U.S. patent application number 11/315219 was filed with the patent office on 2006-06-22 for electronic camera video signal correcting device.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Yoshizo Mori.
Application Number | 20060132625 11/315219 |
Document ID | / |
Family ID | 33562295 |
Filed Date | 2006-06-22 |
United States Patent
Application |
20060132625 |
Kind Code |
A1 |
Mori; Yoshizo |
June 22, 2006 |
Electronic camera video signal correcting device
Abstract
A device stores in ROM white spot addresses, white spot levels,
an OB level median, sensitivity, and time-in-second under dark
shooting, a temperature coefficient correcting the white spot level
according to the temperature under normal shooting, a sensitivity
coefficient for the sensitivity-based correction, and a
time-in-second coefficient for the exposure time-in-second-based
correction. A temperature difference during shooting a subject is
obtained according to the difference between OB level median during
normal shooting and that during dark shooting. A correction value
for the white spot level due to temperature is obtained from
temperature difference and temperature coefficient, and similarly,
correction value due to sensitivity is obtained from sensitivity
difference and sensitivity coefficient, and correction value due to
time-in-second is obtained from time-in-second difference and
time-in-second coefficient for correction. Dark current is
corrected by subtracting OB level median during shooting a subject
from the video signal during shooting a subject.
Inventors: |
Mori; Yoshizo; (Odawara-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
33562295 |
Appl. No.: |
11/315219 |
Filed: |
December 23, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP04/09570 |
Jun 30, 2004 |
|
|
|
11315219 |
Dec 23, 2005 |
|
|
|
Current U.S.
Class: |
348/241 ;
348/E5.081 |
Current CPC
Class: |
H04N 5/367 20130101;
H04N 5/361 20130101 |
Class at
Publication: |
348/241 |
International
Class: |
H04N 5/217 20060101
H04N005/217 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2003 |
JP |
2003-189509 |
Claims
1. A video signal correcting device of an electronic camera
comprising: a storage unit which stores therein a white spot
address, a white spot level, and an optical black level median
obtained from a video signal at a time of dark shooting, and a
sensitivity and a time-in-second at the time of dark shooting, as
well as a temperature coefficient for correcting the white spot
level in accordance with a temperature at a time of shooting by the
electronic camera, a sensitivity coefficient for correcting the
white spot level in accordance with the sensitivity at the time of
shooting by the electronic camera, and a time-in-second coefficient
for correcting the white spot level in accordance with an exposure
time-in-second at the time of shooting by the electronic camera; a
temperature detection unit which obtains a temperature difference
at a time of shooting a subject according to a difference between
the optical black level median at the time of shooting a subject
and the optical black level median at the time of dark shooting
stored in said storage unit; and an operation unit which obtains a
correction value for the white spot level due to a temperature
according to the temperature difference and the temperature
coefficient stored in said storage unit, obtains a correction value
for the white spot level due to a sensitivity according to a
difference between the sensitivity at the time of shooting a
subject and the sensitivity at the time of dark shooting stored in
said storage unit and to the sensitivity coefficient stored in said
storage unit, obtains a correction value for the white spot level
due to a time-in-second according to a difference between the
time-in-second at the time of shooting a subject and the
time-in-second at the time of dark shooting stored in said storage
unit and to the time-in-second coefficient stored in said storage
unit, performs correction on the white spot level included in the
video signal at the time of shooting a subject according to each
correction value for the white spot level due to the temperature,
the sensitivity, and the time-in-second, and subtracts the optical
black level median at the time of shooting a subject from the video
signal at the time of shooting a subject.
2. The video signal correcting device of an electronic camera
according to claim 1, wherein an optical black level average is
used instead of said optical black level median.
3. A video signal correcting device of an electronic camera
comprising: a storage unit which stores therein a white spot
address, a white spot level, and a reference dark current level
median obtained from a video signal at a time of dark shooting, and
a temperature, a sensitivity, and a time-in-second at the time of
dark shooting, as well as a temperature coefficient for correcting
the white spot level and a dark current level median in accordance
with a temperature at a time of shooting by the electronic camera,
a sensitivity coefficient for correcting the white spot level and
the dark current level median in accordance with the sensitivity of
the electronic camera, and a time-in-second coefficient for
correcting the white spot level and the dark current level median
in accordance with an exposure time-in-second of the electronic
camera; a temperature detection unit which detects the temperature
at the time of shooting; and an operation unit which obtains a
correction value for the white spot level due to a temperature and
a correction value for the dark current level median due to a
temperature according to a difference between a temperature at a
time of shooting a subject detected by said temperature detection
unit and the temperature at the time of dark shooting stored in
said storage unit and to the temperature coefficient stored in said
storage unit, obtains a correction value for the white spot level
due to a sensitivity and a correction value for the dark current
level median due to a sensitivity according to a difference between
a sensitivity at the time of shooting a subject and the sensitivity
at the time of dark shooting stored in said storage unit and to the
sensitivity coefficient stored in said storage unit, obtains a
correction value for the white spot level due to time-in-second and
a correction value for the dark current level median due to a
time-in-second according to a difference between a time-in-second
at the time of shooting a subject and the time-in-second at the
time of dark shooting stored in said storage unit and to the
time-in-second coefficient stored in said storage unit, and
performs correction on the white spot level and the dark current
level median both included in the video signal at said time of
shooting a subject according to each correction value for the white
spot level due to the temperature, the sensitivity, and the
time-in-second.
4. The video signal correcting device of an electronic camera
according to claim 3, wherein a dark current level average is used
instead of said dark current level median.
5. The video signal correcting device of an electronic camera
according to claim 3, wherein an optical black level median is used
instead of said dark current level median.
6. The video signal correcting device of an electronic camera
according to claim 3, wherein an optical black level average is
used instead of said dark current level median.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of PCT International
Patent Application No. PCT/JP2004/009570, filed on Jun. 30, 2004,
designating the U.S., and claims the benefit of priority from
Japanese Patent Application No. 2003-189509, filed on Jul. 1, 2003,
the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a video signal correcting
device of an electronic camera suitable for correcting a dark
current and a dark-time white spot included in a video signal of an
electronic camera.
[0004] 2. Description of the Related Art
[0005] Generally, performing long time-in-second shooting with an
electronic camera causes a situation in which a subject cannot be
shot correctly due to the influence of dark currents and dark-time
white spots. In other words, a video signal output from an image
sensor of an electronic camera generally contains dark currents and
dark-time white spots. As a result, it is not possible to correctly
shoot a subject.
[0006] Here, a dark-time white spot is a white spot appearing in a
video signal output from an image sensor when there is a defect
(contamination of impurities etc.) in a photodiode constituting the
image sensor. Due to the defect, charges are generated, even though
no light is irradiated thereto. The dark-time white spot occurs in
parts of many photodiodes constituting the image sensor.
[0007] A dark current level and a white spot level of the dark-time
white spot (magnitude of a signal) change according to the shooting
temperature and the shooting time-in-second (exposure time). In
other words, the higher the temperature is and the longer the
exposure time is, the greater the levels become.
[0008] Further, the higher the temperature is and the longer the
shooting time-in-second is, the larger the number of dark-time
white spots gets. This is because the higher the temperature is and
the longer the shooting time-in-second is, the larger the number of
charges generated by the defect of the photodiode gets. As a
result, the charges generated by the defect of the photodiode
easily exceed the threshold value recognized as a dark-time white
spot in the video signal.
[0009] Moreover, the dark current level and the white spot level of
dark-time white spot also change depending on a shooting
sensitivity. Here, the sensitivity depends on the system of the
electronic camera (gain in amplifying a video signal). In other
words, the higher the sensitivity is, the greater the dark current
level and the white spot level of dark-time white spot become.
Furthermore, the higher the sensitivity is, the larger the number
of dark-time white spots gets. This is because the higher the
sensitivity is, more easily the levels exceed the threshold value
recognized as a dark-time white spot in the video signal of an
electronic camera.
[0010] In the prior art, shooting is performed as follows to remove
the influences of the dark current and the dark-time white
spot.
[0011] That is, after normal shooting is performed, dark shooting
is performed for the same length of time-in-second as that of the
normal shooting. Then, the video signal obtained by the dark
shooting is subtracted from the video signal obtained by the normal
shooting to obtain a video signal from which the influence of the
dark current and the dark-time white spot has been removed.
[0012] Incidentally, as a prior art relating to prevention of the
dark current, there is one that reduces the amount of heat
generated by an electronic camera to prevent the dark current
(refer to Japanese Unexamined Patent Application Publication No.
Hei 10-271398).
[0013] The above-mentioned prior art has the following
problems.
[0014] Firstly, since dark shooting is performed after normal
shooting of a subject is performed for the same length of
time-in-second, it takes double the time of the normal shooting to
complete shooting. In particular, when shooting of a celestial
photograph etc., for example, requires 10-minute dark shooting
after 10-minute normal shooting, and therefore it takes a long time
(20 minutes or longer) until the shooting result can be visually
recognized on a liquid crystal monitor.
[0015] Secondly, shooting twice doubles the power consumption.
SUMMARY OF THE INVENTION
[0016] It is an object of the present invention to provide a video
signal correcting device of an electronic camera that is capable of
obtaining without shooting twice a video signal free from the
influence of a dark current and a dark-time white spot by
performing dark current correction and dark-time white spot
correction.
[0017] An aspect of the first invention includes a storage unit
that stores therein a white spot address, a white spot level, and a
optical black level median obtained from a video signal at the time
of dark shooting, the sensitivity and the time-in-second at the
time of dark shooting, as well as a temperature coefficient for
correcting the white spot level in accordance with the temperature
at the time of shooting by an electronic camera, a sensitivity
coefficient for correcting the white spot level in accordance with
the sensitivity at the time of shooting by the electronic camera,
and a time-in-second coefficient for correcting the white spot
level in accordance with the exposure time-in-second at the time of
shooting by the electronic camera, and also includes a temperature
detection unit which obtains a temperature difference at the time
of shooting a subject according to a difference between the optical
black level median at the time of shooting a subject and the
optical black level median at the time of dark shooting stored in
the storage unit. It also includes an operation unit which obtains
a correction value for the white spot level due to a temperature
according to the temperature difference and the temperature
coefficient stored in the storage unit, obtains a correction value
for the white spot level due to a sensitivity according to a
difference between the sensitivity at the time of shooting a
subject and the sensitivity at the time of dark shooting stored in
the storage unit and to the sensitivity coefficient stored in the
storage unit, obtains a correction value for the white spot level
due to a time-in-second according to a difference between the
time-in-second at the time of shooting a subject and the
time-in-second at the time of dark shooting stored in the storage
unit and to the time-in-second coefficient stored in the storage
unit, performs correction on the white spot level included in the
video signal at the time of shooting a subject according to each
correction value for the white spot level due to the temperature,
the sensitivity, and the time-in-second, and subtracts the optical
black level median at the time of shooting a subject from.
[0018] An aspect of the second invention includes the video signal
correcting device of an electronic camera according to the first
invention, wherein the optical black level median is an optical
black level average.
[0019] An aspect of the third invention includes a storage unit
which stores therein a white spot address, a white spot level, and
a reference dark current level median obtained from a video signal
at the time of dark shooting, the temperature, the sensitivity, and
the time-in-second at the time of dark shooting, as well as a
temperature coefficient for correcting the white spot level and a
dark current level median in accordance with the temperature at the
time of shooting by an electronic camera, a sensitivity coefficient
for correcting the white spot level and the dark current level
median in accordance with the sensitivity of the electronic camera,
and a time-in-second coefficient for correcting the white spot
level and the dark current level median in accordance with the
exposure time-in-second of the electronic camera, and also includes
a temperature detection unit which detects a temperature at the
time of shooting. It also includes an operation unit which obtains
a correction value for the white spot level due to a temperature
and a correction value for the dark current level median due to a
temperature according to a difference between the temperature at
the time of shooting a subject detected by the temperature
detection unit and the temperature at the time of dark shooting
stored in the storage unit and to the temperature coefficient
stored in the storage unit, obtains a correction value for the
white spot level due to a sensitivity and a correction value for
the dark current level median due to a sensitivity according to a
difference between the sensitivity at the time of shooting a
subject and the sensitivity at the time of dark shooting stored in
the storage unit and to the sensitivity coefficient stored in the
storage unit, obtains a correction value for the white spot level
due to a time-in-second and a correction value for the dark current
level median due to a time-in-second according to a difference
between the time-in-second at the time of shooting a subject and
the time-in-second at the time of dark shooting stored in the
storage unit and to the time-in-second coefficient stored in the
storage unit, and performs correction on the white spot level and
the dark current level median both included in the video signal at
the time of shooting a subject according to each correction value
for the white spot level due to the temperature, the sensitivity,
and the time-in-second.
[0020] An aspect of the fourth invention includes the video signal
correcting device of an electronic camera according to the third
invention, wherein the dark current level median is a dark current
level average.
[0021] An aspect of the fifth invention includes the video signal
correcting device of an electronic camera according to the third
invention, wherein the dark current level median is an optical
black level median.
[0022] An aspect of the sixth invention includes the video signal
correcting device of an electronic camera according to the third
invention, wherein the dark current level median is an optical
black level average.
[0023] According to the aspects of the first to sixth inventions,
it becomes possible to correct the dark current and the white spot
level according to the temperature, the sensitivity, and the
exposure time-in-second by storing plural parameters obtained at
the time of dark shooting in the storage unit and using them at the
time of shooting a subject.
[0024] Further, according to the aspects of the first to sixth
inventions, it is possible to provide a video signal correcting
device of an electronic camera that is capable of obtaining without
shooting twice a video signal free from the influence of the dark
current and the dark-time white spot by performing dark current
correction and dark-time white spot correction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a block diagram showing a first embodiment of the
present invention.
[0026] FIGS. 2(a) and 2(b) are diagrams showing an example of a
relationship between an image sensor 1 and a video signal S shown
in FIG. 1.
[0027] FIG. 3 is a diagram showing a histogram (the horizontal axis
represents reference OB level and the vertical axis represents
frequency) when dark shooting is performed with an electronic
camera.
[0028] FIG. 4 is a block diagram showing a second embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] Embodiments of the present invention will be explained
below.
First Embodiment
[0030] FIG. 1 is a block diagram showing a first embodiment of the
present invention.
[0031] In FIG. 1, reference numeral 1 denotes an image sensor
composed of, although not shown in the drawing, plural photodiodes,
and CCDs in plural lines for transferring charges generated in each
photodiode, etc. Reference numeral 2; a correlated double sampling
(referred to as CDS in the figure) circuit, reference numeral 3; a
programmable gain amplifier (referred to as PGA in the figure),
reference numeral 4; an analog-to-digital converter (referred to as
A/D in the figure), reference numeral 5; an optical black level
comparator (referred to as OB level comparator in the figure),
reference numeral 6; a ROM for storing various data, reference
numeral 7; a CPU, and reference numeral 8; an adder.
[0032] Here, the image sensor 1 shoots a subject and outputs a
shooting result as an electric signal. As well known, the
correlated double sampling circuit 2 has a role to reduce low
frequency noise from the electric signal received from the image
sensor 1. The programmable gain amplifier 3 adjusts the output of
the electric signal to an appropriate level by adjusting the gain.
The analog-to-digital converter 4 converts an electric signal,
which is an analog signal, into a digital signal. The OR level
comparator circuit 5 compares an OB level at the time of
acquisition of the reference stored in the ROM 6 and an OB level
included in the video signal S and outputs the difference
therebetween. This is used for calculating the temperature at the
time of shooting from the difference between both of the OB levels,
as will be described later.
[0033] The operation of the CPU 7 and the adder 8 is explained
below together with the operation in the first embodiment shown in
FIG. 1.
[0034] The operation in the first embodiment shown in FIG. 1 will
be explained.
[0035] (1) First, the electronic camera performs dark shooting. At
this time, the CPU 7 stores various data in the ROM 6.
[0036] In the first embodiment, by dark shooting, each of the data
of the white spot address, the reference white spot level, the OB
level median at the time of acquisition of the reference, the
sensitivity at the time of acquisition of the reference, and the
time-in-second (exposure time-in-second) at the time of acquisition
of the reference is stored in the ROM 6.
[0037] Here, the time of acquisition of the reference means the
time of dark shooting. The temperature coefficient, the sensitivity
coefficient, and the time-in-second coefficient obtained in advance
are also stored. The meaning of each of the data is explained
below.
[0038] The white spot address means an address showing a dark-time
white spot resulting from a defective photodiode in the image
sensor 1. It is needless to say that there exist plural white spot
addresses.
[0039] Additionally, the reference white spot level means an output
level of the video signal S at each white spot address. Therefore,
the white spot level is stored corresponding to each of the plural
white spot addresses.
[0040] Next, the OB level median at the time of acquisition of the
reference is explained. First, the OB level at the time of
acquisition of the reference will be explained. The OB level at the
time of acquisition of the reference means an optical black (OB)
level at the time of acquisition of the reference white spot level.
Specifically, the OB level is an output level of the video signal S
to be output from the region in which the photodiode is completely
shut-off optically in the image sensor 1. In other words, the image
sensor 1 comprises plural photodiodes in a region constructed such
that light is completely shut off, and the video signal S output
based on the plural photodiodes in the light shut-off region is the
OB level.
[0041] Using FIGS. 2(a) and 2(b), the OB level will be explained
specifically.
[0042] FIGS. 2(a) and 2(b) are diagrams showing an example of a
relationship between the video signal S and a light receiving
region of the image sensor 1. FIG. 2 (a) is a waveform diagram
showing an example of the video signal S output from the A/D
converter 4 shown in FIG. 1. FIG. 2 (b) is an illustrative diagram
showing plural defective photodiodes (shown as white spots in the
figure) present in a shooting region C of the image sensor 1 shown
in FIG. 1 and light shut-off regions A and B provided for
outputting the OB level.
[0043] The video signal S shown in FIG. 2 (a) is one corresponding
to a line L in the light receiving region of the image sensor 1
shown in FIG. 2 (b). As shown in FIGS. 2 (a) and 2(b), the video
signal S read out from the light shut-off regions A and B is an
output from the region in which the photodiode of the image sensor
1 is optically shut off, therefore, it results in an OB level. In
the video signal S in the light shut-off regions A and B, the OB
level has a meaning of defining a black level in the video signal
S.
[0044] The OB level median at the time of acquisition of the
reference stored in the ROM 6 indicates a reference OB level at
which the frequency becomes maximum when the video signal S output
from the light shut-off regions A and B is expressed in a histogram
(the horizontal axis represents the reference OB level and the
vertical axis represents frequency).
[0045] Using FIG. 3, the OB level median at the time of acquisition
of the reference will be explained. FIG. 3 is a diagram showing an
example of a histogram (the horizontal axis represents the
reference OB level and the vertical axis represents frequency) when
dark shooting is performed. As shown in the drawing, the reference
OB level at which the frequency becomes maximum is the reference OB
level median. Further, a reference OB level at which the frequency
becomes average is the reference OB level average. Additionally, in
this embodiment, the reference OB level median is stored in the ROM
6, however, the reference OB level average may be stored instead of
the reference OB level median.
[0046] The sensitivity at the time of acquisition of the reference
means the sensitivity of the programmable gain amplifier (PGA) 3 at
the time of acquisition of the reference white spot level. The
sensitivity may be expressed by the ISO sensitivity or the gain of
the programmable gain amplifier (PGA) 3.
[0047] The time-in-second at the time of acquisition of the
reference means an exposure time-in-second at the time of
acquisition of the reference white spot level.
[0048] Further, the temperature coefficient is one necessary for
correcting the white spot level in accordance with the temperature
difference between the temperature when the white spot level and
the OB level at the time of acquisition of the reference (the
temperature at the time of dark shooting) are obtained and the
temperature at the time of normal shooting. As described above, the
higher the temperature is, the higher the white spot level becomes.
Therefore, the white spot level is corrected in accordance with the
temperature difference.
[0049] Additionally, as described above, the higher the temperature
is, the larger the number of white spots gets. This is because when
the temperature is high, the number of photodiodes having a defect
of exciting a charge exceeding the threshold value of the white
spot level increases. Therefore, it is preferable for the
temperature when obtaining the OB level at the time of acquisition
of the reference and the white spot level (the temperature at the
time of dark shooting) to be relatively high (for example, about
25.degree. C.) in order to make it easier to obtain a large number
of white spots.
[0050] The sensitivity coefficient is one that corrects the level
of the video signal S in accordance with the sensitivity of the
programmable gain amplifier (PGA) 3 shown in FIG. 1. Since the
video signal S contains a dark current and a white spot level, it
becomes a coefficient which corrects the dark current and the white
spot level as a result. Since the higher the sensitivity of the
programmable gain amplifier (PGA) 3 is, the greater and the higher
the dark current and the white spot level become, the coefficient
is stored for correcting the dark current and the white spot level.
This is not caused by the photodiode but by the system of an
electronic camera. In other words, when the sensitivity is high,
the number of photodiodes having a defect of generating a charge
exceeding the threshold value of the white spot level (the number
of white spots) increases, and the dark current also increases.
[0051] The time-in-second coefficient is one that corrects a dark
current and a white spot level in accordance with an exposure
time-in-second. As described above, the longer the exposure
time-in-second is, the greater and the higher the dark current and
the white spot level become, therefore, the coefficient is stored
for correcting the dark current and the white spot level in
accordance with the exposure time-in-second.
[0052] The temperature coefficient, the sensitivity coefficient,
and the time-in-second coefficient can be obtained in advance by
the test etc. conducted at the time of design of an electronic
camera or of shipping from factory, and the obtained coefficients
are stored in the ROM 6.
[0053] Additionally, it is preferable to perform dark shooting
under the conditions of high temperatures (for example, about
25.degree. C.), long time-in-second shooting, and high sensitivity.
This is because it is possible to obtain a large number of
dark-time white spots (white spot addresses) under these
conditions.
[0054] Further, by performing dark shooting at the time of shipping
from factory, it is possible to save man-hours required for a user
to perform dark shooting and store each of the data in the ROM
6.
[0055] (2) Next, the electronic camera storing various data in the
ROM 6 by dark shooting performs normal shooting of a subject.
Therefore, the video signal S by shooting of the subject is output
from the A/D converter 4.
[0056] (3) Next, the CPU 7 in FIG. 1 reads out each white spot
address and the white spot level corresponding to each white spot
address from the ROM 6. Subsequently, the CPU 7 recognizes the
sensitivity and the exposure time-in-second at the time of shooting
of the subject.
[0057] (4) Next, the OB level comparator 5 obtains the OB level
from the video signal S based on the shooting of the subject and
also obtains the OB level median at the time of acquisition of the
reference from the ROM 6. According to this, the OB level
comparator 5 compares the OB level median at the time of shooting
that is corrected in accordance with the exposure time-in-second
(exposure time) (specifically, (OB level median at the time of
shooting).times.K.times.(time-in-second at the time of acquisition
of the reference/time-in-second at the time of shooting, where K is
a predetermined coefficient)) and the OB level median at the time
of acquisition of the reference at the time of dark shooting, and
obtains the temperature difference between the time of shooting of
the subject and the time of dark shooting based on the difference
between both of the OB levels.
[0058] (5) The CPU 7 calculates the temperature correction value by
multiplying the obtained temperature difference and the temperature
coefficient stored in the ROM 7.
[0059] Further, the CPU 7 obtains the sensitivity difference
between the sensitivity at the time of shooting of the subject
obtained in advance and the sensitivity at the time of acquisition
of the reference stored in the ROM 7, and calculates the
sensitivity correction value by multiplying the sensitivity
difference and the sensitivity coefficient stored in the ROM 7.
[0060] Similarly, the CPU 7 obtains the time-in-second difference
between the exposure time-in-second at the time of shooting of the
subject obtained in advance and the time-in-second at the time of
acquisition of the reference stored in the ROM 7, and calculates
the time-in-second correction value by multiplying the sensitivity
difference by the time-in-second coefficient stored in the ROM
7.
[0061] (6) Next, the CPU 7 performs correction of the white spot
level at each white spot address based on the temperature
correction value, the sensitivity correction value, and the
time-in-second correction value for the video signal S output from
the analog-to-digital converter 5 using the adder 8.
[0062] At the same time, the CPU 7 obtains the OB level of the
video signal S at the time of shooting of the subject by a
well-known method, subtracts the OB level at the time of shooting
of the subject from the video signal S output from the
analog-to-digital converter 5 using the adder 8, and performs dark
current correction.
[0063] Additionally, in the first embodiment described above, the
reference OB level median is stored in the ROM 6, however, the
reference OB level average may be stored instead of the reference
OB level median as described above. In this case, the OB level
comparator S compares the OB level average at the time of
acquisition of the reference at the time of dark shooting and the
OB level at the time of normal shooting of the subject, and obtains
the temperature difference at the time of shooting of the subject
based on the difference between both of the OB levels.
[0064] According to the first embodiment, since it is not necessary
to perform shooting twice, the shooting time can be considerably
shortened and power consumption can be considerably reduced.
[0065] Further, it is not necessary to provide a temperature
sensor.
[0066] Furthermore, since the correction of the white spot level
depending on the temperature, the sensitivity, and the
time-in-second is performed by detecting the temperature at the
time of shooting of the subject using the OB level of the
electronic camera, and at the same time, the correction of the dark
current is performed by subtracting the OB level at the time of
shooting of the subject from the video signal at the time of
shooting of the subject, accurate correction of the dark current
can be made possible.
Second Embodiment
[0067] FIG. 4 is a block diagram showing a second embodiment of the
present invention. In the second embodiment shown in FIG. 4, the
same parts as those in the first embodiment shown in FIG. 1 are
assigned with the same symbols and the explanation thereof will be
omitted.
[0068] The second embodiment differs from the first embodiment in
that a temperature sensor 9 is provided instead of the OB level
comparator 5 in the first embodiment, the reference dark current
level median and the temperature at the time of acquisition of the
reference are stored in the ROM 6, and the OB level median at the
time of acquisition of the reference is not stored in the ROM
6.
[0069] Additionally, instead of the reference dark current level
median, the reference dark current level average may be stored.
[0070] The operation in the second embodiment shown in FIG. 4 will
be explained below.
[0071] (1) First, the electronic camera performs dark shooting and
stores various data shown in the drawing in the ROM 6. As described
above, the reference dark current level median (or the reference
dark current level average) and the temperature at the time of
acquisition of the reference are newly stored in the ROM 6.
[0072] Here, in a histogram (the horizontal axis represents the
dark current level and the vertical axis represents frequency) when
dark shooting is performed, the dark current level at which the
frequency becomes maximum is the reference dark current level
median. Further, the dark current level at which the frequency
becomes the average is the reference dark current level
average.
[0073] The temperature at the time of acquisition of the reference
stored in the ROM 6 is used for performing the temperature
correction of the white spot level and the dark current based on
the difference from the temperature data output from the
temperature sensor 9 at the time of shooting of the subject.
[0074] Since other data stored in the ROM 6 are the same as those
in the first embodiment, the explanation thereof will be
omitted.
[0075] (2) Next, the electronic camera storing various data in the
ROM 6 by dark shooting performs shooting of the subject.
Consequently, the video signal S according to the shooting of the
subject is output from the A/D converter 4.
[0076] (3) In this state, the CPU 7 in FIG. 4 reads out the
reference dark current level median, each white spot address, and
the white spot level at each white spot address from the ROM 6.
[0077] (4) Subsequently, the CPU 7 in FIG. 4 recognizes the
sensitivity and the exposure time-in-second at the time of shooting
of the subject. The sensitivity and the exposure time-in-second at
the time of shooting of the subject themselves are stored in a
memory in the CPU 7.
[0078] Further, the CPU 7 in FIG. 4 obtains the temperature at the
time of shooting of the subject from the temperature sensor 9.
[0079] (5) The CPU 7 obtains the temperature difference between the
temperature at the time of shooting of the subject and the
temperature at the time of acquisition of the reference stored in
the ROM 6, the sensitivity difference between the sensitivity at
the time of shooting of the subject and the sensitivity at the time
of acquisition of the reference, and the time-in-second difference
between the exposure time-in-second at the time of shooting of the
subject and the time-in-second at the time of acquisition of the
reference stored in the ROM 7.
[0080] Subsequently, the CPU 7 calculates the correction value for
each white spot level and the dark current correction value about
the dark current level at the time of acquisition of the reference
based on the temperature coefficient, the sensitivity coefficient,
and the time-in-second coefficient stored in the ROM 6.
[0081] (6) Next, the CPU 7 performs correction of the white spot
level based on the white spot address for the video signal S output
from the analog-to-digital converter 5 using the adder 8. Further,
the CPU 7 performs correction of the dark current using the dark
current correction value for the video signal S output from the
analog-to-digital converter 5 using the adder 8
[0082] Additionally, the second embodiment described above is
configured such that the dark current median is corrected as a dark
current, however, the present invention is not limited to this, and
it may be configured such that the dark current level average, the
OB level median, and the OB level average are corrected.
[0083] According to the second embodiment, since it is not
necessary to perform shooting twice, the shooting time can be
considerably reduced and the power consumption can be considerably
reduced.
[0084] Further, the temperature is detected using the temperature
sensor and the correction of the white spot level is performed
depending on the temperature, the sensitivity, and the
time-in-second in addition to the correction of the dark current,
therefore, accurate correction becomes possible.
[0085] Additionally, in the second embodiment, the temperature
coefficient to be stored in the ROM 6 is obtained in advance,
however, since the temperature sensor 9 is provided in the present
embodiment, it is also possible to obtain the temperature
coefficient from the difference between the temperature at the time
of shooting of the subject and the temperature at the time of dark
shooting.
[0086] The invention is not limited to the above embodiments and
various modifications may be made without departing from the spirit
and scope of the invention. Any improvement may be made in part or
all of the components.
* * * * *