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Digital Camera Patent Abstract
A digital camera includes an imaging device for capturing images
of an object, a signal processor which performs signal processing
on a signal captured by the imaging device to obtain an image signal,
and a single measuring device for measuring color of at least a
part of the object, and for measuring a color temperature of the
object to adjust white balance of the image signal.
Digital Camera Patent Claims
1. A digital camera comprising: an imaging device for capturing
images of an object; a signal processor which performs signal processing
on a signal captured by said imaging device to obtain an image signal;
and a single measuring device for measuring color of at least a
part of said object, and for measuring a color temperature of said
object to adjust white balance of said image signal.
2. The digital camera according to claim 1, further comprising
an AF controller which measures an object distance of said object
and performs AF control on operation of a focusing lens system of
a photographing lens to bring said object into focus automatically;
and a controller which makes an adjustment to said AF control based
on said color of said object that is measured by said single measuring
device.
3. The digital camera according to claim 2, further comprising
a white balance adjustment device, wherein said white balance adjustment
device adjusts a white balance of said image signal captured by
said imaging device in accordance with the measured object color
temperature of said object.
4. The digital camera according to claim 2, further comprising
a look-up table from which said controller obtains a correction
value used for said adjustment to said AF control based on said
color of said object that is measured by said single measuring device.
5. The digital camera according to claim 2, wherein said AF controller
is configured to measure an object distance at at least one predetermined
point on said object, and wherein said single measuring device is
configured so that a photoreceptive area thereof measures color
of said object at said predetermined point on said object.
6. The digital camera according to claim 4 wherein said single
measuring device comprises: a photoreceptor, a light receptive surface
of which is sectioned into a plurality of light receptive areas;
and an optical plate positioned in front of said photoreceptor,
wherein a portion of said plurality of light receptive areas is
configured to measure said color of said object and the remaining
portion of said plurality of light receptive areas is configured
to measure said color temperature of said object, wherein a portion
of said optical plate which corresponds to said portion of said
plurality of light receptive areas is formed as a transparent portion
which allows light of said object to pass therethrough, and wherein
a portion of said optical plate which corresponds to said remaining
portion of said plurality of light receptive areas is formed as
a diffusing portion which diffuses light of said object which is
incident thereon.
7. The digital camera according to claim 6, wherein said single
measuring device comprises at least one color filter, fixed to cover
said plurality of light receptive areas, for having each said plurality
of light receptive areas receive light of said object spectroscopically.
8. The digital camera according to claim 7, wherein each of a plurality
of portions of said color filter which respectively correspond to
said plurality of light receptive areas comprises at least one red-light
filter portion, at least one green-light filter portion and at least
one blue-light filter portion.
9. The digital camera according to claim 6, wherein said single
measuring device is configured so that said photoreceptive area
and said transparent portion are arranged to correspond to at least
one specific point in said AF controller.
10. The digital camera according to claim 1, further comprising
a photometer adapted for exposure settings for capturing images
with said imaging device, wherein said photometer is independent
of said single measuring device.
11. The digital camera according to claim 1, wherein said photographing
lens comprises an interchangeable lens.
12. The digital camera according to claim 1, wherein said digital
camera comprises an SLR digital camera having an image-erecting
optical system, said single measuring device being positioned in
a vicinity of an exit surface of said image-erecting optical system
so that a portion of light which exits out of said exit surface
is incident on said single measuring device.
13. The digital camera according to claim 1, wherein said AF controller
comprises an AF sensor unit and an AF driving mechanism including
a motor which drives said focusing lens system.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a digital camera, more
specifically relates to an AF (autofocus) digital camera capable
of taking color images.
[0003] 2. Description of the Prior Art
[0004] In AF digital cameras, a part of the light bundle of an
object which is formed through a photographing lens is lead to an
AF sensor unit to measure an object distance (defocus amount) at
the AF sensor unit. FIGS. 7A, 7B and 7C are diagrams illustrating
the principle of operation of such an AF sensor unit which is incorporated
in an SLR type of digital camera. Each of these diagrams shows a
state of the aforementioned part of the light bundle of an object,
which is formed through a photographing lens, in the AF sensor unit,
and further shows the distance (image-to-image distance) between
two separate images received by an AF sensor 226 thereon (between
two peaks of a signal output from the AF sensor). The above-mentioned
part of the light bundle of an object, which is formed through a
photographing lefts, is separated into two light bundles by an aperture
mask 224 having two apertures, which are in turn focused on the
AF sensor 226 via two separator lenses 225, respectively. The AF
sensor 226 is a line sensor, or the like, and measures the distance
between two images of the two light bundles focused on the AF sensor
226. Thereafter, an in-focus state is achieved by driving a focusing
lens system (focusing lens group) of the photographing lens by feedback
control performed by an AF controller (focusing device (not shown))
so that the aforementioned image-to-image distance becomes a predetermined
distance.
[0005] In this type of AF sensor unit, the effective focal length
of the optical system of the AF sensor unit varies depending on
differences in color of light of an object, i.e., differences in
wavelength of light incident on the AF sensor unit, and therefore,
the imaging position in the AF sensor 226 varies depending on wavelengths
of the received light, which makes it impossible for the aforementioned
focusing lens system of the photographing lens to obtain a correct
in-focus state, i.e., which becomes a cause of an AF error. For
instance, if the image-to-image distance Lg at the AF sensor 226
upon receiving green light is regarded as a reference distance (see
FIG. 7A), the effective focal length of the optical system of the
AF sensor unit increases as shown in FIG. 7B when the AF sensor
unit 226 receives red light (long-wavelength light), and accordingly,
the image-to-image distance Lr at the AF sensor 226 upon receiving
red light becomes shorter than the reference distance, and the effective
focal length of the optical system of the AF sensor unit decreases
as shown in FIG. 7C upon the AF sensor unit 226 receiving blue light
(short-wavelength light), and accordingly, the image-to-image distance
Lb at the AF sensor 226 upon receiving blue light becomes longer
than the reference distance. Note that the optical path difference
of a light bundle of an object due to the difference of light wavelength
is exaggerated in FIGS. 7A, 7B and 7C for the purpose of illustration.
Such variations of the image-to-image distance that depend on wavelengths
of the received light cause variations in measured distance value,
thus becoming a cause of an AF error.
[0006] To overcome this problem of AF error, a technique of eliminating
AF error such as noted above, which is caused by color difference
in light of an object the object distance of which is to be measured,
by measuring color of the object light and correcting the output
of the AF sensor unit (i.e., a measured object distance value or
an in-focus position) in accordance with the measured color has
been proposed in Japanese unexamined patent publication 2003-241064.
In this publication, the photometric sensor is provided on a part
of the light receptive surface with an optical filter so that the
photometric sensor measures the object color by receiving light
which is passed through the optical filter. In order to correct
the AF error in an effective manner, colorimetric (color measuring)
elements are disposed to carry out color measurements at positions
corresponding to distance measuring points on an object which is
to be photographed, i.e., at positions corresponding to points on
object images which are formed on an AF sensor via separator lenses
in the AF sensor unit.
[0007] In the technique shown in the aforementioned publication,
since the photometric sensor is constructed so that the color measurements
are performed with a part of the light receptive surface of the
photometric sensor, it can be said that the photometric sensor and
a calorimetric sensor (which includes the aforementioned colorimetric
elements) are formed integral with each other, and accordingly,
it is considered that the color measurements may exert an influence
upon a photometering operation.
[0008] More specifically, in the technique shown in the aforementioned
publication, the photometric sensor measures the intensity of visible
light over all wavelengths thereof, whereas the colorimetric sensor
measures the intensities of red, green and blue lights by a plurality
of photoreceivers of the calorimetric sensor which include spectroscopic
color filters for red, green and blue lights. Since the colorimetric
sensor performs color measurements for distance measuring points
on an object to exercise AF control in the AF sensor unit such as
the aforementioned feedback control, the calorimetric sensor influences
the photometric values measured at the distance measuring points.
Namely, when taking a picture with a camera, it is generally the
case that the object distance is measured to bring a portion of
the object which is to be photographed into focus; however, if the
photometric value measured at this portion of the object is influenced
by the operation of the colorimetric sensor, this results in the
colorimetric sensor influencing the correct exposure at object.
A solution to this problem is to separate the photometric sensor
and the calorimetric sensor from each other; however, this inevitably
requires two sensors. Specifically, in the case where the aforementioned
type of photometric and calorimetric techniques is applied to a
digital camera, it is necessary for the digital camera to be provided
with a color temperature sensor (white balance sensor) for determining
a standard of reference used for photographing white light as a
true white, which requires not only a photometric sensor and a calorimetric
sensor but also a color temperature sensor, i.e., three sensors
in total. This increase in number of sensors complicates the overall
structure of the digital camera.
SUMMARY OF THE INVENTION
[0009] The present invention provides an AF digital camera, capable
of taking color images, which includes a color temperature sensor,
a photometric sensor and a colorimetric sensor, wherein the structure
of the digital camera is simplified by a reduction in the number
of sensors included in the digital camera.
[0010] According to an aspect of the present invention, a digital
camera is provided, including an imaging device for capturing images
of an object; a signal processor which performs signal processing
on a signal captured by the imaging device to obtain an image signal;
and a single measuring device for measuring color of at least a
part of the object, and for measuring a color temperature of the
object to adjust white balance of the image signal.
[0011] It is desirable for the digital camera to include an AF
controller which measures an object distance of the object and performs
AF control on operation of a focusing lens system of a photographing
lens to bring the object into focus automatically; and a controller
which makes an adjustment to the AF control based on the color of
the object that is measured by the single measuring device.
[0012] It is desirable for the digital camera to include a white
balance adjustment device, wherein the white balance adjustment
device adjusts a white balance of the image signal captured by the
imaging device in accordance with the measured object color temperature
of the object
[0013] It is desirable for the digital camera to include a look-up
table from which the controller obtains a correction value used
for the adjustment to the AF control based on the color of the object
that is measured by the single measuring device.
[0014] It is desirable for the AF controller to be configured to
measure an object distance at least one predetermined point on the
object, and for the single measuring device to be configured so
that a photoreceptive area thereof measures color of the object
at the predetermined point on the object.
[0015] It is desirable for the single measuring device to include
a photoreceptor, a light receptive surface of which is sectioned
into a plurality of light receptive areas; and an optical plate
positioned in front of the photoreceptor. A portion of the plurality
of light receptive areas is configured to measure the color of the
object and the remaining portion of the plurality of light receptive
areas is configured to measure the color temperature of the object.
A portion of the optical plate which corresponds to the portion
of the plurality of light receptive areas is formed as a transparent
portion which allows light of the object to pass therethrough. A
portion of the optical plate which corresponds to the remaining
portion of the plurality of light receptive areas is formed as a
diffusing portion which diffuses light of the object which is incident
thereon.
[0016] It is desirable for the single measuring device to include
at least one color filter, fixed to cover the plurality of light
receptive areas, for having each the plurality of light receptive
areas receive light of the object spectroscopically.
[0017] It is desirable for each of a plurality of portions of the
color filter which respectively correspond to the plurality of light
receptive areas to include at least one red-light filter portion,
at least one green-light filter portion and at least one blue-light
filter portion.
[0018] It is desirable for the single measuring device to be configured
so that the photoreceptive area and the transparent portion are
arranged to correspond to at least one specific point in the AF
controller.
[0019] It is desirable for the digital camera to include a photometer
adapted for exposure settings for capturing images with the imaging
device, wherein the photometer is independent of the single measuring
device.
[0020] It is desirable for the photographing lens to be an interchangeable
lens.
[0021] It is desirable for the digital camera to include an SLR
digital camera having an image-erecting optical system, the single
measuring device being positioned in a vicinity of an exit surface
of the image-erecting optical system so that a portion of light
which exits out of the exit surface is incident on the single measuring
device.
[0022] It is desirable for the AF controller to include an AF sensor
unit and an AF driving mechanism including a motor which drives
the focusing lens system.
[0023] According to the present invention, a single measuring device
is configured to be capable of performing not only color measurements
but also color temperature measurements. Therefore, even if the
camera is provided with a photometer independently of the single
measuring device, the camera only needs to be provided with two
measuring devices, which simplifies the structure of the digital
camera. Moreover, since the photometer can be provided independently
of the single measuring device, an influence upon a photometering
operation of the photometer which is caused by a color filter used
in performing object color measurements can be eliminated, which
makes both accurate photometric measurements and picture taking
with correct exposure possible. Furthermore, since the single measuring
device can carry out color measurements on at least one predetermined
point on an object at which the object distance is measured, a high-precision
AF control is achieved. Furthermore, since the single measuring
device can carry out color measurements and color temperature measurements
at the same time, an appropriate color temperature adjustment (white
balance adjustment) can be made when photographing color images.
[0024] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 2005-143526 (filed on May 17,
2005) which is expressly incorporated herein in its entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The present invention will be discussed below in detail
with reference to the accompanying drawings, in which:
[0026] FIG. 1 is perspective view of an embodiment of a digital
camera according to the present invention, viewed obliquely from
front of the camera;
[0027] FIG. 2 is a diagram showing the internal structure of the
digital camera shown in FIG. 1;
[0028] FIG. 3 is a perspective view of optical elements of an AF
sensor unit shown in FIG. 2, schematically showing the structure
of the AF sensor unit;
[0029] FIG. 4A is a front elevational view of a colorimetric sensor
of the digital camera shown in FIG. 2;
[0030] FIG. 4B is a cross sectional view of the calorimetric sensor
shown in FIG. 4A;
[0031] FIG. 4C is a circular color measuring area of the calorimetric
sensor shown in FIG. 4A;
[0032] FIG. 5 is a diagrammatic representation of various components
of the digital camera shown in FIG. 1;
[0033] FIG. 6 is a flow chart showing an AF control process; and
[0034] FIGS. 7A, 7B and 7C are diagrams showing the principle of
distance measuring operation with an AF sensor unit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] An embodiment of a digital camera shown in FIG. 1 is constructed
as an SLR digital camera using an interchangeable photographing
lens 8 (schematically shown in FIG. 5) which is detachably attached
to the front of a camera body 1. The camera body 1 is provided on
a front wall thereof with a lens mount 2 to which the photographing
lens 8 is dismountably mounted. The digital camera is provided on
top of the camera body 1 with a rotary main switch 3, a release
button 4, around which the rotary main switch 3 is positioned, an
LCD (liquid crystal display) indicator portion 5 for indicating
various photographic information, and a mode select dial (dial switch)
6 for selecting a desired photographic mode from among various photographic
modes. A photometering operation and a shutter release operation
are performed upon the release button 4 being half and fully depressed,
respectively. Namely, the release button 4 serves as not only a
release switch for releasing a focal plate shutter 18 (see FIG.
5) but also as a photometering switch for performing a photometering
operation. The digital camera is provided in front of the main switch
3 with a front function dial 7 which is operated for exposure adjustment.
A front end of an AF coupler 231, which is driven by an AF motor
232 (see FIG. 2) to move a focusing lens system (e.g., a focusing
lens group; not shown) of the photographing lens 8 to bring an object
into focus, projects forward from a front surface of the lens mount
2. Upon the photographing lens 8 being mounted to the lens mount
2, the AF coupler 231 is coupled to an AF driving mechanism 23 (see
FIG. 5) for driving the focusing lens system.
[0036] FIG. 2 shows the internal structure of the digital camera
shown in FIG. 1 in cross section. Light of an object which is focused
through the photographing lens 8 mounted to the lens mount 2 is
reflected upwards by a swingable half mirror (quick-return mirror)
11 to be incident on a focusing screen 12 to be formed as an object
image thereon. The light of this object image focused on the focusing
screen 12 enters a pentagonal prism (image-erecting optical system)
13, is subsequently reflected more than once by inner surfaces of
the pentagonal prism 13, and exits out of the pentagonal prism 13
to be viewed by the photographer as an erect image through an eyepiece
system 14. The light of the object image which enters the pentagonal
prism 13 to exit therefrom partly enters a twin condenser lens 15
positioned behind the pentagonal prism 13, to be converged by the
condenser lens 15 to two points at which a colorimetric sensor (single
measuring device/dual-purpose measuring device) 17 and a photometric
sensor (photometer) 16 are disposed so that photometric measurements
and color measurements are carried out by the photometric sensor
16 and the calorimetric sensor 17, respectively.
[0037] The focal plane shutter 18 is positioned behind the swingable
half mirror 11. An optical low-pass filter 19 and a CCD image sensor
20 are positioned behind the focal plane shutter 18. Upon the release
button 4 being fully depressed, the swingable half mirror 11 is
lifted up while the focal plane shutter 18 is opened. Thereupon,
the CCD image sensor 20 captures the object image focused thereon
via the photographing lens 8. The CCD image sensor 20 is a color
image sensor capable of taking color images. The object light which
is passed through the swingable half mirror 11 is partly incident
on a secondary mirror 21, which is pivoted at a rear surface of
the swingable half mirror 11, to be reflected downwards to be incident
on an AF sensor unit 22 so that an object distance measuring operation
is performed. Thereupon, based on the distance measurement data
obtained via the AF sensor unit 22, the AF driving mechanism 23
is actuated to move the focusing lens system of the photographing
lens 8 to perform a focusing operation (autofocusing operation).
As shown in FIG. 2, the AF driving mechanism 23 includes the AF
motor 232 for rotating the AF coupler 231 and a transmission 233.
The focusing lens system of the photographing lens 8 mounted to
the lens mount 2 is coupled to the AF driving mechanism 23 so that
the AF driving mechanism 23 can drive the focusing lens system to
perform a focusing operation by rotating the AF coupler 231.
[0038] As shown schematically in FIG. 3, the AF sensor unit 22
includes an IR (infrared) cutoff filter 221, a condenser lens 222,
a mirror 223, an aperture mask 224, a separator lens 225 and an
AF sensor 226. As described above, the object light which is passed
through the swingable half mirror 11 and reflected downwards by
the secondary mirror 21 is incident on the IR cutoff filter 221
so that infrared components are filtered out from the incident light.
Subsequently, the light which is passed through the IR cutoff filter
221 is converged via the condenser lens 222, and the converged light
is reflected by the mirror 223 to be incident on first through fifth
pairs of minute apertures S1, S2, S3, S4 and S5 formed on the aperture
mask 224 to be selectively allowed to pass through the aperture
mask 224 to be formed as five pairs of fine bundles of light. The
separator lens 225 is provided with five pairs of separator lenses
L1, L2, L3, L4 and L5 which are formed at positions corresponding
to the five pairs of minute apertures S1, S2, S3, S4 and S5, respectively.
The five pairs of minute bundles of light which are respectively
passed through the five pairs of minute apertures S1 through S5
of the aperture mask 224, are subsequently passed through the five
pairs of separator lenses L1 through L5 of the separator lens 225
so as to be formed as five pairs of images on the AF sensor 226,
respectively. In the present embodiment of the digital camera, the
five pairs of minute apertures S1 through S5 of the aperture mask
224 and the five pairs of separator lenses L1 through L5 of the
separator lens 225 are arranged to correspond to five points in
a rectangular picture plane: a central point and the remaining four
points (upper, lower, left and right points) around the central
point. The object distance (defocus amount) is measured by measuring
each of the five distances (image-to-image distances) between each
of the five pairs of separate images formed on the AF sensor 226
via the five pairs of separator lenses L1 through L5 of the separator
lens 225, respectively. Accordingly, five points on the AF sensor
226 which respectively correspond to the aforementioned five points
(the central, upper, lower, left and right points) serve as distance
measuring points P1, P2, P3, P4 and P5 in the AF sensor unit 22,
respectively.
[0039] The photometric sensor 16 is made up of a photoreceptor
such as a photodiode, the light receptive surface of which is formed
in a single flat surface, and is made as a single sensor independent
of the calorimetric sensor 17. A conventional photometric sensor
is used as the photometric sensor 16 with no modification, and accordingly,
the detailed description of the photometric sensor 16 is omitted.
On the other hand, the calorimetric sensor 17 can carry out color
measurements and color temperature measurements at the same time.
Namely, the calorimetric sensor 17 is configured to also serve as
a color temperature sensor (white balance adjustment device). FIGS.
4A and 4B show a front elevational view and a cross sectional view
of the calorimetric sensor 17, respectively, and FIG. 4C shows a
circular color measuring area (C1 through C5) of the calorimetric
sensor 17. The colorimetric sensor 17 includes a base 171, a flat
photoreceptor 172, an optical plate 173 and a color filter 174.
The base 171 is in the shape of a rectangular tray. The photoreceptor
172 is made of, e.g., a flat photodiode. The photoreceptor 172 is
fixed to an inner surface of the base 171 to be positioned therein.
The optical plate 173 is fixed to a front end surface of the front
edge of the base 171 to cover the photoreceptor 172. The calorimetric
sensor 17 receives light which is passed through the optical plate
173 on the photoreceptor 172 to carry out color measurements and
color temperature measurements. The optical plate 173 is provided
at five points thereon with five circular transparent portions:
a central transparent portion M1 and four transparent portions (an
upper transparent portion M2, a lower transparent portion M3, a
left transparent portion M4 and a right transparent portion M5)
positioned around the central transparent portions M1. The portion
of the optical plate 173 excluding the five circular transparent
portions M1 through M5 is formed as a translucent white portion
HT which diffuses incident light. The five circular transparent
portions M1 through M5 are arranged in a rectangular picture plane
at positions corresponding to the aforementioned distance measuring
points P1, P2, P3, P4 and P5 of the AF sensor unit 22, respectively.
[0040] The light receptive surface of the flat photoreceptor 172
is sectioned into eight areas: five circular color measuring areas
C1, C2, C3, C4 and C5 and three color temperature measuring areas
T1, T2 and T3. The five circular color measuring areas C1 through
C5 are arranged to correspond to the five circular transparent portions
M1 through M5, respectively, while the entire area of the light
receptive surface of the flat photoreceptor 172 is horizontally
sectioned into substantially equal three areas to form the three
color temperature measuring areas T1 through T3, respectively. Additionally,
each of the five circular color measuring areas C1 through C5 is
circumferentially sectioned into six equal sector areas about the
center of the circular color measuring area: two red-light receptive
areas Cr, two blue-light receptive areas Cb and two green-light
receptive areas Cg as shown in FIG. 4B. The two red-light receptive
areas Cr are positioned radially opposed to each other. Likewise,
the two blue-light receptive areas Cb are positioned radially opposed
to each other, and the two green-light receptive areas Cg are positioned
radially opposed to each other. The three color temperature measuring
areas T1, T2 and T3 serve as a red-light receptive area Tr, a green-light
receptive area Tg and a blue-light receptive area Tb, respectively.
The light receptive surface of the photoreceptor 172 is covered
with the color filter 174. Portions of the color filter 174 which
cover the two red-light receptive areas Cr, the two blue-light receptive
areas Cb and the two green-light receptive areas Cg of each of the
five circular color measuring areas C1 through C5 are formed as
two red-light micro filters R, two blue-light micro filters B and
two green-light micro filters G, respectively. Portions of the color
filter 174 which cover the three color temperature measuring areas
T1 through T3 are formed as a red-light micro filter R, a blue-light
micro filter B and a green-light micro filter G, respectively. The
color filter 174 can be formed on the photoreceptor 172 via semiconductor
manufacturing technology (e.g., color filter manufacturing technology
in manufacturing CCD image sensors) at the same time as the photoreceptor
172 is produced. The photoreceptor 172 outputs independent color
signals for each of the red-light receptive areas Cr, the blue-light
receptive areas Cb and the green-light receptive areas Cg from each
of the five circular color measuring areas C1, C2, C3, C4 and C5,
and outputs independent color-temperature signals for each of the
three color temperature measuring areas T1, T2 and T3.
[0041] FIG. 5 shows a diagrammatic representation of the various
components of the digital camera. An image signal (which includes
a red-image signal, a blue-image signal and a green-image signal)
output from the CCD image sensor 20 is amplified by an amplifier
(AMP) 101, and subsequently converted into a digital image signal
by an A/D converter 102. This digital image signal is subjected
to predetermined signal processes such as color processing and gamma
correction processing by a signal processing circuit 103 to be output
as a required form of signal. Subsequently, this processed signal
is either compressed or not compressed via a compressing/non-compressing
circuit 104 to be stored in a VRAM (image memory) 105. The CCD image
sensor 20 can set a charge accumulation time for the CCD image sensor
20 at a time of exposure by controlling the operation of a CCD driver
107 via a clock generator 106 by a CPU 10. The CPU 10 comprehensively
controls the overall operation of the digital camera.
[0042] The CPU 10 uses the output from a DC-DC converter 112, which
DC-DC-converts power from the battery 111, as a power source. In
a photographing operation, the CPU 10 commands the AF sensor unit
22 to perform a distance measuring operation and controls the operation
of the AF driving mechanism 23. The CPU 10, the sensor unit 22 and
the AF driving mechanism 23 constitute an AF controller. Additionally,
the CPU 10 controls the operation of a mirror driving mechanism
24 (not shown in FIG. 2) to move the swingable half mirror 11, and
further controls the operation of a shutter driving circuit 25 to
control opening/closing operations of the focal plane shutter 18.
At the same time, the CPU 10 controls the operation of a diaphragm
81 provided in the photographing lens 8 via a diaphragm driving
mechanism 26. Furthermore, the CPU 10 operates so that both the
LCD indicator portion 5 and a back LCD indicator portion 9 (see
FIG. 5; not shown in FIG. 1) indicate necessary data. The back LCD
indicator portion 9 is provided on the back of the camera body 1,
and is capable of indicating captured object images and various
information. The CPU 10 controls the operation of a flash control
circuit 28 to bring a flash 27 into operation if necessary.
[0043] Exposure information calculated by an exposure controller
29 in accordance with a photometric value obtained by the photometric
sensor 16 is input to the CPU 10. Moreover, object color information
and color temperature information which are measured by the colorimetric
sensor 17 are input to the CPU 10. An AF-drive-position look-up
table 30 is connected to the CPU 10. The digital camera is provided
with the AF-drive-position look-up table 30 so that the CPU 10 gains
a correction value for correcting an in-focus position of the focusing
lens system of the photographing lens 8 when the CPU 10 performs
an AF control process in accordance with object color measured by
the colorimetric sensor 17. In the AF-drive-position look-up table
30, correlation data on the correlation between object colors and
correction values for making a correction to distance measurement
data, which is obtained via the AF sensor unit 22, in association
with the object colors are written in advance. For instance, with
the use of object distance data which is obtained in the case where
the object color measured by the colorimetric sensor 17 is green
as reference object distance data, correction values for correcting
(revising) this reference object distance data toward plus or minus
direction if the object color is red or blue, respectively. The
correlation data which correlates such correction values with object
colors have been recorded in the AF-drive-position look-up table
30.
[0044] ON-OFF information on the photometering switch and the release
switch of the release button 4 and photographic mode information
set by an operation of the mode select dial 6 are input to the CPU
10. In addition, information on the position of the front function
dial 7 (i.e., photographic mode information) when the front function
dial 7 is operated is input to the CPU 10.
[0045] In the digital camera having the above described structure,
light of an object to be formed as an object image via the photographing
lens 8 partly passes through the swingable half mirror 11 and is
subsequently reflected by the second mirror 21 to be incident on
the AF sensor unit 22. In the AF sensor unit 22, the incident light
is converged by the condenser lens 222 and subsequently reflected
by the mirror 233 to be formed as five pairs of fine bundles of
light via the first through fifth pairs of minute apertures S1 through
S5 of the aperture mask 224. Subsequently, these five pairs of fine
bundles of light are formed as five pairs of separate images on
the AF sensor 226 via the five pairs of separator lenses L1, L2,
L3, L4 and L5, respectively. As described above with reference to
FIG. 7, the five distances (image-to-image distances) between five
pairs of separate images formed on the AP sensor 226 via the five
pairs of separator lenses L1 through L5 of the separator lens 225
are measured, respectively, and from these five distance values
an object distance is determined on each of the five distance measuring
points P1, P2, P3, P4 and P5 in the AF sensor unit 22. Distance
measurement data on these five object distances are input to the
CPU 10, and then the CPU 10 performs a predetermined distance measuring
process based on the input distance measurement data to gain an
object distance.
[0046] On the other hand, a part of the object light which is passed
through the photographing lens 8 is reflected by the swingable half
mirror 11, focused on the focusing screen 12 and is thereafter incident
on the photometric sensor 16 and the calorimetric sensor 17 via
the pentagonal prism 13. The photometric sensor 16 outputs a photometric
signal corresponding to the amount of light received to the exposure
controller 29. The exposure controller 29 determines the object
brightness from the photometric signal input from the photometric
sensor 16, calculates a correct exposure value and outputs this
correct exposure value to the CPU 10. Due to these operations, the
CPU 10 sets a shutter speed (time value) for the focal plane shutter
18 and an aperture value for the diaphragm 81 of the photographing
lens 8.
[0047] Concurrently with this operation of the CPU 10, the calorimetric
sensor 17 measures the object color and the object color temperature
at the same time. Namely, among the rays of object light incident
on the optical plate 173, rays of light which are passed through
the five transparent portions M1 through M5 of the optical plate
173 are incident on the five circular color measuring areas C1,
C2, C3, C4 and C5 of the photoreceptor 172, respectively. In each
of the five circular color measuring areas C1, C2, C3, C4 and C5
rays of object light incident on the circular color measuring area
pass through the associated two red-light micro filters R, the associated
two blue-light micro filters B and the associated two green-light
micro filters G of the color filter 174, which cover the two red-light
receptive areas Cr, the two blue-light receptive areas Cb and the
two green-light receptive areas Cg of the circular color measuring
area, to be received by the two red-light receptive areas Cr, the
two blue-light receptive areas Cb and the two green-light receptive
areas Cg of the circular color measuring area, respectively. The
CPU 10 can perform color measurements on each of the five circular
color measuring areas C1, C2, C3, C4 and C5 by inputting a photometric
signal output from each of these six receptive areas Cr, Cb and
Cg of each of the five circular color measuring areas C1, C2, C3,
C4 and C5 and performing a predetermined colorimetric operation.
This calorimetric operation is known in the art, and accordingly
the detailed description thereof is omitted.
[0048] At the same time, among the rays of object light incident
on the optical plate 173, rays of light which are incident on the
translucent white portion HT and passed therethrough are diffused
by the translucent white portion HT, are incident on the three color
temperature measuring areas T1, T2 and T3 of the photoreceptor 172,
i.e., the red-light receptive area Tr, the green-light receptive
area Tg and the blue-light receptive area Tb. At this time, since
the incident object light is diffused, the light in the entire picture
plane is incident uniformly on the red-light receptive area Tr (the
color temperature measuring area T1), the green-light receptive
area Tg (the color temperature measuring area T2) and the blue-light
receptive area Tb (the color temperature measuring area T3). In
each of the red-light receptive area Tr, the green-light receptive
area Tg and the blue-light receptive area Tb, rays of object light
incident thereon pass through the red-light micro filter R, the
green-light micro filter G and the blue-light micro filter B that
cover the three color temperature measuring areas T1 through T3,
respectively, and a photoreceptive signal obtained from each of
the red-light receptive area Tr, the green-light receptive area
Tg and the blue-light receptive area Tb is input to the CPU 10.
The CPU 10 can measure a color temperature of an object by performing
a predetermined operation (color temperature measuring operation)
in accordance with photometric information obtained from the red-light
receptive area Tr, the green-light receptive area Tg and the blue-light
receptive area Tb. Such a color temperature measuring operation
is known in the art, and accordingly a detailed description thereof
is omitted.
[0049] The AF control process performed at this stage by the CPU
10 will be hereinafter discussed with reference to the flow chart
shown in FIG. 6. In the AF control process, firstly it is determined
whether the photometering switch has been turned ON by a half depression
of the release button 4 (step S101). Upon the release button 4 being
depressed half way, the photometric sensor 16 carries out photometric
measurements on the object while the calorimetric sensor 17 carries
out calorimetric measurements on the aforementioned five points
on the object which respectively correspond to the distance measuring
points P1, P2, P3, P4 and P5 in the AF sensor unit 22, and color
temperature measurements on the object using the red-light receptive
area Tr, the green-light receptive area Tg and the blue-light receptive
area Tb (step S102). Although the CPU 10 sets a shutter speed and
an aperture value in accordance with photometric information on
the object light, the description of this setting operation of the
CPU 10 is omitted from the flow chart shown in FIG. 6. Upon the
operation at step S102 being completed, it is determined from the
measured object color by the CPU 10 whether no AF correction is
necessary (step S103). At this stage, it is determined that no AF
correction is necessary if the object color is green or closer to
green, whereas it is determined that an AF correction is necessary
if the object color is closer to blue or red. If it is determined
that no AF correction is necessary (if YES at step S103), a focusing
object distance is calculated based on distance measurement data
obtained via the AF sensor unit 22 (step S104) Based on this calculated
focusing object distance, the CPU 10 controls the operation of the
AF driving mechanism 23 to move the focusing lens system of the
photographing lens 8 to an in-focus position In this control, this
in-focus position of the focusing lens system of the photographing
lens 8 is precisely set by driving the focusing lens system of the
photographing lens via feedback control in which the position of
the focusing lens system is repeatedly detected (steps S105 and
S106).
[0050] On the other hand, if it is determined at step S103 that
an AF correction is necessary (if NO at step S103), the CPU 10 reads
a correction value corresponding to the measured object color from
the AF-drive-position look-up table 30 (step S107). Subsequently,
a focusing object distance is calculated based on distance measurement
data obtained via the AF sensor unit 22, however, the CPU 10 makes
a correction (AF correction) to the calculated focusing object distance
in accordance with the correction value read from the AF-drive-position
look-up table 30 (at step S108). Thereupon, based on this corrected
focusing object distance, the CPU 10 controls the operation of the
AF driving mechanism 23 by the aforementioned feedback control to
move the focusing lens system of the photographing lens 8 to an
in-focus position (steps S109 and S110). In this manner, the CPU
10 eliminates an AF error, which is caused by color difference in
object light, from object colors measured at five points on an object
which correspond to the distance measuring points P1, P2, P3, P4
and P5 in the AF sensor unit 22, respectively, which makes it possible
to focus the photographing lens 8 on an object automatically with
precision.
[0051] Upon moving to an in-focus position (if YES at step S106
or S110), the focusing lens system of the photographing lens 8 is
stopped (step S111) Thereupon, control waits for the release button
4 to be fully depressed (step S112), i.e., it is determined whether
the release switch of the release button 4 has been turned ON by
a full depression of the release button 4 at step S112. If it is
determined that the release switch of the release button 4 is ON
(if YES at step S112), an image capturing process is performed to
capture an object image, and thereafter control ends. In this image
capturing process (the detailed description of which is not shown
in the flow chart shown in FIG. 6), the swingable half mirror 11
is lifted up and the focal plane shutter 18 is opened so that an
object image is formed on the CCD image sensor 20 via the photographing
lens 8. An aperture value and a shutter speed at this time are set
based on the aforementioned exposure information, which is calculated
by the exposure controller 29 in accordance with a photometric value
measured by the photometric sensor 16. At the same time, a charge
accumulation time for the color CCD image sensor 20 is determined
by the operation of the CCD driver 107. A color image signal is
output from the CCD image sensor 20 and then this image signal is
subjected to predetermined processings to be converted into a digital
image signal as described above. In generating this digital image
signal, the CPU 10 adjusts the white balance thereof in accordance
with the measured object color temperature.
[0052] In this manner, the colorimetric sensor 17 is made to be
capable of performing not only color measurements but also color
temperature measurements in the above illustrated embodiment of
the digital camera. In other words, the calorimetric sensor 17 is
made as a colorimetric sensor which is integral with a color temperature
sensor. Namely, the colorimetric sensor 17 serves as a dual-purpose
sensor for color measurements and color temperature measurements.
Therefore, even in the case where the digital camera needs to be
provided with a calorimetric sensor, a color temperature sensor
and a photometric sensor, the digital camera only needs to be provided
with two sensors: a photometric sensor and a colorimetric sensor
such as the colorimetric sensor 17, which simplifies the structure
of the digital camera. Moreover, since the photometric sensor 16
is provided independently of the colorimetric sensor 17 in this
case, influence on a photometering operation of the photometric
sensor 16 which is caused by a color filter used in performing object
color measurements can be eliminated, which makes both accurate
photometric measurements and photographing with correct exposure
possible. Furthermore, since the calorimetric sensor 17 can measure
the object colors on five points on an object which respectively
correspond to the distance measuring points P1, P2, P3, P4 and P5
and the color temperature of the object at the same time, a proper
and high-precision AF control is achieved while an appropriate color
temperature adjustment (white balance adjustment) can be made to
a color image signal obtained by the imaging operation of the CCD
image sensor 20.
[0053] The present invention has been described based on the above
illustrated embodiment of the digital camera that uses an interchangeable
lens because distance measurement data obtained via an AF sensor
unit is easy to vary by exchanging the photographing lens mounted
to the camera body, since, in the case of normal photographing lenses,
individual color rendering properties often vary depending on the
lens. The present invention is aimed at a digital camera in which
such variation is compensated for. However, the technical idea of
the present invention is not limited solely to a digital camera
using an interchangeable lens. Namely, the present invention can
be applied to any digital camera which includes a photometric sensor,
a calorimetric sensor and a color temperature sensor as indispensable
parts of the camera. Moreover, a colorimetric sensor provided in
a digital camera to which the present invention is applied is not
limited solely to a calorimetric sensor such as the colorimetric
sensor 17 having the above described particular structure. Namely,
the present invention is applicable as long as the color of at least
a part of an object image and the color temperature of the whole
object image can be measured by a single photoreceiver.
[0054] Obvious changes may be made in the specific embodiment of
the present invention described herein, such modifications being
within the spirit and scope of the invention claimed. It is indicated
that all matter contained herein is illustrative and does not limit
the scope of the present invention. |