JP2631216B2 - Exposure control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exposure control device arranged in a camera such as a video camera.

BACKGROUND OF THE INVENTION The amount of exposure in a video camera is determined by the exposure time and the aperture opening at that time. The exposure time is generally one field period, which is 1/60 second in the NTSC system and 1/50 second in the PAL system. Therefore, exposure control is generally performed by adjusting the aperture of the optical system. When an image sensor capable of performing an electronic shutter operation is used, the exposure time can be controlled by controlling the electronic shutter.

As can be understood from the above description, this type of exposure control apparatus performs feedback control of the aperture of the optical system or the electronic shutter of the image sensor so that the video signal level is always constant. FIG. 11 shows an example of a conventional exposure control device. In the figure, 1 is a lens, 2 is an aperture control circuit (which may be an electronic shutter if an image pickup device described later is a solid-state image pickup device), and an exposure control circuit for controlling an exposure amount.
Denotes an image sensor, 4 denotes a signal level detection circuit for generating an exposure control signal, 5 denotes a power supply for generating a level corresponding to an exposure control target value, and 6 denotes a video signal output terminal.

In the above configuration, the subject image that has passed through the lens 1 enters the image sensor 3 where it is converted into a video signal and input to the signal level detection circuit 4. Further, the video signal is input via a video signal output terminal 6 to a signal processing circuit (not shown) for generating a video signal. The signal level detection circuit 4
Generates an exposure control signal based on the input video signal,
The signal is output to the exposure control circuit 2. Then, the exposure control circuit 2 uses the exposure control signal as a measure of exposure,
Control is performed so that this value always becomes a constant level value input from the power supply 5 that generates a level corresponding to the exposure control target value.

Here, in the signal level detection circuit 4, for example, one of the following two types of photometry was performed.

1) Average photometry over the entire surface 2) Peak photometry However, each of the photometry methods has the following disadvantages.

In 1), when a high brightness portion such as the sky or a light source occupies a large area in the screen, the object to be projected sinks black, and when the background darkens, the object becomes overexposed.

In 2), when a high-luminance part enters even a part of the screen, the entire screen darkens.

In addition, 3) there is a photometry system of center-weighted photometry or spot (partial) photometry, which can eliminate the disadvantages of the above 1) and 2) to some extent. When the size of the subject in the screen at that time is considerably small with respect to the photometry area having the above, even if an attempt is made to perform exposure control with the video signal in the photometry area, the influence of the background is included. If the size of the subject in the screen at that time is much larger than the width of the photometric area, sufficient information on the subject can be obtained even if exposure control is performed using a video signal in the photometric area. Therefore, there is a problem that proper exposure control cannot be performed.

(Object of the Invention) It is an object of the present invention to provide an exposure control device that can always provide an optimal exposure even when the size of a subject in a screen changes.

(Features of the Invention) In order to achieve the above object, the present invention provides a calculating means for calculating difference information of a predetermined frequency component in a video signal obtained inside and outside a detection area having a variable size, Determining means for determining the size of a subject in a shooting screen from respective difference information in different areas of the detection area calculated by the means; and photometry in accordance with the size of the subject determined by the determining means. A photometric area width changing means for changing the size of the area, whereby the size of the photometric area is changed according to the size of the subject determined by the determining means, that is, the subject is reflected relatively large. In this case, the photometric area is widened, and when the subject is relatively small, the photometric area is narrowed.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 3 is a block diagram showing one embodiment of the present invention.
The same parts as those in FIG. 11 are denoted by the same reference numerals.

11 is different from FIG. 11 in that a photometric area position control circuit 7 and a synchronization signal input terminal 8 for transmitting a synchronization signal (horizontal and vertical synchronization signals) to the circuit are added. This is a signal level detection circuit 9 for generating an exposure control signal based on a video signal of a photometry area instructed by the control circuit 7.

The subject image that has passed through the lens 1 enters the image sensor 3,
Here, it is converted into a video signal and input to the signal level detection circuit 9 and also input to the photometry area position control circuit 7.
The photometric area position control circuit 7 tracks the photometric area at the position of the subject on the screen and sets the size of the photometric area to a size corresponding to the subject (for details, see FIGS. 1 and 2). ,
A photometric area control signal indicating the position and size of the photometric area in the screen is output to the signal level detection circuit 9 as an HV composite signal synchronized with the synchronization signal. Then, the signal level detection circuit 9 generates an exposure control signal necessary for performing exposure control based on the video signal from the image sensor 3 and the photometric area control signal. The average value of the signals or a value obtained by weighting and adding the video signal in the photometry area to the video signal of the entire screen is used as an exposure control signal (in this case, an area other than the photometry area is used as an auxiliary photometry area). Output to circuit 2. As described above, the exposure control circuit 2 uses the exposure control signal as a measure of exposure, so that this becomes a constant level value input from the power supply 5 that always generates a level corresponding to the exposure control target value.
For example, this is performed by controlling the aperture state of the stop.

FIG. 1 shows an example of the configuration of the photometry area position control circuit 7. In FIG. 1, reference numeral 101 denotes a luminance level detection circuit 101a in the photometry area and a luminance level around the photometry area as shown in FIG. Brightness level detection circuit 101 outside the photometry area to be detected
b, subtraction circuit 101c for calculating the difference between the inside and outside luminance, said subtraction circuit 101
The subject size determination circuit 10 that determines the size of the subject at that time from the absolute values of the plurality of pieces of luminance difference information sent from c.
1d, a photometric area width setting circuit including a photometric area width control circuit 101e that makes the size of the photometric area substantially the same as the determined size of the subject, 102 is a photometric area at a position corresponding to the position of the subject on the screen. A photometric area position setting circuit for setting the position of the photometric area on the screen in accordance with an instruction signal input by the photographer to position the area, a signal 103 indicating the position and size of the photometric area on the screen (synchronous This is a photometric area control signal generation circuit that generates an HV composite signal synchronized with the signal.

Next, the operation in FIGS. 1 and 2 will be described with reference to FIGS. 4 and 5, A is a screen, B (B1 to B3)
Is a photometric area whose area is changed according to the size of the subject, and C (C1, C2) is the subject projected on the screen A.

When a video signal is input, the luminance level detection circuit 101a in the photometry area causes the photometry area B (for example, the photometry area B is initially located at the center of the screen A, and its area is, for example, B2
Brightness level is set to
The luminance level detection circuit 101b outside the photometry area detects the luminance level around the photometry area B, and outputs the detection results of the luminance levels to the subtraction circuit 101c. The subtraction circuit 101c obtains the difference between the input luminance levels and outputs the difference to the subject size calculation circuit 101d. Then, the subject size calculation circuit 101d changes the area of the photometry area B in the screen A in a plurality of stages by a gate control or the like through a circuit (not shown) (in FIG. 4 and FIG. 5, there are three stages). It is assumed that the width of the photometric area B having the largest difference between the inner and outer luminances in each area substantially matches the size of the subject C in the screen A at that time. Determination, that is, the size of the subject C in the screen A is determined. In this embodiment, the detection area for determining the size of the subject C and the photometry area are associated with each other, but a configuration having an area for detecting the size of the subject C may be provided. The photometry area size control circuit 101e sets the size of the photometry area B at that time based on the result determined by the subject size calculation circuit 101d. Here, as described above, since the detection area for judging the size of the subject C and the photometry area are associated with each other, the photometry area having the largest luminance difference between the inside and outside is set as the photometry area B at that time. .

For example, in FIGS. 4 and 5, it is assumed that the subject C has a uniform luminance and a large contrast with the background. Assuming that the absolute values of the luminance difference between the inside and outside of the photometry areas B1 to B3 are a, b, and c, the state shown in FIG. 4, that is, the subject C1 is almost the same size as the photometry area B3 or smaller. In this case, c>b> a, and conversely, in the state shown in FIG. 5, that is, when the subject C2 is larger than or almost equal to the photometric area B1, c <b <a. When the size of the subject C is substantially equal to the size of the photometric area B2, b> a, c.
That is, when the size of the photometry area B is changed, the difference between the inside and outside brightness becomes maximum when the size of the subject C substantially matches the size of the photometry area B, and decreases even if the size is larger or smaller. I do. The photometric area width setting circuit 101 changes the area of the photometric area B in small steps (in the embodiment, 3
The brightness level difference between the inside and the outside is checked, and the width of the photometry area is set so that the difference becomes maximum (such an operation is performed, for example, for each field). As a result, the size of the photometric area B substantially matches the size of the subject C (the photometric area B3 in the state shown in FIG. 4, the photometric area B1 in the state shown in FIG. 5,
Each is set as the photometry area at that time).

In addition to the signal indicating the width of the photometry area B determined as described above, the signal indicating the position of the photometry area B on the screen is supplied to the photometry area control circuit 103 by the photometry area position setting circuit.
A signal indicating the position and size of the photometric area on the screen is generated based on these signals.

As described above, the position and the size of the photometric area B corresponding to the position and the size of the subject C in the screen A are determined. For example, the average value of the video signal in the photometric area B is The value obtained by weighting and adding the video signal in the photometry area B to the video signal of the entire screen is the signal level detection circuit 9 in FIG.
The exposure control signal is output from the power supply 5 that generates a level corresponding to the exposure control target value. Then, for example, the aperture state of the stop is controlled. Such an operation is performed in real time. Therefore, exposure control optimal for the subject C can be performed.

FIG. 6 shows another configuration example of the photometry area position control circuit 7. 3, the position of the photometric area B in the screen A is controlled in accordance with an external signal. However, here, the photometric area position control circuit 202 uses the photometric area width setting circuit 101. The luminance difference information inside and outside the photometry area B whose position is changed in the screen is extracted through the photometry area width setting circuit 201 and the like having substantially the same configuration as that described above. Is configured to move the photometry area B to the position of the subject C in the above. The operation at this time will be described with reference to FIG.

In FIG. 7, assuming that the luminance difference between the inside and outside of the photometric areas B2-1 and B2-2 is ΔL1 and ΔL2, there is a relationship of ΔL1> ΔL2, and the photometric area position control circuit 202 always sets the luminance level near the subject C3 to Then, the photometric area is moved to a position where ΔL becomes maximum, and thereafter, this operation is repeated. Therefore, the position of the subject C and the position of the photometry area B2 in the screen A always coincide.
The position control and the width control of the photometry area B may be performed in parallel with each other, or when the same microcomputer is used for each determination, an algorithm may be sequentially configured. The photometry area control signal generation circuit 103 is based on each signal from the photometry area width setting circuit 201 and the photometry area position control circuit 202, as described above,
A signal indicating the position and size of the photometry area B within the screen A is generated.

FIG. 8 shows another example of the configuration of the photometric area position control circuit 7. Here, as shown in FIG. 9, the screen A is divided into three types of large, medium and small photometric areas B1 to B3. The luminance difference between the inside and outside of each area is monitored, and the photometric area B where the inside and outside luminance difference is always maximum is selected. 8, the photometric area control signal generation circuit 302 corresponding to the photometric area control signal generation circuit 103 in FIG.
Signals indicating three types of areas corresponding to 3 are generated, and the photometric area size setting circuit 301 monitors the luminance difference between the inside and outside of each area. The changeover switch 303 selects and outputs a photometric area control signal of either large, medium or small, that is, a photometric area control signal corresponding to the one closest to the size of the subject C4 (the photometric area B2 in FIG. 9).

FIG. 10 shows the configuration inside the photometric area width setting circuit 301. In the figure, reference numerals 301a to 301c denote luminance level detectors in the photometric area having the same function as the luminance level detector 101a in the photometric area in FIG. 2, and 301d to 301f denote luminance level detectors 101b outside the photometric area in FIG. A luminance level detector outside the photometry area having the same function as that of the photometry area, 301g to 301i are subtractors, and 301j are three types of photometry areas
A subject size determination circuit that receives the difference between the inside and outside brightness levels of B1 to B3 as input, and 301k is a photometry area width control circuit that sets the width of the photometry area B at that time.

By configuring the photometric area width setting circuit 301 as described above, the photometric area B corresponding to the size of the subject C can be selected based on the magnitude relationship of the luminance difference between the inside and outside of the three types of photometric areas B1 to B3. . This will be described with reference to FIGS. 4 and 5. In the state shown in FIG. 4, the absolute values a, b, and c of the average values of the inner and outer luminance differences are a <b <c. In the state shown in FIG. 5, a>b> c. Become. If the size of the subject C4 and the size of the photometric area B2 substantially match as shown in FIG. 9, b> a, c. As described above, it is possible to determine whether the width of the photometry area B should be increased or decreased based on the difference in brightness between the inside and outside.

In the above configuration example, monitoring and control of the area of the photometry area B are always performed. For example, when the area of the photometry area B is once determined, the area is locked, and the brightness of the inside and outside of the area is locked. As long as the level does not change by a certain value or more, it is determined that the proper exposure of the subject C has been obtained, and when the brightness difference between the inside and outside changes by a certain value or more thereafter, the lock is released to control the width of the photometric area B May be performed again.

According to the present embodiment, the size of the subject C in the screen A is determined based on the absolute value of the luminance difference between the inside and outside of the photometric area B, and the size of the subject C is made to match the size of the subject C. Therefore, the optimum exposure can be given to the subject C. Further, since the photometric area B can be moved to the position of the subject C in the screen A at the same time, more optimal exposure can be given, and even if the subject C moves or the camera is moved. Even when panning and tilting are performed, a natural image can be obtained.

(Correspondence between Invention and Embodiment) In this embodiment, the luminance level detection circuit 10
1a, 301a to 301c, luminance level detection circuit 101b, 30 outside the photometry area
1d to 301f, the subtraction circuits 101c, 301g to 301i serve as calculation means of the present invention, and the subject size determination circuits 101d, 301j serve as determination means.
The photometric area size control circuits 101e and 301k correspond to photometric area size changing means, respectively.

(Modification) In the present embodiment, the size of the subject is determined from the luminance difference between the inside and outside of the photometry area B. However, the present invention is not limited to this. For those skilled in the art, it is also possible for those skilled in the art to make a determination based on a difference between high-frequency components on the high-frequency side of the luminance component in each video signal passing through the inside and outside, and to set the width of the photometry area B to this. Will be easy.

(Effects of the Invention) As described above, according to the present invention, a calculating means for calculating difference information of a predetermined frequency component in a video signal obtained inside and outside a detection area having a variable width, Determining means for determining the size of a subject in a shooting screen from respective difference information in different areas of the detection area calculated by the means; and photometry in accordance with the size of the subject determined by the determining means. A photometric area width changing means for changing the size of the area, whereby the size of the photometric area is changed according to the size of the subject determined by the determining means, that is, the subject is reflected relatively large. When the subject is relatively small, the metering area is narrowed.If the subject is relatively small, the optimal exposure is always maintained even if the size of the subject on the screen changes. It is possible to give You.

[Brief description of the drawings]

1 is a block diagram showing a configuration example of a photometry area position control circuit shown in FIG. 3, FIG. 2 is a block diagram showing a specific configuration example in a photometry area width setting circuit shown in FIG. 1, and FIG. FIG. 4 is a schematic block diagram showing an embodiment of the present invention, FIGS. 4 and 5 are diagrams for explaining the relationship between the size of the subject in the screen and the photometric area, and FIG. FIG. 7 is a block diagram showing another example of the configuration of the control circuit. FIG. 7 is a diagram for explaining the photometric area tracking for a subject whose position changes in the screen. FIG. 8 is another example of the configuration of the photometric area position control circuit shown in FIG. FIG. 9 is a diagram for explaining the relationship between the size of the subject in the screen and the photometric area, and FIG. 10 is a diagram showing a specific configuration example in the photometric area width setting circuit shown in FIG. Block Diagram,
FIG. 11 is a block diagram showing an example of a conventional exposure control device. 1 ... lens, 2 ... exposure control circuit, 3 ... image sensor,
5 Power supply 7 Photometric area position control circuit 9 Signal level detecting circuit 101a, 301a to 301c Luminance level detecting circuit in photometric area 101b, 301d to 301f Luminance level detection outside photometric area Circuit, 101c, 301g-301i ..... subtraction circuit, 101d,
301j: subject size determination circuit; 101e, 301k: photometric area width control circuit.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Kunihiko Yamada 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Tamagawa Office of Canon Inc. In-house (72) Inventor Kunio Imai 770 Shimonoge, Takatsu-ku, Kawasaki-shi, Kanagawa Prefecture Tamagawa Works of Canon Inc. (56) References JP-A-63-254871 (JP, A) JP-A-61-213367 (JP, A) JP-A-58-153465 (JP, A) JP-A-64-13032 (JP, U)

Claims (3)

(57) [Claims] An exposure control apparatus for performing exposure control based on a video signal obtained in a photometry area designated in a screen, wherein a predetermined range of a video signal obtained inside and outside a detection area whose width is variable. Calculating means for calculating the difference information of the frequency components, and determining means for determining the size of the subject in the shooting screen from the respective difference information in different areas of the detection area calculated by the calculating means, An exposure control apparatus comprising: a photometric area width changing unit that changes the size of the photometric area according to the size of the subject determined by the determining unit. 2. The exposure control device according to claim 1, wherein said predetermined frequency component is a luminance component in a video signal. 3. The exposure control apparatus according to claim 1, wherein said predetermined frequency component is a high frequency component on a high frequency side of a luminance component in a video signal.