash light can illuminate the subject
with predetermined brightness, a photoelectric conversion time for
which the photoelectric conversion device performs photoelectric
conversion is set to be equal to a predetermined length of time,
and, when the subject lies outside the distance range, the photoelectric
conversion time for which the photoelectric conversion device performs
photoelectric conversion is set to be longer than the predetermined
length of time.
11. A digital camera as claimed in claim 10, wherein, when flash
shooting is performed with the photoelectric conversion time of
the photoelectric conversion device set to be equal to the predetermined
length of time, the image shot is subjected to white balance adjustment
performed based on color characteristics of the flash light, and,
when flash shooting is performed with the photoelectric conversion
time of the photoelectric conversion device set to be longer than
the predetermined length of time, the image shot is subjected to
white balance adjustment performed based on color characteristics
of ambient light.
12. A method of operating a digital camera to generate image data
of a subject, the method comprising the steps of: performing photoelectric
conversion using a photoelectric conversion device for sensing light
from the subject in order to generate the image data of the subject;
emitting light from a flash to illuminate the subject; and when
shooting is performed using the light emitted by the flash, setting
a photoelectric conversion time for which the photoelectric conversion
device performs photoelectric conversion in accordance with a distance
to the subject, wherein when the distance to the subject is equal
to or shorter than a predetermined distance, the photoelectric conversion
time is set equal to a predetermined length of time.
Digital Camera Patent Description
This application is based on application No. H10-212376 filed in
Japan on Jul. 28, 1998, the entire content of which is hereby incorporated
by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera, and more particularly
to a digital camera capable of flash shooting.
2. Description of the Prior Art
Conventionally, digital cameras are known that are provided with
an image sensor having a two-dimensional array of CCDs (charge-coupled
devices). A digital camera of this type senses the light coming
from a subject and takes in, as an image signal, an electric signal
whose level varies in accordance with the amount of the light sensed.
In shooting, in accordance with the brightness of the subject, the
exposure time (the shutter speed) and the aperture value of the
CCD are set in such a way that, the lower the brightness of the
subject, the wider the aperture and the longer the exposure time.
In this way, shooting is performed under appropriate exposure conditions.
When the subject is so dark that, even if the aperture is made
fully open and the exposure time is set at the maximum within the
range that does not cause a hand shake (hereafter the exposure time
thus set is referred to as the maximum hand-shake-free period),
the subject image taken suffers from underexposure, flash shooting
is performed by emitting flash light during photoelectric conversion
to illuminate the subject. Flash shooting is performed with the
exposure time fixed at a predetermined value, for example 1/60 seconds.
The brightness of the subject is controlled by adjusting the amount
of the flash light emitted. Some cameras adopt automatic light amount
adjustment in which the flash light reflected from the subject is
detected to stop flash light emission when the amount of light detected
reaches a predetermined value.
The image signal obtained from the image sensor is converted into
a digital signal, and is thereafter subjected to color adjustment,
i.e. white balance adjustment, in order to faithfully reproduce
the white areas of the image. In normal shooting without flash light
emission, white balance adjustment is performed for every image
in accordance with the color characteristics (wavelength distribution)
of ambient light. On the other hand, in flash shooting, white balance
adjustment is performed uniformly in accordance with the color characteristics
of the flash light.
Quite naturally, there is an upper limit to the amount of flash
light a flash can emit. Moreover, the farther the subject lies away
from the camera, the less flash light the subject receives. Thus,
when the subject lies considerably far away from the digital camera,
even if the maximum amount of flash light is emitted, it is impossible
to illuminate the subject to appropriate brightness, with the result
that the subject image taken suffers from underexposure. In such
a case, in most conventional digital cameras, the subject can not
be shot with appropriate exposure; that is; even if the subject
is illuminated with flash light, degradation of the image quality
is inevitable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a digital camera
that can shoot an image with appropriate exposure irrespective of
the distance to the subject even in flash shooting and that can
achieve proper white balance adjustment in images shot by flash
shooting at all times.
To achieve the above objects, according to one aspect of the present
invention, a digital camera is provided with a photoelectric conversion
device, a flash, and a time setter. The photoelectric conversion
device senses light from a subject to generate image data of the
subject. The flash emits light to illuminate the subject. The time
setter sets, when shooting is performed using the light emitted
by the flash, a photoelectric conversion time for which the photoelectric
conversion device performs photoelectric conversion in accordance
with the distance to the subject. When the subject is close to the
camera, it can be illuminated to appropriate brightness with the
flash light, even if the photoelectric conversion time is set to
be short as in the conventional cameras. In the camera, when the
subject is too far away from the camera to be illuminated to the
predetermined brightness with the flash light, it is possible to
set the photoelectric conversion time to be longer so that a large
amount of ambient light is utilized for illuminating the subject.
Thus, irrespective of the distance to the subject, it is always
possible to obtain images in which the brightness of the subject
is appropriate.
According to another aspect of the present invention, a digital
camera is provided with a photoelectric conversion device, a flash,
a first time setter, a second time setter, a first balance adjuster,
and a second balance adjuster. The photoelectric conversion device
senses light from a subject to generate image data of the subject.
The flash emits light to illuminate the subject. The first time
setter sets, when shooting is performed using the light emitted
by the flash, a photoelectric conversion time for which the photoelectric
conversion device performs photoelectric conversion to be equal
to a predetermined length of time when the distance to the subject
is equal to or shorter than a predetermined distance that corresponds
to the guide number of the flash. The second time setter sets, when
shooting is performed using the light emitted by the flash, the
photoelectric conversion time for which the photoelectric conversion
device performs photoelectric conversion to be longer than the predetermined
length of time when the distance to the subject is longer than the
predetermined distance. The first balance adjuster performs white
balance adjustment on the image data generated by the photoelectric
conversion device based on the color characteristics of the light
emitted by the flash when the distance to the subject is equal to
or shorter than the predetermined distance. The second balance adjuster
performs white balance adjustment on the image data generated by
the photoelectric conversion device based on the color characteristics
of ambient light when the distance to the subject is longer than
the predetermined distance. When flash shooting is performed with
the predetermined photoelectric conversion time, the flash light
becomes dominant in illuminating the subject. In contrast, when
flash shooting is performed with the photoelectric conversion time
longer than the predetermined photoelectric conversion time, the
ambient light becomes dominant in illuminating the subject. Since
white balance adjustment is performed based on the color characteristics
of the dominant light, it is always possible to obtain images of
good color quality.
According to still another aspect of the present invention, a digital
camera shoots an image by means of a photoelectric conversion device
and is capable of performing flash shooting by emitting flash light
to illuminate a subject, during photoelectric conversion. In flash
shooting, in this digital camera, when the subject lies within the
distance range in which the flash light can illuminate the subject
with predetermined brightness, the photoelectric conversion time
for which the photoelectric conversion device performs photoelectric
conversion is set to be equal to a predetermined length of time,
and, when the subject lies outside the predetermined distance range,
the photoelectric conversion time for which the photoelectric conversion
device performs photoelectric conversion is set to be longer than
the predetermined length of time.
BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects and features of this invention will become
clear from the following description, taken in conjunction with
the preferred embodiments with reference to the accompanied drawings
in which:
FIG. 1 is a block diagram schematically showing the configuration
of the digital camera of an embodiment of the present invention;
FIG. 2 is a flowchart showing the outline of the overall operations
performed by the digital camera of the embodiment;
FIG. 3 is a flowchart showing the operations performed by the digital
camera of the embodiment to prepare for shooting;
FIG. 4 is a flowchart showing the operations performed by the digital
camera of the embodiment to perform shooting without flash light
emission; and
FIG. 5 is a flowchart showing the operations performed by the digital
camera of the embodiment to perform shooting with flash light emission.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, a digital camera embodying the present invention will
be described with reference to the drawings. FIG. 1 is a block diagram
schematically showing the configuration of the digital camera of
this embodiment. In FIG. 1, an image sensing section 10 is composed
of a taking lens 101, an aperture stop 102, a CCD 103, and a CCD
control circuit 104. The image sensing section 10 takes in a subject
image as an image signal. The taking lens 101 focuses the light
coming from the subject onto the light-sensing surface of the CCD
103, which performs photoelectric conversion. The aperture stop
102 adjusts the amount of light the CCD 103 receives.
The CCD 103 has a two-dimensional array of a large number of photoelectric
conversion devices (CCDs, for example), and has a single-plate-type
color filter disposed on the front surface thereof. The CCD 103
senses the subject image focused by the taking lens 101 and, in
accordance with the amount of the light sensed, outputs electric
signals individually representing the light components of three
primary colors (R, G, B). Under the control of the CCD control circuit
104, the CCD 103 performs photoelectric conversion, i.e. electric
charge accumulation, and feeds the pixel signals obtained from the
individual photoelectric conversion devices as a result of electric
charge accumulation to a signal processor 11. In the CCD 103, the
photoelectric conversion time (the exposure time) is variable and
is set by an MPU (a microprocessor unit) 21, which will be described
later.
Note that it is possible to use, as the aperture stop 102, an aperture
stop composed of a plurality of blades so as to allow continuous
setting of the aperture value as is used in a lens unit or the like
for a silver-halide-film SLR camera. It is also possible to use
an aperture stop of a roulette type formed as a rotatable roulette
having a plurality of apertures of different sizes formed thereon
so as to allow stepwise setting of the aperture value.
The signal processor 11 is composed of an amplification circuit
111 and an ADC (an analog-to-digital (A/D) converter) 112. The amplification
circuit 111 amplifies the individual pixel signals fed from the
CCD 103 at a predetermined gain. The ADC 112 converts the pixel
signals thus amplified into pixel data. The gain of the amplification
circuit 111 is set by the MPU 21.
A photometry device 12 is an exposure meter employing a photo sensor
such as CdS (cadmium sulfide) and senses the light coming from the
subject to perform photometry. The signal obtained as a result of
photometry is taken in as photometry data by the MPU 21. An aperture
driving circuit 13 sets the aperture stop 102 at the position corresponding
to a control aperture value. An aperture position detector 14 is
an encoder or the like for detecting the aperture position of the
aperture stop 102 and feeds the detected information on the aperture
position to the MPU 21.
A distance measurement module 15 is an ambient-light passive module
composed, for example, of a pair of line sensors that sense the
light coming from the subject. In response to a distance measurement
command from the MPU 21, the distance measurement module 15 senses
the subject image by means of the pair of line sensors to obtain
distance measurement data, which represents the distance to the
subject, on the basis of the deviation of the subject image between
the two line sensors. The distance measurement data thus obtained
is taken in by the MPU 21. A focusing circuit 16 drives the taking
lens 101 to the in-focus position in accordance with the defocus
amount fed from the MPU 21. A lens position detector 17 is an encoder
or the like for detecting the position of the taking lens 101 and
outputs the information on the detected lens position to the MPU
21.
The distance measurement module 15 does not necessarily have to
be realized by the use of an ambient-light passive module as mentioned
above. It is also possible to use instead an active-type module
composed, for example, of an LED (a light emitting diode) and a
PSD (a position sensing device) for sensing the light emitted by
the LED and reflected from the subject so that distance measurement
data, which represents the distance to the subject, is obtained
on the basis of the light-sensing position of the PSD.
A flash 18 is composed of a white light source such as an Xe (xenon)
lamp. A charging/flashing circuit 19, which is provided with a capacitor
(not shown) for charging, starts charging in response to a charge
command from the MPU 21, and then, in response to a trigger signal
from the MPU 21, starts to supply the charged electric power to
the flash 18 to effect light emission. A light control IC 20, in
response to a light control start signal from the MPU 21, starts
to monitor the amount of the light emitted by the flash 18 and reflected
from the subject, and feeds a flash emission stop signal to the
MPU 21 when the monitored amount of light reaches a predetermined
amount that allows the subject to be shot with appropriate exposure.
In response to this signal, the charging/flashing circuit 19 stops
supplying the charged electric power to the flash 18.
The MPU 21 is composed of an exposure time setter 211, an underexposure
checker 212, and a gain setter 213, and controls the entire digital
camera under discussion.
A RAM (random access memory) 22 is used as a working area or the
like of the MPU 21. An EEPROM (electrically-erasable programmable
read-only memory) 23 is used to store various items of information
necessary for controlling the digital camera, such as the settings
of the entire digital camera, the conversion data used to convert
the photometry data into the brightness of the subject (for example,
conversion coefficients in the form of a table or coefficients for
conversion formulae), the focal length data corresponding to the
distance measurement data, the white balance value determined based
on the color characteristics of the flash light emitted by the flash
18, the guide number (GNo) of the flash 18 corresponding to the
sensitivity of the CCD 103 and the gain of the amplification circuit
111, and the open aperture value of the aperture stop 102.
The MPU 21 monitors the states of individual switches provided
in an operation switch section 27 and performs necessary control
to execute the operation specified by a switch operated. Moreover,
the MPU 21 determines, by comparing the count value obtained from
a built-in timer with a predetermined value (several minutes, for
example), whether to stop or not the supply of electric power from
a power source 29 to various parts of the camera. The MPU 21 also
checks whether the voltage across the charging capacitor of the
charging/flashing circuit 19 is lower than a predetermined reference
level or not.
Moreover, the MPU 21 converts the photometry data fed from the
photometry device 12 into the brightness of the subject by using
the conversion data stored in the EEPROM 23, and performs calculation
to determine a control aperture value in accordance with the brightness
of the subject thus obtained. Then, the MPU 21, while monitoring
the information on the aperture position fed from the aperture position
detector 14, controls the aperture driving circuit 13 to drive the
aperture stop 102 to the position corresponding to the control aperture
value. The control aperture value may be determined by calculation
using the brightness of the subject. It is also possible to use
a predetermined table from which to select a control aperture value
in accordance with the brightness of the subject.
The MPU 21 also performs, based on the distance measurement data
fed from the distance measurement module 15 and the focal length
data stored in the EEPROM 23, calculation to determine a defocus
amount for the taking lens 101. Then, in accordance with the defocus
amount thus calculated, the MPU 21, while monitoring the information
on the lens position fed from the lens position detector 17, controls
the focusing circuit 16 to drive the taking lens 101 to the in-focus
position.
Moreover, the MPU 21 performs predetermined image processing on
the image data fed from the ADC 112 (such as black level correction,
white level correction, white balance adjustment, image interpolation,
gradation correction using a lookup table or the like, image compression
according to, for example, the JPEG (joint photographic image coding
experts group) standard, and so forth).
The exposure time setter 211 sets the exposure time of the CCD
103 and feeds it to the CCD control circuit 104. When the flash
18 is not activated, the exposure time is set at an initial value
in a predetermined way. For example, where a continuously-variable
aperture is used, the initial exposure time may be set at a predetermined
value, or, as with AE (automatic exposure) control, may be set,
together with the control aperture value, at a value that achieves
appropriate exposure based on the brightness of the subject. Once
the image data is obtained, the exposure time is set at a value
that is determined, as achieving appropriate exposure, based on
the brightness level of the image data.
If the exposure time set here is longer than the maximum hand-shake-free
period, a warning message is displayed on an LCD 242 (to be described
later) to warn of a possibility of a hand shake. The maximum hand-shake-free
period refers to the maximum length of exposure that does not allow
a hand shake to cause a noticeable shake in the subject image. For
example, if the focal length of the taking lens 101 is assumed to
be f (mm), the maximum hand-shake-free period is about 1/f (second).
When the flash 18 is activated, in accordance with whether illuminating
the subject with flash light results in appropriate exposure or
underexposure, the exposure time is set to be equal to or longer
than a predetermined length of time, for example 1/60 seconds. Specifically,
when the subject lies within the distance range in which appropriate
exposure is obtained with the maximum amount of flash light or less,
the exposure time is set at a predetermined value. In contrast,
when the subject lies at such a distance at which underexposure
results even if the aperture stop 102 is fully opened and the flash
18 emits the maximum amount of flash light, the exposure time is
set to be longer than the predetermined length of time.
When the subject lies far away from the camera, by setting the
exposure time to be longer than the predetermined length of time,
it is possible to illuminate the subject not only with flash light
but also with ambient light and thereby obtain appropriate exposure.
The exposure time thus set can be longer than the maximum hand-shake-free
period. In order to set the exposure time, the exposure time setter
211 uses the check results fed from the underexposure checker 212
described below.
When the flash 18 is activated, the underexposure checker 212 checks
whether the subject suffers from underexposure or not on the basis
of the GNo of the flash 18, the open aperture value of the aperture
stop 102, and the distance measurement data fed from the distance
measurement module 15. Specifically, the underexposure checker 212
divides the GNo value of the flash 18 by the open aperture value,
and, if the distance to the subject as represented by the distance
measurement data fed from the distance measurement module 15 is
greater than the resultant value, recognizes that the subject suffers
from underexposure.
In contrast, when the flash 18 is not activated, the underexposure
checker 212 checks whether the subject suffers from underexposure
or not on the basis of the maximum hand-shake-free period. When
appropriate exposure is not obtained within the maximum hand-shake-free
period even if the aperture stop 102 is fully opened, the underexposure
checker 212 recognizes that the subject suffers from underexposure.
The gain setter 213 sets the gain of the amplification circuit
111. The gain setter 213 sets the gain of the amplification circuit
111 at the same value irrespective of whether the flash 18 is activated
or not. Note that, the exposure time setter 211 and the gain setter
213 may set the exposure time and the gain, respectively, in such
a way that the exposure time multiplied by the gain remains constant.
This makes it possible to obtain uniform image quality irrespective
of the exposure time.
A display section 24 is composed of an LCD (liquid crystal display
panel) 242 and an LCD driver 241. The LCD driver 241 drives the
LCD 242 to display the image data and the character-based information
fed from the MPU 21.
A recording medium 25 is, for example, a disk-shaped medium on
which data is recorded magnetically or magneto-optically, or a semiconductor
data storage device such as an IC memory card. The recording medium
25 is detachably attached to the digital camera under discussion.
The recording medium 25 stores data such as its own type and remaining
storage capacity. A reading/writing circuit 26 performs reading
and writing of data from and to the recording medium 25. Moreover,
on the basis of whether the reading/writing circuit 26 is able to
read out data therefrom or not, the MPU 21 recognizes whether the
recording medium 25 is present or not. Specifically, the MPU 21
recognizes, if data reading is possible, that the recording medium
25 is attached to the digital camera, and, if not, that the recording
medium 25 is not attached to the digital camera.
The operation switch section 27 is composed of a plurality of switches
including a power switch 271, a release switch 272, and a flash
mode switch 273. The release switch 272 has two switches S1 and
S2 which are turned on by half depression and by full depression,
respectively. When the release switch 272 is pressed halfway in,
the switch S1 is turned on and operations preparatory for shooting
are executed; when the release switch 272 is pressed fully in, both
of the switches S1 and S2 are turned on, and shooting operations
are executed. The flash mode switch 273 is used to select one of
the following three modes: the flash shooting mode in which flash
light is always emitted; the automatic flash mode in which whether
flash light is emitted or not is automatically determined in accordance
with the brightness of the subject; and the ambient-light shooting
mode in which flash light is never emitted.
An external terminal section 28 allows the digital camera under
discussion to be connected to an external apparatus such as a personal
computer or a printer so as to feed the data of the images taken
to the external apparatus. The power source 29 is a secondary battery
for supplying electric power to the circuits and drivers provided
in the camera.
FIG. 2 is a flowchart showing the operation of the digital camera
under discussion. When the power switch 271 is turned on, the power
source 29 starts to supply electric power to various parts of the
camera, and the MPU 21 is subjected to resetting and internal initialization
(step #5). Then, the information on the previous settings stored
in the EEPROM 23 is read out. The MPU 21 is initialized into the
state that conforms to the information thus read out (step #10).
Next, through the reading/writing circuit 26, the data such as
the kind and the remaining storage capacity of the recording medium
25 is read out (step #15). At this time, on the basis of whether
reading of the data from the recording medium 25 is possible or
not, whether the recording medium 25 is attached to the digital
camera under discussion or not is checked. Then, the information
obtained from the EEPROM 23 and the recording medium 25 is displayed
on the LCD 242 (step #20). Thereafter, the count value of the timer
is reset (step #25). Then, monitoring of the states of the individual
switches provided in the operation switch section 27 is started
(step #30).
Subsequently, whether the count value of the timer is greater than
a predetermined value or not is checked (step #35). If the count
value is found to be greater, the information on the current settings
is stored in the EEPROM 23, and the supply of electric power to
various parts of the camera is stopped except to the MPU 21, which
needs to detect turning on of the power switch 271 (step #40). Then,
the procedure shown in this flowchart comes to an end.
If, at step #35, the count value is found not to be greater, during
the monitoring performed at step #30, whether the release switch
272 is pressed halfway in to turn on the switch S1 or not is checked
(step #45). If the switch S1 is found on, the [S1] subroutine described
later is executed to prepare for shooting (step #50), and the procedure
returns to step #25.
If the switch S1 is found not on, during the monitoring performed
at step #30, whether any other switch than the release switch 272
provided in the operation switch section 27 is operated or not is
checked (step #55). If any other switch is found operated, the operation
associated with that switch is executed (step #60), and the procedure
returns to step #25. If, at step #55, no other switch is found operated,
the procedure returns to step #30.
FIG. 3 is a flowchart of the [S1] subroutine that is executed to
prepare for shooting. When the [S1] subroutine is called, the MPU
21 converts the photometry data fed from the photometry device 12
into the brightness of the subject using the conversion data stored
in the EEPROM 23 (step #100).
Thereafter, whether or not the flash shooting mode is selected
by operation of the flash mode switch 273 is checked (step #105).
When the flash shooting mode is selected, the "flash-on"
subroutine described later for shooting with light emission by the
flash 18 is executed (step #110).
If, at step #105, the flash shooting mode is not selected, whether
or not the automatic flash mode is selected by operation of the
flash mode switch 273 is checked (step #115). If the automatic flash
mode is not selected, the "flash-off" subroutine described
later for shooting without light emission by the flash 18 is executed
(step #120). When the automatic flash mode is selected, whether
the brightness of the subject obtained at step #100 is lower than
predetermined brightness or not is checked (step #125). If the brightness
of the subject is found to be lower, the procedure proceeds to step
#110, and otherwise the procedure proceeds to step #120.
FIG. 4 is a flowchart of the "flash-off" subroutine for
shooting without light emission by the flash 18. When the "flash-off"
subroutine is called, the MPU 21 determines a control aperture value
that corresponds to the brightness of the subject obtained at step
#100 (FIG. 3). In accordance with the control aperture value thus
determined, the MPU 21, while monitoring the information on the
aperture position fed from the aperture position detector 14, controls
the aperture driving circuit 13 to drive the aperture stop 102 to
the position corresponding to the control aperture value (step #200).
Subsequently, the MPU 21 feeds a distance measurement command to
the distance measurement module 15 to obtain distance measurement
data (step #205). The MPU 21 determines, based on the focal length
data corresponding to the distance measurement data, a defocus amount.
In accordance with the defocus amount thus determined, the MPU 21,
while monitoring the information on the lens position fed from the
lens position detector 17, controls the focusing circuit 16 to drive
the taking lens 101 to the in-focus position (step #210). Then,
the gain of the amplification circuit 111 is set at a predetermined
value (step #215).
Thereafter, the exposure time is set by the exposure time setter
211. The CCD 103 performs photoelectric conversion for the exposure
time thus set (step #220). On completion of photoelectric conversion,
the CCD 103 outputs an image signal (step #225), which is taken
in by the signal processor 11. The image signal thus obtained is
amplified by the amplification circuit 111 and is then subjected
to analog-to-digital (A/D) conversion by the ADC 112 so as to be
converted into image data. The image data is first stored in the
RAM 22 temporarily so as to be subjected to various kinds of processing
including black level correction, white level correction, and white
balance adjustment. Then, the image data is read out from the RAM
22 so as to display the image taken on the LCD 242 for viewing before
shooting (preview). Moreover, based on the brightness level of the
image data thus obtained, the exposure time that achieves appropriate
exposure is determined for the next shot (step #230).
Here, the white balance adjustment is performed based on the image
data itself. The image data reflects the color characteristics of
ambient light, and therefore the white balance adjustment is performed
in accordance with the color characteristics of ambient light.
Subsequently, whether the switch S1 of the release switch 272 is
off or not is checked (step #250). If the switch S1 is found off,
the execution of the "flash-off" subroutine and of the
[S1] subroutine is ended, and the procedure returns to step #25
in FIG. 2.
If, at step #250, the switch S1 is found not off, whether the switch
S2 of the release switch 272 is on or not is checked (step #255).
If the switch S2 is found not on, the procedure returns to step
#220. Thus, the operations in steps #220 to #250 are repeated to
perform white balance adjustment and calculate the exposure time
at step #230. Note that, once an appropriate white balance and an
appropriate exposure time are obtained, they are kept unchanged
unless there is a change in the ambient conditions or the shooting
range.
If, at step #255, the switch S2 is found on, the appropriate exposure
time thus obtained is fed to the CCD control circuit 104. The CCD
103 performs photoelectric conversion for that exposure time (step
#260). On completion of photoelectric conversion, the CCD 103 outputs
an image signal (step #265), which is taken in by the signal processor
11.
The image signal thus obtained is amplified by the amplification
circuit 111 and is then subjected to A/D conversion by the ADC 112
so as to be converted into image data. The image data is first stored
in the RAM 22 temporarily so as to be subjected to black level correction
and white level correction, and is then subjected to processing
including white balance adjustment in accordance with the conditions
determined at step #230 (step #270) and image correction by interpolation
(step #275). Thereafter, the image data is read out from the RAM
22 so as to display the image taken on the LCD 242 for viewing after
shooting (after view). Furthermore, the image data in the RAM 22
is subjected to image compression according to, for example, the
JPEG standard (step #280), and is then recorded on the recording
medium 25 by way of the reading/writing circuit 26 (step #285).
Then, the execution of the "flash-off" subroutine and
of the [S1] subroutine is ended, and the procedure returns to step
#25 in FIG. 2.
FIG. 5 is a flowchart of the "flash-on" subroutine that
is executed to perform shooting with light emission by the flash
18. When the "flash-on" subroutine is called, the MPU
21 determines a control aperture value that corresponds to the open
aperture. In accordance with the control aperture value thus determined,
the MPU 21, while monitoring the information on the aperture position
fed from the aperture position detector 14, controls the aperture
driving circuit 13 to drive the aperture stop 102 to the open aperture
position (step #300).
Subsequently, the MPU 21 feeds a distance measurement command to
the distance measurement module 15 to obtain distance measurement
data (step #305). The MPU 21 determines, based on the focal length
data corresponding to the distance measurement data, a defocus amount.
In accordance with the defocus amount thus determined, the MPU 21,
while monitoring the information on the lens position fed from the
lens position detector 17, controls the focusing circuit 16 to drive
the taking lens 101 to the in-focus position (step #310).
Thereafter, the MPU 21 checks whether the voltage across the charging
capacitor of the charging/flashing circuit 19 is lower than a predetermined
reference level or not. If the voltage is found to be lower, the
MPU 21 feeds a charge command to the charging/flashing circuit 19
to start charging (step #315).
Thereafter, by the exposure time setter 211, the exposure time
is set to be equal to the predetermined length of time mentioned
previously (step #320). The white balance is so set as to be adjusted
in accordance with the white balance adjustment value calculated
based on the color characteristics of flash light stored in the
EEPROM 23 (step #325). Then, the gain of the amplification circuit
111 is set by the gain setter 213 (step #330). The value of the
gain thus set is fed to the light control IC 20.
Thereafter, the underexposure checker 212 checks whether or not
the subject lies within the distance range in which appropriate
exposure is obtained with the flash light emitted by the flash 18
(step #335). Specifically, the underexposure checker 212 reads out
the GNo of the flash 18 from the EEPROM 23, and divides the value
of the GNo by the open aperture value in order to determine a subject
distance Df (hereafter referred to as the effective flash distance)
at which appropriate exposure is obtained with the maximum amount
of flash light emitted by the flash 18. Then, by comparing the distance
to the subject D represented by the distance measurement data obtained
at step #305 with the effective flash distance Df, whether the subject
lies within the distance range in which appropriate exposure is
achieved with the flash light or not is determined.
When the distance to the subject D is equal to or shorter than
the effective flash distance Df, the procedure proceeds to step
#355. When the distance to the subject D is longer than the effective
flash distance Df, i.e., in a case where, even if the aperture stop
102 is fully opened and the flash 18 emits the maximum amount of
flash light, the brightness of the subject fails to reach the level
that achieves appropriate exposure, the exposure time is set anew
at a value that is greater than the value of the predetermined length
of time set at step #320 (step #340). Moreover, the white balance
adjustment is set anew so as to be performed in accordance not with
the predetermined white balance adjustment value stored in the EEPROM
23 but with the data of the taken image itself, i.e., with the color
characteristics of ambient light (step #345).
When the subject cannot be illuminated to appropriate brightness
with the flash light alone, by setting the exposure time longer,
it is possible to use ambient light to compensate for shortage of
light and thereby obtain appropriate exposure. Moreover, as the
exposure time is made longer, the ratio of the amount of flash light
used for illuminating the subject during flash shooting to that
of ambient light varies in such a way that the proportion of the
latter increases. In this case, by performing the white balance
adjustment in accordance not with the color characteristics of the
flash light but with the color characteristics of the ambient light,
it is possible to achieve a more appropriate white balance.
Subsequently, whether the switch S1 of the release switch 272 is
off or not is checked (step #355). If the switch S1 is found off,
the execution of the "flash-off" subroutine and of the
[S1] subroutine is ended, and the procedure returns to step #25
in FIG. 2.
If, at step #355, the switch S1 is found not off, whether the switch
S2 of the release switch 272 is on or not is checked (step #360).
If the switch S2 is found not on, the procedure returns to step
#355.
If, at step #360, the switch S2 is found on, the exposure time
set at step #320 or the exposure time set anew at step #340 is fed
to the CCD control circuit 104. The CCD 103 performs photoelectric
conversion for the exposure time thus obtained. After photoelectric
conversion is started, a light control start signal is fed to the
light control IC 20 to start monitoring of the amount of light emitted
by the flash 18 and reflected from the subject. Immediately after
the start of monitoring, a trigger signal is fed to the charging/flashing
circuit 19 to make the flash 18 emit light (step #365).
If the distance to the subject D is equal to or shorter than the
effective flash distance Df, the amount of light being monitored
reaches an appropriate amount before the charged electric power
runs out in the charging/flashing circuit 19. At that time, a flash
emission stop signal is generated. In response to the flash emission
stop signal, a command is supplied to the charging/flashing circuit
19 to stop supplying the charged electric power to the flash 18.
As a result, the flash 18 stops light emission and automatic light
amount adjustment is performed. In this case, at the end of the
exposure time which is set to be equal to the predetermined length
of time, photoelectric conversion is ended. On the other hand, if
the distance to the subject D is longer than the effective flash
distance Df, the amount of light being monitored never reaches the
appropriate amount even after the charged electric power runs out
in the charging/flashing circuit 19. In this case, at the end of
the exposure time which is set to be longer than the predetermined
length of time, photoelectric conversion is ended.
Subsequently, the CCD 103 outputs an image signal (step #370),
which is taken in by the signal processor 11. The image signal thus
obtained is amplified by the amplification circuit 111 and is then
subjected to A/D conversion by the ADC 112 so as to be converted
into image data. The image data is first stored in the RAM 22 temporarily
so as to be subjected to black level correction and white level
correction, and is then subjected to processing including white
balance adjustment in accordance with the value set at step #325
or the value set anew at step #345 (step #375) and image correction
by interpolation (step #380).
Thereafter, the image data is read out from the RAM 22 so as to
display the image taken on the LCD 242 for viewing after shooting
(after view). Furthermore, the image data in the RAM 22 is subjected
to image compression according to, for example, the JPEG standard
(step #385), and is then recorded on the recording medium 25 by
way of the reading/writing circuit 26 (step #390). Then, the execution
of the "flash-on" subroutine and of the [S1] subroutine
is ended, and the procedure returns to step #25 in FIG. 2.
As will be understood from the foregoing, in flash shooting, when
illuminating the subject with flash light results in appropriate
exposure, the exposure time is set to be equal to a predetermined
length of time, and the white balance of the image taken is adjusted
uniformly based on the color characteristics of the flash light.
In contrast, when illuminating the subject with flash light results
in underexposure, the exposure time is set to be longer than the
predetermined length of time in order to compensate for shortage
of light by the use of ambient light, and the white balance of the
image taken is adjusted in accordance with the color characteristics
of the ambient light. As a result, irrespective of whether the subject
lies relatively close to or considerably far away from the camera,
it is possible to obtain an image of the subject with appropriate
exposure and with an appropriate color balance.
Note that, in the above described embodiment, whether appropriate
exposure is obtained with flash light or not is checked prior to
flash shooting based on the open aperture value of the aperture
stop 102, the GNo of the flash 18, and the distance to the subject
measured by the distance measurement module 15. However, this check
does not necessarily have to be made prior to flash shooting. Alternatively,
it is possible to set the exposure time to be equal to a predetermined
length of time prior to flash shooting so that, if a light control
IC feeds a flash emission stop signal before the end of the exposure
time, photoelectric conversion is ended at the end of that exposure
time and, if the light control IC does not feed a flash emission
stop signal before the end of the exposure time, the exposure time
is extended.
Obviously, many modifications and variations of the present invention
are possible in light of the above teachings. It is therefore to
be understood that within the scope of the appended claims, the
invention may be practiced other than as specifically described. |