JPS6248948B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an automatic light amount control (hereinafter abbreviated as "ALC") device for a color telecine camera.

The ALC device of a color telecine camera eliminates transient phenomena (transient camera output level over-level, hunting, etc.) that occur when a large amount of light suddenly enters the camera from a state where there is no or very small amount of light incident on the camera. Therefore, when the amount of incident light is less than a certain level (ALC threshold level), the ALC loop is automatically disconnected, and the rotating ND filter for adjusting the light amount is returned to the high-density preset position to immediately respond to the next incident light. Generally, a method of waiting for the

Figure 1 is a configuration diagram of the conventional ALC threshold level setting circuit, in which 1 is an input terminal for a DC voltage signal proportional to the amount of incident light, 2 is an ALC threshold level setting adjuster, 3 is a comparator, Reference numeral 4 denotes a comparator output signal terminal, and this output signal is one element of control for transitioning from the ALC loop to the preset or returning from the preset to the ALC loop. Figure 2 is a diagram showing the input/output characteristics of an ALC device using this circuit.
The output signal level is plotted on the axis, and the incident light level is plotted on the X-axis. 5 is an ALC loop characteristic curve, and 6 is a preset characteristic straight line. Also, S is
The ALC threshold level setting value, AP indicates the point of transition from the ALC loop to the preset, and PA indicates the point of return to the ALC loop from the preset.

As shown in FIG. 1, the ALC threshold level setting is fixed once it is set to a predetermined value, so as shown in FIG. 2, the ALC loop characteristic curve 5 shifts to the preset characteristic straight line 6. There is a large hysteresis between the input signal level at that time and the input signal level when returning from the preset characteristic straight line 6 to the ALC loop characteristic curve 5. This is true once you move to preset characteristic line 6.
This shows that it is difficult to return to ALC loop characteristic curve 5. That is, there is a difference between the amount of incident light when switching from the ALC loop characteristic curve 5 to the preset characteristic straight line 6 and the amount of incident light when returning from the preset characteristic straight line 6 to the ALC loop characteristic curve 5 due to hysteresis based on the ALC loop gain. Once switched to the preset characteristic line 6, the ALC loop characteristic curve 5 will not be returned unless an amount of incident light 2 to 3 times that amount is added.

For this reason, when a film starts from a dark scene with a steep preset and a small amount of incident light, it takes a long time to return to the ALC loop characteristic curve 5, resulting in a low camera output level and poor image quality.

The object of the present invention is to eliminate the above-mentioned drawbacks and improve the performance of the ALC.
To provide an automatic light amount control device for a color telecine camera that reduces hysteresis in the level of incident light based on the loop and makes it easy to return to the ALC loop from a preset.

The automatic light amount control device for color telecine cameras of the present invention is characterized by a threshold level setting adjuster that automatically switches from the ALC loop to the preset, and a threshold level setting adjuster that automatically returns from the preset to the ALC loop. by setting the ALC threshold level to
After transitioning from the loop to the preset, the level is automatically switched to a lower level than when operating in the ALC loop.

The present invention will be explained in detail below with reference to Examples.

In addition, in all figures, equivalent parts are given the same symbols.

FIG. 3 is a configuration diagram of an embodiment of the present invention, and 7
is a switching signal input terminal into which a signal is input that has a logic level of ``1'' when this ALC device is operating in preset mode and ``0'' when operating in an ALC loop, 8 is a signal delay circuit, and 9 is a preset signal input terminal. Switching transistor that is “ON” in set mode and “OFF” in ALC loop, 10
is an adjuster that sets the threshold level when returning from preset mode to ALC loop, 11
is a capacitor that delays the switching timing of the threshold level and has the same function as the signal delay circuit 8.

Next, the operation of this embodiment will be explained.

When the ALC device is operating in the ALC loop, the switching signal input terminal 7 is at logic level "0".
Therefore, the switching transistor 9 is turned OFF, and the ALC threshold operates at the value set by the ALC threshold level setting regulator 2, and the ALC threshold level setting circuit shown in FIG. The operation is the same, and when the input signal level falls below this value, the mode shifts to preset mode. When shifting to preset mode, the switching signal input terminal 7 becomes logic level "1" and the switching transistor 9 becomes "ON", so the threshold level is set by the ALC threshold level setting adjuster 2 and the threshold level setting. The regulators 10 will be connected in parallel, and the threshold value for returning to the ALC loop from the preset mode will be small. Its value is set by a threshold level setting regulator 10. The condition is that the threshold level set by this threshold level setting adjuster 10 is set higher than the preset light amount, and also the rotation ND due to the transition from the ALC loop to the preset mode.
This circuit can be stably operated by delaying the threshold switching timing until the operation of the filter (not shown) is completed.

FIG. 4 shows the input/output characteristics of the ALC device using the circuit of this embodiment. By switching to a value lower than the ALC threshold level S (but higher than the preset light level), the hysteresis of the input signal is reduced and the preset characteristic line 6 returns to the ALC loop characteristic curve 5. This shows that it can be made easier.

As described above, according to the present invention, it is easy to return to the ALC loop from the preset, the operation of the ALC device is smooth, and even when a film starts from a dark scene, image quality does not deteriorate. In addition, it was not possible to set the preset light intensity to a small value due to the difficulty of returning to the ALC loop, but since this cause has been resolved, it is now possible to set the preset light intensity to a small value, which also reduces the image pickup tube burn-in phenomenon. .

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional ALC threshold level setting circuit, and Figure 2 is shown in Figure 1.
Using ALC threshold level setting circuit
Figure 3 is a diagram showing the input/output characteristics of the ALC device. Figure 3 is a block diagram of an embodiment of the present invention. Figure 4 is an ALC controller using the ALC threshold level setting circuit of this embodiment shown in Figure 3. FIG. 3 is a diagram showing input/output characteristics of the device. 1... Input terminal for a DC voltage signal proportional to the amount of incident light, 2... ALC threshold level setting adjuster, 3... Comparator, 4... Comparator output terminal, 5... ALC loop characteristic curve, 6... Preset characteristic straight line, 7... Switching signal input terminal, 8...Delay circuit, 9...Switching transistor, 10...Threshold level setting adjuster, 11...Delay capacitor.

Claims (1)

[Claims] 1. In the automatic light control device of a color telecine camera, a threshold level setting adjuster automatically switches from the automatic light control loop to the preset, and a threshold level setting adjuster automatically returns to the automatic light control loop from the preset. An automatic light amount control device characterized by having individually arranged.