|
Digital Camera Patent Abstract
In a digital camera including an electronic flash device using a
light-emitting diode as a flash light source, white balance correction
is performed by using a white balance correction value corresponding
to a color temperature of light actually emitted from the electronic
flash device.
Digital Camera Patent Claims
1. A digital camera having an electronic flash device using a light-emitting
diode as a flash light source, comprising: a storage device which
stores correction information for correcting white balance of an
image obtained by flash shooting, a white balance correcting device
which corrects white balance of the image obtained by flash shooting
based on the correction information stored in the storage device,
a temperature detecting device which detects an ambient temperature
of the light-emitting diode, a modification information storage
device which stores modification information for modifying the correction
information stored in the storage device, the modification information
storage device storing the modification information of the correction
information based on a change in an ambient temperature of the light-emitting
diode, a modifying device which modifies the correction information
stored in the storage device based on a detection result of the
temperature detecting device and the modification information stored
in the modification information storage device; and the white balance
correcting device corrects white balance of the image obtained by
flash shooting based on the correction information modified by the
modifying device.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a digital camera and particularly
relates to a digital camera comprising an electronic flash device
using a light-emitting diode (LED) as a flash light source.
[0003] 2. Description of the Related Art
[0004] In general, a xenon tube is used as a light source in an
electronic flash device of a camera. However, an electronic flash
device using a xenon tube as a light source can emit only instant
light of several milliseconds, so that flash shooting cannot be
performed while a shutter is released slowly. Further, since a xenon
tube has a spectral characteristic close to a daylight color, flash
shooting for backlight correction in the morning and evening results
in a picture with an unnatural color. Hence, in order to solve the
defect of such an electronic flash device using a xenon tube as
a light source, an electronic flash device using an LED as a light
source is proposed (e.g., Japanese Patent Application Publication
No. 2002-116481).
[0005] However, since an LED emits light varied in color temperature
among products, when an LED is used as a flash light source of a
digital camera, a white balance correction result is varied among
products.
[0006] Moreover, an LED emits light varied in color temperature
according to an ambient temperature and an applied current, and
a white balance correction result is varied according to an ambient
temperature and an applied current.
[0007] The present invention is devised in view of such circumstances
and has as its objective the provision of a digital camera achieving
an image of a stable color shade during flash shooting using an
LED as a flash light source.
SUMMARY OF THE INVENTION
[0008] In order to attain the above objective, first aspect of
a present invention provides a digital camera having an electronic
flash device using a light-emitting diode as a flash light source,
comprising: a storage device which stores correction information
for correcting white balance of an image obtained by flash shooting
using the electronic flash device, the storage device storing the
correction information set based on a detection result of a color
temperature of light actually emitted from the electronic flash
device; and a white balance correcting device which corrects white
balance of the image obtained by flash shooting using the electronic
flash device based on the correction information stored in the storage
device.
[0009] According to the first aspect, the white balance correction
information is set based on a detection result of a color temperature
of light actually emitted from the electronic flash device, and
the white balance of the image obtained by flash shooting is corrected
based on the set correction information. Hence, even when light
emitted from the electronic flash device is varied in color temperature
among products, it is possible to obtain images of the same color
shade.
[0010] Further, in order to attain the above object, second aspect
of a present invention provides a digital camera having an electronic
flash device using a light-emitting diode as a flash light source,
comprising: a storage device which stores correction information
for correcting white balance of an image obtained by flash shooting,
a white balance correcting device which corrects white balance of
the image obtained by flash shooting based on the correction information
stored in the storage device, a modification information storage
device which stores modification information for correcting the
correction information stored in the storage device, the modification
information storage device storing the modification information
required to make the correction information stored in the storage
device coincident with correction information set based on a detection
result of a color temperature of light actually emitted from the
electronic flash device, a modifying device which modifies the correction
information based on the modification information stored in the
modification information storage device; and the white balance correcting
device corrects the white balance of the image obtained by flash
shooting based on the correction information modified by the modifying
device.
[0011] According to the second aspect of the present invention,
the white balance correction information stored in the storage device
is modified so as to coincide with the white balance correction
information set based on a detection result of a color temperature
of light actually emitted from the electronic flash device, and
the white balance of the image obtained by flash shooting is corrected
based on the modified correction information. Hence, even when light
emitted from the electronic flash device is varied in color temperature
among products, it is possible to obtain images of the same color
shade.
[0012] Moreover, in order to attain the above object, third aspect
of a present invention provides a digital camera having an electronic
flash device using a light-emitting diode as a flash light source,
comprising: a storage device which stores correction information
for correcting white balance of an image obtained by flash shooting,
a white balance correcting device which corrects white balance of
the image obtained by flash shooting based on the correction information
stored in the storage device, a temperature detecting device which
detects an ambient temperature of the light-emitting diode, a modification
information storage device which stores modification information
for modifying the correction information stored in the storage device,
the modification information storage device storing the modification
information of the correction information based on a change in an
ambient temperature of the light-emitting diode, a modifying device
which modifies the correction information stored in the storage
device based on a detection result of the temperature detecting
device and the modification information stored in the modification
information storage device; and the white balance correcting device
corrects white balance of the image obtained by flash shooting based
on the correction information modified by the modifying device.
[0013] According to the third aspect of the present invention,
the white balance correction information stored in the storage device
is modified according to a change in the ambient temperature of
the light-emitting diode, and the white balance of the image obtained
by flash shooting is corrected based on the modified correction
information. Hence, even when the light-emitting diode changes in
ambient temperature and light emitted from the electronic flash
device changes in color temperature, it is always possible to obtain
images of the same color shade.
[0014] In order to attain the above objective, fourth aspect of
a present invention provides a digital camera having an electronic
flash device using a light-emitting diode as a flash light source,
comprising: a storage device which stores correction information
for correcting white balance of an image obtained by flash shooting,
a white balance correcting device which corrects white balance of
an image obtained by flash shooting based on the correction information
stored in the storage device, a current detecting device which detects
a value of current applied to the light-emitting diode, a modification
information storage device which stores modification information
for the correction information based on a change in a value of current
applied to the light-emitting diode, the modification information
storage device storing the modification information for modifying
the correction information stored in the storage device, a modifying
device which modifies the correction information stored in the storage
device based on a detection result of the current detecting device
and the modification information stored in the modification information
storage device; and the white balance correcting device corrects
the white balance of the image obtained by flash shooting, based
on the correction information modified by the modifying device.
[0015] According to the fourth aspect of the present invention,
the white balance correction information stored in the storage device
is modified according to a change in current applied to the light-emitting
diode, and the white balance of the image obtained by flash shooting
is corrected based on the modified correction information. Hence,
even when current applied to the light-emitting diode changes and
light emitted from the electronic flash device changes in color
temperature, it is always possible to obtain images of the same
color shade.
[0016] As described above, according to the present invention,
white balance correction is performed based on a color temperature
of light actually emitted from an electronic flash device. Thus,
even when an LED is used as a flash light source, it is always possible
to obtain an image of a stable color shade.
[0017] Further, since white balance correction is performed according
to a change in ambient temperature or a change in current applied
to the LED, it is always possible to obtain an image of a stable
color shade.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a front perspective view showing one embodiment
of a digital camera according to the present invention;
[0019] FIG. 2 is a sectional view showing the configuration of
a light-emitting part of an electronic flash device;
[0020] FIG. 3 is a block diagram showing the internal configuration
of the digital camera;
[0021] FIG. 4 is a block diagram showing the internal configuration
of a digital camera according to Embodiment 3;
[0022] FIG. 5 is an xy chromaticity diagram showing a change in
color temperature relative to a change in ambient temperature T
of an LED;
[0023] FIG. 6 is a block diagram showing the internal configuration
of a digital camera according to Embodiment 4; and
[0024] FIG. 7 is an xy chromaticity diagram showing a change in
color temperature relative to a change in current I applied to an
LED.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] The preferred embodiments of a digital camera according
to the present invention will be described below in accordance with
the accompanying drawings.
[0026] FIG. 1 is a front perspective view showing an embodiment
of a digital camera 10 according to the present invention. As shown
in FIG. 1, the front of a camera body 12 comprises a taking lens
14, a finder window 16, an electronic flash device 18, a flash light
control window 20, and so on. The top surface comprises a release
button 22, a power supply switch 24, and so on. Further, the back
(not shown) of the camera body 12 comprises a finder eyepiece, a
liquid crystal monitor, various operation buttons (e.g., a zoom
key, a mode button, a menu button, a cross button) and so on.
[0027] FIG. 2 is a sectional view showing the configuration of
a light-emitting part of the electronic flash device 18 which is
mounted in the digital camera 10 shown in FIG. 1. As shown in FIG.
2, the light-emitting part of the electronic flash device 18 is
constituted of a light-emitting diode (LED) 26 serving as a light
source, a reflector 28 for reflecting forward light emitted from
the LED 26, and a diffuser panel 30 for diffusing light emitted
from the LED 26.
[0028] The LED 26 is mounted on a circuit board 32 and emits white
light with high intensity. The reflector 28 is attached to the circuit
board 32 so as to surround the LED 26. Further, the diffuser panel
30 is integrally attached into the reflector 28 and diffuses light
emitted with high directivity from the LED 26.
[0029] FIG. 3 is a block diagram showing the internal configuration
of the digital camera 10. As shown in FIG. 3, behind a lens unit
34 including the taking lens 14 and an iris 15, a solid-state image
sensing device (CCD) 36 is disposed. On a light-receiving surface
of the CCD 36, a number of photosensors are arranged two-dimensionally.
A subject image formed on the light-receiving surface of the CCD
36 via the taking lens 14 and the iris 15 is converted to signal
charge corresponding to an incident light quantity by the photosensors.
Then, the signal charge accumulated in the photosensors is read
into a shift register by a read gate pulse applied from a CCD driving
circuit 38, and the signal charge is sequentially read by a register
transfer pulse as a voltage signal corresponding to the signal charge.
[0030] Besides, the CCD 36 can sweep the accumulated signal charge
by using a shutter gate pulse, so that time for accumulating charge
(shutter speed) can be controlled (so-called electronic shutter
function).
[0031] Voltage signals sequentially read from the CCD 36 are applied
to a correlated double sampling circuit (CDS circuit) 40. R, G,
and B signals of each pixel are subjected to sampling hold therein
and are applied to an AD converter 42. The AD converter 42 converts
analog R, G, and B signals, which are sequentially applied from
the CDS circuit 40, to digital R, G, and B signals and outputs the
signals therefrom.
[0032] Moreover, the CCD driving circuit 38, the CDS circuit 40,
and the AD converter 42 are driven in synchronization with one another
by a timing signal applied from a timing generation circuit (TG)
44.
[0033] The digital R, G, and B signals outputted from the AD converter
42 are temporarily stored in a memory 46 and are applied to a digital
signal processing circuit 48.
[0034] The digital signal processing circuit 48 is constituted
of a synchronization circuit 50, a white balance correction circuit
52, a gamma-correction circuit 54, a YC signal generation circuit
56, a memory 58, and so on.
[0035] The synchronization circuit 50 sequentially synchronizes
the R, G, and B signals of each pixel which are read from the memory
46, and outputs the R, G, and B signals simultaneously to the white
balance correction circuit 52.
[0036] The white balance correction circuit 52 comprises multipliers
52R, 52G, and 52B for increasing or reducing the digital values
of the R, G, and B signals, respectively. The R, G, and B signals
inputted from the synchronization circuit 50 are applied to the
multipliers 52R, 52G, and 52B, respectively. Further, a white balance
correction value (gain value) W (W.sub.R, W.sub.G, W.sub.B) for
white balance control is applied from a central processing unit
(CPU) 60 to the other inputs of the multipliers 52R, 52G, and 52B.
The multipliers 52R, 52G, and 52B each perform a multiplication
on two inputs and output R', G', and B' signals, which have been
subjected to white balance correction by multiplication, to the
gamma-correction circuit 54.
[0037] The detail will be discussed later regarding the white balance
correction value W applied from the CPU 60 to the white balance
correction circuit 52.
[0038] The gamma-correction circuit 54 changes input/output characteristics
so that the R', G', and B' signals having been subjected to white
balance correction have desired gamma characteristics, and the gamma-correction
circuit 54 outputs the signals to the YC signal generation circuit
56.
[0039] The YC signal generation circuit 56 generates a luminance
signal Y and chroma signals Cr and Cb from the R, G, and B signals
having been subjected to gamma correction. The luminance signal
Y and chroma signals Cr and Cb (YC signals) are stored in the memory
58 having the same memory space as the memory 46.
[0040] Here, the YC signal in the memory 58 is read and outputted
to a liquid crystal monitor 62, so that a through image, a taken
static image, and so on can be displayed on the liquid crystal monitor
62 which is provided on the back of the camera body 12.
[0041] Further, the YC signal after shooting is compressed in a
predetermined format by a compression/expansion circuit 64 and is
recorded in a recording medium such as a memory card by a recording
section 66.
[0042] Further, in a reproduction mode, image data recorded in
a memory card and so on is expanded by the compression/expansion
circuit 64 and is outputted to the liquid crystal monitor 62, so
that a reproduced image is displayed on the liquid crystal monitor
62.
[0043] The CPU 60 exercises control over circuits based on an input
from a camera operation section 68 including the release button
22, the power supply switch 24, and so on, and the CPU 60 performs
autofocus control, automatic exposure control, white balance control,
and so on.
[0044] For example, autofocus control is performed by a contrast
AF system in which the movement of the taking lens 14 is controlled
so that a G signal in a specific focus area has the maximum high-frequency
component. The CPU 60 controls the movement of the taking lens 14
via a lens driving section 14A so that a G signal in a specific
focus area has the maximum high-frequency component.
[0045] Automatic exposure control is performed by calculating a
luminance of a subject (shooting EV value) based on an integrated
value of the R, G, and B signals and controlling an aperture and
a shutter speed based on the calculated shooting EV value. The CPU
60 determines an aperture value and a shutter speed based on the
shooting EV value, controls the iris 15 via an iris driving section
15A so as to have the determined aperture value, and controls a
charge accumulation time via the CCD driving circuit 38 so as to
have the determined shutter speed.
[0046] Moreover, the CPU 60 decides whether or not flash shooting
is necessary based on the shooting EV value. When flash shooting
is necessary, flash light is emitted from the electronic flash device
18 via a flash light-emitting circuit 18A.
[0047] White balance control is performed by determining a light
source type (color temperature of a field), determining a white
balance correction value W (W.sub.R, W.sub.G, W.sub.B) suitable
for the determined light source type, and outputting the determined
white balance correction value W to the multipliers 52R, 52G, and
52B of the white balance correction circuit 52 (upon normal shooting).
[0048] A light source type (color temperature of a field) is determined
as follows: first whole screen is divided into a plurality of areas
(e.g., 8*8) based on the R, G, and B signals temporarily stored
in the memory 46, and an average integrated value for each color
of the R, G, and B signals is calculated in each of the divided
areas. The average integrated value of the R, G, and B signals for
each of the divided areas is calculated by an integration circuit
70 and is applied to the CPU 60. Multipliers 72R, 72G, and 72B are
provided between the integration circuit 70 and the CPU 60, and
an adjusted gain value for adjusting a variation between devices
is applied to the multipliers 72R, 72G, and 72B. The CPU 60 discriminates
a light source type such as day light (fine whether), shade-cloudy,
a fluorescent light, and a tungsten lamp based on the average integrated
value of the R, G, and B signals for each of the divided areas.
The average integrated value has been applied from the integration
circuit 70 via the multipliers 72R, 72G, and 72B.
[0049] In the discrimination of the light source type, ratios R/G
and B/G are calculated for each of the divided areas regarding an
average integrated value for each color of the R, G, and B signals.
Subsequently, the detection frames, each of them indicates a range
of color distribution corresponding to a specific light source type,
are set on a graph where a horizontal axis represents R/G and a
vertical axis represents B/G. Then, the number of areas existing
in each detection frame is calculated based on the ratios R/G and
B/G for each obtained area, and the light source type is discriminated
based on the luminance level of a subject and the number of the
areas existing in each detection frame (Japanese Patent Application
Publication No. 2000-224608).
[0050] Besides, the method of automatically determining a light
source type (color temperature of a field) based on the R, G, and
B signals obtained from the CCD 36 is not limited to the present
embodiment.
[0051] When the light source type (color temperature of a field)
is determined thus, the CPU 60 determines a white balance correction
value W (W.sub.R, W.sub.G, W.sub.B) suitable for the light source
type and outputs the determined white balance correction value W
to the multipliers 52R, 52G, and 52B of the white balance correction
circuit 52. Thus, the R', G', and B' signals having been subjected
to white balance correction are outputted to the gamma-correction
circuit 54 from the multipliers 52R, 52G, and 52B.
[0052] The white balance correction value W (W.sub.R, W.sub.G,
W.sub.B) is determined by making reference to a table recorded in
a ROM 74. The table records the white balance correction value W
corresponding to each light source type (color temperature of a
field). When a light source type (color temperature of a field)
is determined, the white balance correction value W corresponding
to the light source type is uniquely determined. The ROM 74 records
an operation program of a camera and various kinds of data in addition
to the table indicating a relationship between the light source
type and the white balance correction value.
[0053] As described above, in normal shooting not using the electronic
flash device 18, a light source type is determined upon shooting,
a white balance correction value W (W.sub.R, W.sub.G, W.sub.B) suitable
for the determined light source type is determined based on a table,
and the determined white balance correction value W is outputted
to the multipliers 52R, 52G, and 52B of the white balance correction
circuit 52 to perform white balance correction.
[0054] On the other hand, in the case of flash shooting using the
electronic flash device 18, a light source type is not determined
but a white balance correction value W.sub.O (W.sub.OR, W.sub.OG,
W.sub.OB) corresponding to a color temperature of flash light is
used to perform white balance correction. That is, in the case of
flash shooting, the CPU 60 reads the white balance correction value
(white balance correction value suitable for a color temperature
of flash light) W.sub.O (W.sub.OR, W.sub.OG, W.sub.OB) for flash
shooting from the ROM 74 and the CPU 60 outputs the white balance
correction value W.sub.O to the multipliers 52R, 52G, and 52B of
the white balance correction circuit 52.
[0055] In this case, the ROM 74 records, as a white balance correction
value for flash shooting, a white balance correction value W.sub.O
(W.sub.OR, W.sub.OG, W.sub.OB) for emitting flash light of a reference
color temperature T.sub.O. Therefore, by emitting flash light having
the same color temperature from the electronic flash device 18 as
the reference color temperature T.sub.O and performing shooting,
an image is obtained with fine color balance.
[0056] However, the LED serving as a light source of the electronic
flash device 18 emits light varied in color temperature among elements
and thus the LED does not always emit light having the same color
temperature as the reference color temperature.
[0057] Thus, in the digital camera of the present embodiment, a
color temperature T.sub.1 of light actually emitted from the electronic
flash device 18 is measured and a white balance correction value
W.sub.1 (W.sub.1R, W.sub.1G, W.sub.1B) suitable for the color temperature
T.sub.1 is used to perform white balance correction upon flash shooting.
To be specific, white balance correction upon flash shooting is
performed as below.
[0058] First, a color temperature T.sub.1 of light actually emitted
from the electronic flash device 18 is measured. Then, a white balance
correction value W.sub.1 (W.sub.1R, W.sub.1G, W.sub.1B) suitable
for the color temperature T.sub.1 is calculated. A difference .DELTA.W
(.DELTA.W=W.sub.O-W.sub.1) between the determined actual white balance
correction value W.sub.1 (W.sub.1R, W.sub.1G, W.sub.1B) and the
reference white balance correction value W.sub.O (W.sub.OR, W.sub.OG,
W.sub.OB) recorded in the ROM 74 is calculated, and the difference
.DELTA.W is recorded as a modification value in an EEPROM 76. That
is, a modification value .DELTA.W (.DELTA.W.sub.R, .DELTA.W.sub.G,
.DELTA.W.sub.B) is calculated for correcting the reference white
balance correction value W.sub.O, which is recorded in the ROM 74,
to the white balance correction value W.sub.1 (W.sub.1R, W.sub.1G,
W.sub.1B) suitable for the color temperature T.sub.1 of flash light
actually emitted from the electronic flash device 18, and the correction
value .DELTA.W is recorded in the EEPROM 76 (.DELTA.W.sub.R=W.sub.OR-W.sub.1R,
.DELTA.W.sub.G=W.sub.OG-W.sub.1G, .DELTA.W.sub.B=W.sub.OB-W.sub.1B).
[0059] The CPU 60 reads the reference white balance correction
value W.sub.O (W.sub.OR, W.sub.OG, W.sub.OB) for flash shooting
from the ROM 74 and reads the modification value .DELTA.W (.DELTA.W.sub.R,
.DELTA.W.sub.G, .DELTA.W.sub.B) from the EEPROM 76 upon flash shooting.
Then, the reference white balance correction value W.sub.O (W.sub.OR,
W.sub.OG, W.sub.OB) is corrected to the white balance correction
value W.sub.1 (W.sub.1R, W.sub.1G, W.sub.1B) suitable for the color
temperature T.sub.1 of actual flash light by using the modification
value .DELTA.W (.DELTA.W.sub.R, .DELTA.W.sub.G, .DELTA.W.sub.B),
and the corrected value is outputted to the multipliers 52R, 52G,
and 52B of the white balance correction circuit 52.
[0060] Hence, even when the LED emitting light varied in color
temperature is used as a flash light source, each product of camera
can obtain an image of the same color shade without being varied
in color balance.
[0061] Besides, a color temperature T.sub.1 of actual flash light
is measured by a color temperature measuring device after the digital
camera 10 is manufactured. That is, flash light is actually emitted
from the electronic flash device 18 and the color temperature of
the light is measured by the color temperature measuring device.
Then, a white balance correction value W.sub.1 suitable for the
measured color temperature T.sub.1 of the light is calculated, a
difference .DELTA.W is calculated from the reference white balance
correction value W.sub.O for flash shooting that is recorded in
the ROM 74, and a modification value is obtained.
[0062] The obtained modification value .DELTA.W is written in the
EEPROM 76 by using a communicating function (e.g., USB, IEEE 1394,
etc.) provided in the digital camera 10. That is, for example, the
digital camera 10 and a personal computer are connected to each
other via a USB cable, the data of the modification value is transmitted
from the personal computer to the digital camera, and the transmitted
data of the modification value is written in the EEPROM 76.
[0063] Further, the data of the modification value may be obtained
by using a recording medium for recording images. That is, the following
process may be applicable: the recording medium having recorded
the data of the modification value is loaded into the digital camera
10, the data of the modification value is acquired from the recording
medium, and the data is written in the EEPROM 76.
[0064] Moreover, the recording device for recording the data of
the modification value is not limited to the EEPROM and thus another
recording device may be used.
[0065] The following will describe Embodiment 2 of a digital camera
according to the present invention. The basic configuration of the
device is the same as the digital camera of Embodiment 1 and thus
the explanation thereof is omitted.
[0066] In the digital camera of Embodiment 1, the white balance
correction value W.sub.1 suitable for the color temperature of actual
flash light is obtained by correcting the white balance correction
value W.sub.O, which is recorded in the ROM 74, by using the modification
value .DELTA.W recorded in the EEPROM 76.
[0067] In a digital camera 10 of the present embodiment, a white
balance correction value W.sub.1 suitable for the color temperature
of actual flash light is recorded in an EEPROM 76, and the white
balance correction value W.sub.1 recorded in the EEPROM 76 is used
to perform white balance correction.
[0068] In a method of recording the white balance correction value
W.sub.1 in the EEPROM 76, recording is performed by using a communicating
function and a recording medium that are provided in the digital
camera, just like the digital camera 10 of Embodiment 1.
[0069] In the digital camera of the present embodiment, a CPU 60
reads a white balance correction value W.sub.1 (W.sub.1R, W.sub.1G,
W.sub.1B) from the EEPROM 76 and outputs the value to multipliers
52R, 52G, and 52B of a white balance correction circuit 52 to perform
white balance correction.
[0070] Thus, even when an LED emitting light varied in color temperature
is used as a flash light source just like the digital camera of
Embodiment 1, each product of camera can obtain an image of the
same color shade without being varied in color balance.
[0071] Additionally, the table of a white balance correction value
of normal shooting may be recorded in the EEPROM 76 along with a
white balance correction value of flash shooting.
[0072] FIG. 4 is a block diagram showing the internal configuration
of Embodiment 3 according to a digital camera of the present invention.
[0073] As shown in FIG. 4, a digital camera 100 of the present
embodiment is different from the digital camera 10 of Embodiment
1 in that an electronic flash device 18 comprises a temperature
sensor 102 for detecting an ambient temperature of an LED serving
as a flash light source. Since the other configurations are the
same as the digital camera 10 of Embodiment 1, the same components
as the digital camera 10 of Embodiment 1 are indicated by the same
reference numerals and thus explanation thereof is omitted.
[0074] The LED serving as a flash light source emits light varied
in color temperature according to a change in ambient temperature.
FIG. 5 is an xy chromaticity diagram showing a change in color temperature
relative to a change in an ambient temperature T of the LED (current
(forward current) applied to the LED is 20 mA). As shown in FIG.
5, when the ambient temperature of the LED changes from a high temperature
to a low temperature, the color temperature of light emitted by
the LED changes accordingly from a high temperature to a low temperature.
[0075] Therefore, when white balance correction is performed by
using a constant white balance correction value on image data obtained
by flash shooting, an ambient temperature change of the LED may
result in images of different color shades.
[0076] Hence, in the digital camera 100 of the present embodiment,
a white balance correction value is corrected according to a change
in the ambient temperature of the LED.
[0077] As shown in FIG. 4, an electronic flash device 18 comprises
a temperature sensor 102 for detecting the ambient temperature of
the LED serving as a light source. The ambient temperature of the
LED that is detected by the temperature sensor 102 is inputted to
the CPU 60 via an AD converter 104.
[0078] On the other hand, an EEPROM 76 records a table indicating
a correspondence relationship between an ambient temperature T of
the LED and a white balance correction value W.sub.T (W.sub.TR,
W.sub.TG, W.sub.TB). By making reference to the table, the white
balance correction value W.sub.T (W.sub.TR, W.sub.TG, W.sub.TB)
is uniquely determined according to the ambient temperature T of
the LED.
[0079] Upon flash shooting, the CPU 60 acquires the ambient temperature
T of the LED via the AD converter 104 from the temperature sensor
102 and determines the white balance correction value W.sub.T (W.sub.TR,
W.sub.TG, W.sub.TB), which corresponds to the ambient temperature
T, based on the table recorded in the EEPROM 76. Then, the CPU 60
outputs the determined white balance correction value W.sub.T (W.sub.TR,
W.sub.TG, W.sub.TB) to multipliers 52R, 52G, and 52B of a white
balance correction circuit 52 and performs white balance correction
on taken image data.
[0080] Thus, even when the LED changes in ambient temperature and
light emitted from the LED changes in color temperature, it is always
possible to obtain an image with stable color balance.
[0081] In the present embodiment, the white balance correction
value W.sub.T (W.sub.TR, W.sub.TG, W.sub.TB) at each ambient temperature
T of the LED is recorded as a table in the EEPROM 76. A ROM 74 may
record a reference white balance correction value, for example,
a white balance correction value W.sub.20 (W.sub.20R, W.sub.20G,
W.sub.20B) when the LED has an ambient temperature T of 20.degree.
C., and the EEPROM 76 may record a modification value .DELTA.W.sub.T
(modification value of the reference white balance correction value
W.sub.20 at each ambient temperature T) as a table at each ambient
temperature T of the LED.
[0082] In this case, the CPU 60 acquires the modification value
.DELTA.W.sub.T corresponding to the ambient temperature T from the
table recorded in the EEPROM 76 and corrects the reference white
balance correction value W.sub.20. Then, the CPU 60 outputs the
corrected white balance correction value W.sub.T (W.sub.TR, W.sub.TG,
W.sub.TB) to the multipliers 52R, 52G, and 52B of the white balance
correction circuit 52 and performs white balance correction.
[0083] Further, in the method of recording the white balance correction
value in the EEPROM 76, recording is performed using a communicating
function and a recording medium that are provided in the digital
camera, just like the digital camera 10 of Embodiment 1.
[0084] A white balance correction value corresponding to each ambient
temperature T may be uniquely set in all products of digital cameras.
However, the LED emits light varied in color temperature among elements
just like Embodiment 1 and thus it is preferable to perform setting
based on the color temperature of light actually emitted from the
electronic flash device 18.
[0085] FIG. 6 is a block diagram showing the internal configuration
of Embodiment 4 according to the digital camera of the present invention.
[0086] As shown in FIG. 6, a digital camera 110 of the present
embodiment is different from the digital camera 10 of Embodiment
1 in that an electronic flash device 18 comprises an ammeter 112
for measuring current (forward current) applied to an LED. Since
the other configurations are the same as the digital camera 10 of
Embodiment 1, the same components as the digital camera 10 of Embodiment
1 are indicated by the same reference numerals and the explanation
thereof is omitted.
[0087] The LED serving as a flash light source emits light varied
in color temperature according to a change in current applied to
the LED. FIG. 7 is an xy chromaticity diagram showing a change in
color temperature relative to a change in current I applied to the
LED (when the ambient temperature of the LED is 20.degree. C.).
As shown in FIG. 7, as the current I applied to the LED is reduced,
the color temperature of light emitted by the LED also shifts to
a lower temperature.
[0088] Therefore, when white balance correction is performed by
using a constant white balance correction value on image data obtained
by flash shooting, a change in current applied to the LED may result
in images of different color shades.
[0089] Hence, in the digital camera 110 of the present embodiment,
a white balance correction value is corrected according to a change
in current applied to the LED.
[0090] As shown in FIG. 6, the electronic flash device 18 comprises
the ammeter 112 for measuring current applied to the LED serving
as a light source. A current value measured by the ammeter 112 is
inputted to a CPU 60 via an AD converter 114.
[0091] On the other hand, an EEPROM 76 records a table indicating
a correspondence relationship between a current I applied to the
LED and a white balance correction value W.sub.I (W.sub.IR, W.sub.IG,
W.sub.IB). By making reference to the table, the white balance correction
value W.sub.I (W.sub.IR, W.sub.IG, W.sub.IB) is uniquely determined
according to the current I applied to the LED.
[0092] The CPU 60 acquires the current I applied to the LED, via
the AD converter 114 from the ammeter 112. Then, the CPU 60 determines
the white balance correction value W.sub.I (W.sub.IR, W.sub.IG,
W.sub.IB), which corresponds to the current I, based on the table
recorded in the EEPROM 76. Subsequently, the CPU 60 outputs the
determined white balance correction value W.sub.I (W.sub.IR, W.sub.IG,
W.sub.IB) to multipliers 52R, 52G, and 52B of a white balance correction
circuit 52 and performs white balance correction on taken image
data.
[0093] Thus, even when current applied to the LED changes and light
emitted from the LED changes in color temperature, it is always
possible to obtain an image with stable color balance.
[0094] In the present embodiment, the white balance correction
value W.sub.I (W.sub.IR, W.sub.IG, W.sub.IB) at each current applied
to the LED is recorded as a table in the EEPROM 76. A ROM 74 may
record a reference white balance correction value, for example,
a white balance correction value W.sub.20 (W.sub.20R, W.sub.20G,
W.sub.20B) when the current I applied to the LED is 20 mA, and the
EEPROM 76 may record a modification value .DELTA.W.sub.I (modification
value of the reference white balance correction value W.sub.20 at
each current I applied to the LED) as a table at each current I
applied to the LED.
[0095] In this case, the CPU 60 acquires the modification value
.DELTA.W.sub.I corresponding to the current I applied to the LED,
from the table recorded in the EEPROM 76, and the CPU 60 corrects
the reference white balance correction value W.sub.20. Then, the
CPU 60 outputs the corrected white balance correction value W.sub.I
(W.sub.IR, W.sub.IG, W.sub.IB) to the multipliers 52R, 52G, and
52B of the white balance correction circuit 52 and performs white
balance correction on taken image data.
[0096] Further, in the method of recording a white balance correction
value in the EEPROM 76, recording is performed using a communicating
function and a recording medium that are provided in the digital
camera, just like the digital camera 10 of Embodiment 1.
[0097] A white balance correction value corresponding to each current
I may be uniquely set for all products of digital cameras. However,
just like Embodiment 1, the LED emits light varied in color temperature
among elements and thus it is preferable to perform setting based
on the color temperature of light actually emitted from the electronic
flash device 18.
[0098] As described above, according to the digital camera of the
present invention, even when the LED emitting light varied in color
temperature among elements is used as a flash light source, each
product of camera can obtain an image of the same color shade without
being varied in color balance.
[0099] Further, even when emitted light is varied in color temperature
due to a change in ambient temperature and a change in current applied
to the LED, it is always possible to maintain fixed color balance,
achieving a stable image.
[0100] The series of embodiments discussed that the LED emitting
white light is used as a flash light source. The present invention
is similarly applicable to an electronic flash device which uses,
as flash light sources, three LEDs including an LED emitting red
light, an LED emitting green light, and an LED emitting blue light.
[0101] Moreover, in the above-described embodiments, white-balance
processing is performed in the digital signal processing circuit
48. White-balance processing may be performed in an analog signal
processing circuit including a CDS circuit and a gain control amplifier
(not shown).
[0102] Further, white balance correction may be performed by multiplying
gain values to the values of color-difference signals C.sub.r and
C.sub.b.
|