U.S. patent application number 09/866588 was filed with the patent office on 2002-01-03 for exposure control device for use in camera.
Invention is credited to Ohsawa, Toshifumi.
Application Number | 20020001464 09/866588 |
Document ID | / |
Family ID | 18679681 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001464 |
Kind Code |
A1 |
Ohsawa, Toshifumi |
January 3, 2002 |
Exposure control device for use in camera
Abstract
An exposure control device for use in a camera includes a
photosensor having at least two different types of spectral
characteristics, a lightness calculating circuit that calculates
lightness of each zone of the photosensor from the output of the
zone of the photosensor, wherein the photosensor is partitioned
into a plurality of zones, a saturation calculating circuit that
calculates saturation of each zone of the photosensor from the
output of the zone of the photosensor, a cloudy sky determining
circuit that determines whether an area of the object field is a
cloudy sky area, based on the lightness and saturation of each zone
of the photosensor, and an exposure control circuit that performs
exposure control based on the determination result of the cloudy
sky determining circuit.
Inventors: |
Ohsawa, Toshifumi; (Tokyo,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
18679681 |
Appl. No.: |
09/866588 |
Filed: |
May 30, 2001 |
Current U.S.
Class: |
396/50 ; 396/234;
396/67 |
Current CPC
Class: |
G03B 7/09979
20150115 |
Class at
Publication: |
396/50 ; 396/67;
396/234 |
International
Class: |
G03B 007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2000 |
JP |
2000-178223 |
Claims
What is claimed is:
1. An exposure control device for use in a camera, comprising: a
photosensor having at least two different types of spectral
characteristics, said photosensor being partitioned into a
plurality of zones; a lightness calculating circuit that calculates
a lightness of each zone of the photosensor from an output of the
zone of the photosensor; a saturation calculating circuit that
calculates a saturation of each zone of the photosensor from the
output of the zone of the photosensor; a cloudy sky determining
circuit that determines whether an area of an object field is a
cloudy sky area, based on the lightness and saturation of each zone
of the photosensor; and an exposure control circuit that performs
exposure control based on a determination result of the cloudy sky
determining circuit.
2. An exposure control device according to claim 1, wherein the
cloudy sky determining circuit determines that an area is a cloudy
sky area when a lightness thereof is greater than a lightness
reference value and a saturation thereof is less than a saturation
reference value.
3. An exposure control device according to claim 1, wherein the
exposure control circuit performs exposure control in such a manner
that the luminance of a cloudy sky area is weighted with a small
value when an area size of the cloudy sky area is sufficiently
large relative to an area size of the object field, and in such a
manner that the luminance of the cloudy sky area is not accounted
for when the area size of the cloudy sky area is sufficiently small
relative to the size of the object field.
4. An exposure control device for use in a camera, comprising: a
photosensor having at least two different types of spectral
characteristics, said photosensor being partitioned into a
plurality of zones; a range finder unit that measures a range to an
object in an object field; a posture detector unit that detects a
posture of a body of the camera; a lightness calculating circuit
that calculates a lightness of each zone of the photosensor from an
output of the zone of the photosensor; a saturation calculating
circuit that calculates a saturation of each zone of the
photosensor from the output of the zone of the photosensor; a
particular area determining circuit that determines whether an area
of the object field is a particular area, based on the lightness
and saturation of each zone; a cloudy sky determining circuit that
determines whether a particular area is a cloudy sky area, based on
the range to an object and the posture of the camera; and an
exposure control circuit that performs exposure control based on a
determination result of the cloudy sky determining circuit.
5. An exposure control device according to claim 4, wherein the
particular area determining circuit determines that an area of the
object field is a particular area when a lightness thereof is
greater than a lightness reference value and a saturation thereof
is less than a saturation reference value.
6. An exposure control device according to claim 4, wherein the
cloudy sky determining circuit determines that a particular area is
a cloudy sky when the range of an object in the particular area is
distant, and when the particular area is present on a side of the
sky in the object field.
7. An exposure control device according to claim 4, wherein the
exposure control circuit performs exposure control in such a manner
that the luminance of a cloudy sky area is weighted with a small
value when an area size of the cloudy sky area is sufficiently
large relative to an area size of the object field, and in such a
manner that the luminance of the cloudy sky area is not accounted
for when the area size of the cloudy sky area is sufficiently small
relative to the area size of the object field.
8. An exposure control device for use in a camera, comprising: a
photosensor having at least two different types of spectral
characteristics, said photosensor being partitioned into a
plurality of zones; a range finder unit that measures a range to an
object in an object field; a posture detector unit that detects a
posture of a body of the camera; a lightness calculating circuit
that calculates a lightness of each zone of the photosensor from an
output of the zone of the photosensor; a saturation calculating
circuit that calculates a saturation of each zone of the
photosensor from the output of the zone of the photosensor; a
particular area determining circuit that determines whether an area
of the object field is particular area when, a lightness thereof is
greater than a lightness reference value and a saturation thereof
is less than a saturation reference value; a cloudy sky determining
circuit that determines that a particular is a cloudy sky area when
the range of an object in the particular area is distant, and when
the particular area is present on a side of the sky in the object
field, based on outputs of the range finder unit and the posture
detector unit; an optimum luminance calculating circuit that
calculates an optimum luminance for exposure in accordance with an
area size of a cloudy sky area in the object field; and an exposure
control circuit that performs exposure control using a calculated
optimum luminance.
9. An exposure control device according to claim 8, wherein the
cloudy sky determining circuit determines that a particular area is
a cloudy sky area when the range of an object in the particular
area is greater than a reference value, when the particular area is
present on a side of the sky in the object field, and when the
particular area has continuity with another particular area.
10. An exposure control device according to claim 8, wherein the
optimum luminance calculating circuit calculates the optimum
luminance after the luminance of a cloudy sky area is weighted with
a small value when the area size of the cloudy sky area in the
object field is larger than a reference value.
11. An exposure control device according to claim 8, wherein the
optimum luminance calculating circuit calculates the optimum
luminance without regard to the luminance of a cloudy sky area when
the area size of the cloudy sky area in the object field is not
larger than a reference value.
12. An exposure control device according to claim 1, wherein the
photosensor has three types of spectral characteristics in the
visible light region.
13. An exposure control device according to claim 12, wherein the
three types of spectral characteristics are primary colors.
14. An exposure control device according to claim 12, wherein the
three types of spectral characteristics are complementary
colors.
15. An exposure control device according to claim 12, wherein each
zone of the plurality of zones contains each type of the spectral
characteristics of the photosensor.
16. An exposure control device for use in a camera, comprising: a
photosensor having spectral characteristics in the visible-light
region and in the infrared-light region, said photosensor being
partitioned into a plurality of zones; a visible-light luminance
calculating circuit that calculates visible-light luminance in each
zone of the photosensor from an output of the zone of the
photosensor,; an infrared-light luminance calculating circuit that
calculates infrared-light luminance in each zone of the photosensor
from the output of the zone of the photosensor; a cloudy sky
determining circuit that determines whether an area of an object
field is a cloud sky area, based on the visible-light luminance and
infrared-light luminance in each zone; and an exposure control
circuit that performs exposure control based on a determination
result of the cloudy sky determining circuit.
17. An exposure control device according to claim 16, wherein the
cloudy sky determining circuit determines that an area is a cloudy
sky area when the infrared-light luminance is greater than the
visible-light luminance in ratio.
18. An exposure control device according to claim 16, wherein the
exposure control circuit performs exposure control in such a manner
that the luminance of the cloudy sky area is weighted with a small
value when an area size of the cloudy sky area is sufficiently
large relative to an area size of the object field, and in such a
manner that the luminance of the cloudy sky area is not accounted
for when the area size of the cloudy sky area is sufficiently small
relative to the area size of the object field.
19. An exposure control device for use in a camera, comprising: a
photosensor having spectral characteristics in the visible-light
region and in the infrared-light region, said photosensor being
partitioned into a plurality of zones; a range finder unit that
measures a range to an object in an object field; a posture
detector unit that detects a posture of a body of the camera; a
visible-light luminance calculating circuit that calculates
visible-light luminance in each zone of the photosensor from an
output of the zone of the photosensor; an infrared-light luminance
calculating circuit that calculates infrared-light luminance in
each zone of the photosensor from the output of the zone of the
photosensor; a sky area determining circuit that determines whether
an area of the object field is a sky area, base on the
visible-light luminance and infrared-light luminance in the
plurality of zones and the posture of the body of the camera; a
cloudy sky determining circuit that determines whether a sky area
is a cloudy sky area, based on a value of the ratio of the
visible-light luminance to the infrared-light luminance; and an
exposure control circuit that performs exposure control based on a
determination result of the cloudy sky area.
20. An exposure control device according to claim 19, wherein the
sky area determining circuit determines that an area is a sky area
when the visible-light luminance is greater than a reference value,
the range of the object is distant, and the area is on a side of
the sky in the object field.
21. An exposure control device according to claim 19, wherein the
cloudy sky determining circuit determines that an area is a cloudy
sky area when the infrared-light luminance is greater than the
visible-light luminance in ratio.
22. An exposure control device according to claim 19, wherein the
exposure control circuit performs exposure control in such a manner
that the luminance of a cloudy sky area is weighted with a small
value when an area size of a cloudy sky area is sufficiently large
relative to an area size of the object field, and in such a manner
that the luminance of the cloudy sky area is not accounted for when
the area size of the cloudy sky area is sufficiently small relative
to the area size of the object field.
23. An exposure control device for use in a camera, comprising: a
photosensor having spectral characteristics in the visible-light
region and in the infrared-light region, said photosensor being
partitioned into a plurality of zones; a range finder unit that
measures a range to an object in an object field; a posture
detector unit that detects a posture of a body of the camera; a
visible-light luminance calculating circuit that calculates
visible-light luminance in each zone of the photosensor from an
output of the zone of the photosensor; an infrared-light luminance
calculating circuit that calculates the infrared-light luminance in
each zone of the photosensor from the output of the zone of the
photosensor; a sky area determining circuit that determines that an
area of the object field is a sky area, when the visible-light
luminance is greater than a reference value, the range of the
object is distant, and the area is on a side of the sky in the
object field; a cloudy sky determining circuit that determines that
a sky area is a cloudy sky area, when the infrared-light luminance
is greater than the visible-light luminance in ratio; an optimum
luminance calculating circuit that calculates an optimum luminance
for exposure in accordance with an area size of a cloudy sky area
in the object field; and an exposure control circuit that performs
exposure control using a calculated optimum luminance.
24. An exposure control device according to claim 23, wherein the
optimum luminance calculating circuit calculates the optimum
luminance after the luminance of a cloudy sky area is weighted with
a small value when the area size of the cloudy sky area in the
object field is larger than a reference value.
25. An exposure control device according to claim 23, wherein the
optimum luminance calculating circuit calculates the optimum
luminance without regard to the luminance of a cloudy sky area when
the area size of the cloudy sky area in the object field is not
larger than a reference value.
26. An exposure control device according to claim 16, wherein each
zone has spectral characteristics in the visible-light region and
the infrared-light region.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an exposure control device
for use in a camera and, more particularly, to an exposure control
device that reliably controls exposure even under cloudy weather
conditions.
[0003] 2. Description of the Related Art
[0004] In a known technique to achieve an optimum exposure in a
camera, an exposure control device photometers a photographic
object with a photometric sensor having a plurality of
photosensitive elements and determines whether the photographic
object is positioned in a back lighting condition based on a
plurality of luminance signals output by the photometric sensor.
U.S. Pat. No. 5,596,387 discloses a technique in which improved
exposure control is performed by obtaining both luminance
information and color temperature information based on the spectral
component of the object field, by imparting different spectral
characteristics to a plurality of photosensitive elements using a
saturated color filter or a complementary color filter. According
to U.S. Pat. No. 5,596,387, a photograph which conforms to the
image of the time band of photographing in the photographing of an
evening scene or a morning scene is produced, by performing
exposure control based on the luminance information and the color
temperature information of the object field.
[0005] To take a nice picture by providing an appropriate exposure
in outdoor photographing, weather conditions need to be considered.
As already discussed, a technique is known which achieves an
appropriate exposure by determining front lighting or back lighting
during good weather conditions. In contrast, no technique has been
available to provide optimum exposure during cloudy weather
conditions.
[0006] Specifically, a difference between good weather conditions
and cloudy weather conditions is discussed. During good weather
conditions under which a luminance of Bv.apprxeq.9 results with a
18% gray reflective plate photometered in the back lighting, a
luminance Bv.apprxeq.8 to 9 results when the luminance of a blue
sky portion of the sky is measured at a high elevation angle. A
luminance of Bv.apprxeq.9 to 10 results when the luminance of a
white portion of the sky is measured at a low elevation angle. It
is said that the luminance of an object is appropriately obtained
if the 18% gray reflective plate is photometered. Even if sky
appears in the object field, the difference between the luminance
of the sky and the luminance of the 18% gray reflective plate is
about one notch in the Bv value, and the exposure of the object is
not largely in error as long as the photographing is not performed
in the back lighting.
[0007] When the luminance of a uniformly light gray sky portion is
photometered under a cloudy weather condition, a luminance of
Bv.apprxeq.10 results. In contrast, a luminance Bv.apprxeq.6 to 7
results when the 18% gray reflective plate is photometered. In this
case, the luminance difference between the sky portion and an
ordinary object portion is three in the Bv value. When the sky
portion appears in the object field during cloudy weather, the
output of the photometric sensor of a camera is strongly affected
by a high luminance of the sky portion. As a result, the object is
subject to an under-exposure under the cloudy weather condition in
contrast to good weather conditions. There is room for improvements
in exposure control.
SUMMARY OF THE INVENTION
[0008] In accordance with the method of the present invention, an
area having high lightness and low saturation is determined, and
the area is then determined to be a cloudy sky area when an object
range in the area is distant and when the area is on the side of
the sky in the object field. Exposure control is performed in such
a manner that the luminance of the area determined to be a cloudy
sky area is weighted for a smaller value. In this way,
under-exposure is avoided when photographing under a cloudy weather
condition featuring high lightness and low saturation.
[0009] An area is determined to be a cloudy sky area on condition
that an area results in a large visible-light luminance, that the
object range in the area is distant, and that the area is present
on the side of the sky in the object field. Since the luminance of
the determined cloudy sky area is weighted for a smaller value in
exposure control, under-exposure is prevented when photographing
under a cloudy weather featuring a low saturation and a high
luminance.
[0010] The present invention in one aspect relates to an exposure
control device for use in a camera, and includes a photosensor
having at least two different types of spectral characteristics, a
lightness calculating circuit that calculates a lightness of each
zone of the photosensor from the output of the zone of the
photosensor, the photosensor being partitioned into a plurality of
zones, a saturation calculating circuit that calculates saturation
of each zone of the photosensor from the output of the zone of the
photosensor, a cloudy sky determining circuit that determines
whether an area of the object field is a cloudy sky area, based on
the lightness and the saturation of each zone of the photosensor,
and an exposure control circuit that performs exposure control
based on the determination result of the cloudy sky determining
circuit.
[0011] The present invention in another aspect relates to an
exposure control device for use in a camera, and includes a
photosensor having at least two different types of spectral
characteristics, a range finder unit that measures a range to an
object, a posture detector unit that detects a posture of the body
of the camera, a lightness calculating circuit that calculates
lightness of each zone of the photosensor from the output of the
zone of the photosensor, the photosensor being partitioned into a
plurality of zones, a saturation calculating circuit that
calculates saturation of each zone of the photosensor from the
output of the zone of the photosensor, a particular area
determining circuit that determines whether an area of the object
field is a particular area, based on the lightness and the
saturation of each zone, a cloudy sky determining circuit that
determines whether the particular area is a cloudy sky area, based
on the range to the object and the posture of the camera, and an
exposure control circuit that performs exposure control based on
the determination result of the cloudy sky determining circuit.
[0012] The present invention in yet another aspect relates to an
exposure control device for use in a camera, and includes a
photosensor having at least two different types of spectral
characteristics, a range finder unit that measures a range to an
object, a posture detector unit that detects a posture of the body
of the camera, a lightness calculating circuit that calculates
lightness of each zone of the photosensor from the output of the
zone of the photosensor, the photosensor being partitioned into a
plurality of zones, a saturation calculating circuit that
calculates saturation of each zone of the photosensor from the
output of the zone of the photosensor, a particular area
determining circuit that determines whether an area of the object
field is a particular area having a lightness thereof higher than a
lightness reference value and a saturation thereof lower than a
saturation reference value, a cloudy sky determining circuit that
determines that the particular area is a cloudy sky area when the
range of an object in the particular area is distant, and when the
particular area is present on the side of the sky in the object
field, based on the outputs of the range finder unit and the
posture detector unit, an optimum luminance calculating circuit
that calculates an optimum luminance for exposure in accordance
with the area size of the cloudy sky area in the object field, and
an exposure control circuit that performs exposure control using
the calculated optimum luminance.
[0013] The present invention in still another aspect relates to an
exposure control device for use in a camera, and includes a
photosensor having spectral characteristics in the visible-light
region and in the infrared-light region, a visible-light luminance
calculating circuit that calculates visible-light luminance in each
zone of the photosensor from the output of the zone of the
photosensor, the photosensor being partitioned into a plurality of
zones, an infrared-light luminance calculating circuit that
calculates infrared-light luminance in each zone of the photosensor
from the output of the zone of the photosensor, a cloudy sky
determining circuit that determines whether an area of the object
field is a cloudy sky area, based on the visible-light luminance
and the infrared-light luminance in each zone, and an exposure
control circuit that performs exposure control based on the
determination result of the cloudy sky determining circuit.
[0014] The present invention in still another aspect relates to an
exposure control device for use in a camera, and includes a
photosensor having spectral characteristics in the visible-light
region and in the infrared-light region, a range finder unit that
measures a range to an object, a posture detector unit that detects
a posture of the body of the camera, a visible-light luminance
calculating circuit that calculates visible-light luminance in each
zone of the photosensor from the output of the zone of the
photosensor, the photosensor being partitioned into a plurality of
zones, an infrared-light luminance calculating circuit that
calculates infrared-light luminance in each zone of the photosensor
from the output of the zone of the photosensor, a sky area
determining circuit that determines whether an area of the object
field is a sky area, based on the visible-light luminance and the
infrared-light luminance in the zone and the posture of the body of
the camera, a cloudy sky determining circuit that determines
whether a sky area is a cloudy sky area, based on a value of the
ratio of the visible-light luminance to the infrared-light
luminance, and an exposure control circuit that performs exposure
control based on a determination result of the cloudy sky
determining circuit.
[0015] The present invention in yet another aspect relates to an
exposure control device for use in a camera, and includes a
photosensor having spectral characteristics in the visible-light
region and in the infrared-light region, a range finder unit that
measures a range to an object, a posture detector unit that detects
a posture of the body of the camera, a visible-light luminance
calculating circuit that calculates visible-light luminance in each
zone of the photosensor from the output of the zone of the
photosensor, the photosensor being partitioned into a plurality of
zones, an infrared-light luminance calculating circuit that
calculates infrared-light luminance in each zone of the photosensor
from the output of the zone of the photosensor, a sky area
determining circuit that determines whether an area is a sky area
where the visible-light luminance is higher than a reference value,
the range of the object is distant, and the area is on the sky side
in the range of the object field, a cloudy sky determining circuit
that determines whether a sky area is a cloudy sky area where the
infrared-light luminance is higher than the visible-light luminance
in ratio, an optimum luminance calculating circuit that calculates
an optimum luminance for exposure in accordance with an area size
of the cloudy sky area in the object field, and an exposure control
circuit that performs exposure control using the calculated optimum
luminance.
[0016] Further objects, features, and advantages of the present
invention will be apparent from the following description of the
preferred embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional view showing the layout of
optical elements of a camera and an interchangeable lens;
[0018] FIG. 2 shows the structure of a focus detection sensor;
[0019] FIG. 3 shows the structure of a photometric sensor in a
first embodiment of the present invention;
[0020] FIG. 4 is a block diagram showing an electrical circuit for
the camera and the interchangeable lens;
[0021] FIG. 5 is a flow diagram showing operation of the control
circuit of the camera;
[0022] FIG. 6 is a flow diagram showing an exposure calculation in
the first embodiment of the present invention;
[0023] FIG. 7 shows one example of an object field;
[0024] FIG. 8 shows the structure of a photometric sensor in a
second embodiment of the present invention; and
[0025] FIG. 9 is a flow diagram of an exposure calculation
according to the second embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] First Embodiment
[0027] FIG. 1 is a sectional view showing the layout of optical
members in a camera and interchangeable lens of the present
invention.
[0028] As shown, a single-lens reflex camera with an
interchangeable lens includes a camera body 10, and an
interchangeable lens 30. There are shown, in the camera body 10, an
optical axis 11 of an imaging lens, a film plane 12, a
semi-transmissive main mirror 13, and a first reflective mirror 14.
Both the main mirror 13 and the first reflective mirror 14 are
flipped up and down during photographing operations, as is well
known in the art. Also shown are a paraxial imaging plane 15, which
is optically conjugate with the film plane 12 with respect to the
first reflective mirror 14, a second reflective mirror 16, an
infrared blocking filter 17, a diaphragm 18 having two apertures, a
secondary imaging lens 19, and a focus detection sensor 20. The
focus detection sensor 20 is fabricated of an area storage type
photoelectric conversion element such as a CMOS or CCD, and
includes a number of photosensors divided into a pair of zones 20A
and 20B corresponding to the two apertures of the diaphragm 18 as
shown in FIG. 2. Together with the photosensors (including zones
20A and 20B), a signal storage unit and a peripheral circuit for
signal processing are integrated into a single chip. The
construction from the first reflective mirror 14 to the focus
detection sensor (AF sensor) 20 enables focus detection using an
image shifting method at any location within the object field,
e.g., as disclosed in detail in Japanese Patent Laid-Open No.
9-184965.
[0029] Also shown are a focusing plate 21 having a diffusion
characteristic (diffusivity), a penta prism 22, an eyepiece 23, a
third reflective mirror 24, a condenser lens 25, and a photometric
sensor (AE sensor) 26 for collecting information about the
luminance and color of an object. The photometric sensor 26 is an
area storage type photoelectric conversion device, such as a CMOS
or CCD, and is composed a number of photosensor elements and a
color filter having spectral characteristics of the primary colors
(or the complementary colors), in an arrangement as shown in FIG.
3. The photometric sensor 26 substantially covers the entire object
field. FIG. 3 shows an example of the color filter having the
primary color spectral characteristics, in which R represents a
zone of the photosensor provided with a color filter having red
transmissive spectral characteristic, G represents a zone of the
photosensor provided with a color filter having green transmissive
spectral characteristic, and B represents a zone of the photosensor
provided with a color filter having blue transmissive spectral
characteristic. In the same manner as in the focus detection
sensor, a signal storage unit and a peripheral circuit for signal
processing are integrated together with the photosensor into a
single chip. Further shown in FIG. 1 are a lens mount 27 for
mounting the (interchangeable) imaging lens and a junction 28 for
establishing communication with the imaging lens.
[0030] The interchangeable lens 30 includes a diaphragm 31, a
junction 32 for establishing communication with the camera body, a
mount 33 to be mated with the camera, and optical lens elements 34
to 36 forming the imaging lens.
[0031] FIG. 4 is a block diagram showing the electrical circuit of
the camera body 10 of the present invention and the interchangeable
lens 30. In the camera body 10, a control circuit 41 is a one-chip
microcomputer including a ROM (Read-Only Memory), a RAM
(Random-Access Memory), an ALU (Arithmetic and Logic Unit), an
analog-to-digital converter, and a serial communication port, and
generally controls operation of the camera mechanism. The control
operation sequence of the control circuit 41 will be specifically
discussed later. The focus detection sensor 20 and the photometric
sensor 26 here are those described with reference to FIG. 1. The
outputs of the focus detection sensor 20 and the photometric sensor
26 are connected to inputs of the analog-to-digital converter of
the control circuit 41. A shutter 42 is connected to output
terminals of the control circuit 41 and is controlled by the
control circuit 41. A first motor driver 43 is connected to output
terminals of the control circuit 41 and is controlled by the
control circuit 41. The first motor driver 43 drives a first motor
44 to advance the film and to drive the main mirror 13. A posture
detection sensor 45 detects the posture of the camera, and provides
the output thereof to an input terminal of the control circuit 41.
Upon receiving information from the posture detection sensor 45,
the control circuit 41 collects the information and determines
whether a user is holding the camera in a particular orientation,
e.g., in a side down position or an upright position during
photographing. An AF (auto-focus) light source 46 projects infrared
light toward an object when the focus detection sensor 20 detects
focus under a low illuminance condition. The AF light source 46
emits light in response to an output signal of the control circuit
41. A flash unit 47 projects light during photographing when the
luminance of the object is not sufficient. The flash unit 47
flashes light in response to an output signal from the control
circuit 41. A display 48 displays data, e.g., the number of
pictures taken, date information, and photographing information.
The segments of the display 48 are lit in response to an output
signal from the control circuit 41. A plurality of switches 49
including a release button are arranged. The junction 28, already
discussed with reference to FIG. 1, exchanges input/output signals
with the control circuit 41 through the serial communication
port.
[0032] In the interchangeable lens 30, a lens control circuit 51 is
a one-chip microcomputer including a ROM, a RAM, an ALU, and a
serial communication port. A second motor driver 52 is connected to
an output terminal of the lens control circuit 51 and is controlled
by the lens control circuit 51. The second motor driver 52 drives a
second motor 53 to adjust focusing. A third motor driver 54 is
connected to an output terminal of the lens control circuit 51 and
is controlled by the lens control circuit 51. The third motor
driver 54 drives a third motor 55 to control the diaphragm 31 shown
in FIG. 1. A range finding encoder 56 is connected to an input
terminal of the lens control circuit 51 and acquires information
about the projection of a focus adjusting lens, namely, the range
to the object. A zoom detection encoder 57 is connected to an input
terminal of the lens control circuit 51 and acquires focal length
information during photographing when the interchangeable lens 30
is a zoom lens. The junction 32, already described with reference
to FIG. 1, exchanges input/output signals with the lens control
circuit 51 through the serial communication port.
[0033] When the interchangeable lens 30 is mounted onto the camera
body 10, the junctions 28 and 32 are mated to each other, allowing
data communication to be performed between the lens control circuit
51 and the control circuit 41 of the camera body 10. The lens
control circuit 51 outputs, in the data communication to the
control circuit 41 of the camera body 10, optical information
unique to the individual lens required to perform focus detection
and exposure calculation, and the information about the range to
the object and the focal length information provided by the range
finding encoder 56 and the zoom detection encoder 57. Conversely,
the control circuit 41 of the camera body 10 outputs information in
the data communication to the lens control circuit 51 to control
the second motor driver 52 in accordance with focus adjustment
information, and controls the third motor driver 54 in accordance
with diaphragm information.
[0034] The control sequence of the control circuit 41 of the camera
body 10 of the present invention is now discussed with reference to
a flow diagram shown in FIG. 5. When a power switch (not shown) is
pressed ("on"), the control circuit 41 becomes operative. The
sequence begins with step 101 shown in FIG. 5 in response to the
pressing of a first stroke switch of a release button (not
shown).
[0035] In step 101, a control signal is output to the focus
detection sensor 20 to start signal storage.
[0036] In step 102, the control circuit 41 waits until the focus
detection sensor 20 completes the signal storage.
[0037] In step 103, the control circuit 41 analog-to-digital
converts the stored signal while reading the stored signal from the
focus detection sensor 20. The control circuit 41 performs various
data corrections, such as shading, on the read digital data.
[0038] In step 104, the control circuit 41 receives lens
information required to perform focus detection from the lens
control circuit 51, and then calculates the focus state in each
zone of the object field from the digital data from the focus
detection sensor 20. In accordance with the resulting focus state
in each zone of the object field, an area within the field to be
focused is determined using the technique disclosed in Japanese
Patent Laid-Open No. 11-190816. The lens travel distance for
focusing is calculated taking into consideration the focus state in
the determined zone.
[0039] In step 105, the lens travel distance calculated is output
to the lens control circuit 51. In response, the lens control
circuit 51 outputs a signal to the second motor driver 52 to drive
the second motor 53, thereby driving the focus adjusting lens. The
imaging lens is thus focused on the object. After focusing the
imaging lens on the object, the control circuit 41 acquires
information about the range to the object by receiving information
from the range finding encoder 56 through the lens control circuit
51.
[0040] In step 106, the control circuit 41 outputs a control signal
to the photometric sensor 26, thereby starting signal storage.
[0041] In step 107, the control circuit 41 waits until the signal
storage is complete.
[0042] In step 108, the control circuit 41 analog-to-digital
converts the stored signal while reading the signal stored in the
photometric sensor 26.
[0043] In step 109, an exposure calculation is performed. The
control circuit 41 determines the luminance of the object through
calculation, and determines a shutter speed and a diaphragm stop
resulting in an optimum exposure. The control circuit 41 also
determines whether to flash light. The calculation process will be
detailed later referring to a flow diagram shown in FIG. 6.
[0044] In step 110, the control circuit 41 waits until a second
stroke switch of the shutter button is turned on. If the second
stroke switch is not turned on, the control sequence returns to
step 101. If (when) the second stroke switch is turned on, the
control sequence goes to step 111.
[0045] In step 111, the control circuit 41 outputs a control signal
to the first motor driver 43 to drive the first motor 44, thereby
flipping up the main mirror 13 and the first reflective mirror
14.
[0046] In step 112, the control circuit 41 outputs the diaphragm
stop information calculated in step 109 to the lens control circuit
51. In response to this information, the lens control circuit 51
outputs a control signal to the third motor driver 54 to drive the
third motor 55, thereby driving the diaphragm 31. In this way, the
imaging lens is put into a stopped-down aperture state.
[0047] In step 113, the control circuit 41 controls the shutter 42
in accordance with the shutter speed calculated in step 109,
thereby exposing the film to a photographic scene. The flash unit
47 is triggered, as necessary.
[0048] In step 114, the control circuit 41 outputs information to
the lens control circuit 51 to open the diaphragm 31. In response
to this information, the lens control circuit 51 outputs a signal
to the third motor driver 54 to drive the third motor 55, thereby
driving the diaphragm 31. The imaging lens is thus put to an open
diaphragm state.
[0049] In step 115, the control circuit 41 outputs a control signal
to the first motor driver 43 to drive the first motor 44, thereby
flipping down the main mirror 13 and the first reflective mirror
14.
[0050] In step 116, the control circuit 41 outputs a control signal
to the first motor driver 43 to drive the first motor 44, thereby
winding up the film.
[0051] A series of photographing steps is thus completed.
[0052] The exposure calculation executed in step 109 is now
discussed in detail, referring to the flow diagram shown in FIG.
6.
[0053] In step 151, the control circuit 41 receives lens and other
information required to perform the exposure calculation from the
lens control circuit 51, and corrects the digital data derived from
the photometric sensor 26 in step 108 shown in FIG. 5.
[0054] In step 152, the control circuit 41 groups the corrected
digital data according to the zones. For example, adjacent
photosensors, each having R, G, and B color filters, are combined
as a group, and each four adjacent groups are treated as one zone.
The object field is thus partitioned into zones.
[0055] In step 153, the average values of R, G, and B in each zone
are calculated, and are then regarded as luminance data r, g, and b
for each zone. The luminance data r, g, and b is then subjected to
a matrix operation for color space alteration and is thus converted
into lightness L, hue H, and saturation S. The conversion equations
are as follows:
L=7.3r+7.59g+7.11b
c1=7.7r-7.59g-7.11b
c2=-7.3r-7.59g+7.89b
H=tan.sup.-1(c1,c2)
S={square root}(c1.sup.2+c2.sup.2)
[0056] In step 154, focus information, namely, the object range of
the in-focus zone obtained in steps 104 and 105 in FIG. 5, and
information about the relative range of each zone to the relative
object ranges of each zone are related in correspondence to the
zones partitioned in step 152. In this way, the control circuit 41
acquires the information of whether the camera is far from
(distant) or near to (close) the zones of the object field.
[0057] In step 155, the control circuit 41 receives information
from the posture detection sensor 45. The control circuit 41 thus
acquires information of whether the camera is being held in a
particular orientation, e.g., in a side down position or an upright
position, and thereby determines the orientation of the camera in
the object field with respect to the sky and ground
perspective.
[0058] In step 156, the control circuit 41 determines whether an
area having a lightness L thereof higher than a predetermined value
and a saturation S thereof lower than a predetermined value is
presented, based on the lightness L and the saturation S obtained
in step 153 for each zone. If an area satisfying such a condition
is present, the control sequence proceeds to step 157.
[0059] In step 157, the control circuit 41 determines whether a sky
area appears in the object field in connection with each of the
zones having a lightness L thereof higher than the predetermined
value and a saturation S thereof lower than the predetermined
value. Used in the determination are criteria as to whether a far
range portion is present based on the focus information obtained in
step 154, whether the area is on the side of the sky based on the
posture information obtained in step 155, and whether there is a
continuity from a high-lightness and low-saturation area on the
side of the sky in the object field. An area satisfying these
criteria is determined to be a sky area.
[0060] In step 158, if there exists a zone determined to be a sky
area in step 157, the control sequence proceeds to step 159.
[0061] In step 159, the control circuit 41 determines whether the
ratio of the area size of the area determined to be a sky area to
the entire area of the object field is larger than a predetermined
value. When it is determined that the ratio is lower than the
predetermined value, the control sequence proceeds to step 160.
[0062] In step 160, the luminance information of the area
determined to be a sky area is not accounted for in the calculation
of the object luminance to be discussed later. In other words, the
area is treated as a cut area. The control sequence proceeds to
step 162. When there is no area determined to be a sky area in step
158, or when the ratio of the area size of the area determined to
be a sky area to the entire area of the object field is larger than
the predetermined value in step 159, the control sequence proceeds
to step 161.
[0063] In step 161, the area determined not to be a sky area in
step 158 but having a lightness L thereof higher than the
predetermined value and a saturation S thereof lower than the
predetermined value, and where the sky area is determined to have
an area size ratio greater than the predetermined value in step 159
are weighted in luminance thereof with a smaller value compared
with the remaining area in the calculation of the object luminance
to be discussed later. These areas are thus treated as a
low-weighted area. The control sequence then proceeds to step 162.
When it is found in step 156 that there is no area having a
lightness L thereof higher than the predetermined value and a
saturation S thereof lower than the predetermined value, the
control sequence proceeds to step 162 without performing steps 157
through 161.
[0064] In step 162, the object luminance is calculated based on the
information of the lightness L of each zone of the object field. In
the calculation, the area on which the camera focuses in step 104
shown in FIG. 5 is weighted with a large value, the data of the
area determined to be a cut area in step 160 is not accounted for,
and the area weighted with a small value in step 161 is weighted
with a small value. The average of these areas is thus
determined.
[0065] A photographic composition shown in FIG. 7 is now discussed.
There are shown a sky area 71, a mountain area 72, a ground area
73, a person 74, a tree 75, and a billboard 76. Among these areas,
the sky area 71 rises in lightness L in the photographing during
the day time. The person 74 and the billboard 76 can have a high
lightness L when they have a highly reflective color. The sky area
71 becomes relatively high in saturation S in good weather
conditions or in a reddish sky with sunrise glow or sunset glow. On
a cloudy day, the saturation S of the cloudy sky area becomes quite
low. In step 156, the sky area 71 is thus extracted as an area
having a lightness thereof higher than the predetermined value and
a saturation S thereof lower than the predetermined value on a
cloudy day during daylight photographing. Taking into account the
focus information and the posture information, the area is then
determined to be a cloudy area in step 157, and is then treated as
a cut area in step 160. When the person 74 and the billboard 76 are
extracted as an area having a lightness thereof higher than the
predetermined value and a saturation S thereof lower than the
predetermined value due to the color and the reflectance thereof in
step 156, the person 74 is determined to be close (not far) or
distant in step 157 and the billboard 76 is determined to be not
continuous with the sky area. Both the person 74 and the billboard
76 are determined not to be a sky area, and are weighted with a
small value in step 161.
[0066] The luminance of the object is calculated from the lightness
data of the photographing area excluding the sky area 71 in the
photographing on a cloudy day, and is calculated from the lightness
data of the photographing area including the sky area 71 on a fine
day or under sunrise or sunset glow conditions.
[0067] In a photographic composition having the majority of the
object field thereof occupied by the sky area, unlike the
photographic composition shown in FIG. 7, neglecting the effect of
the sky area, even if it is cloudy, in the calculation of the
object luminance is inappropriate. For this reason, the sky area is
treated as a cut area or is weighted with a small value in step
159, depending on the ratio of the area size of the sky area. Under
good weather conditions or sunset glow or sunrise glow conditions,
the sky area is neither treated as a cut area nor weighted with a
small value because even a high luminance area is not low in
saturation.
[0068] In step 163, film speed information is added to the
calculated object luminance. From the result, a shutter speed and a
diaphragm stop resulting in an optimum exposure are determined.
When the object luminance is lower than a predetermined value, the
control circuit 41 decides to use the flash unit 47. There are
available two types of criteria for this decision: a first
predetermined luminance value for a normal operation, and a second
luminance value in which the control sequence flows from step 158
to step 159, namely, in a photographing operation under a cloudy
weather condition. The second predetermined value is higher than
the first predetermined value. In other words, the flashing is
triggered more easily in a photographing operation under cloudy
weather conditions. This is intended to easily take a light hue and
high-contrast picture in a photographing operation under a cloudy
weather conditions.
[0069] The exposure calculation in accordance with the first
embodiment has been discussed in detail.
[0070] Second Embodiment
[0071] In accordance with the first embodiment, the photometric
sensor 26 is an area storage type photoelectric conversion element
which is partitioned into a number of zones, and is provided with a
color filter having primary color spectral characteristics or
complementary color spectral characteristics. In accordance with
the lightness L information and the saturation S information in the
signal from the photometric sensor 26, the cloudy sky area is
determined. The present invention is not limited to this
arrangement.
[0072] A second embodiment employs a photometric sensor 66 instead
of the photometric sensor 26 shown in the first embodiment. The
rest of the construction of the second embodiment remains unchanged
from that shown in FIG. 1 and FIG. 4.
[0073] The photometric sensor 66 is an area storage type
photoelectric conversion device such as a CMOS or CCD, and is
composed of a number of photosensor elements and a color filter V
having visible-light spectral characteristics of the primary colors
and a color filter IR having infrared spectral characteristics, as
shown in FIG. 8. The photometric sensor 66 substantially covers the
entire object field. In the same manner as in the photometric
sensor 26, a signal storage unit and a peripheral circuit for
signal processing are integrated together with the photosensor 66
into a single chip.
[0074] The general control sequence of the second embodiment
remains the same as that of the control circuit 41 of the camera in
the first embodiment shown in FIG. 5. The exposure calculation
executed in step 109 in the second embodiment, different from that
shown in FIG. 6, is discussed, referring to a flow diagram shown in
FIG. 9.
[0075] In step 251, the control circuit 41 receives lens
information required to perform exposure calculation from the lens
control circuit 51, and corrects digital data from the photometric
sensor 66 as in step 108 shown in FIG. 5.
[0076] In step 252, the control circuit 41 divides the corrected
digital data according to zone. For example, photosensor elements
adjacent to each other having a V filter and an IR filter are
paired, and every four pairs are grouped into a zone. The object
field is thus partitioned into zones.
[0077] In step 253, the averages of luminances of the visible-light
V and the infrared-light IR are calculated for each zone, and are
then treated as luminance data v and luminance data ir for each
zone.
[0078] In step 254, focus detection information, namely, the object
range of the in-focus zone obtained in steps 104 and 105 in FIG. 5,
and information about the relative object range of each zone are
related in correspondence to the zones partitioned in step 252. In
this way, the control circuit 41 acquires the information of
whether the camera is far from (distant) or near to (close) the
zones of the object field.
[0079] In step 255, the control circuit 41 receives information
from the posture detection sensor 45. The control circuit 41 thus
acquires information of whether the camera is being held in a
particular orientation, e.g., in a side down position or an upright
position, and thereby determines the orientation of the camera in
the object field with respect to the sky and ground
perspective.
[0080] In step 256, the control circuit 41 determines whether an
area obtained in step 253 and having a visible-light luminance data
v greater than a predetermined value is present. When it is found
that an area satisfies this condition, the control sequence
proceeds to step 257.
[0081] In step 257, the control circuit 41 determines whether a sky
area appears in the object field in connection with each of the
areas having a visible-light luminance data v greater the
predetermined value. Used in the determination are criteria as to
whether a far range portion is present based on the focus
information obtained in step 254, whether the area is on the side
of the sky based on the posture information obtained in step 255,
and whether there is continuity with a high-luminance area on the
sky side in the object field. An area satisfying these criteria is
determined to be a sky area.
[0082] In step 258, if there exists an area determined to be a sky
area, a determination is made of whether it is a good weather
condition or a cloudy weather condition based on the ratio of the
luminance data ir to the luminance data v. As described in Japanese
Patent Laid-Open No. 6-177416, there is a greater possibility that
the visible-light component is blocked by clouds in a cloudy
weather condition than good weather conditions. However, it is
known that infrared light having a longer wavelength is blocked
less than visible light. When the ratio of the infrared-light data
ir to the visible-light data v is higher, it is determined to be
cloudy, and the control sequence proceeds to step 259.
[0083] In step 259, the control circuit 41 determines whether the
ratio of the area size of the area determined to be a sky area to
the entire area of the object field is larger than a predetermined
value. When it is determined that the ratio is lower than the
predetermined value, the control sequence proceeds to step 260.
[0084] In step 260, the luminance information of the area
determined to be a sky area is not accounted for in the calculation
of the object luminance to be discussed later. In other words, the
area is treated as a cut area. The control sequence proceeds to
step 262. When the ratio of the area size of the area determined to
be a sky area to the entire area of the object field is larger than
the predetermined value in step 259, or when it is determined to be
not cloudy in step 258, the control sequence proceeds to step
261.
[0085] In step 261, the area determined not to be a sky area in
step 257, the area determined not to be a cloudy area in step 258
but having a luminance data v greater than the predetermined value
in step 256, and a sky area having the ratio of the area size
thereof to the entire area of the object field determined to be
larger than the predetermined value in step 259 are weighted in
luminance thereof with a smaller value compared with the remaining
area in the calculation of the object luminance to be discussed
later. In other words, these areas are treated as low-weighted
areas. The control sequence then proceeds to step 262.
[0086] When it is determined in step 256 that there is no area
having a visible-light luminance data v greater than the
predetermined value, the control sequence proceeds to step 262
without performing steps 257 through 261.
[0087] In step 262, the object luminance is calculated based on the
information of the lightness L of each zone of the object field. In
the calculation, the area on which the camera focuses in step 104
shown in FIG. 5 is weighted with a large value, the data of the
area determined to be a cut area in step 260 is not accounted for,
and the area regarded as a low-weighted area in step 261 is
weighted with a small value. The average of these areas is thus
determined.
[0088] In step 263, film speed information is added to the
calculated object luminance. From the result, a shutter speed and a
diaphragm stop resulting in an optimum exposure are determined.
When the object luminance is lower than a predetermined value, the
control circuit 41 decides to use the flash unit 47. There are
available two types of criteria for this decision: a first
predetermined luminance value for a normal operation, and a second
luminance value in which the control sequence flows from step 258
to step 259, namely, in a photographing operation under cloudy
weather conditions. The second predetermined value is higher than
the first predetermined value. In other words, a flash is triggered
more easily in a photographing operation under cloudy weather
conditions. This is intended to easily take a light hue and
high-contrast picture in a photographing operation under cloudy
weather conditions.
[0089] The exposure calculation in the second embodiment has been
discussed in detail.
[0090] In accordance with the above embodiments, a high lightness
and low saturation area is detected, using the photometric sensors
having red, green and blue spectral characteristics. A cloudy area
is detected by determining whether the area is on the sky side of
the object field and at a far distance. Under cloudy weather
conditions, the detection of a cloudy area enables optimum exposure
control. Alternatively, a photometric sensor having visible-light
spectral characteristics and infrared-light spectral
characteristics is used instead of the photometric sensor having
the red, green, and blue spectral characteristics. By determining
the ratio of the infrared-light luminance value to the
visible-light luminance value, a cloudy area is also detected.
Further, optimum exposure control is performed by modifying the
weight of these factors depending on the ratio of the particular
area to the entire object field. When a particular area is present,
the flash unit is triggered more easily, and a light hue and
high-contrast photograph is easily obtained in a photographing
operation under cloudy weather conditions.
[0091] While the present invention has been described with
reference to what are presently considered to be the preferred
embodiments, it is to be understood that the invention is not
limited to the disclosed embodiments. On the contrary, the
invention is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims. The scope of the following claims is to be accorded the
broadest interpretation so as to encompass all such modifications
and equivalent structures and functions.
* * * * *