JPH0556335A - Automatic diaphragm adjusting device - Google Patents

Abstract

PURPOSE:To operate a gradient correction optimal to each system by setting a gamma correction coefficient concerned with a peak-to-peak value photometric system smaller than that concerned with a mean value photometric system. CONSTITUTION:This device is equipped with a gamma correcting circuit 18 concerned with a mean value photometric system and a gamma correcting circuit 19 concerned with a peak-to-peak value photometric system, as circuits concerned with a photometric system, and an automatic mean value photometric diaphragm adjusting circuit 20, and a automatic peak-to-peak value photometric diaphragm adjusting circuit 21, as automatic diaphragm adjusting circuits. Then, the gamma correction coefficient concerned with the peak-to-peak value photometric system is set smaller than that concerned with the mean value photometric system. Therefore, when the level of a video input signal 17 is small, a level correction which is larger than that concerned with the mean value photometric system is operated by the peak-to-peak value photometric system, so that the level of a video output signal S can be made larger than that of a video output signal H when the level of the video input signal 17 is small. Thus, a video signal by which the dark parts of an object can be easily observed is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation of a correction amount in a television camera having an automatic aperture adjusting device for gamma-correcting an output signal related to a video signal based on an input signal.

[0002]

2. Description of the Related Art In a television camera, the following photometric methods are mainly used for automatic aperture adjustment. That is, the peak value 1 of the video signal 4 as shown in FIG.
And a peak value metering system that adjusts the aperture to be the same as
The average value photometric method is to adjust the aperture so that the average value of the video signal 8 as shown in FIG. 4 becomes the same as the reference value 7.

Some television cameras have a function of switching between the peak value photometric method and the average value photometric method. Here, when mainly focusing on a bright subject, iris adjustment is performed using the peak value metering method without saturating the image on all parts of the screen,
On the other hand, in the case of mainly focusing on a dark place of a subject, a method of adjusting an aperture using an average value metering method is adopted.

[0004]

However, the peak value metering method according to the conventional automatic aperture adjustment device is, in principle, the average value metering method in a camera capable of expressing only a finite number of gradations for an object in a large luminance range. In comparison, this is a method in which a gradation difference is focused on a portion having high brightness, which is about the brightness of the subject. However, in either of the photometric methods, the purpose is to set a target subject to be imaged in a range having a gradation. Here, in the case of peak value photometry, the high-brightness portion is used as a reference, so that the high-brightness portion has a peak value at the limit of the range with the gradient, rather than at the center of the range with the gradient. The level of the subject will be set. In this case, the image level of a subject having a luminance far from the peak luminance becomes a small value, and when viewed on a monitor, it is often too dark. The effect may be that there is good contrast, but in general, it is often difficult to see the image. If the image level of a subject having a peak value is set outside the range with the gradient, the peak value level will be saturated, and the meaning of the peak metering system will be lost. In addition to video signal processing in aperture control using the average value photometry method, this processing method is basically used to maintain the gradation near the peak value level and raise the video level of a subject with relatively low brightness to make it easier to see. Was desired.

The present invention has been made in view of such a conventional situation, and in an automatic aperture adjusting device in a television camera having an automatic aperture adjusting circuit using a peak value photometry method or an average value photometry method, It is an object of the present invention to provide an automatic aperture adjustment device that can perform gradation correction most suitable for each method.

[0006]

Therefore, the present invention is directed to a lens system or a light source system for adjusting a diaphragm so that a peak value of a video signal becomes equal to a predetermined first reference value. A value metering method and an average value metering method that adjusts the aperture so that the average value of the video signal is the same as the predetermined second reference value are selected to perform automatic aperture adjustment and In an automatic aperture adjustment device for a television camera having a gamma correction circuit for gamma-correcting an output signal based on an input signal, a gamma correction coefficient related to a peak value metering method is set smaller than a gamma correction coefficient related to an average value metering method. I did it.

[0007]

[Function] The smaller the gamma correction coefficient, the larger the level correction is made when the image input signal before gamma correction is small,
As a result, the video output signal after gamma correction becomes large, so
By setting the gamma correction coefficient for the peak value metering method smaller than the gamma correction coefficient for the average value metering method,
When the image input signal is small, the level correction amount according to the peak value photometry method is larger than the level correction amount according to the average value photometry method. Therefore, when the image input signal level is small without changing the peak value level, that is, the darker the screen is, the larger the level correction is made in the peak value metering method, and the peak value metering method is used. Even if the aperture is adjusted, a video signal in which the dark part of the subject can be easily observed can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a circuit according to one embodiment of the present invention. This circuit is a circuit related to a photometric system, and a gamma correction circuit 18 related to an average value photometric system and a gamma correction circuit related to a peak value photometric system. It also has a correction circuit 19 and also has an average value photometric automatic aperture adjustment circuit 20 and a peak value photometric automatic aperture adjustment circuit 21 as automatic aperture adjustment circuits.

The level detection of the video signal in the control loop of the automatic aperture adjustment circuit system is performed by detecting the video signal in FIG.
The target is 17 and the level of the video signal for each photometric system is detected from the signal. The average value photometric level detection circuit 20 outputs a voltage of a specified level when the level average value of the video signal is a specified value (eg, a value at which the output of the gamma correction circuit becomes 70%), and the peak value photometric level The detection circuit 21 detects that the peak value of the video signal is at a specified level (eg,
The specified voltage is output when the gamma correction circuit output reaches a value of 110%. The gamma correction circuit at the next stage of the video signal specified by each of the photometric methods corrects the video signal. Here, the gamma correction curve is switched according to the selection of the photometric method.

Further, the circuit related to the photometric system and the automatic aperture adjustment circuit are switched in conjunction with each other by the interlock switch 22, and the video signal 17 input to this circuit is a gamma-corrected video output signal. 23 and diaphragm control signal
It is output as 24. Here, the video output signal H related to the gamma correction circuit 18 is H = Y ^r ... where Y is a video input signal before gamma correction γ is a normal gamma correction coefficient (0 <γ <1) The video output signal S related to the gamma correction circuit 19 is as follows: S = Y ^(ra) ... where Y: video input signal before gamma correction γ-a; gamma correction coefficient (0 < γ <1,0 <a <
γ) a is represented by an expression that is a correction amount from a normal value.

In the gamma correction circuit 19 relating to the peak value photometry method expressed by the above equation, γ-a becomes smaller as a becomes larger, so that a larger gamma correction is made when the level of the video input signal Y is small. In this range, the level of the video output signal S increases. In the automatic aperture adjustment circuit for average value photometry, the aperture is controlled so that the input signal level of the gamma correction circuit becomes the specified value of the average value of the image. The diaphragm is controlled so that the level becomes a specified value. Here, the specified values are different. In the case of aperture control by average value photometry, the high brightness portion is compressed with the result. In contrast, in many cases where aperture control by peak value photometry is used, the peak value is set to the upper limit value as the standard of the video signal, so the average value of the video signal has the same gamma correction coefficient. If it is,
It is usually lower than the average value photometry. Conversely speaking, there is a peak value metering method as a diaphragm control method when a subject having a peak value level with a large difference between the average value and the peak value is imaged as a main subject. Even in the case of this peak value metering, the gamma correction coefficient of the peak value metering method is used for the average value metering method to increase the brightness level and make it easier to observe images of subjects with levels near the average value. It is smaller than the value of the coefficient in.

That is, as shown in FIG. 2, by setting the gamma correction coefficient relating to the peak value photometric method smaller than the gamma correction coefficient relating to the average value photometric method, the average value is obtained when the level of the video input signal Y is low. As compared with the level correction related to the value metering method, the peak value metering method performs a larger level correction, and as a result, when the video output signal S has a smaller level of the video input signal Y than the video output signal H. It will be a big level.

Therefore, when the level of the image input signal Y is small without changing the level of the peak value, that is, the darker the screen is, the larger the level correction is made in the peak value metering method, and the peak value metering method is performed. Even if the automatic aperture adjustment is performed using, it is possible to obtain an image signal in which the dark part of the subject can be easily observed.

[0014]

As described above, according to the present invention,
Since the automatic aperture adjustment device adjusts the aperture automatically by setting the gamma correction coefficient for the peak value metering method smaller than the gamma correction coefficient for the average value metering method, the peak value metering is performed in darker areas of the subject. In this method, a large level correction is performed, and there is an effect that it is possible to obtain a video signal in which a dark portion of a subject can be easily observed even if automatic aperture adjustment using a peak value photometry method is performed.

[Brief description of drawings]

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the gamma correction action in the peak value photometry method and the average value photometry method.

FIG. 3 is a diagram showing a video signal in the case of the peak value photometry method.

FIG. 4 is a diagram showing a video signal in the case of an average photometry method.

FIG. 5 is a characteristic diagram for explaining gamma correction.

[Explanation of symbols]

 18 Gamma correction circuit for average value metering system 19 Gamma correction circuit for peak value metering system 20 Average value automatic iris adjustment circuit 21 Peak value metering automatic iris adjustment circuit

Claims (1)

[Claims] 1. A peak value metering method for adjusting an aperture for a lens system or a light source system so that a peak value of a video signal becomes equal to a predetermined first reference value, and an average value of the video signal is predetermined. Of the average value metering method that adjusts the aperture so that the aperture becomes the same as the second reference value, the automatic aperture adjustment is performed, and the output signal related to the video signal is gamma-corrected based on the input signal. An automatic aperture adjustment device for a television camera having a gamma correction circuit, wherein a gamma correction coefficient for a peak value photometric method is set smaller than a gamma correction coefficient for an average value photometric method.