Digital Camera Patent Abstract
A digital camera includes a CCD imager mounted at a front with a
primary color filter. An optimal shutter speed is calculated based
on a camera signal outputted from the CCD imager upon a pre-exposure.
Where a calculated optimal shutter speed is low, a timing generator
drives the CCD imager by a pixel-mixing scheme. Charges are first
read out of part of the light receiving elements and transferred
in a vertical direction. When the charges are transferred by a predetermined
distance, the remaining part of the light receiving elements are
read out. As a result of this, the charges of a same color of color
components are mixed together. That is, a filtering process is effected
within the CCD imager to remove aliasing components. Digital Camera Patent Claims
What is claimed is:
1. A digital camera comprising: a color filter formed by a plurality
of color elements having N (N: integer greater than one) of colors
distributed; an imager having a plurality of light receiving elements
respectively corresponding to said plurality of color elements;
a determiner for determining an exposure period of said imager by
evaluating a luminance of an object scene; a sweeper for sweeping
at a start timing of the exposure period charges generated by said
plurality of light receiving elements; a reader for reading after
a lapse of the exposure period the charges generated by at least
a part of said plurality of light receiving elements; and a changer
for changing a reading scheme of said reader between a first scheme
and a second scheme depending upon the exposure period, wherein
said plurality of light receiving elements include a plurality of
first light receiving elements which respectively correspond to
a plurality of first color elements having N colors distributed,
and a plurality of second light receiving elements which respectively
correspond to a plurality of second color elements having N colors
distributed, the first scheme is a scheme for reading only first
charges generated by said plurality of first light receiving elements,
the second scheme is a scheme for reading at a first timing the
first charges, and reading at a second timing second charges generated
by said plurality of second light receiving elements so as to mix
with each other the read first charges and second charges which
correspond to the same color of the color elements, and said changer
validates the first scheme when the exposure period is equal to
or less than a threshold value, and validates the second scheme
when the exposure period is greater than the threshold value.
2. A digital camera according to claim 1, wherein said imager has
a vertical transfer register, and said reader includes a first charge
reader for reading the first charges onto said vertical transfer
register, a vertical transfer or for transferring the first charges
read onto said vertical transfer register in a vertical direction,
and a second charge reader for reading the second charges onto said
vertical transfer register when said first charges have been transferred
in the vertical direction by a predetermined distance.
3. The digital camera according to claim 2, further comprising:
an exposure device to expose a subject image to said CCD imager;
a calculation device for calculating an optimal amount of exposure
by said CCD imager; a setting device for setting said optimal amount
of exposure to said exposure device; and a disabler for disabling
said second charge reader depending upon said optimal amount of
exposure.
4. The digital camera according to claim 3, wherein said optimal
amount of exposure is defined based on a shutter speed, and said
disabler disables said second charge reader when said shutter speed
is higher than a predetermined value.
5. A digital camera according to claim 2, wherein said changer
changes the reading scheme by enabling/disabling the second charge
reader.
6. A digital camera according to claim 2, wherein said vertical
transfer register is formed by a plurality of metals, and at least
three of said plurality of metals are assigned to one of said plurality
of light receiving elements.
7. A digital camera according to claim 1, wherein said color filter
is a filter arranged with primary colors of color elements in a
Bayer arrangement.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates generally to imaging apparatuses and digital
cameras and, more particularly, to an imaging apparatus for reading
charges out of light receiving elements of a CCD imager to create
a low-resolution camera signal, and to a digital camera provided
with such an imaging apparatus. Description of the related art.
In a conventional digital camera in which, where charges are read
with thinning out from a CCD imager, the read-out charges are transferred
to the CCD imager and then outputted therefrom in a separate fashion.
However, such charge reading with thinning out is equivalent to
charge sampling. According to a sampling theorem, such an output
camera signal contains aliasing components. A filter can eliminate
such aliasing components. The addition of a filter, however, raises
cost correspondingly.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention is to
provide, at low cost, an imaging apparatus in which noise is prevented
from occurring.
Another object of the invention is to provide at low cost a digital
camera in which noise is prevented from occurring.
An imaging apparatus of the present invention comprises: a CCD
imager of an interline transfer scheme having a plurality of light
receiving elements and a plurality of vertical transfer registers;
a color filter having a plurality of color elements arranged such
that one of the color components corresponds to one of the light
receiving elements; and a pulse generator for generating a drive
pulse to drive the CCD imager; wherein the color filter has a vertical
column arranged with a plurality of colors of color elements, and
the drive pulse is a pulse to drive the CCD imager such that charges
of a same color of color elements are mixed together on a corresponding
vertical transfer register to the vertical column.
According to this invention, the CCD imager of an interline transfer
scheme has a plurality of light receiving elements and a plurality
of vertical transfer registers while a color filter has a plurality
of color elements, each of which corresponds to associated one of
the light receiving elements. The CCD imager is driven by a drive
pulse generated by a pulse generator. Here, the color filter has
a vertical column arranged with a plurality of color elements. Also,
the drive pulse is a pulse to drive the CCD imager such that the
charges of a same color of the color components are mixed together
on a corresponding one of the vertical transfer registers to the
vertical column.
The drive to the CCD imager such that the charges of a same color
of the color elements are mixed together provides a filtering process
to be performed within the CCD imager, thereby removing aliasing
components. Accordingly, there is no necessity of newly providing
a filter circuit to remove noise.
In one embodiment of the invention, the drive pulse includes a
first read pulse to read a first charge produced by a first light
receiving element onto the corresponding vertical transfer register,
a vertical transfer pulse to transfer the first charge in a vertical
direction, and a second read pulse to read a second charge produced
by a second light receiving element onto the vertical transfer register
when the first charge has been transferred in the vertical direction
by a predetermined distance. Here, the first light receiving element
and the second light receiving element have a same color of color
elements.
Preferably, the vertical column is arranged alternately with two
color of colors elements, and the predetermined distance corresponding
to a length of two light receiving elements in the vertical direction.
In another embodiment of the invention, the color filter is a filter
arranged with primary colors of color elements in a Bayer arrangement.
In still another embodiment of the invention, the vertical transfer
register is formed by a plurality of metals, and at least three
of the metals is assigned to one of the light receiving elements.
A digital camera according to the present invention comprises a
CCD imager of an interline transfer scheme having a plurality of
light receiving elements and a plurality of vertical transfer registers;
a color filter having a plurality of color elements arranged such
that one of the color components corresponds to one of the light
receiving elements; and a driver for driving the CCD imager; wherein
the color filter has a vertical column arranged with a plurality
of colors of color elements, and the drive means driving the CCD
imager such that charges of a same color of color elements are mixed
together on a corresponding vertical transfer register to the vertical
column.
According to this invention, the CCD imager of an interline transfer
scheme has a plurality of light receiving elements and a plurality
of vertical transfer registers while a color filter has a plurality
of color element each of which correspond to associated one of the
light receiving elements. The CCD imager is driven by a drive means.
Here, the color filter has a vertical column arranged with a plurality
of color elements. Also, the driver drives the CCD imager such that
the charges of a same color of the color components are mixed together
on a corresponding one of the vertical transfer registers to the
vertical column.
The drive to the CCD imager such that the charges of a same color
of the color elements are mixed together provides a filtering process
to be performed within the CCD imager, thereby removing aliasing
components. Accordingly, there is no necessity of newly providing
a filter circuit to remove noise.
In one embodiment of the invention, the drive means includes a
first read means to read a first charge produced by a first light
receiving element onto the vertical transfer register, a vertical
transfer means to transfer the first charge in a vertical direction,
and a second read means to read a second charge produced by a second
light receiving element onto the vertical transfer register when
the first charge has been transferred in the vertical direction
by a predetermined distance. Here, the first light receiving element
and the second light receiving element have a same color of color
elements.
Preferably, the vertical column is arranged alternately with two
colors of color elements, and the predetermined distance corresponding
to a length of two light receiving elements in the vertical direction.
In another embodiment of the invention, the color filter is a filter
arranged with primary colors of color elements in a Bayer arrangement.
In still another embodiment of the invention, the vertical transfer
register is formed by a plurality of metals, and at least three
of the metals being assigned to one of the light receiving elements.
In yet another embodiment of the invention, an exposure means exposes
a subject image to the CCD imager. Here, a calculation means calculates
an optimal amount of exposure by the CCD imager. A setting means
sets the optimal amount of exposure to the exposure means. A disabling
means disables the second read means depending upon the optimal
amount of exposure.
Preferably, the optimal amount of exposure is defined based on
a shutter speed, and the disabling means disabling the second read
means when the shutter speed is higher than a predetermined value.
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 CCD imager;
FIG. 3 is an illustrative view showing a primary color filter;
FIG. 4 is an illustrative view showing part of operation of the
FIG. 1 embodiment;
FIG. 5 is an illustrative view showing part of operation in a thinning-out
reading mode;
FIG. 6 is an illustrative view showing part of operation in a pixel-mixing
reading mode;
FIG. 7 is a block diagram showing an example of a filter;
FIG. 8 is a block diagram showing an example of TG;
FIG. 9 is a timing chart showing part of operation in a thinning-out
reading mode;
FIG. 10 is a timing chart showing another part of operation in
the thinning-out reading mode;
FIG. 11 is a timing chart showing still another part of operation
in the thinning-out reading mode;
FIG. 12 is a timing chart showing part of operation in the pixel-mixing
reading mode;
FIG. 13 is a timing chart showing another part of operation in
the pixel-mixing reading mode;
FIG. 14 is a timing chart showing still another part of operation
in the pixel-mixing reading mode;
FIG. 15 is a flowchart showing part of operation in the FIG. 1
embodiment;
FIG. 16 is a flowchart showing another part of operation in the
FIG. 1 embodiment; and
FIG. 17 is an illustrative view showing a complementary color filter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a digital camera 10 of this embodiment includes
a lens 12. An incident optical image from the lens 12 is passed
through an aperture-stop unit 16 and then provided to a CCD imager
20 of an interline transfer scheme provided on an imaging apparatus
14. The CCD imager 20 has a plurality of light receiving elements
20a formed as shown in FIG. 2. Each light receiving element 20a
constitutes a pixel for the CCD imager 20. At a front of the light
receiving elements 20a is provided a primary color filter 20d having
color elements R, G and B in a Bayer arrangement. Each light receiving
element 20a has any one of color elements R, G and B. That is, one
color element corresponds to one light receiving element. The subject
image is passed through the primary color filter 20d thus configured
and then provided to the light receiving elements 20a where photoelectric
conversion is conducted on the image.
If it is considered herein that the primary color filter 20a is
a gathering of color blocks each formed by 2 lines X 2 pixels, then
the color block has a color element G on >one diagonal line and
color elements R and B on the other diagonal line. A plurality of
such color blocks exist throughout the primary color filter 20a
so that the color blocks are adjacent to one another in both vertical
and horizontal directions. Meanwhile, if considering vertical columns
forming the primary color filter 20a, color elements R and G are
alternately arranged at an interval of one pixel on a certain vertical
column while color elements G and B are alternately placed at an
interval of one pixel on another vertical column. That is, on any
vertical column two color elements are alternately arranged at an
interval of one pixel.
Referring back to FIG. 2, the CCD imager 20 includes a plurality
of light receiving elements 20a corresponding to respective pixels,
a plurality of vertical transfer registers 20b for vertically transferring
the charges photoelectrically converted and stored by the light
receiving elements 20a, and a horizontal transfer register 20c provided
at the ends of the vertical transfer registers 20b to horizontally
transfer the charges transferred through the vertical transfer registers
20b. The CCD imager 20 is driven by drive pulses outputted from
a timing generator (TG) 22. Here, the drive pulses involve a read
pulse to read charges out of the light receiving element 20a onto
the vertical transfer register 20b, a vertical transfer pulse to
vertically transfer the read charges line by line, a horizontal
transfer pulse to horizontally transfer the charges over the horizontal
transfer register 20c, and a sweep-out pulse to sweep out onto an
overflow drain (not shown) the charges created by the light receiving
elements 20a during a non-exposure time, or charge non-storage period.
If a camera mode is established by a mode set button 46 and a release
button 48 is pushed, a pre-exposure is first effected, to thereby
provide charges to be read out of the CCD imager 20. During the
pre-exposure, the TG 22 controls an output period of a sweep-out
pulse depending upon initial shutter speed data set by a microcomputer
40. As shown in FIG. 4, a sweep-out period starts at a beginning
of a 1-frame period being considered. An end time of the sweep-out
period is controlled by the shutter speed data. In this manner,
the charge storage period is varied to realize an exposure with
a desired shutter speed (exposure time). Note that the technique
of controlling a shutter speed using a sweep-out pulse output period
is well-known as an electronic shutter function.
The output pixel signal (camera signal) of the CCD imager 20 is
converted by an A/D converter 24 into a digital signal, or pixel
data. This pixel data is written onto a RAM 26 by a write/read control
circuit 28. The pixel data stored on the RAM 26 is read out by the
same write/read control circuit 28 and inputted to an arithmetic
operation circuit 30.
The input pixel data has any one of the color components R, G and
B. The arithmetic operation circuit 30 performs color interpolation
and YUV conversion on the pixel data, thus creating Y data, U data
and V data. Among these, the Y data is inputted to a weighting circuit
32. The weighting circuit 32 multiplies the Y data by a weighting
amount held within a weighting amount table 34. The weighting amount
table 34 receives reading address data sent from the write/read
control circuit 28, and outputs a corresponding weighting amount.
The Y data is subjected to a weighting process using this weighting
amount, thereby making possible center-weighted photometry. The
Y data outputted from the weighting circuit 32 is integrated at
an interval of a 1-frame period by an integrator 36. An arithmetic
operator 38 divides the integration data outputted from the integrator
36 by a sum of weighting to calculate a luminance evaluation value
to be evaluated upon exposure adjustment. Incidentally, the U data
and V data calculated together with the Y data by the arithmetic
operator 30 are delivered to a (not-shown) white balance adjustment
circuit.
The microcomputer 40 fetches the luminance evaluation value outputted
from the arithmetic operator 38, and updates a shutter speed depending
upon the luminance evaluation value. After calculating an optimal
shutter speed (optimal exposure time), the microcomputer 40 effects
a main exposure, producing a camera signal. The camera signal is
delivered through a switch SW1 to a signal processing circuit 42
where the signal is subjected to a predetermined processing and
then stored to a recording medium 44.
The microcomputer 40 sets either of a thinning-out reading scheme
or a pixel-mixing reading scheme onto the TG 22 depending upon the
optimal shutter speed. Considering vertically-succeeding 4 pixels,
in the thinning-out reading scheme charges are read out of predetermined
2 pixels of these 4 pixels. On the other hand, in the pixel-mixing
reading scheme charges are read out of the all 4 pixels and the
pixels with a same color component are mixed with. Accordingly,
even if any scheme is set, a resulting camera signal will have the
number of pixels.
With reference to vertically-lined pixels as shown in FIG. 5(A),
FIG. 5(B), FIG. 6(A) and FIG. 6(B), the reading schemes are explained
in greater detail. The vertical transfer register 20b is formed
by a plurality of metals (electrodes) M, wherein one light receiving
element 20a (pixel) is assigned with three metals M. Because the
color filter 20d is a primary color filter having R, G and B in
a Bayer arrangement, an odd-numbered vertical column (odd numbered
column) has pixels R and B alternately arranged at an interval of
1 pixel while an even-numbered vertical column (even numbered column)
has pixels G and B alternately placed at an interval of 1 pixel.
Considering the three metals M assigned to each pixel, a pulse VI
is applied to an uppermost-positioned metal M. A pulse V3 is applied
to a central metal M. A pulse V2A or V2B is applied to an lowermost-positioned
metal M. The destinations to be applied by the pulses V2A and V2B
are switched at an interval of 2 pixels. That is, if on an odd-numbered
column a pulse V2A is applied to R and G pixels as a former half
of succeeding pixels R, G, R and G, a pulse V2B will be given to
a latter half of pixels R and G. Also on an even-numbered column,
when a V2A pulse is applied to a former half of pixels G and B of
the succeeding 4 pixels, a pulse V2B will be given to the pixels
G and B as a latter half.
In the CCD imager 20 having light receiving elements each assigned
with three metals M as above, it is possible to perform progressive
scanning of pixels. This is meant to transfer the charges read out
of adjacent light receiving elements in a separate fashion even
where charges are simultaneously read from all the light receiving
elements. That is, even during all-pixel reading, the signals R,
G and B obtained from the pixels are outputted from the CCD imager
20 without being mixed with each other.
Referring to FIG. 5(A) and FIG. 5(B), if a thinning-out reading
scheme is selected, the reading charges from the pixels to which
the V2B pulse is applied suspended so that only the pixels applied
by the V2A pulse are read of charges therefrom. As a result of this,
vertically-succeeding two pixels are read out at an interval of
2 pixels. On an odd-numbered column, signals R4, G4, R2 and G2 are
read out and vertically transferred over a corresponding vertical
transfer register 20b in a separate fashion. On the other hand,
on an even numbered column, signals G4, B4, G2 and B2 are read out
and vertically transferred over a corresponding vertical transfer
register 20b in a separate manner. That is, when a thinning-out
reading scheme is selected, the color blocks to be read out are
those existing every other block with respect to the vertical direction.
The vertically-transferred pixel signals are then horizontally transferred
on a line-by-line basis. The camera signal outputted from the CCD
imager 20 contains all the color components of R, G and B.
Referring to FIG. 6(A) and FIG. 6(B), when a pixel-mixing reading
scheme is selected, charges are read out of all the pixels. In such
a case, charges are first read from the pixels applied by the V2A
pulse, and then the pixels applied by the V2B pulse are read of
charges when the read charges have been transferred by two pixels.
On an odd numbered column, signals R4, G4, R2 and G2 are first read
onto and transferred over the vertical transfer register. After
vertical transfer by two lines has been completed, signals R3, G3,
R1 and G1 are read out. As a result of this, the charges of a same
color element are mixed with each other, thereby providing signals
(R3+R4), (G3+G4), (R1+R2) and (G1+G2). On an even numbered column,
signals G4, B4, G2 and B2 are first read onto the vertical transfer
register 20b. When these signals have been vertically transferred
by 2 lines, signals G3, B3, G1 and B1 are read onto the same vertical
register 20b. This provides signals (G3+G4), (B3+B4), (G1+G2) and
(B1+B2).
That is, if a pixel-mixing reading scheme is selected, pixel signals
are first read out of the color blocks positioned every other block
with respect to the vertical direction. When the pixel signals have
been vertically transferred by 2 lines, pixel signals are then read
from the remaining color blocks. This causes mixing together of-the
pixel signals of a same color component. The mixed pixel signals
are vertically transferred in a manner of not mixed with different
color components, and then horizontally transferred on a line-by-line
basis. That is, a camera signal containing all the color components
R, G and B is outputted from the CCD imager 20.
In a thinning-out reading scheme, an aliasing component will be
included in the camera signal according to a sampling theorem. Consequently,
noise will appear unless an aliasing component is removed from the
camera signal by using a filtering process. Contrary to this, in
the pixel-mixing reading scheme when one pixel signal has been vertically
transferred by 2 lines, the other pixel signal is read out, followed
by mixing the both pixel signals. This transfer scheme is equivalent
to a filtering process, as shown in FIG. 7. That is, considering
signals R1 and R2, a signal R1 is read out with a delay to a signal
R2, followed by adding together the both. Where a pixel-mixing reading
scheme is selected, a filtering process is performed in this manner,
whereby an aliasing component is removed from the camera signal.
The TG 22 for charge transfer is configured as shown in FIG. 8.
An H counter 22a counts the horizontal number of pixels. The horizontal
count value is reset responsive to a picture taking instruction
or horizontal synchronizing signal given from the microcomputer
40, and incremented in response to a pixel clock. On the other hand,
a V counter 22b counts the vertical number of lines. The vertical
count value is reset responsive to a picture taking instruction
or vertical synchronizing signal, and incremented responsive to
a horizontal synchronizing signal. The horizontal and the vertical
count values are both delivered to decoders 22c-22k. The decoder
22c creates a charge sweep-out pulse SUB based on these count values
and shutter speed data given from the microcomputer 40. Also, the
decoder 22d creates a horizontal transfer pulse HI (pulse HI) from
an input count values. The decoders 22e and 22f respectively create
a vertical transfer pulse VI (pulse, V1) and a vertical transfer
pulse V3 (pulse V3) from the count values.
Furthermore, the decoders 22g-22k respectively create timing pulses
XV2A, XSGA, XV2B1, XV2B2 and XSGB. Among them, the timing pulses
XV2A and XSGA are supplied directly to a driver 22m. On the other
hand, the timing pulses XV2B1 and XV2B2 are supplied to the driver
22m through a switch SW2 while the timing pulse XSGB is directly
supplied to the driver 22m. The microcomputer 40 connects the switch
SW2 to a decoder 22i side when a thinning-out reading scheme is
selected, and connects the switch SW2 to a decoder 22j side when
a pixel-mixing reading scheme is selected. Consequently, during
thinning-out reading, a timing pulse XV2B1 is inputted to a driver
22n. During pixel-mixing reading, a timing pulse XV2B2 is inputted
to the driver 22n. The drivers 22m and 22n respectively create a
vertical transfer pulse V2A (V2A pulse) and a vertical transfer
pulse V2B (V2B pulse) based on timing pulses supplied.
As can be seen in FIG. 9 and FIG. 12, the pulses HI, VI, V2A and
V3 are common between those reading schemes whereas the pulse V2B
is different depending upon a reading scheme. During thinning-out
reading, only the pulse V2A assumes a positive polarity in a period
A with a result that charges are read out of the pixels applied
by the V2A pulse. That is, charge reading is made impossible from
the pixels applied by the V2B pulse. Meanwhile, during pixel-mixing
reading, in the same period A only the pulse V2A assumes a positive
polarity and then the pulse V2B becomes a positive polarity. Consequently,
charges are read out of the pixels applied by the V2A pulse and
then charges are read from the pixels applied by the V2B pulse.
Note that the pulses V2A and V2B have respective positive polarity
portions serving as read-out pulses.
When a thinning-out reading scheme is selected, the respective
pulses vary in the period A hi a manner as shown in FIG. 10. When
the pulse V2A turns into a plus level, charges are read from the
corresponding pixels onto the vertical transfer register. After
charge reading out, the pulses V2A and V2B assume a minus level
twice, transferring vertically the charges by 2 lines. As can be
seen in FIG. 11, the pulses V2A and V2B become a minus level in
other predetermined timing than the period A. In almost the same
timing, the pulses VI and V3 also become a minus level. As a result,
the charges are transferred in the vertical direction. The vertically
transferred charges are thereafter horizontally transferred by the
pulse HI and then outputted from the CCD imager 20.
When a pixel-mixing reading scheme is selected, the pulses in the
period A vary in a manner as shown in FIG. 13. The pulse V2A assumes
a plus level once, and then the pulses V2A and V2B simultaneously
assume a minus level twice. This causes the first-read charges to
be vertically transferred by 2 lines. Subsequently, the pulse V2B
assumes a plus level once, and the charges read out in response
thereto are mixed with the vertically-transferred charges. In other
periods than the period A, the pulses vary in a manner shown in
FIG. 14. As a result of this, the mixed charges are transferred
in the vertical direction. The mixed charges, after vertical transfer,
are horizontally transferred by the pulse H1.
The microcomputer 40 performing processing represented by a flowchart
shown in FIG. 15 and FIG. 16 to calculate a main-exposure amount
and record a taken subject image onto a recording medium 44. Note
that the process of this flowchart commences in response to pushing
the release button 48.
First, in step SI setting is made on aperture stop to a predetermined
F value, and in step S3 an exposure time (shutter speed) is initialized.
That is, initial shutter speed data of 1/250 second is set onto
the TG 22. Subsequently, in step S4 the switch SW2 is switched to
a decoder 22i side to set a thinning-out reading scheme onto the
TG 22, and in step S5 an instruction is provided to the TG 22 to
take a picture. The TG22 performs a pre-exposure according to the
shutter speed data setting, and reads out created charges by a thinning-out
reading scheme.
The microcomputer 40 in step S7 fetches a luminance evaluation
value outputted from the arithmetic operator 38, based on a camera
signal obtained by the pre-exposure. The microcomputer 40 in step
S9 then calculates a next-time shutter speed. Specifically, the
luminance evaluation value is compared with a target evaluation
value to be obtained in an optimal exposure state, calculating a
shutter speed that the luminance evaluation value is coincident
with the target evaluation value. For example, if the luminance
evaluation value is "50" and the target evaluation value
is "100", then the luminance is half of that of an optimal
state and, accordingly, a next-time exposure time is set to be 1/125
second. The microcomputer 40 in step S11 updates the shutter speed
data to be set to the TG22, and in step S13 determines whether or
not the process of the steps S5-S11 has been executed three times
or not or not. That is, this process is repeated three tunes in
order to accurately calculate a shutter speed at which a desired
exposure is to be obtained (optimal shutter speed).
If determined "YES" in the step S13, the microcomputer
40 in step S15 compares the optimal shutter speed (optimal exposure
time) with time data of 1/1000 second. If the optimal exposure time
is equal to or greater than 1/1000second, then in step S17 the switch
SW2 is switched to the decoder 22j side to set a pixel-mixing reading
scheme. Then, the process proceeds to step S19. Meanwhile, if the
optimal exposure time is less than 1/1000 second, the process proceeds
to step S19 while maintaining the thinning-out reading scheme. Accordingly,
in the case that the optimal exposure time is for example 1/500
second, then a pixel-mixing reading scheme will be selected.
Because this embodiment employs an electronic shutter of FIG. 4
for shutter control, required charges are stored after sweeping
away unwanted charges. Charge reading out is conducted when a predetermined
storage period has elapsed. This means that, in the pixel-mixing
reading scheme for reading out pixels at different timing, the higher
the increase in shutter speed the greater the deviation in timing
of reading increases. That is, as the exposure time decreases the
difference increases between a charge amount to be read out earlier
and a charge amount to be read later. On the contrary, this embodiment
switches between the charge reading schemes depending upon an optimal
shutter speed value. Note that a change-over threshold was taken
1/1000 second because it requires 1/1000 second to transfer read-out
charges by 1 line.
The microcomputer 40 in step S19 instructs the TG22 to take a picture.
As a result of this, a main exposure is effected at an optimal shutter
speed. This produces charges to be read out by a desired scheme.
If a camera signal is outputted from the CCD imager 20 in this manner,
the microcomputer 40 in step S21 performs a recording process. The
camera signal is inputted through the switch SW1 to the signal processing
circuit 42 where it is subjected to a predetermined process. The
signal processing circuit 42 outputs a still image signal to be
recorded on the recording medium 44.
According to this embodiment, by selecting a pixel-mixing reading
scheme, a filter process, as shown in FIG. 14, is performed in the
CCD imager 20. This can eliminate aliasing components from a camera
signal without the necessity of adding a filter circuit. Also, because
the pixel-mixing reading scheme was selected only when the optimal
shutter speed is low, there is no possibility of occurring deviation
in charge amount largely between the charges to be first read out
and those to be read subsequently.
Incidentally, because this embodiment has been explained using
an aperture-stop preference mode, it is natural that this invention
is applicable also to a shutter speed preference mode or program
AE mode. In the shutter speed preference mode the exposure amount
is changed by controlling a stop amount while in the program AE
mode the exposure amount is varied by controlling both the shutter
speed and aperture stop. Consequently, it is possible to obtain
a camera signal without introducing aliasing components by limiting
the shutter speed to be set in the shutter speed preference mode
to a speed less than 1/1000 second.
Also, although this embodiment was explained on the case to taking
a still picture, it is needless to say that this invention is also
applicable in shooting a motion picture. Meanwhile, this invention
is also applicable to a through-image mode in which motion pictures
(through-pictures) are displayed in real time on a liquid crystal
display.
Furthermore, although in this embodiment the shutter speed was
controlled by the electronic shutter, the shutter speed may be controlled
by so-called a mechanical shutter in taking a still picture. Also,
although in this embodiment a thinning-out reading scheme was set
during a pre-exposure, it is of course possible to set a pixel-mixing
reading scheme in place thereof. Furthermore, although this embodiment
employed the primary color filter having R, G and B color components
in the Bayer arrangement, a complimentary color filter having color
components of Ye, Cy, Mg and G as shown in FIG. 17 may be used in
place of the primary color filter.
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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