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Digital Camera Patent Abstract
The present invention provides a digital camera that is capable
of capturing a picture in which the brightness between a main subject
and a nighttime background are well balanced. When an image capture
instruction is received while a night scene portrait mode is set,
in a pixel addition output mode, an image sensor 16 is set to a
high sensitivity state by performing pixel addition, and outputs
low resolution non-flash image data. Further, in an overall pixel
output mode, the image sensor 16 outputs high resolution flash image
data in a low sensitivity state without performing pixel addition.
Next, a resolution conversion circuit 40 converts a resolution of
non-flash image data to be equivalent to a resolution of flash image
data. Then, an image combining circuit 60 adds respective pixel
values of corresponding pixels in the non-flash image data and the
flash image data having the same resolution and combines both sets
of image data to generate image data for recording.
Digital Camera Patent Claims
1. A digital camera, comprising: an image sensor that converts subject
image information into an image signal and outputs the image signal;
and a flash circuit for emitting flash light, wherein the image
sensor has a first image capture mode in which a first image signal
having a relatively large number of pixels captured at a relatively
low sensitivity is output, and a second image capture mode in which
a second image signal having a relatively small number of pixels
captured at a relatively high sensitivity is output, the digital
camera further comprising: an image capture control circuit that
performs an operation for capturing and outputting the second image
signal in the second image capture mode without emission of flash
light by the flash circuit and an operation for capturing and outputting
the first image signal in the first image capture mode with emission
of flash light by the flash circuit; and an image combining circuit
that combines the first image signal and the second image signal
after resizing a number of pixels of at least one image signal of
the first image signal and the second image signal.
2. The digital camera according to claim 1, wherein electric charges
of a plurality of pixels of the image sensor are added up to thereby
capture and output the signal at the high sensitivity in the second
image capture mode.
3. The digital camera according to claim 2, wherein exposure of
the image sensor is controlled with reference to different exposure
program diagram in the first image capture mode and the second image
capture mode.
4. The digital camera according to claim 2, wherein exposure in
the first image capture mode is started in parallel with the operation
for outputting the second image signal immediately after the exposure
ends in the image capture operation of the second image capture
mode.
5. The digital camera according to claim 2, wherein the image capture
control circuit controls an exposure period by means of an electronic
shutter in the second image capture mode, and controls the exposure
period by means of a mechanical shutter in the first image capture
mode.
6. The digital camera according to claim 1, wherein an image combining
circuit combines both images after resizing the number of the pixels
of at least one of the first image signal and the second image signal
to set the number of the pixels of one image signal to be equivalent
to that of the pixels of the other image signal.
7. A digital camera which performs a night scene portrait image
capture, comprising: a flash circuit which emits flash light; an
image sensor which outputs image data at a high or low sensitivity;
an image capture control circuit which performs a high sensitivity
image capture control and a low sensitivity image capture control
in a case where an instruction for the night scene portrait image
capture is received and which allows the image sensor to perform
exposure and output low resolution image data having a relatively
low resolution at the high sensitivity without the emission of the
flash light by the flash circuit in the high sensitivity image capture
control and which allows the image sensor to perform the exposure
and output high resolution image data having a relatively high resolution
at the low sensitivity with the emission of the flash light by the
flash circuit in the low sensitivity image capture control; and
an image combining circuit which combines the low resolution image
data and the high resolution image data output from the image sensor
in the night scene portrait image capture after resizing an image
size of at least one of the low resolution image data and the high
resolution image data.
8. The digital camera according to claim 7, wherein the image sensor
operates in a first output mode in which the image data is output
at a predetermined resolution and a second output mode in which
a plurality of pixels are added up to thereby output the image data
at a resolution that is lower than the predetermined resolution,
and the image capture control circuit controls the image sensor
in such a manner that the image data is output in the second output
mode to thereby output the low resolution image data and the image
data is output in the first output mode to thereby output the high
resolution image data in a case where the instruction for the night
scene portrait image capture is received.
9. The digital camera according to claim 7, further comprising:
an image capture permission judgment section which permits the night
scene portrait image capture in a case where a luminance of a subject
field before the emission of the flash light is not more than a
predetermined threshold luminance, wherein the image capture control
circuit enables the night scene portrait image capture in a case
where the image capture permission judgment section permits the
night scene portrait image capture.
10. The digital camera according to claim 9, wherein the threshold
luminance is a value obtained by subtracting a predetermined value
from a target luminance of the subject field required for securing
predetermined adequate exposure.
11. The digital camera according to claim 10, wherein the threshold
luminance is a value which is lower than a flash threshold luminance
as a judgment standard in a case where the image capture control
circuit judges based on the luminance of the subject field whether
or not the flash light needs to be emitted in order to secure the
predetermined adequate exposure.
12. The digital camera according to claim 9, wherein the image
capture permission judgment section changes the threshold luminance
based on a zoom position of a zoom lens.
13. The digital camera according to claim 9, wherein the image
capture permission judgment section judges whether or not a main
subject exists in an illumination region illuminated with the flash
light emitted by the flash circuit, and permits the night scene
portrait image capture in a case where the main subject exists in
the illumination region.
14. An image capture method of performing night scene portrait
image capture, comprising: a step of allowing an image sensor to
perform exposure and output low resolution image data having a relatively
low resolution at a high sensitivity without emission of flash light
by a flash circuit, and allowing the image sensor to perform the
exposure and output high resolution image data having a relatively
high resolution at a low sensitivity with the emission of the flash
light by the flash circuit in a case where an instruction for the
night scene portrait image capture is received; and a step of allowing
an image combining circuit to combine the low resolution image data
and the high resolution image data output from the image sensor
in the night scene portrait image capture after resizing an image
size of at least one of the low resolution image data and the high
resolution image data.
15. An image capture control program for performing night scene
portrait image capture by use of a digital camera comprising: a
flash circuit which emits flash light; and an image sensor which
outputs image data at a high or low sensitivity, the program allowing
the digital camera to execute: an image capture control step of
performing a high sensitivity image capture control and a low sensitivity
image capture control in a case where an instruction for the night
scene portrait image capture is received, allowing the image sensor
to perform exposure and output low resolution image data having
a relatively low resolution at the high sensitivity without the
emission of the flash light by the flash circuit in the high sensitivity
image capture control, and allowing the image sensor to perform
the exposure and output high resolution image data having a relatively
high resolution at the low sensitivity with the emission of the
flash light by the flash circuit in the low sensitivity image capture
control; and an image combining step of combining the low resolution
image data and the high resolution image data output from the image
sensor in the night scene portrait image capture after resizing
an image size of at least one of the low resolution image data and
the high resolution image data.
16. A digital camera which performs night scene portrait image
capture, comprising: a flash circuit which emits flash light; an
image sensor which outputs image data; an image capture control
circuit which allows the image sensor to perform exposure and output
non-flash image data without the emission of the flash light by
the flash circuit and which allows the image sensor to perform the
exposure and output flash image data with the emission of the flash
light by the flash circuit in a case where an instruction for the
night scene portrait image capture is received; an image combining
circuit which combines the non-flash image data and the flash image
data output from the image sensor in the night scene portrait image
capture; and an image capture permission judgment section which
permits the night scene portrait image capture in a case where a
luminance of a subject field before the emission of the flash light
is not more than a predetermined threshold luminance, wherein the
image capture control circuit enables the night scene portrait image
capture in a case where the image capture permission judgment section
permits the night scene portrait image capture.
Digital Camera Patent Description
FIELD OF THE INVENTION
[0001] The present invention relates to a digital camera that is
capable of selecting an image capture mode to photograph a main
subject in a nighttime background with emission of flash light.
BACKGROUND OF THE INVENTION
[0002] Heretofore, it has been very difficult to obtain a picture
in which brightness between a person and a nighttime background
is well-balanced in a case where the person or the like that is
a main subject is photographed with a nighttime background with
emission of flash light.
[0003] As described in Japanese Patent Application Laid-Open No.
2000-66087, and Japanese Patent Application Laid-Open No. 2000-307941,
there exists a technique in which image capture with emission of
flash light and image capture without emission of flash light are
continuously performed in a case where a person is photographed
in a nighttime background by use of a digital camera, and two images
are combined after the image capture to generate a captured image
in the nighttime background.
[0004] However, in the above-described conventional technique,
when an exposure period is lengthened in order to obtain a satisfactory
captured image with respect to a nighttime background portion, camera
shake and the like are easily caused, and it is difficult to obtain
the satisfactory captured image. When the exposure period is shortened
in order to reduce the effects of the hand shake and the like, and
an amplification factor of image data output from a solid-state
image sensor is raised, the image is easily affected by noise such
as thermal noise. Even in this case, it is difficult to obtain the
satisfactory captured image.
SUMMARY OF THE INVENTION
[0005] An object of the present invention is to provide a digital
camera that is capable of capturing a picture in which brightness
between a main subject and a nighttime background is well-balanced.
[0006] According to the present invention, there is provided a
digital camera comprising: an image sensor that converts subject
image information into an image signal and outputs the image signal;
and a flash circuit for emitting flash light, wherein the image
sensor has a first image capture mode in which a first image signal
having a relatively large number of pixels captured at a relatively
low sensitivity is output, and a second image capture mode in which
a second image signal having a relatively small number of pixels
captured at a relatively high sensitivity is output, the digital
camera further comprising: an image capture control circuit that
performs an operation for capturing and outputting the second image
signal in the second image capture mode without emission of flash
light by the flash circuit and an operation for capturing and outputting
the first image signal in the first image capture mode with emission
of flash light by the flash circuit; and an image combining circuit
that combines the first image signal and the second image signal
after resizing the number of pixels of at least one image signal
of the first image signal and the second image signal.
[0007] In one mode of the digital camera according to the present
invention, in the second image capture mode, electric charges of
a plurality of pixels of the image sensor are added up to thereby
capture and output an image at a high sensitivity.
[0008] According to the present invention, when an instruction
for night scene portrait image capture is received, the image capture
control circuit performs the operation for capturing and outputting
the second image signal in the second image capture mode without
emission of flash light by the flash circuit and the operation for
capturing and outputting the first image signal in the first image
capture mode with emission of flash light by the flash circuit.
Moreover, the image combining circuit resizes the number of the
pixels of at least one of the first and second image signals to
combine both of the image signals. Accordingly, it is possible to
capture the picture in which the brightness between the main subject
and the nighttime background is well-balanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a diagram schematically showing functional blocks
of a digital camera in the present embodiment;
[0010] FIG. 2 is a diagram specifically showing functional blocks
of the digital camera in the present embodiment;
[0011] FIG. 3 is a timing chart in a case where the digital camera
of the present embodiment performs image capture in a night scene
portrait mode;
[0012] FIG. 4 is a diagram schematically showing functional blocks
of the digital camera in a modification of the present embodiment;
[0013] FIG. 5A is an explanatory view of a threshold luminance
LVf indicating a standard for judging whether or not to permit the
night scene portrait mode;
[0014] FIG. 5B is an explanatory view of the threshold luminance
LVf indicating the standard for judging whether or not to permit
the night scene portrait mode;
[0015] FIG. 5C is an explanatory view of the threshold luminance
LVf indicating the standard for judging whether or not to permit
the night scene portrait mode;
[0016] FIG. 6 is a flowchart in judging whether or not the digital
camera set to the night scene portrait mode permits the image capture
in the night scene portrait mode; and
[0017] FIG. 7 is a diagram showing functional blocks in a modification
of a resolution conversion circuit.
DETAILED DESCRIPTION OF THE INVENTION
[0018] According to the present embodiment, a digital camera is
capable of selecting a night scene portrait mode suitable for photographing
a main subject such as a person in a nighttime background. The digital
camera set to the night scene portrait mode successively performs
an image capture (hereinafter referred to as the "non-flash
image capture") without emission of flash light and an image
capture with emission of flash light in response to one image capture
instruction. The digital camera combines image data (hereinafter
referred to as the "non-flash image data") obtained by
the non-flash image capture with image data (hereinafter referred
to as the "flash image data") obtained by flash image
capture to thereby generate image data for recording.
[0019] FIG. 1 is a diagram showing functional blocks of the digital
camera according to the present embodiment. An image capture section
10 comprises a solid-state image sensor that is capable of outputting
image data (hereinafter referred to as the "low resolution
image data") having a low resolution at a high sensitivity,
and outputting image data (hereinafter referred to as the "high
resolution image data") having a high resolution at a low sensitivity.
The image capture section 10 outputs the low resolution image data
in a case where the non-flash image data is output, and outputs
the high resolution image data in a case where the flash image data
is output. A resolution conversion circuit 40 resizes the number
of the pixels of at least one image data to be equivalent to that
of the image data output from the image capture section 10. An image
combining circuit 60 combines two sets of image data whose image
size agree with each other to thereby generate the image data for
recording, and records the data in a recording device 80.
[0020] FIG. 2 is a diagram showing more detailed functional blocks
of the digital camera according to the present embodiment. An image
capture lens 12 is a lens group constituted of various types of
lenses such as a focus lens and a zoom lens. A mechanical shutter
14 physically interrupts light which enters an image sensor 16 from
a subject field. The light from the subject field is transmitted
to the image sensor 16 via the image capture lens 12 and the mechanical
shutter 14.
[0021] The image sensor 16 photoelectrically converts the incident
light into a signal charge by a light receiving element array to
output the signal charge. The light receiving element array of the
image sensor 16 is constituted of longitudinal M.times.lateral N
(M, N are integers) pixels to which filters of colors of red (R),
green (G), and blue (B) have been added. The signal charge output
from the image sensor 16 constitutes the image data having color
components R, G, and B. The image sensor 16 is a solid-state image
sensor that is capable of appropriately switching between modes.
These modes are: a mode (hereinafter referred to as the "pixel
addition output mode") in which the signal charges of nine
pixels having the same color components are added up and output
to multiply a sensitivity ninefold, and the low resolution image
data having a relatively low resolution is output at a high sensitivity;
and a mode (hereinafter referred to as the "overall pixel output
mode") in which the signal charge of one pixel is independently
output to thereby output the high resolution image data having a
relatively high resolution at a low sensitivity. It is to be noted
that when the number of signal charges to be added up is increased,
the sensitivity can be further enhanced.
[0022] Additionally, in a case where the image capture is performed
without the emission of the flash light in a night scene, an exposure
period usually needs to be lengthened comparatively in order to
secure adequate exposure. However, when the exposure period is lengthened,
it is difficult to obtain satisfactory image data owing to camera
shake, movement of a person or the like as the subject, etc. On
the other hand, when an amplification factor of the image data output
from the image sensor is raised in order to secure the adequate
exposure while shortening the exposure period, noise increases.
In this case, it is also difficult to obtain the satisfactory image
data. To solve the problem, in the present embodiment, in a case
where the non-flash image capture is performed in the night scene
portrait mode, the image sensor 16 operates in the pixel addition
output mode, and adds up the pixels to output the resultant image
data. Accordingly, the high sensitivity is realized while shortening
the exposure period. Consequently, degradation of an image quality
due to camera shake or movement of the person can be prevented at
the time of a non-flash image capture.
[0023] A correlated double sampling (CDS)-analog/digital (AD) circuit
18 extracts the image signal component of each pixel constituting
the image data output from the image sensor 16 by correlated double
sampling, and converts the data into a digital signal.
[0024] A white balance (WB) circuit 20 multiplies pixel values
of the respective color components R, G, and B included in the image
data by desired gains, respectively. Accordingly, the WB circuit
20 subjects the image data to white balance adjustment. A non-flash
correction gain memory 22 stores a correction gain (hereinafter
referred to as the "non-flash correction gain") for use
in a case where the WB circuit 20 performs the white balance adjustment
with respect to the non-flash image data. On one hand, a flash correction
gain memory 24 stores a correction gain (hereinafter referred to
as the "flash correction gain") for use in a case where
the WB circuit 20 performs the white balance adjustment with respect
to the flash image data. A first selector 36 operates a switch based
on a switch signal from a timing control circuit 30. The WB circuit
20 performs the white balance adjustment by use of the non-flash
correction gain in a case where the switch is connected to a contact
A. On the other hand, the WB circuit 20 performs the white balance
adjustment by use of the flash correction gain in a case where the
switch is connected to a contact B.
[0025] A YC separation circuit 26 converts the non-flash image
data and the flash image data output from the WB circuit 20 into
a color space of YCrCb. The non-flash image data output from the
YC separation circuit 26 is input into the resolution conversion
circuit 40 via a contact C of a second selector 38. On the other
hand, the flash image data output from the YC separation circuit
26 is input into the resolution conversion circuit 40 via a contact
D of the second selector 38.
[0026] The timing control circuit 30 outputs a control signal to
each circuit or the like constituting the digital camera. To be
more specific, the timing control circuit 30 outputs a reference
pulse to a timing generator (TG) 32. The timing control circuit
30 outputs to the TG 32 a mode switch signal indicating an instruction
for switching an output mode of the image sensor 16. The timing
control circuit 30 outputs a switch changeover signal to the first
selector 36 or the second selector 38. Furthermore, the timing control
circuit 30 outputs a mechanical shutter signal for instructing opening/closing
of the mechanical shutter 14, or a flash emission signal for instructing
a flash circuit 34 to emit the flash light.
[0027] The TG 32 outputs a horizontal synchronizing signal (HD)
and a vertical synchronizing signal (VD) required for driving the
light receiving element array included in the image sensor 16, and
a synchronizing signal required for the CDS-AD circuit 18 to process
signals based on the reference pulse output from the timing control
circuit 30 to synchronize the image sensor 16 with the CDS-AD circuit
18.
[0028] The flash circuit 34 emits the flash light for irradiating
a subject in order to achieve adequate exposure during the image
capture. Furthermore, the flash circuit 34 emits slight flash light
(hereinafter referred to as "pre-emission") for exposure
measurement prior to the emission.
[0029] A frame memory 42 is a buffer that temporarily holds the
non-flash image data until the flash image data is output. A resolution
enlargement circuit 44 converts the resolution of the non-flash
image data to be equivalent to that of the flash image data to thereby
match an image size of the non-flash image data with that of the
flash image data. That is, in the present embodiment, the flash
image data is the image data obtained without adding up the pixels.
Therefore, there is a ninefold difference between the resolutions
of the non-flash image data and the flash image data. Therefore,
the resolution enlargement circuit 44 converts, for example, each
pixel that constitutes the non-flash image data into nine pixels
to thereby multiply the resolution of the non-flash image data ninefold.
It is to be noted that the resolution enlargement circuit 44 may
use a pixel value of an original pixel before the pixel conversion
as the pixel value of a new pixel generated by performing the pixel
conversion. The resolution enlargement circuit 44 may determine
the pixel value of the new pixel by use of a known pixel interpolating
method. For example, the resolution enlargement circuit 44 may obtain
the pixel value of the new pixel by performing predetermined-weighted-averaging
(including simple averaging) of the pixel values based on distances
between the new pixel and a plurality of original pixels around
the new pixel.
[0030] The image combining circuit 60 adds up the pixel values
of the associated pixels based on the input non-flash and flash
image data to thereby combine the non-flash image data with the
flash image data. The image combining circuit 60 outputs the resultant
combined image data as the image data for recording. An RGB conversion
circuit 62 converts into RGB the image data for recording which
has been converted into the color space of YCrCb. A gamma correction
circuit 64 performs nonlinear conversion adapted to an output device
(e.g., monitor or the like) with respect to the image data for recording
which has been converted into the RGB. The recording device 80 stores
the gamma-corrected image data for recording as the image data for
recording.
[0031] When the digital camera constituted as described above receives
an image capture instruction in a state in which the night scene
portrait mode is set, the image sensor 16 performs the exposure
without the emission of the flash light, and outputs the low resolution
image data at high sensitivity in the pixel addition output mode.
Furthermore, the image sensor 16 performs the exposure with emission
of the flash light, and outputs the high resolution image data at
low sensitivity in the overall pixel output mode. Moreover, after
the resolution conversion circuit 40 converts the resolution of
the low resolution image data to be equivalent to that of the high
resolution image data, the image combining circuit 60 adds up and
combines the two sets of image data.
[0032] Next, there will be described an image capture procedure
of the digital camera set to the night scene portrait mode with
reference to a timing chart shown in FIG. 3.
[0033] First, when the image capture section 10 detects that a
shutter button is fully pressed, the image sensor 16 switches an
output mode to the pixel addition output mode at a time when a vertical
synchronizing signal (VD1) just after a mode switch instruction
turns to a negative polarity based on the mode switch instruction
output from the timing control circuit 30. When the image sensor
16 switches to the pixel addition output mode, the timing generator
32 outputs one or more sub-pulses to the image sensor 16. The image
sensor 16 starts substantial exposure for performing non-flash image
capture at a time when the outputting of the sub-pulses stops, and
ends the exposure at a time when the existing vertical synchronizing
signal (VD2) turns to the negative polarity. That is, an exposure
period Ta for the non-flash image capture is from the time when
the outputting of the sub-pulses stops until the existing vertical
synchronizing signal turns to the negative polarity. Therefore,
when the number of outputs of the sub-pulses is controlled, the
exposure period Ta for the non-flash image capture can be controlled.
After the end of the exposure for the non-flash image capture, the
timing generator 32 outputs a read pulse, and accordingly the image
sensor 16 outputs the non-flash image data.
[0034] Moreover, while outputting the non-flash image data, the
image sensor 16 starts the exposure for flash image capture at a
time when the vertical synchronizing signal (VD3) turns to a positive
polarity. Furthermore, the image sensor 16 ends the exposure at
a time when the mechanical shutter 14 closes. That is, the image
sensor 16 performs the exposure for the flash image capture while
outputting the non-flash image data in the pixel addition output
mode. The flash circuit 34 emits the flash light in an exposure
period Tb. Thereafter, after the end of the outputting of the non-flash
image data in the pixel addition output mode, the image sensor 16
is switched to the overall pixel output mode to start the outputting
of the flash image data.
[0035] As will be apparent from the timing chart shown in FIG.
3, the exposure period Ta at a non-flash image capture time is adjusted
by the outputting of the sub-pulses, and the exposure period Tb
at a flash image capture time is adjusted by opening/closing the
mechanical shutter 14. The image sensor 16 performs the exposure
for the flash image capture while outputting the non-flash image
data in the pixel addition output mode. Consequently, in the present
embodiment, there is hardly any time lag between the non-flash image
capture and the flash image capture. Therefore, a synthesized picture
can be an intended picture, even if the main subject moves from
a time when the non-flash image capture is completed until the flash
image capture is completed.
[0036] As described above, in the present embodiment, the image
sensor 16 adds up the pixels in the pixel addition output mode to
thereby output the low resolution non-flash image data at high sensitivity.
On the other hand, the image sensor 16 outputs the high resolution
flash image data at low sensitivity in the overall pixel output
mode without adding up the pixels. Subsequently, the resolution
conversion circuit 40 converts the resolution of the non-flash image
data to be equivalent to that of the flash image data. Moreover,
the image combining circuit 60 adds up and combines the non-flash
image data and the flash image data that have the equal resolution
to thereby generate the image data for recording.
[0037] Consequently, according to the present embodiment, the non-flash
image data is output in the pixel addition output mode to thereby
realize high sensitivity. Therefore, it is possible to shorten the
exposure period for outputting the non-flash image data. This can
prevent degradation of the image quality due to camera shake or
movement of the person.
[0038] Moreover, the non-flash image data is output in the pixel
addition output mode to thereby realize high sensitivity. Therefore,
it is possible to prevent increase of noise at a time when the exposure
period is shortened and the amplification factor of the image data
output by the image sensor 16 is raised.
[0039] Furthermore, the image data is output in the pixel addition
output mode, and the resolution of the image data having comparatively
less noise is enlarged. Therefore, the resolution can be converted
into high resolution while keeping a certain degree of image quality.
[0040] As described above, according to the present embodiment,
a user can obtain a picture in which both of the nighttime background
and the main subject are shown clearer than those in a picture obtained
by simply performing the non-flash or flash image capture.
[0041] Additionally, there is preferably a certain degree of luminance
difference between a main subject portion illuminated with the flash
light and a background portion that is not illuminated with the
flash light in order to add up and combine the non-flash image data
and the flash image data as described above and obtain a picture
in which the main subject and the background are shown clearly.
That is, the background portion of the image obtained from the flash
image data is preferably as dark as possible. Accordingly, the background
portion of the image obtained from the non-flash image data appears
more clearly in the combined image. However, it is difficult for
the user to judge the luminance of the subject field and judge whether
or not the image capture is possible in the night scene portrait
mode.
[0042] To solve the problem, in a modification of the present embodiment,
as described later, after a digital camera judges whether or not
a scene can be photographed in the above-described night scene portrait
mode based on a predetermined judgment standard, the scene is photographed
in the night scene portrait mode only when the photographing is
judged to be possible. On the other hand, when the photographing
is judged to be impossible, the scene is photographed in a usual
portrait mode. It is to be noted that the portrait mode is an image
capture mode suitable for taking a clear picture of a main subject
such as a person in preference to the background.
[0043] FIG. 4 is a diagram showing functional blocks of the digital
camera in the modification. In FIG. 4, the same circuits and the
like as those shown in FIG. 1 are denoted with the same reference
numerals, and description thereof is omitted.
[0044] In FIG. 4, an image capture control section 100 controls
an image capture section 10 in accordance with a set image capture
mode. In the present modification, to facilitate the description,
a night scene portrait mode and a portrait mode are prepared as
image capture modes selectable by the digital camera.
[0045] A program chart storage section 102 stores a exposure program
diagram required for each image capture mode. Here, the exposure
program diagram is data which determines conditions for determining
a value of at least one of a shutter speed, a diaphragm value, and
an ISO sensitivity based on a luminance of a subject field in order
to obtain adequate exposure. One exposure program diagram is usually
prepared for one image capture mode. However, in the present modification,
two exposure program diagrams for non-flash image capture and flash
image capture are prepared for the night scene portrait mode, and
stored beforehand in the exposure program diagram storage section
102, respectively. Therefore, in the night scene portrait mode,
exposure conditions can be individually determined depending on
whether or not the flash light is to be emitted. Especially in the
present modification, the exposure program diagram for the flash
image capture in the night scene portrait mode is determined on
conditions different from those of the exposure program diagram
for use at a flash image capture time in the portrait mode. To be
more specific, the exposure program diagram for the flash image
capture is predetermined in the night scene portrait mode in such
a manner that the shutter speed in the night scene portrait mode
at the flash image capture time is higher than that in the portrait
mode at the flash image capture time. When the shutter speed is
set to be high in this manner, light from a background portion that
is not illuminated with flash light does not easily enter the image
sensor 16, and it is possible to obtain image data in which the
background portion is comparatively dark. Accordingly, the background
portion is shown more clearly in a picture obtained from a combined
image. For example, when the shutter speed at a usual flash image
capture time is set to 1/30 [sec], the shutter speed in the night
scene portrait mode at a flash image capture time is set to 1/200
[sec].
[0046] However, in a case where the luminance (i.e., the luminance
of the whole subject field before emission of the flash light) of
the subject field portion that is not illuminated with the flash
light has a certain degree of magnitude, even if the shutter speed
is set to be high, the light other than the flash light enters the
image sensor 16. That is, in a case where the luminance has a certain
degree of magnitude, even if the shutter speed is set to be high,
the background portion of the image obtained from the flash image
data becomes bright to a certain degree. Therefore, the background
portion of the image obtained from the non-flash image data is not
clearly shown in the combined image. Therefore, in a case where
the luminance of the subject field has a certain degree of magnitude,
it is preferable not to perform the image capture in the night scene
portrait mode.
[0047] To solve the problem, in the present modification, a threshold
luminance LVf is determined, and the image capture in the night
scene portrait mode is permitted when the luminance of the subject
field is not more than the threshold luminance LVf. As the threshold
luminance LVf, a value is obtained by, for example, subtracting
a predetermined luminance difference .DELTA.LVa from a target luminance
LVt (i.e., the luminance of the subject field portion illuminated
with the flash light) required for obtaining adequate exposure in
a case where the flash image capture is performed in the night scene
portrait mode. Here, to obtain the luminance difference .DELTA.LVa,
the image capture may be performed in the night scene portrait mode
on various luminance conditions to determine an optimum value. The
threshold luminance LVf may be changed depending on a zoom position
of a zoom lens. This is because it is considered that the target
luminance LVt required for securing the adequate exposure determined
by the exposure program diagram differs with the zoom position.
[0048] FIG. 5A is a diagram showing a relation between the target
luminance LVt and the threshold luminance LVf in each zoom position
of the zoom lens. In FIG. 5A, a broken line 200 indicates the target
luminance LVt, and a one-dot chain line 202 indicates the threshold
luminance LVf. FIG. 5A shows that the digital camera performs image
capture in the night scene portrait mode in a case where the luminance
of the subject field is not more than the threshold luminance LVf,
and the digital camera performs the image capture in the portrait
mode in a case where the luminance of the subject field is higher
than the threshold luminance LVf.
[0049] In FIG. 5B, in addition to the target luminance LVt and
the threshold luminance LVf, a flash threshold luminance LVp determined
in the exposure program diagram for the portrait mode is shown by
a solid line 204. Here, the flash threshold luminance LVp is a threshold
value for judging whether or not illumination with the flash light
is required in order to obtain adequate exposure. That is, the digital
camera judges that emission of the flash light is required in a
case where the luminance of the subject field before the emission
of the flash light is not more than the flash threshold luminance
LVp. The digital camera judges that the emission of the flash light
is not required in a case where the luminance is larger than the
flash threshold luminance LVp. When each threshold luminance is
determined as shown in FIG. 5B, the digital camera operates as follows.
That is, when the luminance of the subject field is not less than
the flash threshold luminance LVp, the digital camera performs the
non-flash image capture in the portrait mode. When the luminance
of the subject field is in a range of the flash threshold luminance
LVp to the threshold luminance LVf, the digital camera performs
the flash image capture in the portrait mode. Furthermore, when
the luminance of the subject field is not more than the threshold
luminance LVf, the digital camera performs the non-flash image capture
and the flash image capture in the night scene portrait mode.
[0050] In FIGS. 5A and 5B, the threshold luminance LVf is determined
in such a manner that the predetermined luminance difference .DELTA.LVa
is made between the luminance (target luminance LVt) of the subject
field portion illuminated with the flash light and the luminance
of the subject field portion that is not illuminated with the flash
light. However, as seen from FIG. 5B, when the zoom position is
on a telephotographic side, the difference between the flash threshold
luminance LVp and the threshold luminance LVf increases. This means
that the image capture cannot be performed in the night scene portrait
mode although the subject field has such a low luminance as to require
the flash light. Therefore, when the threshold luminance LVf is
determined in this manner, there are more scenes in which the night
scene portrait mode cannot be selected on the telephotographic side,
and there is a possibility that ease of use for the user will be
degraded. To solve the problem, as shown in FIG. 5C, a value obtained
by subtracting a certain value .DELTA.LVb from the flash threshold
luminance LVp may be described as the threshold luminance LVf. In
FIG. 5C, a two-dot chain line 206 indicates the threshold luminance
LVf.
[0051] As described above, in the present modification, the image
capture in the night scene portrait mode is permitted in a case
where the luminance of the subject field is lower than the threshold
luminance LVf predetermined by actual measurement or the like.
[0052] Furthermore, even in a case where the luminance is low to
a certain degree, when the digital camera is distant from the main
subject, the main subject is not illuminated with the flash light.
Therefore, the luminance difference between the main subject portion
and the background portion decreases. Therefore, it is preferable
not to perform the image capture in the night scene portrait mode
even in a case where the main subject is not illuminated with the
flash light.
[0053] In addition, the image capture in the night scene portrait
mode is effective for photographing the night scene well. Therefore,
it is preferable not to perform the image capture in the night scene
portrait mode even in a case where the subject field is so bright
that the main subject does not have to be illuminated with the flash
light.
[0054] Moreover, the image capture in the night scene portrait
mode cannot be performed in a state in which the emission of the
flash light is prohibited in the digital camera. Here, examples
of the prohibited state include: a case where a flash device built
into the digital camera is of a so-called manual popup type, and
the flash device is closed up; and a case where the digital camera
is set in such a manner as to forcibly prohibit the emission of
the flash light.
[0055] From the above-described viewpoint, in a case where the
night scene portrait mode is selected, the image capture control
section 100 judges whether or not to permit the image capture in
the night scene portrait mode based on a flowchart shown in FIG.
6. Moreover, the digital camera performs the image capture in the
night scene portrait mode, when the image capture is permitted as
a result of the judgment. The digital camera performs the image
capture in the portrait mode in a case where the image capture in
the night scene portrait mode is not permitted.
[0056] In FIG. 6, first, when the night scene portrait mode is
selected, the image capture control section 100 judges whether or
not the emission of the flash light is prohibited (S100). When the
emission of the flash light is permitted as a result of the judgment
(the judgment result of S100 is negative "N"), the image
capture control section 100 waits until the shutter button is half
pressed. Thereafter, when the image capture control section 100
detects that the shutter button has been half pressed (S102), the
section acquires a luminance LVs of the subject field from a photometry
device or the like (S104), and judges whether or not the luminance
LVs is higher than the flash threshold luminance LVp (S106).
[0057] When the luminance LVs is judged to be lower than the threshold
luminance LVp as a result of the judgment of S106 (the judgment
result of S106 is negative "N"), the image capture control
section 100 waits until the shutter button is fully pressed. Thereafter,
when the image capture control section 100 detects that the shutter
button has been fully pressed (S108), the section judges whether
or not the main subject exists in a region illuminated with the
flash light (S110). This judgment is performed by, for example,
the flash circuit 34 that utilizes pre-emission prior to substantial
emission in response to the operation of fully pressing the shutter
button. That is, the image capture control section 100 acquires
a quantity of light reflected from the main subject illuminated
with the pre-emission from a photometry circuit. Moreover, the image
capture control section 100 judges whether or not the main subject
exists in the region illuminated with the flash light by judging
whether or not the reflected light quantity reaches a predetermined
threshold light quantity.
[0058] When it is judged that the main subject exists in the region
illuminated with the flash light as a result of the judgment of
S110 (the judgment result of S110 is affirmative "Y"),
the image capture control section 100 acquires the threshold luminance
LVf (S112), and judges whether or not the luminance LVs is higher
than the threshold luminance LVf (S114). As a result of the judgment,
when the luminance LVs is judged to be not more than the threshold
luminance LVf (the judgment result of S114 is negative "N"),
the image capture control section 100 acquires the non-flash and
flash exposure program diagrams in the night scene portrait mode
from the exposure program diagram storage section 102 (S116). The
image capture control section 100 determines image capture conditions
such as the shutter speed, the diaphragm value, and the ISO sensitivity
for each acquired exposure program diagram (S118). Thereafter, the
image capture control section 100 controls the image capture section
10 in such a manner as to perform the image capture in the night
scene portrait mode (S120).
[0059] Moreover, when it is judged that the emission of the flash
light is prohibited in S100 (the judgment result of S100 is affirmative
"Y"), the image capture cannot be performed in the night
scene portrait mode, and the image capture control section 100 therefore
waits until the shutter button is half pressed. Thereafter, when
the image capture control section 100 detects that the shutter button
has been half pressed (S122), the section acquires the luminance
LVs of the subject field (S124). Furthermore, the image capture
control section 100 acquires the exposure program diagram for the
portrait from the exposure program diagram storage section 102 (S126),
and determines the image capture conditions based on the exposure
program diagram for the portrait (S128). Every time the image capture
control section 100 detects that the shutter button has been fully
pressed (S130), the section controls the image capture section 10
in such a manner as to perform the non-flash image capture in the
portrait mode (S132).
[0060] Furthermore, when it is judged in S110 that the main subject
does not exist in the region illuminated with the flash light (the
judgment result of S110 is negative "N"), and it is judged
in S114 that the luminance LVs is higher than the threshold luminance
LVf, the image capture control section 100 acquires the exposure
program diagram for the portrait from the exposure program diagram
storage section 102 (S134). Moreover, the image capture control
section 100 determines the image capture conditions based on the
exposure program diagram (S136), and controls the image capture
section 10 in such a manner as to perform the flash image capture
in the portrait mode (S138).
[0061] As described above, according to the present modification,
the digital camera judges whether or not the scene can be photographed
in the night scene portrait mode based on the predetermined judgment
standard. Thereafter, the only scene from which a satisfactory picture
is presumed to be obtained is photographed in the night scene portrait
mode, and the scene from which the satisfactory picture is not presumed
to be obtained is photographed in the portrait mode. Accordingly,
there is a high possibility that a satisfactory picture will be
obtained in a case where the image capture in the night scene portrait
mode is performed.
[0062] In the above-described embodiment, the example has been
described in which nine pixels of the same color are added up in
a case where the image sensor 16 outputs the image data in the pixel
addition output mode. However, the number of pixels to be added
up in the pixel addition output mode is not limited to nine, and
the image sensor 16 may add up, for example, four pixels to output
the non-flash image data.
[0063] Moreover, the example has been described in which the image
sensor 16 outputs the flash image data in the overall pixel output
mode. However, in a case where the image sensor 16 can output the
image data in a plurality of pixel addition output modes in which
the number of the pixels to be added up varies, the image sensor
16 may output the flash image data in the pixel addition output
mode in which pixels less than those of the non-flash image data
are added up.
[0064] Furthermore, the example has been described in which the
resolution conversion circuit 40 enlarges the resolution of the
non-flash image data to thereby convert the resolution of the flash
image data to be equivalent to that of the non-flash image data.
However, as shown in FIG. 7, a resolution reduction circuit 46 may
be disposed on a flash image data side to control a third selector
48. Accordingly, the resolution conversion circuit 40 may reduce
the resolution of the flash image data while enlarging the resolution
of the non-flash image data to thereby set the resolutions of both
of the image data to be equivalent to each other.
[0065] In addition, in the above-described embodiment, the example
of the digital camera has been described that is capable of selecting
a plurality of image capture modes such as the night scene portrait
mode and the portrait mode. However, the present invention is not
limited to such a digital camera, and can be realized even by a
digital camera which is for exclusive use in night scene portrait
image capture without operating in a plurality of image capture
modes.
[0066] Moreover, in the digital camera according to the present
embodiment, the above-described function of the present embodiment
is realized by reading and executing a control program stored in
a storage medium by a computer, but the present invention is not
limited to this constitution. Needless to say, the present invention
includes a case where a part or all of actual processing of an operating
system (OS) operating on the computer is performed based on an instruction
of the control program, and the above-described function of the
present embodiment is realized by the processing.
[0067] Furthermore, examples usable as the storage medium to store
the control program include Floppy (registered trademark) disk,
a hard disk, an optical disk, a magneto-optical disk, a compact
disk read only memory (CD-ROM), a compact disk recordable (CD-R),
a magnetic tape, a nonvolatile memory card, and a ROM chip.
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