Television – Camera – system and detail – Solid-state image sensor
Reexamination Certificate
1998-06-02
2002-07-16
Ho, Tuan (Department: 2712)
Television
Camera, system and detail
Solid-state image sensor
C348S296000
Reexamination Certificate
active
06421086
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to automatic exposure control and automatic gain control which are performed by an image pickup apparatus of an electronic still camera or the like.
More particularly, the present invention relates to an operation of a camera which is performed when a shutter is operated.
FIG. 21
a diagram showing the structure of automatic exposure adjustment for an image pickup apparatus disclosed in Japanese Patent Publication No. Hei 5-37595. Referring to
FIG. 21
, reference numeral
20
represents a lens,
21
represents an aperture mechanism,
22
represents a drive circuit,
23
represents an image pickup device,
24
represents a preamplifier, represents a variable gain amplifier,
26
represents an A/D converter,
27
represents a synchronization separation circuit,
28
represents a switching circuit,
29
represents a switching control circuit,
30
represents an integrating circuit,
31
represents an abnormality determination circuit,
32
represents an average value calculating circuit,
33
represents a comparison circuit,
34
represents a desired-value memory and
35
represents a reference-value memory.
The operation will now be described. The quantity of light made incident from a subject on the lens
20
is adjusted because the aperture of the lens
20
is adjusted by the aperture mechanism
21
. Then, incident light is photoelectrically converted by the image pickup device
23
so as to be transmitted as a picked-up image signal. The A/D converter
26
converts a brightness signal in the picked up image signal into a digital signal which is supplied to a selected integrating circuit
30
by the switching circuit
28
.
The synchronization separation circuit
27
separates the picked up image signal into vertical and horizontal synchronizing signals. The following switching control circuit
29
controls the switching operation of the switching circuit
28
in response to clock signals which have been used to control the two synchronizing signals and the image pickup device
23
. Thus, switching is performed to correspond to the divided sampling areas, as shown in FIG.
22
. That is, a value obtained by A/D-converting the picked up image signal in area A is supplied to an integrating circuit
30
A. Similarly, values obtained by A/D-converting the image signals in areas B, D, D, E and F are supplied to integrating circuits
30
B,
30
C,
30
D,
30
E and
30
F.
Each of the integrating circuits
30
A to
30
F integrates supplied image signals for one field so as to transmit a result of integration to the abnormality determination circuit
31
. Abnormality determination circuits
31
A to
31
F delete integrated values in areas each including brightness not higher than a constant level determined by the reference-value memory
35
and brightness not lower than a predetermined level to transmit results to the average value calculating circuit
32
. The average value calculating circuit
32
calculates average brightness.
The comparison circuit
33
performs comparison with a predetermined brightness level previously stored in the desired-value memory
34
. Then, the aperture mechanism
21
and the variable gain amplifier
25
are controlled in such a manner that the average brightness approaches the determined brightness level stored in the desired-value memory
34
.
As described above, the conventional image pickup apparatuses have mainly employed TTL metering which requires the comparison circuit for causing the integrated value of an image signal to approach a predetermined level and arranged to adjust exposure in accordance with a result of the comparison performed by the comparison circuit. Although the above-mentioned conventional example comprises the mechanical aperture for adjusting exposure, a similar structure is constituted even if an image pickup device having a variable charge storage time is employed.
In addition to the TTL metering method, an external metering method is known which uses a photometry sensor for measuring the brightness of a picked up image similarly to the metering operation which is performed by the silver salt film, as shown in FIG.
23
. Referring to
FIG. 23
, the same reference numerals as those shown in
FIG. 21
represent the same or corresponding elements. Reference numeral
42
represents an A/D converter and
43
represents a microcomputer.
The operation will now be described.
The quantity of incident light converged by the lens
20
is adjusted by the aperture mechanism
21
so that the picked up image is formed on the image pickup device
23
. The variable gain amplifier
25
amplifiers a signal transmitted from the image pickup device
23
, and then transmits an image signal. A lens
40
for a photometry sensor is disposed in such a manner that an image is formed on the photometry sensor
40
with the same field angle as that of the image formed on the image pickup apparatus
23
. The photometry sensor
41
is arranged to transmit a voltage level which is changed in accordance with the quantity of incident light. The transmitted voltage level is converted into a digital signal by the A/D converter
42
, and then supplied to the microcomputer
43
. The microcomputer
43
is able to detect the quantity of incident light, that is, the brightness of the subject which is being picked up in accordance with the voltage level supplied from the photometry sensor
41
. The microcomputer
43
transmits the predetermined degree of aperture of the aperture mechanism
21
and the gain of the variable gain amplifier
25
in such a manner that a predetermined image signal can be obtained in accordance with the value obtained from the photometry sensor
41
. Moreover, the microcomputer
43
controls the exposure in such a manner that the level of the image signal which is transmitted from the variable gain amplifier
25
is made to be constant.
The two examples of the exposure control method adapted to the conventional image pickup apparatuses have been described above. Video cameras and electronic still cameras usually employ the TTL metering method shown in
FIG. 21
or the external metering method shown in
FIG. 23
to control the exposure.
The exposure control which is performed by the conventional image pickup apparatus employing the TTL metering method is arranged in such a manner that the integrated value in each field is subjected to a comparison in the comparison circuit at each operation so as to converge the obtained values in such a manner that a constant brightness level can be realized. To realize a predetermined brightness level, comparison must be performed to correspond to the steps of the degrees of the aperture. Therefore, a long time is required to realize a predetermined image signal level. If the steps of the degree of the aperture is enlarged to shorten the required time, there arises a problem in that the aperture encounters hunting.
The exposure control which is performed by the external metering method is arranged in such a manner that an image similar to that obtainable by the image pickup device is formed on the photometry sensor. Therefore, a precise photometry sensor lens is required. Since the image pickup device has a narrow input dynamic range as compared with that of the silver salt camera, precise exposure control must be performed. Therefore, the accuracy of the aperture mechanism and environmental dependency, such as the temperature characteristic of the photometry sensor, must be considered. As a result, there arises a problem in that the structure becomes too complicated.
What is worse, also the exposure control which is performed by the TTL metering method is required to continuously operate all of the circuits until a required image is picked up. Therefore, there arises a problem in that a battery is consumed extremely quickly if electric power is supplied from the battery.
SUMMARY OF THE INVENTION
An object of the present invention, attempted to solve the above-mentioned problems, is to obtain an image pickup apparatus which is capable of performing pre
Kuno Tetsuya
Matoba Narihiro
Sugiura Hiroaki
Yamashita Koichi
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