Television – Camera – system and detail – Optics
Reexamination Certificate
1995-04-11
2004-10-19
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Optics
C348S364000, C348S333010
Reexamination Certificate
active
06806907
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image pickup apparatus and, more particularly, to an exposure control apparatus.
2. Related Background Art
FIGS. 1A and 1B
are block diagrams showing the arrangement of a conventional image pickup apparatus. Referring to
FIGS. 1A and 1B
, the image pickup apparatus comprises an imaging lens group
1
for an object image, an aperture mechanism
2
such as an iris for controlling the incident light amount, an image pickup element
3
for photoelectrically converting incident light, an iris detection unit
4
comprising, e.g., a Hall element for detecting the state of the aperture mechanism
2
, a driving motor
5
such as an IG meter for driving the aperture mechanism
2
, an image pickup element control circuit
6
which controls the image pickup element
3
to read out a photoelectrically converted signal, and controls the signal accumulation time, i.e., controls a so-called electronic shutter function, a sample & hold (S/H) circuit
7
for sampling a signal photoelectrically converted by the image pickup element
3
, an auto-gain control circuit (to be referred to as an AGC circuit hereinafter)
8
for electrically amplifying a signal, and a camera signal processing circuit
9
for performing processing of a signal such as gamma correction, color separation, color difference matrix, and the like, and thereafter, adding a synchronization signal to the processed signal to generate a standard TV signal. As the camera signal processing circuit
9
, as shown in
FIG. 13
, an analog signal processing circuit
9
a
for performing processing in an analog signal state, or a digital signal processing circuit
9
b
for analog-to-digital converting a video signal, performing processing in a digital signal state, and thereafter digital-to-analog converting the processed signal is available. In this case, the analog signal processing circuit
9
a
is used.
The apparatus also comprises a video tape recorder (to be referred to as a VTR hereinafter)
10
for recording a video signal from the camera signal processing circuit
9
on a magnetic tape, an electronic viewfinder
11
for monitoring the video signal, an AE detection circuit
15
for gating an output signal from the AGC circuit
8
as needed, and performing photometry for exposure control, such as selective central area photometry, an exposure control circuit
16
for controlling the shutter speed of the electronic shutter controlled by the image pickup element control circuit
6
, the gain of the AGC circuit
8
, and the like, an iris driving circuit
17
for driving the aperture mechanism
2
in accordance with an output from the exposure control circuit
16
, a gate pulse control circuit
18
for generating gate pulses used for gating an image area required for detection in the AE detection circuit
15
, a program mode change unit
19
for selecting a program mode, and a system control circuit
24
for controlling the program mode.
The AE detection circuit
15
comprises a selective central area photometry circuit
15
a
, weighting circuits
15
b
and
15
c
, and an adder
15
d
. The exposure control circuit
16
comprises an exposure control operation unit
16
a
, an AGC control unit
16
b
, an electronic shutter control unit
16
c
, and an iris control unit
16
d
. The system control circuit
24
comprises look-up tables (LUTs)
12
,
22
,
32
, and
42
corresponding to program modes
1
to
4
, and an LUT data control unit
24
a
. Note that the AE detection circuit
15
and the exposure control circuit
16
constitute exposure control means.
The image pickup apparatus with the above-mentioned arrangement realizes photographing control system called a “program mode” which sets a mode for selecting a plurality of control parameters such as exposure control parameters, white balance control parameters, gamma correction, aperture correction, and color suppression correction parameters as camera signal processing parameters, and the like under conditions optimal for the respective photographing conditions, under some typical photographing conditions, so as to allow optimal photographing operations in various places and various conditions.
An example of a program mode that places an importance on exposure control will be described below.
Control parameters for determining exposure include the aperture mechanism, AGC, electronic shutter, and the like, and the system control circuit
24
stores data, which are set in correspondence with objects and photographing conditions in units of program mode, in the form of LUTs, i.e., the LUT
12
corresponding to program mode
1
, the LUT
22
corresponding to program mode
2
, the LUT
32
corresponding to program mode
3
, and the LUT
42
corresponding to program mode
4
. The system control circuit
24
reads out data of an LUT corresponding to the program mode set by the program mode switch unit
19
, and controls the respective parameters on the basis of the readout data, thus realizing the program mode.
For example, when the motion of an object is fast, the electronic shutter for controlling the accumulation time of the image pickup element
3
is preferentially set at high speeds, thus achieving a so-called “sport mode” which allows a photographing operation with a good dynamic resolution. On the other hand, when the aperture mechanism is preferentially set at the full-open side, and exposure control is performed based on other parameters, a so-called “portrait mode” which can provide an effect of blurring the background image due to a small field depth, and is suitable for a photographing operation of a person is achieved. In this manner, photographing operations optimal for photographing conditions can be realized.
Furthermore, the AE detection circuit
15
controls the photometry distribution on the basis of the photometry area and detection position of a video signal for exposure control, which are set by the gate pulse control circuit
18
, thus realizing an optimal photographing operation. For example, the AE detection circuit
15
can realize so-called average photometry which detects a whole image area, and performs exposure control, so that the detection signal from the whole image area has a predetermined level, as shown in FIG.
5
A. Also, the AE detection circuit
15
realizes selective central area photometry which detects only a central portion of the image area, and performs exposure control, so that the detection signal from the image area has a predetermined level, as shown in FIG.
5
B.
When the AE detection circuit
15
performs exposure control on the basis of detection data obtained by weighting detection data from the whole image area and the selective central area in the weighting circuits
15
b
and
15
c
, and adding the weighted data by the adder
15
d
at a predetermined ratio, exposure control based on a photometry method as a combination of the average photometry and selective central area photometry can be realized. By changing the weighting coefficients in correspondence with an object and a photographing condition in each program mode, optimal exposure control that can effectively utilize the merits of the respective photometry methods can be realized. For example, when a main object is illuminated with spot light, and its background portion is dark, or when a main object is irradiated with back light, the weighting coefficient of the selective central area photometry is increased. On the other hand, when a proper exposure state is to be attained not only for a main object but also for a background object with a good balance, the weighting coefficient of the average photometry is increased.
Also, as shown in
FIG. 5C
, the frame is divided into division areas, image detection is performed in units of division areas, and the areas of detection data used in exposure control are limited or the weighting coefficient is changed in correspondence with an object or a photographing condition in each program mode, thus allowing flexible exposure control.
However, even in t
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Garber Wendy R.
Nguyen Luong T.
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