Digital Camera Patent Abstract
A method, system and computer readable medium for controlling a
digital camera including setting a shutter speed; receiving a light
flux from an object to be photographed to form an image thereof
at the set shutter speed; converting the received light flux into
an image signal; amplifying the image signal with a variable gain;
judging whether or not the shutter speed is set slower than a predetermined
blur avoiding speed; and increasing the variable gain to a predetermined
value when the shutter speed is set slower than the predetermined
blur avoiding speed. Another embodiment includes a method, system
and computer readable medium for controlling a digital camera including
setting a shutter speed; receiving a light flux from an object to
be photographed to form an image thereof at the set shutter speed;
converting the received light flux into an image signal; amplifying
the image signal with a variable gain; judging whether or not the
shutter speed is set slower than a predetermined blur avoiding speed;
selectively setting a photographing mode to one of: a blur avoiding
photographing mode in which the variable gain is increased to a
predetermined value when the shutter speed is set slower than the
predetermined blur avoiding speed, and a normal photographing mode
in which the variable gain is not increased even when the shutter
speed is set slower than the predetermined blur avoiding speed;
and increasing the variable gain to a predetermined value when the
blur avoiding photographing mode is set and when the shutter speed
is set slower than the predetermined blur avoiding speed. Digital Camera Patent Claims
What is claimed as new and is desired to be secured by Letters Patents
of the United States:
1. A digital camera, comprising: means for setting a shutter speed;
an optical system; an imaging device which receives a light flux
from an object to be photographed, the light flux being passed through
the optical system to form an image of the object to be photographed,
at the shutter speed set by the shutter speed setting means, and
converts the received light flux into an image signal; a variable
gain amplifier that amplifies the image signal output by the imaging
device with a variable gain; means for judging whether the shutter
speed set by the shutter speed setting means is slower than a predetermined
blur avoiding speed; means for increasing the gain of the variable
gain amplifier to a predetermined value when the judging means judges
that the shutter speed set by the shutter speed setting means is
slower than the predetermined blur avoiding speed; and means for
manually setting a value as the predetermined value for the gain
of the variable gain amplifier.
2. The digital camera of claim 1, further comprising a strobe,
wherein, when the strobe is flashed, the gain increasing means does
not increase the gain of the variable gain amplifier even when the
judging means judges that the shutter speed set by the shutter speed
setting means is slower than the predetermined blur avoiding speed.
3. The digital camera of claim 1, further comprising means for
displaying an image of the image signal for the object, wherein,
when the displaying means displays an image of the image signal
being output by the imaging device, the gain increasing means does
not increase the gain of the variable gain amplifier, even when
the judging means judges that the shutter speed set by the shutter
speed setting means is slower than the predetermined blur avoiding
speed, if the shutter speed is faster than a predetermined blur
avoiding speed which is set when the displaying means displays the
image of the image signal being output by the imaging device.
4. The digital camera of claim 1, further comprising: means for
displaying messages for an operator; and means for controlling the
message displaying means to display a message indicating that the
object will be photographed with an increased gain of the variable
gain amplifier when the object is photographed with the increased
gain of the variable gain amplifier.
5. The digital camera of claim 4, wherein, when the gain of the
variable gain amplifier is increased and the object is photographed
with a shutter speed slower than the predetermined blur avoiding
speed, the message displaying control means displays a message to
indicate that the object will be photographed with the shutter speed
slower than the predetermined blur avoiding speed.
6. The digital camera of claim 1, wherein the predetermined blur
avoiding speed is variable according to a focal length of the optical
system.
7. A digital camera, comprising: means for setting a shutter speed;
an optical system; an imaging device which receives a light flux
from an object to be photographed, the light flux being passed through
the optical system to form an image of the object to be photographed,
at the shutter speed set by the shutter speed setting means, and
converts the received light flux into an image signal; a variable
gain amplifier that amplifies the image signal output by the imaging
device with a variable gain; means for judging whether the shutter
speed set by the shutter speed is slower than a predetermined blur
avoiding speed; means for selectively setting a photographing mode
to one of: a blur avoiding photographing mode in which the gain
of the variable gain amplifier is increased to a predetermined value
when the judging means judges that the shutter speed is slower than
the predetermined blur avoiding speed, and a normal photographing
mode in which the gain of the variable gain amplifier is not increased
even when the judging means judges that the shutter speed is slower
than the predetermined blur avoiding speed; means for increasing
the gain of the variable gain amplifier to a predetermined value
when the blur avoiding photographing mode is set and when the judging
means judges that the shutter speed set by the shutter speed setting
means is slower than the predetermined blur avoiding speed; and
means for manually setting a value as the predetermined value for
the gain of the variable again amplifier.
8. The digital camera of claim 7, further comprising a strobe,
wherein, when the strobe is flashed, the gain increasing means does
not increase the gain of the variable gain amplifier even when the
judging means judges that the shutter speed set by the shutter speed
setting means is slower than the predetermined blur avoiding speed.
9. The digital camera of claim 7, further comprising means for
displaying an image of the image signal for the object, wherein,
when the displaying means displays an image of the image signal
being output by the imaging device, the gain increasing means does
not increase the gain of the variable gain amplifier, even when
the judging means judges that the shutter speed set by the shutter
speed setting means is slower than the predetermined blur avoiding
speed, if the shutter speed is faster than a predetermined blur
avoiding speed which is set when the displaying means displays the
image of the image signal being output by the imaging device.
10. The digital camera of claim 7, further comprising: means for
displaying messages for an operator; and means for controlling the
message displaying means to display a message indicating that the
object will be photographed with an increased gain of the variable
gain amplifier when the object is photographed with the increased
gain of the variable gain amplifier.
11. The digital camera of claim 10, wherein, when the gain of the
variable gain amplifier is increased and the object is photographed
with a shutter speed slower than the predetermined blur avoiding
speed, the message displaying control means displays a message to
indicate that the object will be photographed with the shutter speed
slower than the predetermined blur avoiding speed.
12. The digital camera of claim 7, wherein the predetermined blur
avoiding speed is variable according to a focal length of the optical
system.
13. A method of controlling a digital camera, comprising: setting
a shutter speed; receiving a light flux from an object to be photographed
to form an image thereof at the set shutter speed; converting the
received light flux into an image signal; amplifying the image signal
with a variable gain; judging whether or not the shutter speed is
set slower than a predetermined blur avoiding speed; manually setting
a predetermined value for the variable gain; and increasing the
variable gain to the predetermined value when the shutter speed
is set slower than the predetermined blur avoiding speed.
14. The method of claim 13, further comprising: increasing the
variable gain even when the shutter speed is set slower than the
predetermined blur avoiding speed, when a strobe is flashed.
15. The method of claim 13, further comprising: displaying an image
of the object; and not increasing the variable gain even when the
shutter speed is set slower than the predetermined blur avoiding
speed, if the shutter speed is set faster than a predetermined blur
avoiding speed when the image is displayed.
16. The method of claim 13, further comprising: displaying a message
indicating that the object will be photographed with an increased
variable gain when the object is photographed with the increased
variable gain.
17. The method of claim 16, further comprising: displaying a message
indicating that the object will be photographed with the shutter
speed slower than the predetermined blur avoiding speed, when the
variable gain is increased and the object is photographed with a
shutter speed set slower than the predetermined blur avoiding speed.
18. The method of claim 13, wherein the predetermined blur avoiding
speed is variable according to a focal length of the optical system.
19. A method of controlling a digital camera, comprising: setting
a shutter speed; receiving a light flux from an object to be photographed
to form an image thereof at the set shutter speed; converting the
received light flux into an image signal; amplifying the image signal
with a variable gain; judging whether or not the shutter speed is
set slower than a predetermined blur avoiding speed; selectively
setting a photographing mode to one of: a blur avoiding photographing
mode in which the variable gain is increased to a predetermined
value when the shutter speed is set slower than the predetermined
blur avoiding speed, and a normal photographing mode in which the
variable gain is not increased even when the shutter speed is set
slower than the predetermined blur avoiding speed; manually setting
a predetermined value for the variable gain; and increasing the
variable gain to the predetermined value when the blur avoiding
photographing mode is set and when the shutter speed is set slower
than the predetermined blur avoiding speed.
20. The method of claim 16, further comprising: increasing the
variable gain even when the shutter speed is set slower than the
predetermined blur avoiding speed, when a strobe is flashed.
21. The method of claim 19, further comprising: displaying an image
of the object; and not increasing the variable gain even when the
shutter speed is set slower than the predetermined blur avoiding
speed, if the shutter speed is set faster than a predetermined blur
avoiding speed when the image is displayed.
22. The method of claim 19, further comprising: displaying a message
indicating that the object will be photographed with an increased
variable gain when the object is photographed with the increased
variable gain.
23. The method of claim 22, further comprising: displaying a message
indicating that the object will be photographed with the shutter
speed slower than the predetermined blur avoiding speed, when the
variable gain is increased and the object is photographed with a
shutter speed set slower than the predetermined blur avoiding speed.
24. The method of claim 19, wherein the predetermined blur avoiding
speed is variable according to a focal length of the optical system.
25. A computer readable medium storing computer instructions for
controlling a digital camera, by performing the steps of: setting
a shutter speed; receiving a light flux from an object to be photographed
to form an image thereof at the set shutter speed; converting the
received light flux into an image signal; amplifying the image signal
with a variable gain; judging whether or not the shutter speed is
set slower than a predetermined blur avoiding speed; manually setting
a predetermined value for the variable gain; and increasing the
variable gain to the predetermined value when the shutter speed
is set slower than the predetermined blur avoiding speed.
26. The computer readable medium of claim 25, further storing computer
instructions for performing the step of increasing the variable
gain even when the shutter speed is set slower than the predetermined
blur avoiding speed, when a strobe is flashed.
27. The computer readable medium of claim 25, further storing computer
instructions for performing the steps comprising: displaying an
image of the object; and not increasing the variable gain even when
the shutter speed is set slower than the predetermined blur avoiding
speed, if the shutter speed is set faster than a predetermined blur
avoiding speed when the image is displayed.
28. The computer readable medium of claim 25, further storing computer
instructions for performing the step of displaying a message indicating
that the object will be photographed with an increased variable
gain when the object is photographed with the increased variable
gain.
29. The computer readable medium of claim 28, further storing computer
instructions for performing the step of displaying a message indicating
that the object will be photographed with the shutter speed slower
than the predetermined blur avoiding speed, when the variable gain
is increased and the object is photographed with a shutter speed
set slower than the predetermined blur avoiding speed.
30. The computer readable medium of claim 25, wherein the predetermined
blur avoiding speed is variable according to a focal length of the
optical system.
31. A computer readable medium storing computer instructions for
controlling a digital camera, by performing the steps of: setting
a shutter speed; receiving a light flux from an object to be photographed
to form an image thereof at the set shutter speed; converting the
received light flux into an image signal; amplifying the image signal
with a variable gain; judging whether or not the shutter speed is
set slower than a predetermined blur avoiding speed; selectively
setting a photographing mode to one of: a blur avoiding photographing
mode in which the variable gain is increased to a predetermined
value when the shutter speed is set slower than the predetermined
blur avoiding speed, and a normal photographing mode in which the
variable gain is not increased even when the shutter speed is set
slower than the predetermined blur avoiding speed; manually setting
a predetermined value for the variable gain; and increasing the
variable gain to the predetermined value when the blur avoiding
photographing mode is set and when the shutter speed is set slower
than the predetermined blur avoiding speed.
32. The computer readable medium of claim 31, further storing computer
instructions for performing the step of increasing the variable
gain even when the shutter speed is set slower than the predetermined
blur avoiding speed, when a strobe is flashed.
33. The computer readable medium of claim 31, further storing computer
instructions for performing the steps comprising: displaying an
image of the object; and not increasing the variable gain even when
the shutter speed is set slower than the predetermined blur avoiding
speed, if the shutter speed is set faster than a predetermined blur
avoiding speed when the image is displayed.
34. The computer readable medium of claim 31, further storing computer
instructions for performing the step of displaying a message indicating
that the object will be photographed with an increased variable
gain when the object is photographed with the increased variable
gain.
35. The computer readable medium of claim 34, further storing computer
instructions for performing the step of displaying a message indicating
that the object will be photographed with the shutter speed slower
than the predetermined blur avoiding speed, when the variable gain
is increased and the object is photographed with a shutter speed
set slower than the predetermined blur avoiding speed.
36. The computer readable medium of claim 31, wherein the predetermined
blur avoiding speed is variable according to a focal length of the
optical system.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera, and more particularly
to a digital camera that avoids blurring of a photograph which may
be caused by movement of the camera when the photograph is taken.
2. Discussion of the Background
As digital cameras for taking a high quality photographs continue
to improve, the demand for avoiding blurring of photographs due
to camera movement is accordingly increasing. Japanese Patent Laid-Open
Publication No. 58481/1992 describes a related digital video camera
having a blur compensating device for compensating for blurring
of a photograph caused by movement of the camera when the photograph
is taken. The video camera of JP No. 58481/1992 includes a solid-state
imager with a variable speed shutter, a shutter speed control device
which changes a shutter speed of the imager, and a control device
which synchronously controls the blur compensating device and the
shutter speed control device. The digital video camera is configured
such that the shutter speed is changed in cooperation with an operation
of the blur compensating device and thereby the degradation of an
image resolution of the photograph due to the blurring is avoided.
However, the electronic circuit for the blur compensating device
of JP 58481/1992 is rather complicated, and the constitution of
the digital video camera is complicated due to this circuit. As
a result, the cost of the camera is increased, and moreover the
size of a body of the camera is relatively large. In addition, power
consumption of the camera is increased due to this circuit, which
inevitably reduces the battery duration time for the camera.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide
a novel and improved digital camera that avoids blurring of a photograph
which may be caused by movement of the camera when the photograph
is taken with a simple constitution at a low cost.
It is another object of the present invention to reduce the power
consumption of the camera for enabling a long battery operation
of the camera with a compact body.
It is another object of the present invention to simplify the structure
of a blur compensating device for a digital camera for decreasing
the overall body size of the camera, for reducing the power consumption
of the camera so as to enable a longer duration time with the battery
operation, and for reducing the production cost of the camera.
The above and other objects are achieved according to the present
invention by providing a new and improved method, system and computer
readable medium for controlling a digital camera including setting
a shutter speed; receiving a light flux from an object to be photographed
to form an image thereof at the set shutter speed; converting the
received light flux into an image signal; amplifying the image signal
with a variable gain; judging whether or not the shutter speed is
set slower than a predetermined blur avoiding speed; and increasing
the variable gain to a predetermined value when the shutter speed
is set slower than the predetermined blur avoiding speed.
Another embodiment includes a method, system and computer readable
medium for controlling a digital camera including setting a shutter
speed; receiving a light flux from an object to be photographed
to form an image thereof at the set shutter speed; converting the
received light flux into an image signal; amplifying the image signal
with a variable gain; judging whether or not the shutter speed is
set slower than a predetermined blur avoiding speed; selectively
setting a photographing mode to one of: a blur avoiding photographing
mode in which the variable gain is increased to a predetermined
value when the shutter speed is set slower than the predetermined
blur avoiding speed, and a normal photographing mode in which the
variable gain is not increased even when the shutter speed is set
slower than the predetermined blur avoiding speed; and increasing
the variable gain to a predetermined value when the blur avoiding
photographing mode is set and when the shutter speed is set slower
than the predetermined blur avoiding speed.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant
advantages thereof will be readily obtained as the same becomes
better understood by reference to the following detailed description
when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a block diagram illustrating the structure of an exemplary
digital camera according to the present invention;
FIG. 2 is a block diagram illustrating an example of an image pre-processor
of the camera shown in FIG. 1;
FIG. 3 is a graph illustrating a relation between a control voltage
and a measured gain of a variable gain amplifier of the camera shown
in FIG. 1;
FIG. 4 is an exposure value (Ev) diagram which is utilized for
an automatic exposure control when the camera is operated in a monitoring
mode;
FIG. 5 is an exposure value (Ev) diagram which is utilized for
an automatic exposure control in a normal photographing mode;
FIG. 6 is an exposure value (Ev) diagram which is utilized for
an automatic exposure control in a blur avoiding photographing mode;
FIG. 7 is a diagram illustrating a displayed image of a display
panel when the camera is operated in the blur avoiding photographing
mode;
FIG. 8 is a diagram illustrating another displayed image of the
display panel in the blur avoiding photographing mode;
FIG. 9 is a diagram illustrating still another displayed image
of the display panel in the blur avoiding photographing mode; and
FIG. 10 is a diagram illustrating a displayed image of the display
panel in other modes than the blur avoiding photographing mode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the present invention will hereinafter be described in connection
with preferred embodiments thereof, it will be understood that it
is not intended to limit the invention to these embodiments. On
the contrary, it is intended to cover all alternatives, modifications
and equivalents wherein the spirit and scope of the invention are
included. Furthermore, in the drawings, like reference numerals
have been used throughout the drawings to identify identical elements.
FIG. 1 shows an example of the overall construction of a digital
camera to which the present invention is applied. A digital camera
100 includes a lens system 101, an optic mechanical system 102 including
an aperture, a filter, and so forth, a charge coupled device (CCD)
103 as an imaging device, a correlate dual sampling (CDS) circuit
104, a variable gain control (VG) amplifier 105, an analog to digital
(A/D) converter 106, an image pre-processor (IPP) 107, a discrete
cosine transformer (DCT) 108, a Huffman encoder/decoder 109, a memory
card controller (MCC) 110, a dynamic random-access memory (DRAM)
111, a memory card interface circuit 112, a central processing unit
(CPU) 121, a display panel 122, an operation panel 123, a device
control signal generator (SG) 126, a strobe flash 127, a battery
128, a DC-DC converter 129, an electrical erasable programmable
read only memory (EEPROM) 130, a focus driver 131, a stepping motor
132 for focusing, a zoom driver 133, a stepping motor 134 for zooming,
and a motor driver 135. A memory card 150 can be attached to the
camera 100 via the memory card interface circuit 112, and an optional
remote control unit (not shown) may be included in the camera 100.
The lens unit of the camera 100 includes the lens system 101 and
the optic mechanical system 102. An electronically controlled mechanical
shutter that is provided inside the optic mechanical system 102
simultaneously exposes both of two interlaced field images to form
a complete raster image of the two field images. The lens system
101 comprises, for example, a variable focal lens which is composed
of a focus lens 101a and a zoom lens 101b.
The focus driver 131 drives the stepping motor 132 for focusing
according to a control signal provided by the CPU 121 to move the
focal lens 101a along its optical axis. The zoom driver 133 drives
the stepping motor 134 for zooming in accordance with a control
signal provided by the CPU 121 to move the zoom lens 101b along
its optical axis. The motor driver 135 drives the optic mechanical
system 102 according to a control signal provided by the CPU 121,
for example, to set an aperture value.
The CCD imaging device 103 converts optical images, which are input
thereto via the lens unit, into analog electrical signals. The CDS
circuit 104 reduces noise of the analog electrical signals, and
thereby enhances the image quality resulting from the electrical
signals. The CDS circuit 104 is particularly tuned to reduce inherent
CCD sensor noises, such as thermal noise.
The VG amplifier 105 corrects the amplitude of an analog electrical
signal that has been processed by the CDS circuit 104 into a predetermined
amplitude. The gain level of the VG amplifier 105 is set by the
CPU 121. The CPU 121 first reads digital data, which is provided
inside the EEPROM 130 and which defines a relation between a control
voltage and a measured gain of the VG amplifier 105, and inputs
the read data to a digital to analog (D/A) converter (not shown)
built in the CPU 121 to convert the read data to an analog voltage,
which is then set at the VG amplifier 105. The A/D converter 106
converts the analog image data from the VG amplifier 105 into digital
image data. The A/D converter 106 converts the data with an optimum
sampling frequency, such as, for example, a multiple number of the
sub-carrier frequency of the NTSC signal format.
The IPP 107, the DCT 108, and the Huffman encoder/decoder 109,
functioning as a digital signal processor, separate the digital
data which is input from the AID converter 106 into color-difference
data and luminance data, and then perform various processes on the
separated data including processes for correcting and converting
the separated data into optimum data for compression/decompression.
The Huffman encoder/decoder 109 carries out, for example, an orthogonal
transformation and a Huffing encoding/decoding for the original
digital data, which are required in data compression and expansion
in the Joint Photographic Expert Group (JPEG) standard.
The memory card controller (MCC) 110 temporarily stores encoded
data therein and then writes the data in the memory card 150 through
the memory card interface circuit 112. The MMC 110 also reads out
stored data from the memory card 150.
The CPU 121 controls operation of the camera 100 according to instructions
input through the operation panel 123 or from the outside of the
camera 100, for example, through the optional remote control unit
(not shown). The CPU 121 executes the control of the operation of
the camera 100 in accordance with a series of program codes (instructions),
which are stored in a ROM (not shown) internal to the CPU 121, using
a RAM (not shown) internal to the CPU 121 as a working area. More
specifically, the CPU 121 controls a photographing operation, an
automatic exposure (AE) control operation, an automatic white balancing
(AWB) operation, and an automatic focusing (AF) operation.
Power to the camera 100 is input to the DC to DC converter 129
from the battery 128, which includes, for example, a nickel cadmium
battery, a nickel hydrogen battery, or a lithium battery. The voltage
is converted to an appropriate level by the DC to DC converter 129
and then supplied to the entire camera 100 system.
The display panel 122 includes, for example, a liquid crystal display,
a light emitting diode display or an electronic luminescence display,
etc. The display panel 122 displays an image of digital image data
of a photograph just taken or an image of image data which is compressed
and stored in the memory card 150. The operation panel 123 is provided
with a plurality of buttons for selecting desired functions and
inputting instructions for setting photographing conditions. In
addition, the EEPROM 130 contains parameters which the CPU 121 uses
in executing the above-mentioned controls.
The camera 100 provides three operational modes, for example, including
a monitoring mode, a photographing/recording mode and a displaying
mode. The monitoring mode enables displaying an image photographed
by the CCD 103 in the display panel 122 before recording the image
in the memory card 150 and setting either the blur avoiding photographing
mode or the normal photographing mode. The photographing/recording
mode enables photographing an image either with the blur avoiding
photographing mode or the normal photographing mode and storing
resulting image data into the memory card 150. The blur avoiding
photographing mode enables photographing an image while avoiding
blurring of a photograph due to movement of the camera by increasing
the gain of the VG amplifier 105. The normal photographing mode
enables photographing an image without increasing the gain of the
VG amplifier 105. The displaying mode enables reading out of stored
image data from the memory card 150 and displaying images of the
data on the display panel 122.
FIG. 2 is a block diagram illustrating an example of the image
pre-processor (IPP) 107. A color separation module 1071 separates
digital image data from the A/D converter 106 into a set of red
(R), green (G), and blue (B) data. A signal interpolation module
1072 interpolates new data in each of the separated R, G, and B
data. A pedestal level adjustment module 1073 adjusts a black level
of each of the R, G, and B data. A white level adjustment module
1074 adjusts a white level of each of the R, G, and B data. A digital
gain control module 1075 adjusts a signal level of each of the R,
G, and B data with a gain which is set by the CPU 121. A gamma control
module 1076 converts a gamma of each of the R, G, and B data into
another gamma. A matrix module 1077 converts the set of R, G, and
B data into color-difference signals (Cb and Cr) and a luminance
signal (Y). A video signal processing module 1078 converts the Cb,
Cr, and Y signals into NTSC format video signals, respectively,
and sends out these signals to the display panel 122.
A first arithmetic module 1079 detects the intensity of a luminance
signal which is output from the pedestal level adjustment module
1073. A band pass filter (BPF) 1080 passes a specific frequency
band of the luminance signal detected by the first arithmetic module
1079. An automatic focus (AF) evaluation circuit 1081 calculates
the integral of digital values according to the luminance signals
passed the BPF 1080, and outputs the integral to the CPU 121 as
an AF evaluation value. An automatic exposure (AE) evaluation circuit
1082 calculates a digital value (described below) according to the
intensity of the luminance signal which is detected by the first
arithmetic module 1079 and outputs the value to the CPU 121 as an
AE evaluation value. An AE evaluation value represents a difference
between the exposure value for an optimum exposure for the sensitivity
of the CCD 103 and the exposure value according to the time value
(shutter speed) and the aperture value arbitrarily set in an automatic
exposure operation. A second arithmetic module 1083 detects the
intensity of a luminance signal of each of the R, G, and B data
which is adjusted by the white level adjustment module 1074. An
automatic white balance (AWB) evaluation circuit 1084 counts each
of the luminance data of R, G, and B and outputs the data to the
CPU 121 as an AWB evaluation value for each color. A CPU interface
circuit 1085 is an interface between the IPP 107 and the CPU 121.
A DCT interface circuit 1086 works as an interface between the IPP
107 and the DCT 108.
The AE evaluation circuit 1082 calculates the AE evaluation value
by means of a weighted calculation of luminance values of a set
of six luminance areas of a light receiving area of the CCD 103.
More specifically, the first arithmetic module 1079 outputs luminance
data for each picture element (pixel) of an image received by the
CCD 103 to the AE evaluation circuit 1082. The AE evaluation circuit
1082 adds up the received pixel luminance data for each of the six
areas to obtain a luminance value for each area. The AE evaluation
circuit 1082 then performs a weighted calculation of the set of
six luminance values for six areas to obtain a calculated value
as the AE evaluation value for the image received by the CCD 103.
FIG. 3 is a graph illustrating a relation between a control voltage
and a measured gain of the VG amplifier 105. The horizontal axis
represents the control voltage and the vertical axis represents
the measured gain of the VG amplifier 105, respectively. The data
representing this relation is stored in the EEPROM 130.
Next, an example of an automatic exposure (AE) control operation
according to the present invention is described. Specifically, in
the AE control operation, the CPU 121 controls the shutter speed
of the CCD 103 or the gain of the VG amplifier 105 such that the
AE evaluation value calculated as described above becomes a criterion
value for an optimum exposure.
The automatic exposure (AE) control operation will be described
for each of the monitoring mode, the normal photographing mode,
and the blur avoiding photographing mode referring to a specific
exposure value (Ev) diagram for each mode. For simplifying the explanation,
for example, the aperture is fixed such that f-number is four or
an aperture value (Av) equals four.
An exposure value (Ev) diagram is used for illustrating the combination
of a time value (Tv) defining the shutter speed and an aperture
value (Av) defining the size of an opening of an aperture, with
which a goal exposure value (Ev), which defines an optimum amount
of light to expose a film or to be received by an imaging device
such as the CCD 103, can be obtained. These three values have a
relation satisfying the following equation:
Furthermore, a light value (Lv) is a measured intensity of the
light of an image to be photographed and the following relation
is satisfied when an optimum exposure is accomplished:
Furthermore, 1/T is equal to 2.sup.Tv, wherein T is a shutter speed,
and f-number.sup.2 is equal to 2.sup.Av.
In addition, an exposure value (Ev) is related to a brightness
value (Bv) representing a luminance of an image to be photographed
as expressed by an equation:
wherein the ISO sensitivity value (Sv) represents a sensitivity
of the film or the imaging device used. Thus, if the aperture value
(Av) is a constant number, the brightness value (Bv) is available
with the combination of a given time value (Tv) and a ISO sensitivity
value (Sv). In another word, an optimum exposure can be obtained
by setting a time value (Tv) in combination with a ISO sensitivity
value (Sv) in accordance with a luminance (brightness) of an image
to be photographed. Therefore, the Ev diagram could be called a
Bv diagram theoretically. However, because the term "Bv diagram"
is not common, the term "Ev diagram" is used in the following
description.
Monitoring Mode:
FIG. 4 is an exposure value (Ev) diagram for use in the AE control
operation in the monitoring mode, i.e., when displaying an image
to be photographed in the display panel 122 before actually photographing
the image. The diagram covers the whole range of the focal length
of the lens system 101. In FIG. 4, the ISO sensitivity is determined
in accordance with the sensitivity of the CCD 103 and the gain level
set at the VG amplifier 105. The ISO sensitivity is defined as "100"
when the gain of the VG amplifier 105 that enables the CCD 103 to
output an optimum image signal to the IPP 107 is 0 dB or the control
voltage is 0.3 V in FIG. 3. The ISO sensitivity is increased from
100 to 200 by increasing the gain for the VG amplifier 105 from
0 dB to 6 dB and from 200 to 400 by increasing the gain for the
VG amplifier 105 from 6 dB to 12 dB.
In FIG. 4, when the exposure value (Ev) is in the range from 9
to 17, the shutter speed is changed in the range from 1/30 of a
second to 1/8000 of a second for an optimum exposure. When an image
to be photographed is dark and the exposure value (Ev) is less than
9, the shutter speed is kept at 1/30 of a second and the gain of
the VG amplifier 105 is increased by the amount corresponding to
two steps of the exposure value (Ev) at most and thereby the image
of the photograph is displayed with an optimum brightness in the
display panel 122. When the exposure value (Ev) is 8, the gain of
the VG amplifier 105 is increased up to 6 db which is equivalent
to increasing the ISO sensitivity from 100 to 200, and when the
exposure value (Ev) is 7 the gain of the VG amplifier 105 is increased
up to 12 db which is equivalent to increasing the ISO sensitivity
from 100 to 400. In the monitoring mode, when the lens system 101
includes a wide angle lens, even when the exposure value is in a
range requiring a shutter speed slower than a criterion shutter
speed for not causing blurring of a photograph in the wide angle
lens system (i.e., 1/60 of a second), if the exposure value is in
the range requiring the shutter speed faster than above 1/30 of
a second, the gain of the VG amplifier 105 will not be increased.
Likewise, when the lens system 101 includes a telephoto lens, even
when the exposure value is in a range requiring a shutter speed
slower than a criterion shutter speed for not causing blurring of
a photograph in the telephoto lens system (i.e., 1/250 of a second),
if the exposure value is in the range requiring the shutter speed
faster than above 1/30 of a second, the gain of the VG amplifier
105 will not be increased. Thus, in the monitoring mode, increasing
of the gain of the VG amplifier 105 is prohibited in a range requiring
a shutter speed faster than 1/30 of a second, and thereby an error
in the automatic exposure control, focusing control or white balancing
control operations, which may be caused by increasing of the gain
of the VG amplifier 105, is avoided.
Normal Photographing Mode:
FIG. 5 is an exposure value (Ev) diagram for the normal photographing
mode, where the ISO sensitivity of the CCD 103 is set to 100. In
the normal photographing mode, even when the exposure value (Ev)
is less than 9, the gain of the VG amplifier 105 is not increased
and instead the shutter speed is changed to accomplish an optimum
exposure. When the exposure value (Ev) is less than 9, the shutter
speed is set to 1/30 of a second or slower. The shutter speeds slower
than 1/30 of a second are called a "long-shutter" and
may cause blurring of a photograph if the camera is moved when the
photograph is taken. When the shutter speed is 1/500 of a second
or faster, because one step of the electronic controlled shutter
speed is extremely short, such as 63.55 microseconds, the shutter
is likely to generate a quantization error, which may cause a deviation
from an optimum exposure. Therefore, the camera 100 is adapted to
compensate the quantization error with the gain of the VG amplifier
105 by the amount corresponding to one step of the exposure value
(Ev) at most.
When an automatic strobe flashing mode is set, when the exposure
value (Ev) is less than a predetermined value, the shutter speed
is maintained at the predetermined speed and a strobe is flashed.
Specifically, in this embodiment, as illustrated in FIG. 5, when
a wide angle lens is used, when the shutter speed is 1/60 of a second
and slower, the shutter speed is maintained at 1/60 of a second
and the strobe is flashed. When a telephoto lens is used, when the
shutter speed is 1/250 of a second and slower, the shutter speed
is maintained at 1/250 and the strobe is flashed. When a strobe-off
mode is set, the strobe is not flashed and instead the shutter speed
is slowed up to 1/4 of a second. When a strobe-on mode is set, a
strobe is flashed regardless of the shutter speed.
Blur Avoiding Photographing Mode:
FIG. 6 is an exposure value (Ev) diagram for the blur avoiding
photographing mode, where the ISO sensitivity of the CCD 103 is
set to 100. The diagram applies not only to the lens system 101
having a standard focal length but also to the lens system 101 having
a focal length for wide-angle or telephoto photography. The gain
of the VG amplifier 105 is increased by the amount corresponding
to two steps of the exposure value (Ev) at most to avoid blurring
of a photograph due to movement of the camera 100 when the exposure
value (Ev) is 10 or less when the wide angle lens system 101 is
used, and when the exposure value (Ev) is 12 or less when the telephoto
lens system 101 is used.
When the lens system 101 includes a wide-angle lens, when the exposure
value (Ev) is between 10 to 17, the shutter speed is changed in
the range from 1/60 of a second through 1/8000 of a second for an
optimum exposure. When the exposure value (Ev) is between 8 to 10,
the shutter speed is fixed at 1/60 of a second and the gain of the
VG amplifier 105 is changed in the range from the ISO sensitivity
100 to the ISO sensitivity 400. When the exposure value (Ev) is
less than 8, the shutter speed is changed in the range slower than
1/15 of a second with the ISO sensitivity being fixed at 400.
When the lens system 101 includes a telephoto lens, when the exposure
value (Ev) is between 12 to 17, the shutter speed is changed in
the range from 1/250 of a second to 1/8000 of a second for an optimum
exposure. When the exposure value (Ev) is between 10 to 12, the
shutter speed is fixed at 1/250 of a second and the gain of the
VG amplifier 105 is changed in the range from the ISO sensitivity
100 to the ISO sensitivity 400. When the exposure value (Ev) is
less than 10, the gain of the VG amplifier 105 is fixed at the ISO
sensitivity 400 and the shutter speed is changed in the range slower
than 1/60 of a second.
As described above, the point of the exposure value (Ev) to start
increasing the gain of the VG amplifier 105 for correcting the amplitude
of signals output from the CCD 103 is 10 for the wide angle lens,
and 12 for the telephoto lens, and the end point of the exposure
value (Ev) with the increased gain of the VG amplifier 105 up to
400 is 8 and 10 respectively. The reason why the beginning point
of the exposure value (Ev), to increase the gain of the VG amplifier
105 for the telephoto lens, is higher than the for the wide angle
lens is that the degree of blurring of a photograph due to movement
of the camera is proportional to the focal length of the lens system
101. Furthermore, the high gain of the VG amplifier 105 sometimes
causes noise that deteriorates an image quality. Therefore, the
beginning point of the exposure value (Ev) to increase the gain
of the VG amplifier 105 is set at a highest possible point for each
focal length so that the maximum gain is suppressed.
When the lens system 101 includes a standard lens having a standard
focal length, i.e., a focal length between that of a wide angle
lens and a telephoto lens, the point of the exposure value (Ev)
to start increasing the gain of the VG amplifier 105 is set in proportion
to the focal length for the other lens system 101 including a wide
angle lens or a telephoto lens. In this embodiment, the beginning
point of the exposure value to start increasing the gain of the
VG amplifier 105 is 11 and the end point of the exposure value with
the increased gain of the VG amplifier 105 up to ISO 400 is 9. That
is, when the exposure value (Ev) is 11 or more, the shutter speed
is changed in the range 1/125 of a second and above for an optimum
exposure. When the exposure value (Ev) is between 9 to 11, the shutter
speed is fixed at 1/125 of a second and the gain of the VG amplifier
105 is changed in the range from the ISO sensitivity 100 to 400.
When the exposure value (Ev) is less than 9, the gain of the VG
amplifier 105 is fixed at the ISO sensitivity 400 and the shutter
speed is changed in the range slower than 1/30 of a second.
Next, a method of setting a blur avoiding photographing mode is
described. FIGS. 7 through 10 are diagrams illustrating an example
of an operation mode setting screen displayed on the display panel
122. The operation panel 123 (FIG. 1) has at least a button marked
with a triangle and a button marked with an inverse triangle for
setting the blur avoiding photographing mode and the normal photographing
mode, a shutter release button for releasing the shutter, and a
button marked with "DATE" for setting date and time (not
shown). The shutter release button has two steps for activating
functions, a first step to activate an automatic exposure control
and an automatic focusing control, and a second step to release
the shutter for photographing. When both the triangle-marked button
and the DATE-marked button are simultaneously depressed, the CPU
121 displays an operation mode setting screen on the display panel
122. When the triangle-marked-button is depressed, the display panel
122 displays a message "NORMAL" indicating that the normal
photographing mode is selected. Furthermore, each time when the
triangle-marked button is depressed, the display panel 122 displays
the messages, "GAIN LEVEL UP 0.5,""GAIN LEVEL UP
1.0,""GAIN LEVEL UP 1.5,""GAIN LEVEL UP 2.0"
and "GAIN LEVEL UP 2.5" in sequence, indicating that the
blur avoiding photographing mode with a respective gain level is
selected, respectively. When the inverse triangle-marked button
is depressed, the display panel 123 displays the above messages
in reverse sequence.
When the blur avoiding photographing mode is set as above and when
the shutter release button is depressed to the first step, the display
panel 122 displays messages, as described below, according to the
focal length of the lens system 101 and the exposure value (Ev).
When the exposure value (Ev) is between 6 to 8 with a wide-angle
lens, the messages "GAIN LEVEL UP" and "SLOW SHUTTER"
are displayed on the display panel 122 as shown in FIG. 7. When
the exposure value (Ev) is between 6 to 9 with a standard lens,
or between 6 to 10 with a telephoto lens, the same messages are
shown as well. When the exposure value (Ev) is between 8 to 10 with
the wide angle lens, or between 9 to 11 with the standard lens,
or between 10 to 12 with the telephoto lens, the message "GAIN
LEVEL UP" is displayed as shown in FIG. 8. When the exposure
value (Ev) is more than 10 with the wide angle lens, more than 11
with the standard lens, or more than 12 with the telephoto lens,
the messages "GAIN LEVEL UP" and "SLOW SHUTTER"
are not displayed on the display panel 122 as in FIG. 9. Thus, the
display panel 122 displays the message indicating that the gain
of the VG amplifier 105 is increased as the gain of the VG amplifier
105 is increased.
In the normal photographing mode, when the exposure value (Ev)
is between 6 to 10 with the wide-angle lens, the message of "SLOW
SHUTTER" is displayed on the display panel 122 as shown in
FIG. 10. When the exposure value (Ev) is between 6 to 11 with the
standard lens, or between 6 to 12 with the telephoto lens, the message
"SLOW SHUTTER" is also displayed.
When the exposure value (Ev) is more than 10 with the wide-angle
lens, or more than 11 with the standard lens, or more than 12 with
the telephoto lens, neither the "GAIN LEVEL UP" nor the
"SLOW SHUTTER" message is displayed on the display panel
122 as illustrated in FIG. 9.
As described above, in a digital camera of the present invention,
in the blur avoiding photographing mode, when an exposure value
is in a range requiring a shutter speed slower than a criterion
shutter speed for not causing blurring of a photograph even when
the camera is moved when the photograph is taken, the shutter speed
is maintained at the criterion shutter speed for not causing blurring
of the photograph even when the camera is moved and the CPU 121
automatically increases the gain of the VG amplifier 105 such that
the amplitude of signals representing an image to be photographed
is increased to a predetermined level for an optimum exposure. Thus,
blurring of a photograph due to movement of the camera during taking
of the photograph is avoided. In an ordinary camera that uses photographic
film, when an image to be photographed by the camera is dark and
if a film having a low sensitivity is used, the shutter speed must
be made slow for an optimum exposure, and consequently blurring
of a photograph due to movement of the camera is inevitable. Therefore,
in such a case, a high sensitivity film is used instead of the low
sensitivity film and the shutter speed is kept at a speed not causing
blurring of a photograph due to movement of the camera when the
photograph is taken. The digital camera of the present invention
accomplishes the same effect as changing a film to a high sensitivity
film in ordinary cameras so as to maintain the shutter speed at
a speed not causing blurring of a photograph even when the camera
is moved when the photograph is taken, by means of increasing the
gain of the VG amplifier 105 to a predetermined level, such that
the amplitude of signals representing an image to be photographed
are set for an optimum exposure. Moreover, increasing the gain of
the VG amplifier 105, which corresponds to changing of the film
in ordinary cameras, is automatically done in accordance with the
brightness of an image to be photographed.
Furthermore, in the digital camera of the present invention, as
described above, either the blur avoiding photographing mode or
the normal photographing mode can be chosen. Therefore, a user can
select between photographing an image with the blur avoiding photographing
mode, in which the shutter speed is maintained at a speed not causing
blurring of a photograph due to movement of the camera, for example,
when manually holding the camera, or photographing the image with
the normal photographing mode, in which the gain of the VG amplifier
105 is not increased and accordingly the noise level is not increased,
for example, when holding the camera in a tripod, thereby accomplishing
photographing of the image at a high quality. Furthermore, because
the gain level of the VG amplifier 105 can be selected when setting
the blur avoiding photographing mode as described above, the user
can select an appropriate gain level of the VG amplifier 105 according
to the quality level of the photograph desired by the user. As the
gain level of the VG amplifier 105 is increased, the noise level
of output signals is increased accordingly and thereby the quality
of the image, for example, the resolution of the image, is deteriorated.
Accordingly, the user may select a relatively lower gain level of
the VG amplifier 105 when the user desires to photograph the image
at a higher quality.
Still further, when a strobe is used, an automatic increase of
the gain of the VG amplifier 105 is not activated, and thereby over-exposure
is prevented.
Also, in the monitoring mode, when the lens system 101 includes
a wide angle or telephoto lens, an automatic increase of the gain
of the VG amplifier 105 is not activated, even when the exposure
value is in a range requiring a shutter speed slower than the criterion
shutter speed, for not causing blurring of a photograph for the
wide angle lens or telephoto lens system, when the exposure value
is in the range requiring the shutter speed faster than the slowest
shutter speed (1/30 of a second) which can be used in the monitoring
mode. This enables an accurate automatic exposure control and focusing
control operations and a white balancing operation.
Furthermore, in the blur avoiding photographing mode, the display
panel 122 displays a message indicating that the gain of the VG
amplifier 105 is increased, and thereby an operator can be notified
that a lower quality photograph might be produced.
Still further, when the photographing environment is extraordinary
dark and the shutter speed is still slower than the predetermined
criterion speed for not causing blurring of a photograph, even though
the gain of the VG amplifier 105 is increased, the display panel
122 displays a message indicating that the shutter speed is slow,
and thereby the operator is properly informed.
Furthermore, the criterion shutter speed for not causing blurring
of a photograph can be set according to the focal length of the
lens system. Therefore, an appropriate range of the exposure value
for increasing the gain of the VG amplifier 105 can be set according
to the focal length of the lens system of the camera 100.
The mechanisms and processes set forth in the present description
may be implemented using a conventional general purpose microprocessor
programmed according to the teachings in the present specification,
as will be appreciated to those skilled in the relevant art(s).
Appropriate software coding can readily be prepared by skilled programmers
based on the teachings of the present disclosure, as will also be
apparent to those skilled in the relevant art(s).
The present invention thus also includes a computer-based product
which may be hosted on a storage medium and include instructions
which can be used to program a microprocessor to perform a process
in accordance with the present invention. This storage medium can
include, but is not limited to, any type of disk including floppy
disks, optical disks, CD-ROMs, magneto-optical disks, ROMs, RAMs,
EPROMs, EEPROMs, flash memory, magnetic or optical cards, or any
type of media suitable for storing electronic instructions.
Obviously, numerous modifications and variations of the present
invention are possible in light of the above teachings. It is therefore
to be understood that within the scope of the appended claims, the
invention may be practiced otherwise than as specifically described
herein.
This document claims priority and contains subject matter related
to Japanese patent application No. 09-336395 filed in the Japanese
patent Office on Nov. 19, 1997, the entire contents of which are
hereby incorporated by reference. |