JP3205941B2 - Automatic aperture adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television camera having an automatic iris adjustment device, and to the operation of the amount of correction in gamma correction of an output signal relating to a video signal based on an input signal.

[0002]

[Prior art]Correction of optical characteristics of CRT of receiver
Gamma interpolation as non-linear processing performed on the television camera side
Positive is known. Such a gamma correction is shown in FIG.
Thus, for the video input signal Y, the video output signal is Y
^r (Γ: gamma correction coefficient). Place
so,Used for automatic aperture adjustment in television cameras
The following photometric methods are mainly used. That is, in FIG.
As shown, the peak value 1 of the video signal 4 is the same as the reference value 3.
The peak value metering method that adjusts the aperture so that it is shown in FIG.
Such that the average value of the video signal 8 is the same as the reference value 7.
And an average value metering method for adjusting the aperture.

[0003] Some television cameras have a function of switching between the peak value metering method and the average value metering method. Here, when mainly focusing on a bright subject, the aperture is adjusted using the peak value metering method without saturating the image in all parts of the screen,
On the other hand, when mainly focusing on a dark place of a subject, a method of adjusting the aperture using an average value photometry method is adopted.

[0004]

However, the peak value metering method according to the conventional automatic aperture adjustment device is, in principle, an average value metering method in a camera capable of expressing a subject in a large luminance range with only a finite gradation. In comparison, this is a method in which a high-luminance portion, such as the brightness of the subject, is prioritized with a gradation difference. However, in either of the photometric methods, the purpose is to set the target subject to be imaged in a range having a gradient. Here, in the case of peak value metering, since a high luminance portion is used as a reference, the high luminance portion has a peak value not at the center of a certain gradient range but at the limit of a certain gradient range. The level of the subject will be set. In this case, the image level of a subject having a luminance different from the luminance of the peak value becomes a small value, and when viewed on a monitor, it often becomes too dark. As an effect, there may be a case where a contrast may be sufficient, but in general, it is often difficult to view an image. If the image level of a subject having a peak value is set outside a certain range of the gradient, the level of the peak value will be saturated, and the meaning as the peak photometry method will be lost. In addition to video signal processing in aperture control using the average value photometry method, this processing method is based on a technique that raises the video level of a subject with a relatively low level of brightness without losing the gradation near the peak value level and makes it easier to see. Was desired.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional situation, and is directed to an automatic iris adjustment device for a television camera having an automatic iris adjustment circuit using a peak value metering method or an average value metering method. It is an object of the present invention to provide an automatic iris adjustment device that performs gradation correction most suitable for each system.

[0006]

Therefore, a peak value metering system for adjusting the aperture of a lens system or a light source system so that the peak value of a video signal is equal to a predetermined first reference value, and An automatic aperture adjustment is performed by selecting one of the average value metering methods for adjusting the aperture so that the average value of the video signal is equal to a predetermined second reference value, and an output signal related to the video signal is input. in the automatic iris adjustment device of a television camera having a gamma correction circuit for gamma correction based on the signal, the gamma correction in the mean value metering method the gamma correction coefficient in the calculation formula for the gamma correction in the peak metering mode arithmetic expression It is set smaller than the gamma correction coefficient in the leaflets
The correction amount of the video signal in the head value metering method is
Is larger than the correction amount of the video signal .

[0007]

The larger the gamma correction coefficient is, the larger the level correction is made when the video input signal before gamma correction is small.
As a result, the video output signal after gamma correction increases,
By setting the gamma correction coefficient according to the peak value metering method smaller than the gamma correction coefficient according to the average value metering method,
When the video input signal is small, the level correction amount according to the peak value metering method is larger than the level correction amount according to the average value metering method. Therefore, when the video input signal level is small without changing the peak value level, that is, in a darker part of the screen, a large level correction is performed by the peak value metering method. It is possible to obtain a video signal in which a dark part of the subject can be easily observed even when the aperture is adjusted.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention. The circuit is a gamma correction circuit 18 based on an average value photometry method and a gamma based on a peak value photometry method as a circuit based on a photometry method. It has a correction circuit 19, and has an average aperture metering automatic aperture adjustment circuit 20 and a peak value metering automatic aperture adjustment circuit 21 as automatic aperture adjustment circuits.

The detection of the level of the video signal in the control loop in the automatic iris adjustment circuit is performed by detecting
17, and the level of the video signal for each photometric method is detected from the signal. The average value metering 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 that is 70% in the output of the gamma correction circuit). The detection circuit 21 detects the peak value of the video signal at a specified level (eg,
When the value of the gamma correction circuit is 110%, a specified voltage is output. 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 photometry method.

Further, the circuit relating to the photometry system and the automatic aperture adjustment circuit are switched in an interlocked manner by an interlock switch 22, and the video signal 17 input to this circuit is a gamma-corrected video output signal. 23 and aperture control signal
Output as 24. Here, the video output signal H relating to the gamma correction circuit 18 is represented by the following formula: H = Y ^r ... Where Y: video input signal γ before gamma correction; normal gamma correction coefficient (0 <γ <1) The video output signal S relating to the gamma correction circuit 19 is expressed 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 the following equation: correction amount from normal value.

In the gamma correction circuit 19 according to the peak value metering method represented by the above equation, γ-a decreases as a increases, so that a larger gamma correction is performed when the level of the video input signal Y is low. In this range, the level of the video output signal S increases. In the automatic aperture adjustment circuit of the average value metering, the aperture is controlled so that the input signal level of the gamma correction circuit becomes a specified value of the average value level of the image, and in the peak value metering, the peak value of the image is The aperture is controlled so that the level becomes a specified value. Here, the specified values are different. In the case of aperture control using average value photometry, a portion having a high luminance is compressed as a result. On the other hand, in many cases where the aperture control by peak value metering is used, the peak value is set to the upper limit as the video signal standard, so that the average value of the video signal has the same gamma correction coefficient. If it is,
Normally, it is lower than average value photometry. Conversely, the difference between the average value and the peak value is large, and there is a peak value metering method as an aperture control method in a case where a subject having a peak value level 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 set to the average value metering method so that the image of the subject having the level near the average value can be easily observed by slightly increasing the brightness level. Is smaller than the value of the coefficient.

That is, as shown in FIG. 2, by setting the gamma correction coefficient according to the peak value metering method smaller than the gamma correction coefficient according to the average value metering method, when the level of the video input signal Y is small, In the peak value metering method, a large level correction is performed as compared with the level correction related to the value metering method. As a result, when the level of the video input signal Y is smaller than that of the video output signal H, It is a big level.

When the level of the video input signal Y is small without changing the level of the peak value, that is, the darker the portion of the screen, the greater the level correction is performed by the peak value metering method. Thus, an image signal in which a dark portion of a subject can be easily observed can be obtained even when the automatic aperture adjustment using is performed.

[0014]

As described above, according to the present invention,
Since the automatic iris adjustment device performs automatic iris adjustment by setting the gamma correction coefficient according to the peak value metering method to be smaller than the gamma correction coefficient according to the average value metering method, the darker the subject, the higher the peak value metering. In this method, a large level correction is performed, and there is an effect that a video signal in which a dark portion of a subject can be easily observed can be obtained even when an automatic aperture adjustment using a peak value metering method is performed.

[Brief description of the 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 a gamma correction operation in a case of a peak value metering method and a case of an average value metering method.

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

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/222-5/257 H04N 5/202

Claims (1)

(57) [Claims] 1. A peak value metering method for adjusting an aperture of a lens system or a light source system such that a peak value of a video signal is equal to a predetermined first reference value, and a mean value of the video signal is predetermined. The automatic aperture adjustment is performed by selecting one of the average value metering methods for adjusting the aperture so as to be the same as the second reference value, and the output signal related to the video signal is gamma-corrected based on the input signal. In an automatic iris adjustment device for a television camera having a gamma correction circuit, the gamma correction coefficient in the gamma correction arithmetic expression in the peak value metering method is added to the gamma correction arithmetic expression in the average value metering method .
Kicking is set smaller than the gamma correction factor, the peak value AE Metering
The amount of correction of the video signal in the formula is the average value photometric video signal
An automatic iris adjustment device, characterized in that the correction amount is larger than the correction amount .