Digital Camera Patent Abstract
In a digital camera, a gain for a variable gain amplifier is controlled
by a controller so that when a signal level of an image signal for
a CCD is corrected by the variable gain amplifier, a quantization
error or an exposure error generated when a shutter speed is set
by a unit of CCD electric charge sweep-away pulse will be offset.
Digital Camera Patent Claims
What is claimed is:
1. A digital camera having a CCD as an image pickup device for
imaging an object and setting a shutter speed by a pulse unit for
electric charge sweep-away control for said CCD comprising:
a variable gain amplifier for correcting a signal level of an image
signal for said CCD;
a control means for controlling a gain in said variable gain amplifier
so that quantization errors generated when a shutter speed is set
by a pulse unit for sweeping away an electric charge in said CCD
will be offset.
2. A digital camera according to claim 1; wherein said controller
has a data table which maintains a shutter speed set against a time
value (TV) in exposure adjustment and a quantization error in a
tabular format.
3. A digital camera according to claim 1; wherein said controller
controls a gain in said variable gain amplifier so that, of the
quantization error s, especially a quantization error generated
when a shutter speed is set to a high-speed side will be offset.
4. A digital camera according to claim 3; wherein said controller
has a data table which maintains a shutter speed set against a time
value (TV) in exposure adjustment and a quantization error in a
tabular format.
5. A digital camera having a CCD as an image pickup device for
imaging an object and setting a shutter speed by a pulse unit for
electric charge sweep-away control for said CCD comprising:
a digital gain adjuster for correcting a signal level of an image
signal for said CCD; and
a controller for controlling a gain in said digital gain adjuster
so that quantization errors generated when a shutter speed is set
by a pulse unit for sweeping away an electric charge in said CCD
will be offset.
6. A digital camera according to claim 5; wherein said digital
gain adjuster comprises multipliers provided for each of RGB and
adjusts a signal level of an image signal by multiplying RGB image
signals inputted into said multipliers by gain data computed by
said controller.
7. A digital camera having a CCD as an image pickup device for
imaging an object and setting a shutter speed by a pulse unit for
electric charge sweep-away control for said CCD comprising:
a variable gain amplifier for correcting a signal level of an image
signal for said CCD;
a digital gain adjuster for correcting a signal level of an image
signal for said CCD; and
a controller for controlling a gain in at least one of said variable
gain amplifier and said digital gain adjuster so that quantization
errors generated when a shutter speed is set by a pulse unit for
sweeping away an electric charge in said CCD will be offset.
8. A digital camera according to claim 7; wherein said controller
controls a gain in said variable gain amplifier so that, of said
quantization errors, a quantization error generated when a shutter
speed is set to the high-speed side will be offset, and also controls
a gain in said digital gain adjuster so that, of said quantization
errors, a quantization error generated when a shutter speed is set
to the low-speed side will be offset.
9. A digital camera having a CCD as an image pickup means for imaging
an object and setting a shutter speed by a pulse unit for electric
charge sweep-away control for said CCD comprising:
a variable gain amplifying means for correcting a signal level
of an image signal for said CCD;
a control means for controlling a gain in said variable gain amplifying
means so that quantization errors generated when a shutter speed
is set by a pulse unit for sweeping away an electric charge in said
CCD will be offset.
10. A digital camera according to claim 9; wherein said control
means has a data table which maintains a shutter speed set against
a time value (TV) in exposure adjustment and a particular quantization
error in a tabular format.
11. A digital camera according to claim 9; wherein said control
means controls a gain in said variable gain amplifying means so
that, of the quantization errors, especially a quantization error
generated when a shutter speed is set to a high-speed side will
be offset.
12. A digital camera according to claim 11; wherein said control
means has a data table which maintains a shutter speed set against
a time value (TV) in exposure adjustment and a particular quantization
error in a tabular format.
13. A digital camera having a CCD as an image pickup means for
imaging an object and setting a shutter speed by a pulse unit for
electric charge sweep-away control for said CCD comprising:
a digital gain adjusting means for correcting a signal level of
an image signal for said CCD; and
a control means for controlling a gain in said digital gain adjusting
means so that quantization errors generated when a shutter speed
is set by a pulse unit for sweeping away an electric charge in said
CCD will be offset.
14. A digital camera according to claim 13; wherein said digital
gain adjusting means comprises multipliers provided for each of
RGB and adjusts a signal level of an image signal by multiplying
RGB image signals inputted into said multipliers by gain data computed
by said control means.
15. A digital camera having a CCD as an image pickup means for
imaging an object and setting a shutter speed by a pulse unit for
electric charge sweep-away control for said CCD comprising:
a variable gain amplifying means for correcting a signal level
of an image signal for said CCD;
a digital gain adjusting means for correcting a signal level of
an image signal for said CCD; and
a control means for controlling a gain in at least one of said
variable gain amplifying means and said digital gain adjusting means
so that quantization errors generated when a shutter speed is set
by a pulse unit for sweeping away an electric charge in said CCD
will be offset.
16. A digital camera according to claim 15; wherein said control
means controls a gain in said variable gain amplifying means so
that, of said quantization errors, a quantization error generated
when a shutter speed
is set to the high-speed side will be offset, and also controls
a gain in said digital gain adjusting means so that, of said quantization
errors, a quantization error generated when a shutter speed is set
to the low-speed side will be offset.
Digital Camera Patent Description
FIELD OF THE INVENTION
The present invention relates to a digital camera, and more particularly
to a digital camera which enables a wide and correct exposure control
only with an electronic shutter by offsetting a quantization error
or an exposure error generated when a shutter speed is set by a
pulse unit for sweeping away an electric charge in a CCD by controlling
a gain in a variable gain amplifier.
BACKGROUND OF THE INVENTION
As a conventional type of digital camera, there has been disclosed,
for instance, in Japanese Patent Laid-Open Publication No. HEI 2-60378
with the title of "Imaging Apparatus" (First Example of
Conventional Technology), an imaging apparatus with improved convenience
in use realized by controlling a diaphragm, a shutter speed of an
imaging unit and the gain in the variable gain amplifier according
to a signal level of an output signal from or an input signal to
the variable gain amplifying circuit.
Also disclosed in Japanese Patent Laid-Open Publication No. HEI
1-288070 with the title of "Electronic Imaging Apparatus"
(Second example of conventional technology) is an apparatus which
controls a gain relating to optoelectronic conversion output from
an imaging unit dependent on an exposure rate according to a gain
control signal given by a gain control unit, obtains a signal indicating
a value corresponding to a shortage of the actual exposure rate
from a specified exposure rate as a gain control signal, supplies
said gain control signal to said control unit, and continues an
imaging operation at a continuously imaging speed set at the point
of time with a unit for preserving an operation mode with preference
in a continuously imaging speed even under conditions or in a region
outside the optimal exposure conditions.
In the second example of conventional technology described above,
a shuttering second time (a continuously imaging speed in the continuously
imaging mode) set by a photographer can be maintained, and in a
case where exposure is short in the continuously imaging mode, the
shortage in exposure is compensated by gain control for an image
signal, whereby it becomes possible to obtain an image with an optimal
quantity of light.
However, in the conventional type of digital cameras as described
above, a speed of an electronic shutter can be set only by a pulse
XSUB unit for sweeping away an electric charge in a CCD sensor,
and for this reason as the shutter speed is set to a higher value,
displacement of the actual shutter speed from a theoretical value
(quantization error) becomes larger. Detailed description is made
below for this phenomenon.
FIG. 9 shows configuration of a representative camera based on
the conventional technology. In this figure, the digital camera
based on the conventional technology comprises a lens 401, a mechanism
402 including an auto-focus or the like, a CCD 403, CDS circuit
404, an A/D converter 406, an IPP 107, a DCT 108, a coder 109, an
MCC 110, a RAM (internal memory) 111, a PC card interface 112, a
CPU 421 incorporating a ROM table 421a, a display section 122, an
operating section 123, a transfer section 124, a motor driver 425,
and an SG (signal generating) section 426. Also a dismountable PC
card 150 is connected thereto via the PC card interface 112.
The lens unit comprises the lens 401, the mechanism 402 including
an auto-focus (AF)/diaphragm/filter section, and a mechanical shutter
in the mechanism 402 simultaneously executes exposure of two fields.
The CCD (charge coupled device) 403 converts an image inputted thereto
via a lens unit to an electric signal (analog image data). The CDS
(correlated double sampling) circuit 404 is a circuit for reducing
noises in a CCD type of imaging element. The A/D converter 406 converts
analog image data inputted via the CDS circuit 404 from the CCD
403 to digital image data. Namely, an output signal from the CCD
403 is converted to a digital signal at an optimal sampling frequency
(for instance, an integer number times larger than a subcarrier
frequency of an NTSC signal) by the A/D converter 406.
Also the IPP (Image Pre-Processor) 107 which is a digital signal
processing section, the DCT (Discrete Cosine Transform) 108, and
the coder (Huffman Encoder/Decoder) 109 divide digital image data
inputted from the A/D converter 406 to several portions according
to a color difference (Cb, Cr) and brightness (Y), and subject the
portions to various types of processing for correcting, compressing
or expanding the image. The image compressing/expanding section
107 executes such processing as, for instance, orthogonal transformation
or Huffman encoding/decoding, each of which is one step of image
compression/expansion based on JPEG standard.
Further, the MCC (Memory Card Controller) 110 stores a compressed
image once and records the image via the PC card interface 112 into
the PC card 150 or reads out the image from the PC card 150.
Herein controls for operations of the electronic shutter are provided
upon input of a control signal con 41 from the CPU 421 according
to a control signal group c41 supplied to the CCD 403 by the SG
(control signal generating) section 426. FIG. 10 is a timing chart
for each of a vertical synchronizing signal VD, a horizontal synchronizing
signal HD, a CCD electric charge read pulse XSG1, a continuously
variable shutter control signal TRIG, and a CCD electric charge
sweep-away pulse XSUB, each of which is included in the control
signal group c41.
Also FIG. 10 is a view for illustrating controls over a shutter
speed according to the continuously variable shutter control signal
TRIG. Namely, when the shutter is operated in he ordinary mode,
a terminal for the continuously variable shatter control signal
TRIG is set to open or a potential of a power supply unit, but in
a case where the shutter is operated in the continuously variable
mode, a clock pulse is inputted into the terminal for the continuously
variable shutter control signal TRIG.
Namely, the shutter speed is decided by removing a pulse for the
CCD electric charge sweep-away pulse XSUB within a time frame of
a lagging edge of the CCD electric charge read pulse XSG1 as well
as of the continuously variable shutter control signal TRIG and
stopping the pulse for the CCD electric charge sweep-away pulse
XSUB within a time frame between a lagging edge of the continuously
variable shutter control signal TRIG and the next CCD electric charge
read pulse XSG1. It should be noted that, in a case where the shutter
speed is controlled according to the continuously variable shutter
control signal TRIG as described above, a preset value for the shutter
speed according to a shutter speed control signal described hereinafter
must be set to 1/10000 to broaden the control range.
For the reasons as described above, it is understood that speed
setting for an electric shutter can be made only by a unit of CCD
sensor electric charge sweep-away pulse XSUB.
Next description is made for control over a shutter speed according
to a shutter mode select signal and a shutter speed control signal.
At first, upon input of a shutter mode select signal, in the NTSC
system, the operation mode is set to any of the high-speed shutter
mode in which the shutter speed is faster than 1/60 sec, a low-speed
shutter mode in which the shutter speed is slower than 1/60 sec,
or a no-shutter mode in which a shuttering operation is not executed.
Then in the high-speed shutter mode or in the low-speed shutter
mode, a shutter speed is computed according to the shutter speed
control signal. Namely, as shown in FIGS. 11A and 11B, in the NTSC
system, a load value is read out from the ROM table 421a incorporated
in the CPU 421 for each of the high-speed shutter mode (Refer to
FIG. 11A) and low-speed shutter mode (Refer to FIG. 11B), and the
shutter speed is computed. Namely, if the load value is set to IPP
107, exposure is executed according to the computed shutter speed.
Assuming that LH is a load value, in a case of the high-speed shutter
mode, the shutter speed is computed through the following expression:
The representative shutter speed obtained through this expression
is shown in the chart in FIG. 11A. It should be noted that a figure
without any attended character and D as an attended character to
a figure indicate a decimal number, and "H" as an attended
character to an alphanumerical character indicates a hexadecimal
number. With this, in a case of the NTSC system, it is understood
that a unit of a shutter speed is 63.56 [.mu.s].
Also in a case of the low-speed shutter mode, the shutter speed
is computed through the expression of N=2.times.(FFH-LH) [FLD].
Herein 1 [FLD] indicates 1/60 second, and a product of the FLD value
by 1/60 second becomes the specified shutter speed.
Further FIG. 12 shows an example of EV diagram. Herein the EV diagram
is a view showing a combination of an aperture value AV (Aperture
Value) and a time value TV (Time Value) for achieving a desired
exposure value EV (Exposure Value), and there is a relation of EV=AV+TV
among the exposure value EV, aperture value AV, and time value TV
in the exposure adjustment. A light value Lv (Light Value) is a
value obtained by measuring intensity of light, and there is a relation
of EV=Lv under appropriate exposure. It should be noted that 1/T
is equal to TV-th power of 2, and a square of FNo. is equal to an
AV-th power of 2.
In the example of EV diagram shown in FIG. 12, the F value can
be set only to either F2 or F8, and for switching it, F2 is selected
in a range up to Lv12, and F8 is selected in a faster beyond Lv12.
Further, as only F2 and F8 are available for selecting the F value,
a desired exposure rate is obtained by changing the shutter speed
by a unit of 1/16 TV.
Next description is made for a quantization error in a shutter
speed. Charts shown in FIG. 13, FIG. 14 and FIG. 15 are views for
illustrating a change of a value against each TV value obtained
by a unit of 1/16 TV. Herein the term of the difference (mS) indicates
a value obtained by subtracting a time (mS) for the subsequent value
from a value for the current value.
Namely, FIG. 13, FIG. 14, and FIG. 15 show how the CCD sensor electric
charge sweep-away pulse XSUB unit (63.56 [.mu.s]) affects the exposure.
In the figures, the section with .star-solid. indicates the effect,
and for instance, the difference between a shutter speed when the
VT value is 9.375 and that when the shutter speed is 9.4375 is 0.0639
[mS]=63.9 [.mu.S]. For this reason, a change rate for the shutter
speed required to change the TV value by 1/16 when the TV value
is around 9.375 is 63.9 [.mu.S], which is around 1 XSUB, and from
this it is understood that the TV value may be changed by 1/16 for
a change of 1 XSUB.
This is a quantization error due to the CCD sensor electric charge
sweep-away pulse XSUB, and summarizing from FIG. 13, FIG. 14, and
FIG. 15, influence of 1 XSUB to exposure is as shown below.
______________________________________ Difference in Round number
shutter speed by XSUB unit Round number TV (.DELTA.TV = 1/16) (63.56
.mu.S) for .DELTA.TV/XSUB ______________________________________
8.375 127.7 2 1/32 9.375 63.9 1 1/16 10.375 31.5 0.5 1/8 11.375
16.0 0.25 1/4 12.375 8.0 0.125 1/2 13.375 4.0 0.063 1 ______________________________________
Thus, it is understood that the higher the shutter speed is, the
larger a quantization error is.
As described above, in the conventional technology, an operating
speed of the electronic shutter can be made only by the CCD sensor
electric charge sweep-away pulse XSUB, so that, as a shutter speed
is set to a higher value, displacement of the actual shutter speed
from the theoretical value (quantization error) becomes larger.
Further, if a diaphragm (iris) can be set without step, the quantization
error can be offset by controlling the diaphragm (iris), but in
a case where, for instance, the diaphragm (iris) can be set only
step by step (as shown in FIG. 12) due to restrictions in system
designing for the apparatus or to requirements for cost reduction
in the apparatus, the quantization error becomes an exposure error,
and when the shutter speed become higher, it may becomes disadvantageously
unignorable.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a digital camera
which enables appropriate exposure control in a broad range only
with an electronic shutter by offsetting with gain control a quantization
error or an exposure error generated when the shutter speed is set
by a CCD electric charge sweep-away pulse unit.
With the digital camera according to the present invention, when
a signal level of an image signal for a CCD is corrected with a
variable gain amplifier, a gain for the variable amplifier is controlled
by a control unit so that a quantization error or an exposure error
generated when the shutter speed is set by a unit of CCD electric
charge sweep-away pulse will be offset, so that , even in a case
where the diaphragm can be set only step by step due to restrictions
in system designing for an apparatus, or because of requirements
for cost reduction in the apparatus, an exposure error can be reduced
even when the shutter speed becomes higher, whereby it is possible
to provide a digital camera which can execute appropriate exposure
control only with an electronic shutter.
With the digital camera according to the invention, the control
unit controls a gain for a variable gain amplifier so that, of quantization
errors, a quantization error generated when a shutter speed is set
to the high-speed side will be offset, so that it is possible to
provide a digital camera which can use, in gain control for the
variable gain amplifier, a section having linearity in a gain against
a setup value, and is advantageous for system designing with the
same control form as that in gain control for the variable gain
amplifier performed in imaging under low illuminance.
With the digital camera according to the invention, the control
unit generates a signal for gain control for a variable gain amplifier
by referring to a shutter speed set for a time value (TV) in exposure
adjustment as well a to a data table in which a quantization error
then is stored in a tabular form, so that complicated computing
is not required with computing load to the control unit reduced,
also the processing can be executed at a higher speed, and further
appropriate exposure control can be made without repeating measurement
of light with a CCD when a gain for the variable gain amplifier
is changed by offsetting the quantization error; whereby it is possible
to provide a digital camera which can generally execute required
operations at a higher speed.
With the digital camera, when a signal level of an image signal
for a CCD is corrected with a digital gain adjusting unit, the control
unit controls a gain for the digital gain adjusting unit so that
a quantization error or an exposure error generated when a shutter
speed is set by a unit of CCD electric charge sweep-away pulse (included
in a control signal group c1) will be offset, so that an exposure
error can be reduced when a shutter speed becomes higher even in
a case where the diaphragm can be set only step by step due to restrictions
in system designing for an apparatus or because of requirements
for cost reduction in the apparatus; whereby it is possible to provide
a digital camera which can execute appropriate exposure control
in a broad range only with an electronic shutter. Also the digital
gain adjusting unit can execute gain adjustment in a broad range,
so that it is possible to correct a signal level of an image signal
in a broad range.
With the digital camera according to the invention, the digital
gain adjusting unit comprises multipliers provided for R, G, and
B, and a signal level of an image signal is adjusted by multiplying
image signals for R, G and B inputted to the multipliers by the
gain data computed by the control unit; whereby it is possible to
provide a digital camera which can digitally correct a signal level
of an inputted image signal with simple configuration.
With the digital camera according to the invention; when a signal
level of an image signal for a CCD is corrected with a variable
gain amplifier and/or a digital gain adjusting unit, a gain for
the variable gain amplifier and/or the digital gain adjusting unit
is controlled by the control unit so that a quantization error or
an exposure error generated when the shutter speed is set by a unit
of CCD electric charge sweep-away pulse (included in the control
signal group c1) will be offset, so that, even in a case where the
diaphragm can be set only step by step due to restrictions in system
designing for an apparatus or because of requirements for cost reduction
in the apparatus, an exposure error can be reduced even when the
shutter speed becomes higher; whereby it is possible to provide
a digital camera which can execute exposure control in a broad range
with an electronic shutter. Also it becomes possible to execute
gain adjustment in a broad range, so that it becomes possible to
correct a signal level of an image signal in a broad range.
With the digital camera according to the invention, the control
unit controls a gain for a variable gain amplifier so that, of quantization
errors, a quantization error generated when the shutter speed is
set to the high-speed side will be offset, and also the control
unit controls a gain for the digital gain adjusting unit so that,
of the quantization errors, a quantization error generated when
the shutter speed is set to the lower speed side will be offset,
so that a section having linearity in a gain against a setup value
can be used in gain control for the variable gain amplifier, and
also gain adjustment can be executed by the digital gain adjusting
unit for a section having no linearity in a gain for the variable
gain amplifier, so that gain adjustment can be executed in a broad
range, whereby it is possible to provide a digital camera which
can correct a signal level of an image signal in a broad range.
Other objects and features of this invention will become understood
from the following description with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing general configuration of a digital
camera according to Embodiment 1 of the present invention;
FIG. 2 is an explanatory view for illustrating a relation between
a setup value for a gain in an AGC amplifier and a quantization
error in Embodiment 1;
FIG. 3 is a chart showing contents of a ROM table incorporated
in the CPU shown in FIG. 1 (Case 1);
FIG. 4 is a chart showing contents of a ROM table incorporated
in the CPU shown in FIG. 1 (Case 2);
FIG. 5 is a block diagram showing detailed configuration of an
IPP according to Embodiment 2 of the present invention;
FIG. 6 is a flowchart for illustrating a method for computing gain
data multiplied in a digital gain adjusting section.
FIG. 7 is an explanatory view showing a relation between an input
control voltage (V) and an output gain (dB) in an AGC amplifier
according to Embodiment 3 of the present invention;
FIG. 8 is a flowchart for illustrating a method for computing gain
data set in the AGC amplifier as well as in the digital gain adjusting
section.
FIG. 9 is a block diagram showing configuration of a representative
digital camera based on the conventional technology.
FIG. 10 is an explanatory view showing control over a shutter speed
according to a continuously variable shutter control signal;
FIGS. 11A and 11B are explanatory views for a ROM table incorporated
in the CPU, and FIG. 11A shows the high-speed shutter mode, while
FIG. 11B shows the low-speed shutter mode;
FIG. 12 is an explanatory view showing an example of EV diagram;
FIG. 13 is an explanatory view for illustrating change of a value
against each TV value obtained by a unit of 1/16 TV (Case 1);
FIG. 14 is an explanatory view for illustrating change of a value
against each TV value obtained by a unit of 1/16 TV (Case 2); and
FIG. 15 is an explanatory view for illustrating change of a value
against each TV value obtained by a unit of 1/16 TV (Case 3).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Next description is made for outline of the digital camera according
to the present invention as well as for embodiments of the digital
camera according to the present invention with reference to the
related drawings.
In the digital camera according to the present invention, as shown
in FIG. 1, when correcting a signal level of an image signal for
the CCD 103 with the variable gain amplifier 105, a gain in the
variable gain amplifier 105 is controlled by the control unit 121
and 126 so that a quantization error or an exposure error generated
when a shutter speed is set by a CCD electric charge sweep-away
pulse (included in the control signal group c1) will be offset.
With this, in a case where a diaphragm (iris) can be set only step
by step due to restrictions in system designing for the apparatus
or requirements for cost reduction, an exposure error can be reduced
even at a high shutter speed, which enables an appropriate exposure
control in a broad range only with an electronic shutter.
In the digital camera according to the invention, the control unit
121 and 126 control a gain in the variable gain amplifier 105 so
that, of quantization errors, a quantization error generated when
the shutter speed is set to the high-speed side will be offset.
Namely, the control is provided so that, of the shutter speeds which
can be set, a shutter speed higher than a theoretical shutter speed,
which is close to the theoretical shutter speed, is set to offset
a generated quantization error.
Generally in gain control for the variable gain amplifier 105,
if an initial value is set to a value insuring an excellent image,
linearity of gain to a setup value in a direction in which the gain
is lowered is not provided, so that, when the shutter speed is set
as described above, a quantization error is set to the high-speed
side of the shutter speed to execute correction with a higher gain.
With this feature, in gain control for the variable gain amplifier
105, a section having linearity of a gain against a setup value
can be used, and the control form is like that in gain control for
the variable gain amplifier 105 in imaging under low illuminance,
which is advantageous for system designing.
Further, in the digital camera, the control unit 121 and 126 generate
a signal for gain control over the variable gain amplifier 105 by
referring to a data table 121a which stores therein a shutter speed
set for a time value (TV) in exposure adjustment and a quantization
error in the step.
With this, a load for computing to the control unit is reduced
because complicated computing is not required, and the processing
is executed at a higher speed. Also, in a case where there is not
provided the data table 121a, it is necessary to require until an
appropriate exposure rate is obtained light measurement with the
CCD 103 when a gain in the variable gain amplifier 105 is changed,
but also this operation is not necessary and appropriate exposure
control can be executed by offsetting a quantization error, and
also the processing for operations of the entire system can be made
at a higher speed.
In the digital camera according to the invention, as shown in FIG.
1 and FIG. 5, when a signal level of an image signal for the CCD
103 is corrected by the digital gain adjusting unit 1075, a gain
in the digital gain adjusting unit 1075 is controlled by the control
unit 121 so that a quantization error or an exposure error generated
when the shutter speed is set by a CCD electric charge sweep-away
pulse unit (included in the control signal group c1).
With this feature, in a case where a diaphragm (iris) can be set
only step by step due to restrictions in system designing for the
apparatus or requirements for cost reduction, an exposure error
can be reduced even if the shutter speed becomes higher, and also
appropriate exposure control can be executed in a broad range only
with an electronic shutter. Also the digital gain adjusting unit
1075 allows gain control in a broad range, so that it becomes possible
to correct a signal level of an image signal in a broad range.
In the digital camera according to the invention, the digital gain
adjusting unit 1075 comprises multipliers 1075r, 1075g, and 1075b
provided for each of R, B, and G, and a signal level of an image
signal is adjusted by multiplying image signals for RGB inputted
to the multipliers 1075r, 1075g, 1075b by gain data computed with
the control unit 121.
With this feature, a signal level of an inputted image signal can
digitally be corrected with simple configuration.
In the digital camera, as shown in FIG. 1 and FIG. 5, when a signal
level of an image signal for the CCD 103 is corrected by the variable
gain amplifier 105 and/or the digital gain adjusting unit 1075,
a gain in the variable gain amplifier 105 and/or digital gain adjusting
unit 1075 is controlled by the control unit 121 and 126 so that
a quantization error or an exposure error generated when the shutter
speed is set by a CCD electric charge sweep-away pulse (included
in the signal group c1) will be offset.
With this feature, in a case where a diaphragm can be set only
step by step due to restrictions in system designing for an apparatus
or because of requirements of cost reduction for the apparatus,
an exposure error can be reduced even if the shutter speed becomes
higher, and exposure control can be executed in a broad range only
with an electronic shutter. Also it is possible to execute gain
control in a broad range, it is possible to correct a signal level
of an image signal in a broad range.
In a digital camera according to the present invention, the control
unit 121 and 126 control a gain in the variable gain amplifier 105
so that, of quantization errors, a quantization error generated
when the shutter speed is set to a high-speed side will be offset,
while the control unit 121 controls a gain in the digital gain adjusting
unit so that, of the quantization errors, a quantization error generated
when the shutter speed is set to the lower speed side will be offset.
Namely, when, of selectable shutter speeds, a shutter speed close
to the theoretical shutter speed and at the same time in the higher
speed side is selected, a gain in the variable gain amplifier 105
is controlled, while, when, of selectable shutter speeds, a shutter
speed close to the theoretical shutter speed and at the same time
in the lower speed side is selected, a gain in the digital gain
adjusting unit 1075 is controlled to offset a generated quantization
error.
Generally, in gain control for the variable gain amplifier 105,
when an initial value is set to a value insuring an excellent image,
as linearity of a gain against a setup value is not insured in a
direction in which a gain is lowered (a direction in which a gain
is minus), so that, in the variable gain amplifier 105, in a case
where a quantization error is set to a higher speed side of the
shutter speed, a signal level of an image signal is corrected by
raising the gain (assuming that the gain is pulse). On the other
hand, in gain control for the digital gain adjusting unit 1075,
a gain adjustment can be executed in a broad range (in a direction
in which a gain is minus and in a direction where a gain is pulse),
so that, in a case where a quantization error is set to a lower
speed side of the shutter speed, a signal level of an image signal
is corrected by lowering the gain (assuming that the gain is minus).
With this, in gain control for the variable gain amplifier 105,
a section having linearity of a gain against a setup value for the
variable gain amplifier 105 (in a direction where a gain is pulse)
is used, as for a range where there is no linearity of a gain for
the variable gain amplifier 105 (in a direction where a gain is
minus), gain adjustment is executed by the digital gain adjusting
unit 1075, so that gain adjustment can be executed in a broad range,
and a signal level of an image signal can be corrected in a broad
range.
FIG. 1 is a block diagram showing a digital camera according to
one embodiment (Embodiment 1) of the present invention.
In this figure, the digital camera according to this embodiment
comprises a lens 101, a mechanism 102 including an auto-focus or
the like, a CCD 103, a CDS circuit 104, a variable gain amplifier
(AGC amplifier) 105, an A/D converter 106, an IPP 107, a DCT 108,
a coder 109, an MCC 110, a RAM (internal memory) 111, a PC card
interface 112, a CPU 121 incorporating a ROM table 121a, a display
section 122, an operating section 123, a motor driver 125, and an
SG (control signal generating) section 126, a strobe 127, a battery
128, and a DC--DC converter 129. Also a dismountable PC card 150
is connected thereto via the PC card interface 112.
The lens unit comprises the lens 101, the mechanism including an
auto-focus (AF)/diaphragm/filter section or the like, and a mechanical
shutter in the mechanism 102 executes simultaneous exposure to two
fields. The CCD (charge coupled device) 103 converts an image inputted
via the lens unit to an electric signal (analog image data). The
CDS (correlated double sampling) circuit 104 is a circuit for reducing
noises in a CCD type of imaging element.
Also the AGC amplifier 105 corrects a level of a signal subjected
to correlated double sampling in the CDS circuit 104. Further the
A/D converter 106 converts analog image data inputted via the AGC
amplifier 105 from the CCD 103 to digital image data. Namely, an
output signal from the CCD 103 is converted to digital signal via
the CDS circuit 104 and AGC amplifier 105 and also by the A/D converter
105 at an optimal sampling frequency (for instance, an integer number
larger than a subcarrier frequency of an NTSC signal).
Also the IPP (Image Pre-Processor) 107 which is a digital signal
processing section, the DCT (Discrete Cosine Transform) 108, and
the coder (Huffman Encoder/Decoder) 109 divides digital image data
inputted from the A/D converter 106 to several portions according
to a color difference (Cb, Cr) and brightness (Y), and subject the
portions to various types of processing for correcting, compressing
or expanding the image. The image compressing/expanding section
107 executes such processing as, for instance, orthogonal transformation
or Huffman encoding/decoding, each of which is one step of image
compression/expansion based on JOEG standard.
Further, the MCC (Memory Card Controller) 110 stores a compressed
image once and records the image via the PC card interface 112 into
the PC card 150 or reads out the image from the PC card 150.
The CPU 121 controls all operations inside the digital camera according
to instructions from the operating section 123 or according to external
operating instructions from a remote controller or the like now
shown herein. Also power for the camera is inputted from, for instance,
a NiCd, nickel hydrogen, or lithium battery or the like into the
DC--DC converter 129 and supplied into the inside of the digital
camera.
The display section 122 is realized with an LCD, an LED, an EL
or the like, and displays imaged digital data, or recorded image
data having been subjected to processing for expansion, and a state
of the digital camera or other data is displayed on a display screen
in the mode display section. The operating section 123 has buttons
for setting various types of operation mode such as function selection,
or instruction for imaging from the outside.
Herein control over operations of the electronic shutter are executed
upon input of a control signal con1 from the CPU 121 according to
a control signal group c1 supplied from the SG (control signal generating)
section 126 to the CCD 103. The control signal group c1 includes,
like in the conventional technology, a vertical synchronizing signal
VD, a horizontal synchronizing signal HD, a CCD electric charge
read pulse XSG1, a continuously variable shutter control signal
TRIG, a CCD electric charge sweep-away pulse XSUB, a shutter mode
select signal, and a shutter speed control signal, and basic operations
according to the signals are also the same as those in the conventional
technology (Refer to FIG. 10 and FIGS. 11A and 11B).
For the reasons as described above, also in this embodiment, an
operating speed of the electronic shutter is set by a unit of CCD
sensor CCD electric charge sweep-away pulse XSUB like in the conventional
technology.
Also in this embodiment, because of restrictions in system designing
for an apparatus or requirements for cost reduction in the apparatus,
the diaphragm may be set only step by step. Namely, in this case,
for the EV diagram, like in the conventional technology, and also
as shown in FIG. 12, only either one of F2 or F8 can be selected
as an F value, and as for switching of the value, F2 is selected
in a range up to Lv12, and F8 is selected in a range from Lv12 and
on respectively.
Next description is made for gain control for the AGC amplifier,
which is one of the features of this embodiment. Namely, in this
embodiment, when a signal level of an image signal for the CCD 103
is corrected by the AGC amplifier, a gain in the AGC amplifier 105
is controlled by the CPU 121 and SG section 126 so that a quantization
error or an exposure error generated when the shutter speed is set
by a unit of CCD electric charge sweep-away pulse XSUB will be offset.
FIG. 2 is a view illustrating a relation between a gain a setup
value in the AGC amplifier 105 and a quantization error in this
embodiment. FIG. 3 is a chart showing one example of contents of
the ROM table 121a incorporated in the CPU 121. In the figure, 301
shows a TV value and a 1/T value based on theoretical values respectively,
302 shows a TV value and a 1/T value based on load values respectively,
and 303 shows .DELTA.TV and AGC setup value (expressed with decimal
numbers).
The ROM table 121a is a data table which stores therein a shutter
speed set against a time value (TV) in exposure adjustment and a
quantization error in this step. Especially the data table shown
in FIG. 3 is set in a direction in which a quantization error .DELTA.TV
is minus, and an AGC setup value assuming a pulse gain is set to
offset this minus quantization error .DELTA.TV.
In FIG. 3, TV indicates a time value, 1/T indicates a shutter speed,
a load value indicates a shutter speed which the CPU 121 sets in
the IPP 107, .DELTA.TV indicates a difference between TV based on
a theoretical value and that based on a load value, and AGC is a
gain value to be set in the AGC amplifier 105 obtained from the
.DELTA.TV through the relation shown in FIG. 2.
The .DELTA.TV in FIG. 3 indicates a quantization error generated
as a difference between TV based on a theoretical value and that
based on a load value, and the .DELTA.TV (gain) in FIG. 2 indicates
a value corrected as a converted TV value according to a setup value
(AGC setup value) in the AGC amplifier 105 (SG section 126 executing
gain control thereof) when correcting .DELTA.TV in FIG. 3 as a gain
for the AGC amplifier 105. Namely, .DELTA.TV generated as a difference
between a TV value based on a theoretical value and that based on
a load value is corrected as a gain in the AGC amplifier 105 to
obtain appropriate exposure, and a quantity corrected as a gain
according to the AGC setup value is used as .DELTA.TV (gain) in
conversion of a TV value.
For instance, in a case where it is necessary to select TV10 for
obtaining appropriate exposure, a load value corresponding to the
theoretical value TV10 is "263" as shown in FIG. 3. If
the AGC setup value is the initial value (20H) as shown in FIG.
2, a difference .DELTA.TV between a TV value based on a theoretical
value and that based on a load value is -0.0789 as shown in FIG.
3, so that, by setting the AGC setup value to "35", the
.DELTA.TV (gain) is corrected by 0.0789, thus appropriate exposure
being realized.
In the digital camera according to this embodiment, when gain control
for the AGC amplifier 105 is executed by the CPU 121 as well as
by the SG section 126, control is provided so that, of quantization
errors, a quantization error generated when the shutter speed is
set to the higher speed side will be offset.
Generally in gain control for the AGC amplifier 105, if an initial
value of the AGC setup value is set to a value insuring an excellent
image ("20H" in FIG. 2), linearity of a gain against a
setup value is lost in a direction in which a gain is lowered, and
for this reason, when a shutter speed is set, a quantization error
is set so that the shutter speed will be in the higher speed side
to correct the shutter speed by making a gain larger.
For instance, in FIG. 3, when the theoretical value TV is 10.125,
the shutter speed based on the theoretical value is "1/1116.68
[sec]", but an error is generated in the shutter speed in a
load value based on an unit of the CCD electric charge sweep-away
pulse XSUB. Namely, only the values of "263 (shutter speed:
1/1081.53 [sec])" and "262 (shutter speed: 1/1161.36 [sec])"
are available as selectable load values.
Herein the load value "263" is a shutter speed closer
to the theoretical value, but in this embodiment, of the shutter
speeds close to the theoretical value, the load value "262",
which is a shutter speed in the high-speed side, is selected as
the shutter speed. In this case, .DELTA.TV is equal to -0.0566,
so that, by setting the AGC setup value to "34", the .DELTA.TV
(gain) is corrected by "0.0566", thus appropriate exposure
being realized.
As described above, by setting a quantization error in the high-speed
side
of the shutter speed (gain in the plus side), a section having
linearity against a setup value can be used in gain control for
the AGC amplifier 105.
Further, the control form is like that in gain control for the
AGC amplifier 105 executed in imaging under low illuminance, which
is advantageous for system designing. Namely, under low illuminance,
the shutter speed becomes lower, and vibration caused by manual
operation easily occurs. So, when the shutter speed is lower than
a certain value which is, for instance, 1/60 [sec], 1/60 [sec] at
which vibration by manual operation does not occur is selected as
the shutter speed, and the difference .DELTA.TV between the value
and the shutter speed theoretically to be set is used as a gain
for the AGC amplifier 105 for correction.
At last description is made for operations for setting a shutter
speed in this digital camera. At first, an operator selects the
imaging mode via the operating section 123. The CPU determines exposure
according to brightness data from the IPP 107, and controls the
CCD electric charge read pulse XSG and CCD electric charge sweep-away
pulse XSUB according to a result of determination on exposure.
The CPU 121 computes a TV value, decides from the TV value a shutter
speed (load value) to be set in the IPP 107 and an AGC value to
be set in the AGC amplifier 105 by referring to the ROM table 121a
shown in FIG. 3, and sets a gain for the AGC amplifier 105 via the
SG section 126 according to the control signal group C3.
It should be noted that, although an AGC amplifier having no linearity
in the minus side of gain (.DELTA.AT) as shown in FIG. 2 is used
in the embodiment described above, also it is possible to set a
quantization error in the lower side of the shutter speed (namely
gain in the minus side) in a case where an AGC amplifier having
linearity in the minus side of gain is used.
FIG. 4 is a chart showing contents of the ROM table 121a for correcting
a gain to the minus side. For instance, in FIG. 4, when a theoretical
value TV is 10.125, the shutter speed based on the theoretical value
is "1/1116.68 [sec]", but a quantization error is generated
in the shutter speed if a load value based on the CCD electric charge
sweep-away pulse XSUB is used. In this case, as shown in FIG. 4,
the value of "263" (shutter speed: 1/1081.53 [sec]) is
set as a load value.
For this reason, in this case, the quantization error .DELTA.TV
is 0.0461, so that, by setting the AGC setup value to "31",
the .DELTA.TV (gain) is corrected by -0.0461, thus appropriate exposure
being realized.
In Embodiment 1 described above, an example was shown in which
a signal level of an image signal for the CCD 103 is corrected by
controlling a gain for the AGC amplifier 105, but in Embodiment
2 of the present invention, a signal level of an image signal for
the CCD 103 is corrected by controlling a gain for the digital gain
adjusting section 1075 in the IPP 107. For this reason, description
is made only for different portions.
The digital camera according to Embodiment 2 may has the same block
configuration as that of the digital camera (shown in FIG. 1) according
to Embodiment 1.
FIG. 5 is a view showing detailed configuration of the IPP 107
shown in FIG. 1.
The IPP 107 comprises a color separating section 1071 for separating
digital image data inputted from the A/D converter 106 to color
components for R,G, and B; a signal interpolating section 1072 for
interpolating each separated image data for R and B; a pedestal
adjusting section 1073 for adjusting black level of each image data
for R, G, and B; a white balance adjusting section 1074 for adjusting
a white level of each image data for R, G and B; a digital gain
adjusting section 1075 for correcting each image data for R, G,
and B with a gain set by the CPU 121; a gamma conversion section
1076 for subjecting each image data for R,G, and B to .gamma. conversion;
a matrix section 1077 for separating each image data for R, G, and
B to a color difference signal (Cb, Cr) and a brightness signal
(Y); a video signal processing section 1078 for generating a vide
signal depending on the color difference signal (Cb, Cr) and the
brightness signal (Y) and outputting the vide signal to the display
section 122; a CPU I/F 1079 which is an interface with the CPU 121;
and a DCT I/F 1080 which is an interface with the DCT 108.
The digital gain adjusting section 1075 described above has multipliers
1075r, 1075g, 1075b for R, G and B respectively, and image data
for R, G, and B inputted to the multipliers 1075r, 1075g, 1075b
respectively are multiplied by each gain data for R, G, and B set
by the CPU 121 to adjust a signal level of each image data for R,
G, and B.
Also in this embodiment, an operating speed of the electronic shutter
is set by a unit of CCD sensor electronic charge sweep-away pulse
XSUB like in Embodiment 1.
Also in this embodiment, a case is allowable where a diaphragm
can be set only step by step due to restrictions in system designing
for an apparatus or because of requirements in cost reduction for
the apparatus. Namely, as for the EV diagram, like in the conventional
technology, only F2 and F8 are available as an F value as shown
in FIG. 12, and for switching it, F2 is selected in a range up to
Lv12, and F8 is selected in a range from Lv12 and on.
Next description is made for gain control for the digital gain
adjusting section 1075 in the IPP 107 which is a feature in this
embodiment. Namely, in this embodiment, when a signal level of an
image signal for the CCD 103 is corrected with the digital adjusting
section 1075 in the IPP 107, a gain for the digital gain adjusting
section 1075 is controlled by the CPU 121 so that a quantization
error or an exposure error generated when a shutter speed is set
by a unit of CCD electric charge sweep-away pulse XSUB will be offset.
Also in this embodiment, a gain setup value is decided by using
the ROM table 121a used in FIG. 3. For instance, if it is necessary
to set a TV value to 10 for realizing appropriate exposure, a load
value corresponding to the theoretical value of TV10 is "263"
as understood from FIG. 3. Also in this case, a difference .DELTA.TV
between TV based on the theoretical value and that based on the
load value is -0.0789 as understood from FIG. 3, so that appropriate
exposure can be obtained by correcting the .DELTA.TV (gain) in the
digital gain adjusting section 1075 by "0.0789".
Then, description is made for a method of computing gain data multiplied
in the digital gain adjusting section 1075 according to an AGC setup
value with reference to the flowchart shown in FIG. 6.
FIG. 6 is a flowchart for illustrating a method of computing gain
data to be multiplied in the digital gain adjusting section 1075.
At first, description is made for parameters used in the flow chart
in FIG. 6.
A unit of the parameters described below is EV (The same meaning
is provided even with Lv, TV, and AV), and 1/16 EV is 1.
1) agc.sub.-- value: A gain setup value, which corresponds to a
gain (.DELTA.TV) for correcting a quantization error .DELTA.TV in
the table shown in FIG. 3 and is expressed with hexadecimal numbers.
When the quantization error .DELTA.TV in FIG. 3 is minus, the agc.sub.--
value becomes plus. Namely the agc.sub.-- value becomes plus when
a gain is made larger, and becomes minus when a gain is made smaller.
2) agc.sub.-- data: D/A output setting data for the CPU 121, and
a gain for the AGC amplifier 105 can be set with this data.
3) agc.sub.-- def: An input control voltage value for the AGC amplifier,
when a gain for the AGC amplifier 15 is 1 time (D/A setup value
for the CPU)
4) agc.sub.-- data.sub.-- cwe 5-7: Gain data for R, G, and B multiplied
in the multipliers 1075r, 1075g, 1075c in the digital gain adjusting
section 1075 in the IPP 107.
5) from.sub.-- cwe 5-7: Adjusting values for colors for R, G, and
B in the CCD 103
6) agc.sub.-- tbl [agc.sub.-- data.sub.-- calc]: A function for
AGC computing agc.sub.-- tbl [0-32]={32, 33, 34, 36, 38, 39, 41,
43, 45, 47, 49, 51, 53, 56, 58, 61, 64, 66, 69, 72, 76, 79, 83,
86, 90, 94, 98, 103, 107, 112, 117, 122, 128}
Specifically, agc.sub.-- tbl [0]=32, agc.sub.-- tbl [32]=128
In a case where agc.sub.-- tbl [agc.sub.-- data.sub.-- calc] is
[32], the gain data is 1 time (+0 EV), in a case of [64], the gain
data is 2 times (+1 EV), and in a case of [128], the gain data is
4 times (+2 EV).
In FIG. 6, at first, in step S1, agc.sub.-- data is made equal
to agc.sub.-- def, and then agc.sub.-- data.sub.-- calc is made
equal to agc.sub.-- value (step S2). And, gain data for R, namely
agc.sub.-- data.sub.-- cwe 5 is made equal to agc.sub.-- from cwe
5 *agc.sub.-- tbl [agc data.sub.-- calc]/32, gain data for G, namely
agc.sub.-- data.sub.-- cwe is made equal to agc.sub.-- from.sub.--
cwe 6 *agc.sub.-- tbl [agc.sub.-- data.sub.-- calc]/32, and also
gain data for B, namely agc.sub.-- data.sub.-- cwe 5 is made equal
to agc.sub.-- from.sub.-- cwe 7 * agc.sub.-- tbl [agc.sub.-- data.sub.--
calc]/32 (step 32), and then this operating flow ends.
The agc.sub.-- data.sub.-- cwe 5-7 computed in the above processing
for computing a gain is multiplied as a gain in the multipliers
1075r, 1075g, and 1075c for R, G, and B in the digital gain adjusting
section 1075 in the IPP 107, and the computed agc.sub.-- data is
set as a gain for the AGC amplifier 105.
Thus, a signal level of an image signal is corrected by controlling
a gain for the digital gain adjusting section 1075, so that gain
adjustment in a broad range becomes possible and also it becomes
possible to correct a signal level of an image signal in a broad
range.
Finally, description is made for operations for setting a shutter
speed in the digital camera. At first, an operator selects the imaging
mode via the operating section 123. The CPU 121 determines exposure
according to illuminance data from the IPP 107, and controls the
CCD electric charge read pulse XSG and CCD electric charge sweep-away
pulse XSUB according to a result of the determination of exposure.
Also the CPU 121 computes a TV value, and decides a shutter speed
(load value) to be set in the IPP 107 from the TV value by referring
to the ROM table 121a.
Then the CPU 121 computes gain data (agc.sub.-- data.sub.-- cwe
5-7) for R, G, and B multiplied in the multipliers 1075r, 1075g,
and 1075c in the digital gain adjusting section 1075 referring to
the ROM table 121a shown in FIG. 3, multiplies the computed gain
data for R, G, and B with the multipliers 1075r, 1075g, and 1075c
in the digital gain adjusting section 1075 in the IPP 107 for adjusting
a signal level of an image signal.
The above description assumes a case where a gain for the digital
gain adjusting section 1075 is adjusted using a table shown in FIG.
3 in which a gain is set to the plus side (Refer to FIG. 3), but
gain adjustment for the gain adjusting section 1075 may be executed
using the table shown in FIG. 4 in which a gain is set to the minus
side.
In the AGC amplifier, a section having linearity in a gain for
a setup value is limited, while gain adjustment can be made with
the digital gain adjusting section 1075 in a broad range.
In Embodiment 3 of the present invention, a signal level of an
image signal for the CCD 103 is corrected by using a gain for the
AGC amplifier 105 as well as for the digital gain adjusting section
1075 in the IPP 107. For this reason, description is made only different
portions.
The digital camera according to Embodiment 3 may have the same
configuration as that of the digital camera described in Embodiment
1 (Refer to FIG. 1), and also the IPP 107 may have the configuration
as that described in Embodiment 2 and shown in FIG. 5.
Also in this embodiment, an operating speed of an electronic shutter
is set by a unit of the CCD sensor electric charge sweep-away pulse
XSUB like in Embodiment 1.
Also in this embodiment, there may be a case where a diaphragm
can be set only step by step due to restrictions in system designing
for an apparatus or because of requirements for cost reduction for
the apparatus. Namely, in the case, as for the EV diagram, like
in the conventional technology, only F2 and F8 are available for
selecting as an F value as shown in FIG. 12, and for switching it,
F2 is selected in a range up to Lv12, and F8 is selected in a range
from Lv12 and on.
Next description is made for gain control for the AGC amplifier
105 as well as for the IPP 107, which is one of the features in
this embodiment.
In this embodiment, when a signal level of an image signal for
the CCD 103 is corrected by the AGC amplifier 105 as well as by
the gain adjusting section 1075 in the IPP 107, a gain for the AGC
amplifier 105 is controlled by the CPU 121 and SG section 126, or
a gain for the digital gain adjusting section 1075 in the IPP 107
is controlled by the CPU 121, so that a quantization error or an
exposure error generated when a shutter speed is set by a unit of
CCD electric charge sweep-away pulse XSUB will be offset.
Generally, in gain control for the AGC amplifier 105, if an initial
value is set to a value insuring an excellent image, there is no
linearity in a gain for a setup value in a direction in which a
gain is lowered (in a direction where a gain is minus), so that,
in the AGC amplifier 105, in a case where a quantization error is
set to the higher speed side of the shutter speed, a signal level
of an image signal is corrected by raising a gain (in a direction
where a gain is plus), on the contrary, in gain control for the
digital gain adjusting section 1075, gain adjustment can be made
in a broad range (in a direction where a gain is minus and also
in a direction where a gain is plus), so that, in a case where a
quantization error is set to the lower speed side of the shutter
speed, a signal level of an image signal is adjusted by lowering
a gain (in a direction where a gain is minus).
Namely in this embodiment, gain control for the AGC amplifier 105
is executed using a table shown in FIG. 3 in which a gain is plus,
and gain control for the digital gain adjusting section 1075 in
the IPP 107 is executed using the table shown in FIG. 4 in which
a gain is minus.
As for a criteria as to which of the table shown in FIG. 3 and
that shown in FIG. 4 should be selected, for instance, a table,
in which an absolute value of a quantization error .DELTA.TV from
a theoretical value of the shutter speed becomes smaller, may be
selected. Concretely, in a case where it is necessary to set a tTV
value to 10.125, in the table shown in FIG. 3, as load value corresponding
to the theoretical value TV of 10.125 is 262, and the quantization
error .DELTA.TV then is -0.0566. On the other hand, in the table
shown in FIG. 4, a load value corresponding to the theoretical value
TV of 10.125 is 262, and the quantization error .DELTA.TV then is
0.0461. For this reason, in a case where it is necessary to set
a time value TV to 10.125, it is necessary to use the table shown
in FIG. 4 in which an absolute value of the quantization error is
smaller. With this, a change rate in a gain can be made smaller.
FIG. 7 is a view for illustrating a relation between an input control
voltage (V) and an output gain (dB) in the AGC amplifier 105 according
to this embodiment.
The curve in FIG. 7 shows characteristics of the input control
voltage (V) and output gain (dB) when a control voltage Vcc is set
to 4.5 V, 4.75 V, and 5 V respectively. As shown in FIG. 7, in a
case where an output gain (dB) is not more than 8 dB, linearity
is lost.
Next description is made for a method of computing gain data set
in the AGC amplifier 105 and in the digital gain adjusting section
1075.
FIG. 8 is a flowchart for showing a method for computing gain data
set in the AGC amplifier 105 and in the digital gain adjusting section
1075.
At first, description is made for parameters used in the flow chart
shown in FIG. 8.
A unit of the parameters described below is EV (The same meaning
is provided even with Lv, TV, and AV), and 1/16 EV is 1.
1) agc.sub.-- value: A gain setup value, which corresponds to a
gain (.DELTA.TV) for correcting a quantization error .DELTA.TV in
the tables in FIG. 3 and FIG. 4 (expressed with hexadecimal numbers).
In a case where the quantization error .DELTA.TV becomes minus as
shown in FIG. 3, agc.sub.-- value becomes plus, while, in a case
where the quantization error .DELTA.TV becomes plus as shown in
FIG. 4, the agc.sub.-- value becomes minus. Namely, the agc.sub.--
value becomes plus when a gain is to
be made larger, and becomes minus when a gain is to be made smaller.
Concretely, a relation between agc.sub.-- value and an output gain
(dB) for the AGC amplifier 105 is as described below. When agc.sub.--
value is zero (0), and output gain for the AGC amplifier 105 is
8 dB; when agc.sub.-- value is 0.times.08, an output gain for the
AGC amplifier 105 is 8+(6*0.5), namely 11 dB; when agc.sub.-- value
is 0.times.10, an output gain for the AGC amplifier 105 is 8+(6
*1.0), namely 14 dB; and when agc.sub.-- value is 0.times.18, an
output gain for the AGC amplifier 105 is 8+(6*1.5), namely 17 dB.
2) agc.sub.-- data : D/A output setup data for the CPU 121. With
this data, a gain for the AGC amplifier 105 can be set.
3) agc data cwe 5-7: Gain data for R, G, and B multiplied in the
multipliers 1075r, 1075g, 1075c in the digital gain adjusting section
1075 in the IPP 107.
4) from.sub.-- cwe 5-7: Adjusting value for non-uniformity in colors
R, G, and B in the CCD 103.
5) agc.sub.-- k.sub.-- plus, agc.sub.-- k.sub.-- plus 1-3: Output
gain (dB) against input control voltage in each section at which
a gain for the AGC amplifier 105 does not linearly change against
a setup value (D/A value).
Concretely, agc.sub.-- k.sub.-- plus indicates an increase factor
of an output gain (dB) against an input control voltage in a range
from 8 dB to 11 dB; agc.sub.-- k.sub.-- plus.sub.-- 1 indicates
an increase factor of an output gain against an input control voltage
in a range from 11 dB to 14 dB; agc.sub.-- k.sub.-- plus.sub.--
2 indicates an increase factor against an input control voltage
in an area from 14 dB to 17 dB; and agc.sub.-- k.sub.-- plus.sub.--
3 indicates an increase factor of an output gain against an input
control voltage in a range of 17 dB or higher.
6) agc.sub.-- def, agc.sub.-- def 1-3: Shift value for agc.sub.--
k.sub.-- plus, and agc.sub.-- k.sub.-- plus 1-3. Concretely, agc.sub.--
def indicates an input control voltage value (D/A setup value for
the CPU) for an output gain of 8 dB for the AGC amplifier 105; agc.sub.--
def.sub.-- 1 indicates an input control voltage value (D/A setup
value for the CPU) for an output gain of 11 dB for the AGC amplifier
105; agc.sub.-- def.sub.-- 2 indicates an input control voltage
value (D/A setup value for the CPU) for an output gain of 14 dB
for the AGC amplifier 105; and agc.sub.-- def.sub.-- 3 indicates
an input control voltage value (D/A setup value for the CPU) for
an output gain of 17 dB for the AGC amplifier 105.
7) agc.sub.-- tbl [agc.sub.-- data.sub.-- calc] :A function for
AGC computing agc.sub.-- tbl [0-32]={32, 33, 34, 36, 38, 39, 41,
43, 45, 47, 49, 51, 53, 56, 58, 61, 64, 66, 69, 72, 76, 79, 83,
86, 90, 94, 98, 103, 107, 112, 117, 122, 128}
Concretely, agc.sub.-- tbl [0] is equal to 32, and agc.sub.-- tbl
[32] is equal to 128.
In a case where agc.sub.-- tbl [agc.sub.-- data.sub.-- calc] is
[32], gain data is 1 time (.+-.0 EV); in a case where agc.sub.--
tbl [agc.sub.-- data.sub.-- calc] is [64], gain data is 1/2 times
(-1 EV); and in a case where agc.sub.-- tbl [agc.sub.-- data.sub.--
calc] is [128], gain data is 1/4 times (-2 EV).
Next description is made for the flowchart in FIG. 8. In FIG. 8,
at first, determination is made as to whether agc.sub.-- value is
smaller than [0] or not (step S10), and in a case where it is determined
that agc.sub.-- value is smaller than [0], system control shifts
to step S11, and in a case where it is determined that agc.sub.--
value is not less than [0], system control shifts to step S14.
In step S11, agc.sub.-- data is made equal to agc.sub.-- def, and
then agc.sub.-- data.sub.-- calc is made equal to -(agc.sub.-- value)
(step S3). Then gain data for R, i.e., agc.sub.-- data.sub.-- cwe
5 is made equal to agc.sub.-- from.sub.-- cwe 5*32/agc.sub.-- tbl
[agc.sub.-- data.sub.-- calc]; gain data for G, i.e., agc.sub.--
data.sub.-- cwe6 is made equal to agc.sub.-- from.sub.-- cwe6*32/agc.sub.--
tbl [agc.sub.-- data.sub.-- calc]; and gain data for B, i.e., agc.sub.--
data.sub.-- cwe5 is made equal to agc.sub.-- from.sub.-- cwe7*32/agc.sub.--
tbl [agc.sub.-- data.sub.-- calc] (step 4), and then the flow is
terminated.
In step S14, determination is made as to whether agc.sub.-- value
is [0] or not, and in a case where it is determined that agc.sub.--
value is not [0], system control shifts to step S16, and in a case
where it is determined that agc.sub.-- value is [0], system control
shifts to step S15 with agc.sub.-- data set to 0, and then system
control shifts to step S23.
In step S16, determination is made as to whether agc.sub.-- value
is larger than [0.times.18] or not, and in a case where it is determined
that agc.sub.-- value is not more than [0.times.18], system control
shifts to step S18, and in a case where agc.sub.-- value is lager
than [0.times.18], agc.sub.-- data is set to (agc.sub.-- value-0.times.18)
* agc.sub.-- k.sub.-- plus3/16+agc.sub.-- def.sub.-- 3 (step S17),
and then system control shifts to step S23.
In step S18, determination is made as to whether agc.sub.-- value
is larger than [0.times.10] or not, and in a case where it is determined
that agc.sub.-- value is not more than [0.times.10], system control
shifts to step S20, and in a case where it is determined that agc.sub.--
value is larger than [0.times.10], agc.sub.-- data is set to (agc.sub.--
value-0.times.10) *agc.sub.-- k.sub.-- plus2/16+agc.sub.-- def.sub.--
2 (step S19), and system control shifts to step S23.
In step S20, determination is made as to whether agc.sub.-- value
is larger than [0.times.08] or not, and in a case where it is determined
that agc.sub.-- value is not more than [0.times.08], system control
shifts to step S22, and in a case where it is determined that agc.sub.--
value is larger than [0.times.08], agc.sub.-- data is set to (agc.sub.--
value-0.times.08) *agc.sub.-- k.sub.-- plus1/16+agc.sub.-- def.sub.--
1 (step S21) with the system control shifted to step S23.
In step S22, agc.sub.-- data is set to agc.sub.-- value*agc.sub.--
k.sub.-- plus/16+agc.sub.-- def, and system control shifts to step
S23.
In step S23, agc.sub.-- data.sub.-- calc is set to zero (0), and
then gain data for R, i.e., agc.sub.-- data.sub.-- cwe5 is set to
agc.sub.-- from.sub.-- cwe5, gain data for G, i.e., agc.sub.-- data.sub.--
cwe6 to agc.sub.-- from.sub.-- cwe6, and further gain data for B.
i.e., agc.sub.-- data.sub.-- cwe5 to agc.sub.-- from.sub.-- cwe7
(step S24), and then this flow comes to the end.
The agc.sub.-- data.sub.-- cwe 5 to 7 computed in the above sequence
is multiplied as gain with the multipliers 1075r, 1075g, and 1075b
for R, G, and B in the digital gain adjusting section 1075 in the
IPP 107, and also the agc.sub.-- data computed in the above sequence
is set as a gain for the AGC amplifier 105.
As described above, in gain control for the AGC amplifier 105,
a section having linearity in a gain for a setup value for the AGC
amplifier 105 is used (in a direction in which a gain is plus),
and as for a range in which there is no linearity in a gain for
the AGC amplifier 105 (in a direction in which a gain is minus),
gain adjustment is executed by the digital gain adjusting unit 1075,
so that gain adjustment can be made in a broad range and a signal
level of an image signal can be corrected in a broad range.
Next description is made for operations for setting a shutter speed
in the digital camera. At first, an operator sets the imaging mode
via the operating section 123. The CPU 121 determines exposure according
to illuminance data from the IPP 107, and controls the CCD electric
charge read pulse XSG and CCD electric charge sweep-away pulse XSUB
in response to a result of the determination of exposure.
The CPU 121 computes a TV value, and decides a shutter to be set
(a load value) in the IPP 107 from the TV value by referring to
the ROM table 121a shown in FIG. 3 or FIG. 4. Then, the CPU 121
computes gain data (agc.sub.-- data) to be set in the AGC 105 and
gain data for R, G, and B to be multiplied with the multipliers
1075r, 1075g, 1075b in the digital gain adjusting section 1075.
Then, the CPU 121 sets the computed gain data (agc.sub.-- data)
in the AGC amplifier 105, and also multiplies the computed gain
data for R, G, and B (agc.sub.-- data.sub.-- cwe 5-7) with the multipliers
1075r, 1075g, and 1075c in the digital gain adjusting section 1075
for adjusting a signal level of an image signal.
This application is based on Japanese patent applications No. HEI
8-190289 and No. HEI 9-190278 filed in the Japanese Patent Office
on Jul. 19, 1996 and Jul. 15, 1997, respectively, the entire contents
of which are hereby incorporated by reference.
Although the invention has been described with respect to a specific
embodiment for a complete and clear disclosure, the appended claims
are not to be thus limited but are to be construed as embodying
all modifications and alternative constructions that may occur to
one skilled in the art which fairly fall within the basic teaching
herein set forth. |