Digital Camera Patent Abstract
A digital camera includes a flash lamp and a CCD imager. A microcomputer
first exposes the CCD imager without a light-emission of the flash
lamp. Therefore, a luminance evaluation value is calculated by a
calculator on the basis of a luminance signal included in a camera
signal generated by the CCD imager. The microcomputer succeedingly
makes the flash lamp perform a preliminary light-emission, and exposes
the CCD imager by 1/1500 seconds. The calculator evaluates the luminance
evaluation value on the basis of the luminance signal included in
the camera signal obtained at this time. Then, the microcomputer
calculates a major light-emission amount of the flash lamp on the
basis of the two luminance evaluation values obtained in such a
manner. Digital Camera Patent Claims
What is claimed is:
1. A digital camera for taking a picture of an object by making
a flash lamp perform a major light-emission with a major light-emission
amount and exposing a picture taking means for a first period, comprising:
a detection means for detecting a luminance signal from a camera
signal outputted from said picture taking means;
an evaluation means for evaluating said luminance signal and outputting
a luminance evaluation value;
a first control means for exposing said picture taking means without
a light-emission of said flash lamp;
a second control means for making said flash lamp perform a preliminary
light-emission with a preliminary light-emission amount and exposing
said picture taking means for a second period shorter than said
first period; and
a calculation means for calculating said major light-emission amount
on the basis of a first non-emission luminance evaluation value
outputted from said evaluation means in response to a control of
said first control means and a preliminary light-emission luminance
evaluation value outputted from said evaluation means in response
to a control of said second control means;
wherein:
said first control means exposes said picture taking means for
a third period; and
said calculation means includes a luminance evaluation value calculation
means for calculating a second non-emission luminance evaluation
value in exposing said picture taking means for said first period
without the light-emission of said flash lamp, on the basis of said
first period, said third period and said first non-emission luminance
evaluation value, and a light-emission amount calculation means
for calculating said major light-emission amount on the basis of
said second non-emission luminance evaluation value, a target luminance
evaluation value, said preliminary light-emission luminance evaluation
value and said preliminary light-emission amount.
2. A digital camera according to clam 1, wherein
said luminance evaluation value calculation means calculates said
second non-emission luminance evaluation value in accordance with
a following equation (1),
said light-emission amount calculation means calculates said major
light-emission amount in accordance with a following equation (2);
3. A digital camera according to claim 1, further comprising:
an exposure period calculation means for calculating a most suitable
exposure period that said target luminance evaluation value is obtained
without the light-emission of said flash lamp on the basis of said
third period, said first preliminary light-emission luminance evaluation
value and said target luminance evaluation value;
a comparison means for comparing said most suitable exposure period
and a longest exposure period; and
a cancellation means for canceling said major light-emission in
a case where said most suitable exposure period is shorter than
said longest exposure period.
4. A digital camera for taking a picture of an object by making
a flash lamp perform a major light-emission with a major light-emission
amount and exposing a picture taking means for a first period, comprising:
a detection means for detecting a luminance signal from a camera
signal outputted from said picture taking means;
an evaluation means for evaluating said luminance signal and outputting
a luminance evaluation value;
a first control means for exposing said picture taking means without
a light-emission of said flash lamp;
a second control means for making said flash lamp perform a preliminary
light-emission with a preliminary light-emission amount and exposing
said picture taking means for a second period shorter than said
first period; and
a calculation means for calculating said major light-emission amount
on the basis of a first non-emission luminance evaluation value
outputted from said evaluation means in response to a control of
said first control means and a preliminary light-emission luminance
evaluation value outputted from said evaluation means in response
to a control of said second control means;
wherein said second period is longer than a period necessary for
said preliminary light-emission.
5. A digital camera for taking a picture of an object by making
a flash lamp perform a major light-emission with a major-light emission
amount and exposing a picture taking means, the camera comprising:
a detection means for detecting a luminance signal from a camera
signal outputted from said picture taking means;
an evaluation means for evaluating said luminance signal and outputting
a luminance evaluation value;
a first control means for exposing said picture taking means without
a light-emission of said flash lamp;
a second control means for making said flash lamp perform a preliminary
light-emission with a preliminary light-emission amount and exposing
said picture taking means;
a calculation means for calculating said major light-emission amount
on the basis of a non-emission luminance evaluation value outputted
from said evaluation means in response to a control of said first
control means, a preliminary light-emission luminance evaluation
value outputted from said evaluation means in response to a control
of said second control means, a target luminance evaluation value
and said preliminary light-emission value; and
a third control means for making said flash lamp perform said major
light-emission with said major light-emission amount and exposing
said picture taking means for a first period;
wherein said first control means exposes said picture taking means
for a second period shorter than said first period, and said calculation
means includes a multiplying means for multiplying said non-emission
luminance value by said first period, and a dividing means for dividing
a multiplication value produced by said multiplying means by said
second period.
6. A digital camera for taking a picture of an object by making
a flash lamp perform a major light-emission with a major light-emission
amount and exposing a picture taking means for a first period, the
camera comprising:
a detection means for detecting a luminance signal from a camera
signal outputted from said picture taking means;
an evaluation means for evaluating said luminance signal and outputting
a luminance evaluation value;
a first control means for exposing said picture taking means without
a light-emission of said flash lamp;
a second control means for making said flash lamp perform a preliminary
light-emission with a preliminary light-emission amount and exposing
said picture taking means for a second period shorter than said
first period and longer than a period necessary for said preliminary
light-emission; and
a calculation means for calculating said major light-emission amount
on the basis of a non-emission luminance evaluation value outputted
from said evaluation means in response to a control of said first
control means and a preliminary light-emission luminance evaluation
value outputted from said evaluation means in response to a control
of said second control means.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera. More specifically,
the present invention relates to a digital camera for taking a picture
of an object by making a flash lamp perform a light-emission with
a major light-emission amount and by exposing a picture taking means
for a first period.
2. Description of the Prior Art
In a conventional digital camera where a luminance level of the
object is lower than a desired luminance level, a luminance level
of the object is calculated by making a flash lamp perform a preliminary
light-emission, and the major light-emission amount of the flash
lamp is calculated on the basis of the luminance level. More specifically,
referring to FIG. 13, in a case where a luminance level E.sub.0
without the light-emission of the flash lamp is lower than a desired
luminance level Et, a luminance level Es is detected by making the
flash lamp perform the preliminary light-emission, the major light-emission
amount is calculated on the basis of a luminance level Es, and the
flash lamp is light-emitted with the major light-emission amount,
therefore, a shortage amount of the luminance level is supplemented.
However, in such a prior art, in a case where the object exists
under a fluorescent lamp which generates a flicker, since the luminance
level Es in the preliminary light-emission changes about 5%, there
was a problem that it is difficult to precisely calculate the major
light-emission amount. That is, in the prior art, though the shortage
amount is divided by the luminance level Es whereby the major light-emission
amount is calculated, if an exposure period in the preliminary light-emission
is long, the luminance level Es is varied by an influence of the
flicker, therefore, there was a possibility that the major light-emission
amount drastically deviates.
SUMMARY OF THE INVENTION
Therefore, the principal object of the present invention is to
provide a novel digital camera.
Another object of the present invention is to provide a digital
camera capable of precisely calculating a major light-emission element
of a flash lamp.
Further object of the present invention is to provide a digital
camera capable of calculating a most suitable major light-emission
element in a set mode.
According to the present invention, a digital camera for taking
a picture of an object by making a flash lamp perform a major light-emission
with a major light-emission amount and exposing a picture taking
means for a first period comprises: a detection means for detecting
a luminance signal from a camera signal outputted from the picture
taking means; an evaluation means for evaluating the luminance signal
and outputting a luminance evaluation value; a first control means
for exposing the picture taking means without a light-emission of
the flash lamp; a second control means for making the flash lamp
perform a preliminary light-emission with a preliminary light-emission
amount and exposing the picture taking means for a second period
shorter than the first period; and a calculation means for calculating
the major light-emission amount on the basis of a first non-emission
luminance evaluation value outputted from the evaluation means in
response to a control of the first control means and a preliminary
light-emission luminance evaluation value outputted from the evaluation
means in response to a control of the second control means.
The first control means exposes the picture taking means without
the light-emission of the flash lamp, therefore, the first non-emission
luminance evaluation value is obtained from the evaluation means.
The second control means makes the flash lamp perform the preliminary
light-emission with the preliminary light-emission amount, and exposes
the picture taking means for the second period, therefore, the preliminary
light-emission luminance evaluation value is obtained from the evaluation
means. The calculation means calculates the major light-emission
amount on the basis of the first non-emission luminance evaluation
value and the preliminary light-emission luminance evaluation value.
The flash lamp is fired with the major light-emission amount, and
the picture taking means is exposed for the first period at this
time. In addition, the second period is defined to be shorter than
the first period.
In an aspect of the present invention, the first control means
exposes the picture taking means for a third period. Then, a luminance
evaluation value calculation means calculates a second non-emission
luminance evaluation value in exposing the picture taking means
for the first period without the light-emission of the flash lamp,
on the basis of the first period, the third period and the first
non-emission luminance evaluation value. Furthermore, a major light-emission
amount calculation means calculates the major light-emission amount
on the basis of the second non-emission luminance evaluation value,
a target luminance evaluation value, the preliminary light-emission
luminance evaluation value and the preliminary light-emission amount.
In an embodiment of the present invention, an exposure period calculation
means calculates a most suitable exposure period in which the target
luminance evaluation value is obtained without the light-emission
of the flash lamp, on the basis of the third period, the first non-emission
luminance evaluation value and the target luminance evaluation value.
If the most suitable exposure period is shorter than a longest exposure
period which is a longest period capable of exposing the picture
taking means, a cancellation means cancels the major light-emission.
That is, since the target luminance evaluation value is obtained
without the major light-emission, the cancellation means cancels
the major light-emission.
According to the present invention, since an exposure period in
the preliminary light-emission is defined to be shorter than the
exposure period in the major light-emission, the preliminary light-emission
luminance evaluation value is not influenced by an external light,
therefore, it is possible to precisely calculate the major light-emission
amount.
According to the present invention, a digital camera for taking
a picture of an object by making a flash lamp performs a major light-emission
with a major light-emission amount and by exposing a picture taking
means, the camera comprises: a mode setting means for setting one
of a first mode and a second mode; a first weighting amount table
in which first weighting amount data is stored; a second weighting
amount table in which second weighting amount data is stored; a
detection means for detecting a luminance signal from a camera signal
outputted from the picture taking means; a weighting means for weighting
the luminance signal with a table corresponding to a set mode; a
calculation means for calculating an output of the weighting means
and outputting a luminance evaluation value; a first control means
for making the flash lamp perform a preliminary light-emission and
exposing the picture taking means; and a first computing means for
computing the major light-emission amount on the basis of a preliminary
light-emission luminance evaluation value outputted from the calculation
means in response to an operation of the first control means.
The first control means makes the flash lamp perform the preliminary
light-emission and exposes the picture taking means, whereby the
camera signal is outputted from the picture taking means. When the
first mode is set by the mode setting means, the weighting means
weights the luminance signal included in the camera signal with
the first weighting amount table. Furthermore, when the second mode
is set by the mode setting means, the weighting means weights the
luminance signal included in the camera signal with the second weighting
amount table. The output of the weighting means is calculated by
the calculation means, and the fist computing means computes the
major light-emission amount on the basis of the preliminary light-emission
luminance evaluation value outputted from the calculation means.
In an aspect of the present invention, the second control means
exposes the picture taking means without the light-emission of the
flash lamp, and the weighting means selects the first weighting
amount table at this time. Then, a second computing means computes
a most suitable exposure period in which a target luminance evaluation
value is obtained without the light-emission of the flash lamp,
on the basis of a second luminance evaluation value outputted from
the calculation means in response to an operation of a second control
means.
In the first mode, the most suitable exposure period is compared
with a longest exposure period which is a longest period capable
of exposing the picture taking means, if the most suitable exposure
period is shorter than the longest exposure period, the major light-emission
is cancelled. In addition, the first mode is an automatic light-emission
mode in which the major light-emission is performed in response
to the most suitable exposure period, and the first weighting amount
data in a surrounding portion of the object is smaller than the
first weighting amount data in a center portion of the object and
larger than "0".
In the second mode, the most suitable exposure period and the longest
exposure period are compared with each other, if the most suitable
exposure period is shorter than the longest exposure period, the
most suitable exposure period is held as an exposure period in the
major light-emission, and if the most suitable exposure period is
equal to the longest exposure period or longer than the longest
exposure period, the longest exposure period is held as the exposure
period in the major light-emission. In addition, the second mode
is a forced light-emission mode for making the flash lamp perform
the major light-emission without respect to the most suitable exposure
period, and the second weighting amount data has a value of "0"
in the surrounding portion of the object.
According to the present invention, since the table is changed
in response to the set mode, it is possible to calculate the most
suitable major light-emission amount for the mode.
The above described objects and other objects, features, aspects
and advantages of the present invention will become more apparent
from the following detailed description of the present invention
when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing one embodiment of the present
invention;
FIG. 2 is an illustrative view showing a portion of FIG. 1 embodiment;
FIG. 3 is an illustrative view showing another portion of FIG.
1 embodiment;
FIG. 4 is an illustrative view showing the other portion of FIG.
1 embodiment;
FIG. 5 is an illustrative view showing a further portion of FIG.
1 embodiment;
FIG. 6 is an illustrative view showing the other portion of FIG.
1 embodiment;
FIG. 7 is a flowchart showing a portion of an operation of FIG.
1 embodiment;
FIG. 8 is a flowchart showing another portion of the operation
of FIG. 1 embodiment;
FIG. 9 is a flowchart showing the other portion of the operation
of FIG. 1 embodiment;
FIG. 10 is a flowchart showing further portion of the operation
of FIG. 1 embodiment;
FIG. 11 is a flowchart showing the other portion of the operation
of FIG. 1 embodiment;
FIG. 12 is a flowchart showing further portion of the operation
of FIG. 1 embodiment; and
FIG. 13 is an illustrative view showing a portion of an operation
of a prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
One embodiment of the present invention is described in accordance
with the drawings in the above. FIG. 1 is a block diagram showing
a digital camera 10 of this embodiment.
A reference numeral "12" denotes a CCD imager for subjecting
an optical image applied through an optical system to a photoelectric
conversion and outputting a camera signal. A plurality of light
receiving portions 12 are formed on the CCD imager 12 as shown in
FIG. 2, a color filter 13 in which the three primary colors of R,
G and B are arranged in mosaic like as shown in FIG. 3 is attached
in front of the light receiving portions 12a. The light receiving
portions 12a constitute respective pixels of the CCD imager 12,
and one of R, G and B arranged in the color filter 13 corresponds
to one light receiving portion 12a.
The optical image passed through a lens (not shown) is applied
to the light receiving portions 12a of the CCD imager 12 through
the color filter 13 and subjected to the photoelectric conversion.
Charges obtained in such a manner are accumulated in an exposure
period, that is a charge accumulation period, determined in response
to a shutter speed, thereafter, the charges are outputted.
In describing in detail, as shown in FIG. 2, the CCD imager 12
includes the plurality of light receiving portions 12a each of which
corresponds to one pixel, a plurality of vertical transfer registers
12b for transferring in the vertical direction the charges obtained
by the photoelectric conversion and accumulated in such light receiving
portions 12a and a vertical transfer register 12c provided at ends
of the respective vertical transfer registers 12b and for transferring
in the horizontal direction the charges transferred by the vertical
transfer registers 12b. The CCD imager 12 is driven by timing signals
outputted from a timing generator 18 (see FIG. 1). Now, in the timing
signals, there are a reading pulse for reading out the charges from
the light receiving portions 12a to apply the charges to the vertical
transfer registers 12b, a vertical transfer pulse for transferring
the charges in the vertical transfer registers 12b for each line
in the vertical direction, a horizontal transfer pulse for transferring
the charges in the horizontal transfer register 12c for each pixel
in the horizontal direction, a sweeping pulse for sweeping the charges
generated by the light receiving portions 12a in a non-exposure
period, that is, non-charge accumulation period, and etc.
The timing generator 18 controls a period for outputting the sweeping
pulse in response to a shutter speed instruction signal described
below. Therefore, the charge accumulation period is controlled,
and a desired shutter speed is obtained. In addition, a technology
for controlling the shutter speed in response to an output period
of the sweeping pulse in such a manner is well-known as an electronic
shutter function.
Thus, the charges are generated by the CCD imager 12 for the respective
pixels, and successively outputted as an image signal. Now, since
the color filter 13 is formed as shown in FIG. 3, when accumulation
of the charges is completed in the CCD imager 12, a G signal passed
through a filter element of green existing at a lower left end is
first outputted, succeedingly, a B signal passed through the filter
element of blue adjacent to the filter element of green at the right
side is outputted. Thus, when an output from the lowest line is
completed, such a color signals are successively outputted from
the second lowest line in the same manner.
A reference numeral "14" (see FIG. 1) denotes an A/D
converter for successively digitizes the image signal outputted
from the CCD imager 12, that is the color signals corresponding
to the respective filter elements, and an output of the A/D converter
14 is sequentially written to a RAM 16 as image data.
Writing to the RAM 16 is controlled by a writing control signal
from a memory control circuit 40. A plurality of addresses corresponding
to the respective pixels of the CCD imager 12 are previously applied
to the RAM 16. The memory control circuit 40 controls the writing
on the basis of the timing signals from the timing generator 18
such that each color data included in the image data is stored at
a desired address in the RAM. In addition, which pixel of the CCD
imager 12 the inputted color data corresponds to is determined by
a count value of a vertical counter which is reset by the reading
pulse and incremented by the vertical transfer pulse, and a count
value of a horizontal counter which is reset by the vertical transfer
pulse and incremented by the horizontal transfer pulse.
Thus, the charges of all the pixels are fetched out at every time
the CCD imager 12 is exposed, and the image data in which each pixel
has one color component of R, G and B is to be written in the RAM
16.
As shown in FIG. 4, one block is defined by three pixels including
the filter elements of R, G and B one by one like a character "L"
in the color filter 13, and a plurality of blocks Bm, n (m, n: integer)
such as B.sub.1,1, B.sub.1,2 . . . are formed. When the writing
of all the color data to the RAM 16 is completed, the color data
of R, G or B is read out at every block in accordance with a reading
control signal from the memory control circuit 40. In addition,
underlines are applied to the filter element forming each block,
and the each block is surrounded by a bold solid line. Furthermore,
the filter elements of R, G and B included in each block are divided
by dotted lines.
A reference numeral "20", shown in FIG. 1, denotes a
calculator for generating luminance data Dy showing a level of a
luminance signal Y, color difference data Dr showing a level of
a color difference signal R--Y and color difference data Db showing
a level of a color difference signal B--Y by substituting the color
data of R, G and B included in the same block and read out into
a predetermined equation. If the respective color data of R, G and
B in a black are defined by "r", "g" and "b",
the equation is shown as below.
The luminance data Dy calculated in such a manner is inputted to
a weighting circuit 22. The weighting circuit 22 subjects the luminance
data to a weighting operation Dy in accordance with weighting amount
data K held in a first weighting amount table 28 or a second weighting
amount table 30. That is, the weighting circuit 22 multiplies the
luminance data Dy by the weighting amount data K. Now, the first
weighting amount table 28 and the second weighting amount table
30 receive reading address data from the memory control circuit
40, and recognize from which block of R, G and B data the luminance
data and the color difference data outputted from the calculator
20 are generated. Then, the first weighting amount table 28 and
the second weighting amount table 30 output the weighting amount
data K corresponding to a noted block.
In describing in detail, the first weighting amount table 28 is
divided into 256 areas Ai, j (i, j: integers from 1 to 16) having
16 areas in the vertical direction and 16 areas in the horizontal
direction as shown in FIG. 5, and the weighting amount data K having
a value of "1", "2" or "3" corresponds
to each area. Each area Ai, j is larger than each block Bi, j, and
a plurality of blocks Bm, n included in one area Ai, j have the
same weighting amount data K. The first weighting amount table 28
detects an area relating to the luminance data and the color difference
data outputted from the calculator 20, and applies the weighting
amount data K corresponding to the detected area to the weighting
circuit 22.
Similarly, the second weighting amount table 30 is also divided
into 256 areas Ai, j (i, j: integers from 1 to 16) having 16 areas
in the vertical direction and 16 areas in the horizontal direction
as shown in FIG. 6, and the weighting amount data K having a value
of "0", "1", "2", "4" or
"6" corresponds to each area. The second weighting amount
table 30 detects an area relating to the luminance data and the
color difference data outputted from the calculator 20, and applies
the weighting amount data K corresponding to the detected area to
the weighting circuit 22.
By the way, since a main object mainly exists in a center of a
screen, in the first weighting amount table 28 shown in FIG. 5,
the weighting amount data K has a value of "3" in 16 areas
of the center, the weighting amount data K has a value of "2"
in 36 areas which surround the 16 areas and in which a possibility
of existence of the main object is slightly lower, and the weighting
amount data K has a value of "1" in the remaining areas
of the outside in which the possibility is drastically lower. By
subjecting the weighting operation to the luminance data in accordance
with the weighting amount data K, it is possible to perform center
emphasis photometry that a luminance level of the center of the
screen is considered to be the most important and the luminance
level of a surrounding area is also sufficiently considered.
On the other hand, in the second weighting amount table 30 shown
in FIG. 6, the weighting amount data K has a drastically large value
"6" in 4 areas of the center in which there is a high
possibility of the existence of the main object, and the weighting
amount data K has a value "4" a little smaller than "6"
in 8 areas which surround the 4 areas and that the possibility of
the existence of the main object is slightly lower. Furthermore,
the weighting amount data K has a value "2" a little smaller
than "4" in 20 areas which surround such 8 areas and that
the possibility lower yet, and the weighting amount data K has a
value "1" a little smaller than "2" in 20 areas
which surrounds such 20 areas and that the possibility even lower.
Furthermore, in the remaining areas surrounding such 20 areas, since
the possibility of the existence of the main object is the lowest,
and the possibility of the existence of a drastically high luminance
light source such as a fluorescent lamp and the solar is high in
a back light, a value "0" is applied to the remained area.
Now, the value "0" means that the luminance level in the
remained areas is substantially excluded in calculating an evaluation
value described later.
Referring back to FIG. 1, a reference symbol SW2 denotes a switch
for selecting one of the weighting amount data outputted from the
first weighting amount table 28 and the second weighting amount
table 30 to apply to the weighting circuit 22, and the switch SW2
is controlled by a second switching signal from a microcomputer
32 described later.
A reference numeral 24 denotes an integrator for calculating a
total sum of the luminance data equal to one screen to which the
weighting operation is performed in the weighting circuit 22, that
is, for digitally integrating the luminance data through one screen.
Each of the first weighting amount table 28 and the second weighting
amount table 30 has 256 weighting amount data in response to the
respective luminance data Dy. The calculator 26 normalizes an integrated
value from the integrator 24 by dividing the integrated value with
a total sum of the 256 weighting amount data so as to calculate
a luminance evaluation value Vy being an evaluation object in an
exposure adjustment.
In addition, the two color difference data simultaneously outputted
from the calculator 20 with the luminance data are used for a white
balance adjustment operation in a white balance adjustment circuit
not shown.
The microcomputer 32 determines the exposure period of the CCD
imager 12, that is the shutter speed, for the exposure adjustment
on the basis of the luminance evaluation value Vy applied from the
calculator 26. The microcomputer 32 also instructs a timing of the
exposure of the CCD imager 12, that is a timing of picture taking,
on the basis of the determined shutter speed. Furthermore, the microcomputer
32 controls a light-emission of the flash lamp 38 and switching
of the switches SW1 and SW2 on the basis of a shutter release instruction
from a shutter release button 36 and the luminance evaluation value
Vy.
The flash lamp 38 emits a light by a period instructed by a flash
instruction from the microcomputer 32. A light-emission period of
the flash lamp 38 determines a light-emission amount, the longer
the light-emission period is, the larger the light-emission amount
is. The shutter release button 36 inputs the shutter release instruction
to the microcomputer 32 in response to a depression of the button
by an operator.
A signal processing circuit 42 receives the image data stored in
the RAM 16 through the switch SW1 after the shutter release instruction
is inputted, and subjects a well-known signal processing such as
a color separation, a gamma correction, signal compression and etc.
to the image data, and generates still image data. The still image
data is recorded into a record medium 44 such as a flash memory
and a memory card, for example, by the microcomputer 32. In addition,
the switch SW1 is controlled by a first switching signal outputted
from the microcomputer 32.
A reference numeral 34 denotes a mode selecting button 34 for selecting
one of an automatic light-emission mode and a forced light-emission
mode in response to an operation of the operator, and a mode setting
signal for setting a selected mode is inputted to the microcomputer
32. The microcomputer 32 controls the switch SW2 by the second switching
signal in response to the mode setting signal. More specifically,
in a case where the automatic light-emission mode is selected by
the mode selecting button 34, the switch SW2 is connected to a side
of the first weighting amount table 28. In a case where the forced
light-emission mode is selected, the switch SW2 is connected to
the side of the first weighting amount table 30 in the exposure
adjustment, and the switch SW2 is connected to a side of the second
weighting amount table 30 in calculating the light-emission amount
of the flash lamp 38.
Now, the automatic light-emission mode means a mode for making
the flash lamp 38 perform a major light-emission to supplement a
shortage amount in only a case where an exposure shortage cannot
be eliminated even if the shutter speed is set into a minimum speed
by the exposure adjustment operation, and it is desirable to select
the automatic light-emission mode in a normal picture taking state.
On the other hand, the forced light-emission mode means a mode for
back light correction in which the flash lamp 38 always emits the
light to optimize illumination of the main object in a case where
the main object in the center of the screen becomes a back light
state by drastically high luminance behind the main object.
Succeedingly, with referring to flowcharts shown in FIGS. 7 to
12, an operation of the exposure adjustment and the light-emission
control of the flash lamp 38 is described attaching importance to
processing of the microcomputer 32. In addition, FIGS. 7 to 9 show
flowcharts of the automatic light-emission mode, and FIGS. 10 to
12 show flowcharts of the forced light-emission mode. In a case
where the automatic light-emission mode is selected by the mode
selecting button 34, the operation is executed in accordance with
the flowcharts shown in FIGS. 7 to 9, and inversely, in a case where
the forced light-emission mode is selected, the operation is executed
in accordance with the flowcharts shown in FIGS. 10 to 12.
Accordingly, the operation of the automatic light-emission mode
is first described. In a case where the automatic light-emission
mode is selected, the first weighting amount table is selected by
the switch SW2 in a step S1, the process proceeds to a step S3.
If it is determined that the shutter release button 36 is depressed
by the operator whereby the shutter release instruction is inputted
to the microcomputer 32 in the step S3, the microcomputer 32 first
starts the exposure adjustment operation. That is, the microcomputer
32 applies a shutter speed setting signal to the timing generator
18 so as to initialize the shutter speed into 1/250 second as a
middle speed in a step S5. The timing generator 18 receives the
shutter speed setting signal, and controls the output period of
the sweeping pulse to the CCD imager 12 such that the charge accumulation
period becomes 1/250 seconds. Succeedingly, a variable N is initialized
into "1" so as to repeat the exposure adjustment for 3
flames in a step S7, and a first exposure is performed at the shutter
speed of 1/250 seconds in a step S9. Thereafter, the luminance evaluation
value Vy is calculated in a step S11.
More specifically, the image data generated by this exposure is
written into the RAM 16, thereafter, the calculator 20 calculates
the luminance data and the color difference data on the basis of
the image data. Only the luminance data Dy is subjected to the weighting
operation in the weighting circuit 22 in accordance with the weighting
amount data K stored in the first weighting amount table 28, whereby
the luminance data, having attached importance to the center of
the screen, is obtained. The integrator 24 digitally integrates
the luminance data equal to 1 frame, and the accumulator 26 divides
the integrated value by the total sum of the weighting amount data,
whereby the luminance evaluation value Vy is calculated attaching
importance to the center of the screen.
The microcomputer 32 compares the luminance evaluation value Vy
with a target evaluation value Yt to be obtained at a most suitable
exposure state in a step S13, and renews the shutter speed such
that the luminance evaluation value Vy is consistent with the target
evaluation value Yt. More specifically, the microcomputer 32 multiplies
a current shutter speed by Yt/Vy to obtain a renewed shutter speed
for a succeeding exposure. If the luminance evaluation value is
"50" and the target evaluation value is "100",
for example, since the luminance level is only a half of a most
suitable value, the shutter speed is renewed, here decreased, from
the current 1/250 second to 1/125 second of a low speed.
Succeedingly, the microcomputer 32 determines whether or not the
exposure for adjusting the shutter speed has been executed for three
times in a step S15, if under three times, the microcomputer 32
increments the variable N in a step S17. Furthermore, the microcomputer
32 determines whether or not the shutter speed for the succeeding
exposure renewed in the step S13 is lower speed than 1/30 second,
that is, the exposure period is longer than 1/30 second in a step
S19, if "YES", the microcomputer 32 sets the shutter speed
into 1/30 second. Processes of the steps S19 and S21 are provided
with considering that a minimum value of the shutter speed is 1/30
second, and the shutter speed cannot be actually set into a lower
speed than the minimum value in the digital camera 10 of this embodiment.
Accordingly, in a case where a shutter speed lower than the minimum
value is calculated during the exposure adjustment operation, the
shutter speed is forcedly set into the minimum value.
Thereafter, the process is returned back to the step S9, a series
of operation described above is repeated. That is, the shutter speed
for a third exposure is obtained by a second exposure, and the shutter
speed of a fourth exposure is obtained by the third exposure. When
the exposure adjustment has been repeated for three times in such
a manner, it is determined that the exposure adjustment has been
completed, the process proceeds from the step S15 to a step S23,
and it is determined whether or not the light-emission of the flash
lamp 38 is needed.
More specifically, it is determined whether or not the shutter
speed for the fourth exposure which is finally obtained in a step
S13 is lower than 1/30 second which is the lowest speed value of
the shutter speed that the digital camera 10 of this embodiment
permits, that is, whether or not the luminance evaluation value
Vy does not reach the target evaluation value Yt if the charge accumulation
period is not longer than 1/30 second in a first exposure after
the exposure adjustment is completed. In a case where it is determined
that the shutter speed is 1/30 second or higher than 1/30 second,
that is, it is determined that the exposure period is 1/30 second
or shorter than 1/30 second, since the most suitable exposure is
obtained at the shutter speed, it is determined that no light-emission
of the flash lamp 38 is needed. On the other hand, in a case where
it is determined that the most suitable exposure state cannot be
obtained if the shutter speed is not longer than 1/30 second, since
the light-emission of the flash lamp 38 is needed, the process proceeds
to a step S25 to control the light-emission of the flash lamp 38.
If it is determined that no light-emission of the flash lamp 38
is needed in the step S23, the process proceeds to a step S41, and
the CCD imager 12 is exposed at the shutter speed renewed in the
step S13 and the most suitable exposure state is obtained. That
is, the microcomputer 32 cancels the light-emission of the flash
lamp 38 and takes the picture of the object. Then, the image data
obtained in a step S55 is recorded into the record medium 44 through
the signal processing circuit 42 as the still image data. In addition,
in a case where it is determined that no light-emission of the flash
lamp 38 is needed in the step S23, the image data due to the exposure
in the step S41 can be inputted to the signal processing circuit
42 by outputting the first switching signal to open the switch SW1
at a timing that a predetermined period has passed from the exposure
in the step S41.
On the other hand, in an operation of the light-emission control
of the flash lamp 38, the shutter speed setting signal is outputted
so as to set the shutter speed in a major light-emission into 1/30
second as the minimum value in the step S25, succeedingly, the luminance
evaluation value expected to be obtained by exposing the CCD imager
12 at the shutter speed of 1/30 second without emitting the flash
lamp 38 is calculated as a non-emission luminance evaluation value
Y.sub.0. That is, the non-emission luminance evaluation value Y.sub.0
is calculated by a following equation.
In addition, the shutter speed used in the third exposure is stored
in a memory 32a included in the microcomputer 32 before the shutter
speed for the fourth exposure is calculated in the step S13. In
addition, 1/30 second is equal to a first period, and the shutter
speed used in the third exposure is equal to the third period. Furthermore,
the luminance evaluation value Vy obtained by the third exposure
is equal to a first non-emission luminance evaluation value, and
non-emission luminance evaluation value Y.sub.0 is equal to a second
non-emission luminance evaluation value.
When the non-emission luminance evaluation value Y.sub.0 is calculated
as the luminance evaluation value at the shutter speed of 1/30 second
in such a manner, a difference between the target evaluation value
Yt and the non-emission luminance evaluation value Y.sub.0, that
is, Yt-Y.sub.0 is calculated as the shortage amount U of the luminance
in a step S29, and furthermore, the shutter speed setting signal
is applied to the timing generator 18 so as to set the shutter speed
into 1/1500 second in a step S31. Now, in a case where the shutter
speed is 1/1500 second, in other words, the charge accumulation
period is drastically short such as 1/1500 second, an influence
of an external light including a light of the object on the image
data becomes drastically small.
Succeedingly, the CCD imager 12 starts the exposure at the shutter
speed of 1/1500 second in a step S33. On the other hand, the microcomputer
16 outputs the flash instruction for a preliminary light-emission
to the flash lamp 38 at the same time as an output of the shutter
speed setting signal. If the flash lamp 38 receives the flash instruction
for the preliminary light-emission, the flash lamp 38 emits the
light such as the light-emission amount becomes P during the exposure
of the CCD imager 12. In addition, this light-emission state is
called as the preliminary light-emission state that the light-emission
is preliminarily performed before the major light-emission described
later.
If it is determined that the exposure at the shutter speed of 1/1500
second has been completed in a step S37, the image data obtained
is written into the RAM 16. Succeedingly, the weighting operation
attaching importance to the center is performed in similar to the
weighting operation in a non-emission state described above in a
step S39, and the luminance evaluation value Vy in the preliminary
light-emission is calculated by the calculator 26. The microcomputer
32 regards the luminance evaluation value Vy in the preliminary
light-emission as a preliminary light-emission luminance evaluation
value Ys in a step S43.
Thereafter, the microcomputer 32 calculates a major light-emission
amount Q of the flash lamp 38 in the major light-emission in accordance
with a following equation in a step S45.
In this equation, by dividing the shortage amount U of the luminance
by the preliminary light-emission luminance evaluation value Ys,
how many times of the evaluation value obtained by one preliminary
light-emission is necessary to supplement the shortage amount is
calculated, and furthermore, by multiplying the light-emission amount
in the preliminary light-emission with a magnification calculated,
the major light-emission amount Q is finally obtained. Now, since
the shutter speed is set into a drastically short period such as
1/1500 second in the preliminary light-emission, it is considered
that the preliminary light-emission luminance evaluation value Ys
itself depends on only the light-emission of the flash lamp 38.
Accordingly, it is possible to exclude the influence of the external
light in calculating the major light-emission amount, therefore,
a fluctuation of the luminance due to the flicker causes no particular
problem.
The microcomputer 32 thereafter outputs the shutter speed setting
signal for setting the shutter speed into 1/30 second to the timing
generator 18 in a step S47.
Thus, the major light-emission amount Q of the flash lamp 38 is
determined and the shutter speed is defined, and the CCD imager
12 starts a major exposure in a step S49. On the other hand, the
microcomputer 32 outputs the flash instruction for the major light-emission
to the flash lamp 38, and the flash lamp 38 emits the light during
the exposure of the CCD imager 12 by a period equal to the major
light-emission amount Q in a step S51.
If it is determined that the exposure at the shutter speed of 1/30
second is completed in a step S53, the image data obtained is written
into the RAM 16. Furthermore, in a case where it is determined that
the light-emission of the flash lamp 38 is needed in the step S23,
the microcomputer 32 outputs the first switching signal so as to
close the switch SW1 which is keeping an open state until now at
a time that a predetermined period has passed from the start of
the exposure in the step S49. The switch SW1 becomes a close state
in response to the first switching signal. Now, since the predetermined
period is set into a period through a time that the image signal
due to the major light-emission is outputted from the CCD imager
12 to a time that the image data is completely written into the
RAM 16, the signal processing circuit 42 subjects the signal processing
to the image data obtained due to the exposure in the step S55 and
read out from the RAM 16, and the still image data processed by
the signal processing circuit 42 is recorded into the record medium
44.
As described above, in the automatic light-emission mode, a little
weighting amount data is applied to a surrounding area of the main
object on the assumption of the center emphasis photometry in calculating
the luminance evaluation value. Accordingly, the luminance of the
surrounding area is considered in determining necessity of the light-emission
of the flash lamp 38 and the major light-emission amount, therefore,
an object included in the surrounding can receive a suitable light
amount.
Succeedingly, the operation of the forced light-emission mode is
described in accordance with the flowcharts shown in FIGS. 10 to
12. In addition, a description of these figures which duplicates
that in FIGS. 7-9 is omitted.
If the forced light-emission mode is selected by the mode selecting
button 34, the switch SW2 selects in a step S61 the first weighting
amount table 28 for the exposure adjustment precedingly executed,
and in the exposure adjustment in the forced light-emission mode,
the luminance evaluation value is calculated using the weighting
amount data of the first weighting amount table 28.
Thereafter, if the shutter release button 36 is depressed, the
exposure adjustment operation from a step S65 to a step S81 is executed
for three times, and then the process proceeds to a step S83. In
addition, the luminance data Dy obtained due to a third exposure
in a step S69 is held in a memory (not shown) provided between the
calculator 20 and the weighting circuit 22. Furthermore, the shutter
speed obtained by a third process of a step S73 also stored in the
same memory.
In the step S83, it is determined whether or not the shutter speed
finally obtained in a step S73 by a third exposure evaluation is
lower speed than 1/30 second, if it is a lower speed than 1/30 second,
the shutter speed is forcedly set into 1/30 second in a step S85.
Though the shutter speed for a major exposure is obtained in the
step S73 or S85 in such a manner, since the shutter speed is changed
for the preliminary light-emission succeedingly executed, the shutter
speed for the major exposure once obtained is held in the memory
32a (see FIG. 1) included in the microcomputer 32 so as to save
the shutter speed in a step S87.
Thereafter, though a light-emission amount setting operation is
to be started for setting the light-emission amount of the flash
lamp 38, preceding the light-emission setting operation, the second
switching signal connects the switch SW2 to the side of the second
weighting amount table 30 in a step S89 shown in FIG. 11. Accordingly,
in calculating the luminance evaluation value of the screen hereafter,
the second weighting amount table 30 considering only the center
of the screen is used.
In a step S91, the luminance evaluation value Vy is calculated
from the luminance data Dy precedingly held in the memory and based
on the third exposure, succeedingly, a non-emission luminance evaluation
value Ya is calculated in accordance with a following equation.
The shutter speed calculated at a time that the first weighting
amount table 28 is selected is reflected to the equation. That is,
the non-emission luminance evaluation value Ya is calculated with
considering to some extent a surrounding luminance. Accordingly,
the non-emission luminance evaluation value Ya becomes large in
this case in comparison with a case where the non-emission luminance
evaluation value Ya is calculated on the basis of only the luminance
of the center, therefore, saturation of the surrounding luminance
is controlled in a back light state.
Then, the non-emission luminance evaluation value Ya and the target
evaluation value Yt are compared with each other in a step S93.
In a case where Yt>Ya, since the luminance evaluation value does
not reach the target evaluation value Yt even if the shutter speed
is set into the minimum value, and the light-emission of the flash
lamp 38 is necessary, the major light-emission amount is determined
in steps S97 to S111. On the other hand, in a case where Yt.ltoreq.Ya
is determined in the step S93, it is recognized that the main object
in the center of the screen is sufficiently illuminated on the screen
evaluation by the exposure adjustment precedingly executed, the
light-emission amount of the flash lamp 38 is in a step S95 set
into a minimum light-emission amount Pmin previously defined, thereafter
the process proceeds to a step S113.
In determining the major light-emission amount after the step S97,
though the luminance evaluation value Vy is calculated in the preliminary
light-emission state in a step S107 in similar to the automatic
light-emission mode described above, since the second weighting
amount table 30 is selected at this time instead of the first weighting
amount table 28, a surrounding object is ignored and the main object
existing in the center is noted in the screen evaluation in the
preliminary light-emission. Accordingly, the major light-emission
amount Q calculated in the step S111 on the basis of the luminance
evaluation value Vy also becomes a light-emission amount considering
only a center area.
When the major light-emission amount Q is determined in such a
manner, the shutter speed for the major light-emission saved in
the previous step S87 is fetched from the memory 32a, and the shutter
speed setting signal showing the fetched shutter speed is applied
to the timing generator 18, and the major exposure is executed in
a step S117 at the shutter speed. During the major exposure, the
flash lamp 38 emits the light with the major light-emission amount
Q determined in the step S111 or the major light-emission amount
Pmin determined in the step S95, and the image data obtained after
the exposure has completed is recorded into the record medium 44
in a step S121.
In addition, the major light-emission amount Pmin is set into the
minimum value capable of slightly increasing the luminance of the
main object considering the operator selected the forced light-emission
mode, though the exposure shortage concerning the main object is
already eliminated by the exposure adjustment.
As described above, in the forced light-emission mode, the luminance
of the screen is evaluated with using the first weighting amount
table 28, therefore, the exposure adjustment is executed attaching
importance to the main object in the center of the screen and considering
the surrounding area. Accordingly, a suitable exposure is obtained
concerning the object in the surrounding area. Furthermore, in a
case where the exposure shortage occurs even if the exposure adjustment
is executed, the luminance of the screen is evaluated considering
only the center area with using the second weighting amount table
30. That is, a light source etc. being put in the surrounding area
is excluded from an evaluation object, and the exposure shortage
concerning to only the main object in the center area is supplemented.
Therefore, it is possible to correct the back light.
Furthermore, the shutter speed in the preliminary light-emission
is made high such that the influence of the external light excepting
a light of the flash lamp can be excluded in any mode, even if a
light of illumination is included in the object, and the light of
the illumination is changed by the flicker, it is possible to precisely
determine the major light-emission amount Q without the influence
of the flicker.
In this embodiment, though the luminance data of all the blocks
are digitally integrated to obtain the luminance evaluation value,
needless to say the luminance evaluation value may be calculated
through thinning out some blocks, such as a specific one block out
of ten blocks, where the latter are to be digitally integrated in
both the horizontal direction and the vertical direction so as to
shorten a processing period.
Furthermore, functions of the weighting amount table 28, the weighting
circuit 22, the calculators 20 and 26, the integrator 24 and the
signal processing circuit 42 may be put into a single microcomputer
with a function of the microcomputer 32 so as to implement such
functions by software.
Furthermore, in this embodiment, though the luminance evaluation
value Ys in the preliminary light-emission is calculated at the
shutter speed of 1/1500 second, the shutter speed is not particularly
restricted to 1/1500 second. That is, since a light-emission period
of the flash lamp 38 in the preliminary light-emission is approximately
50 microseconds, the shutter speed has only to satisfy a condition
that the shutter speed, that is, the exposure period is longer than
the light-emission period, and to sufficiently restrain the influence
of the external light, and even if the shutter speed is 1/2000 second,
1/5000 second and 1/10000 second as a maximum speed, a similar advantage
is obtained. It is ideally desirable that the shutter speed, that
is, the exposure period is extremely close to the light-emission
period of the flash lamp 38.
Similarly, though the shutter speed is set into 1/30 second in
the main light-emission, the shutter speed is not restricted to
the speed, and the shutter speed may be set into 1/29 second etc.,
for example, so as to obtain a sufficient exposure. Furthermore,
the shutter speed may be set into 1/50 second, for example, with
considering unintentional vibration.
Although the present invention has been described and illustrated
in detail, it is clearly understood that the same is by way of illustration
and example only and is not to be taken by way of limitation, the
spirit and scope of the present invention being limited only by
the terms of the appended claims.
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