JPH02145067A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To avoid even that a black level of a video signal is whity by constituting the circuit such that a video signal before AD conversion is inputted to a clamp circuit in which a clamp voltage is adjustable and adjusting the clamp level lower than the black level of an A/D converter by a setup value of the video signal. CONSTITUTION:A clamp circuit 4 clamps a front porch of an output signal of a variable resistor 3 to a voltage set by a variable resistor 5. The voltage set by the variable resistor 5 is adjusted lower than the black level of an A/D converter 7 by a setup value possessed by an output signal of the variable resistor 3 and then an output signal C of the clamp circuit 4 is clamped for the pedestal level lower than the black level of the A/D converter 7 by the setup value. Moreover, since the circuit state is monitored by a CRT monitor, the fluctuation of the black level due to the dispersion in the setup value between various video signals is adjusted minutely by adjusting the variable resistor 5 while observing the monitor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for adjusting a clamp voltage when AD converting a video signal.

[Conventional technology]

When AD converting a video signal, a circuit as shown in FIG. 3 has conventionally been used for preprocessing. A video signal shown in FIG. 4i is supplied to the input terminal 13 in the same figure. The video signal i is sent to A by the amplifier 14.
The signal is amplified to match the dynamic range of the D converter 17.

A clamp pulse j shown in FIG. 4 is supplied to the clamp circuit 15, which clamps the video signal amplified by the amplifier 14 so that its pedestal level matches the black level of the AD converter 17. The output of the clamp circuit 15 is supplied to a blanking circuit 16, and the synchronizing signal is removed by the blanking pulse shown in FIG. 4, resulting in the AD converter manual signal shown in FIG. 4.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, the pedestal level of the video signal is clamped to match the black level of the AD converter, so for a video signal with a set-up, the AD-converted data is When displaying an image using such data, which shifts toward white by the amount of the setup, there is a problem in that the black of the displayed image becomes whiter than the original black.

Another problem is that the black level varies due to variations in set amplifiers among various video signals.

[Means to solve the problem]

In order to solve the above problems, the present invention makes it possible to adjust the clamp level of the video signal, and adjusts the clamp level by the cent amplifier of the video signal.
By adjusting the black level lower than the black level of the color converter,
This solves the problem that the black of the video signal appears whitish as described above.

Furthermore, the configuration allows adjustments to be made while looking at a CRT monitor, allowing detailed adaptation to variations in setup between various video signals.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a signal waveform diagram at various locations in FIG.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

A video signal a having a waveform as shown in FIG. 2 g inputted to terminal 1 in FIG. Ru.

The output of the amplifier 2 is adjusted to an appropriate amplitude by the volume 3 to match the dynamic range of the AD converter 7, and is supplied to the clamp circuit 4. The clamp circuit 4 converts the front porch of the output signal of the volume 3 into the 2. Clamp pulse b with waveform as shown in Figure 2, volume 5.
Clamp to the voltage set by . The voltage set by the volume 5 is adjusted to be lower than the black level of the AD converter 7 by the set-up of the output signal of the volume 3, and therefore the output signal C of the clamp circuit 4 (shown in Fig. 2g) is also adjusted to be lower than the black level of the AD converter 7. , the pedestal level is clamped lower than the black level of the AD converter 7 by the amount of the set amplifier. In the blanking circuit, the signal C replaces the synchronizing signal section with a constant voltage by a blanking pulse d (shown in Figure 2 d), and becomes a signal e (with the synchronizing signal deleted).
(as shown in FIG. 2g), and this signal is supplied to the AD converter 7. The AD-converted data is again converted into an analog video signal g (shown in FIG.
The video signal is added to the composite shift f (shown in Figure 2 f) separated from the input video signal a by the buffer filter, resulting in a video signal h (shown in Figure 2) from which the set amplifier is removed. 11 and is monitored by a CRT monitor 12.

〔Effect of the invention〕

According to the present invention, by adjusting the volume 5 in FIG. 1 so that the pedestal level of the video signal is clamped lower than the black level of the AD converter 7 by the amount of the set-up, the black level is reduced by the set-up amplifier of the video signal. It is possible to prevent whiteness from appearing. Furthermore, since monitoring is performed using a CRT monitor, variations in the black level due to variations in set-up among various video signals can be dealt with in detail by adjusting the volume 5 while looking at the monitor. Further, the contrast can be adjusted using the volume 9, and together with the volume 5, the image quality can be adjusted. Furthermore, by inputting the signal whose set-up portion has been canceled as described above to the AD converter, the dynamic range of the AD converter can be effectively used, which is advantageous for gradation expression.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
3 is a block diagram of a conventional preprocessing circuit for video signals to be AD converted,
FIG. 4 is a waveform diagram of each part in FIG. 3. [Explanation of symbols of main parts] 1-----...Input terminal 2----1--Amplifier 3--...Amplitude adjustment volume 4 Clamp circuit 5-- ...-Clamp level adjustment volume 6--
---・----~Blanking circuit 7--・・--AD
Converter f3 DA converter 9-・・−・−・・−Synchronization separation circuit 10−−−−−・
−・Adder circuit buffer amplifier

Claims (1)

[Claims] In a circuit that converts a video signal from AD to AD, converts it from analog to analog again to reproduce the video signal, and monitors the video signal on a CRT monitor, a clamp circuit whose clamp voltage can adjust the clamp voltage of the video signal before AD conversion is provided. A video signal processing circuit characterized in that it is configured to input an input signal to a video signal processing circuit.