JPS6226229B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a CRT phototypesetting system in which a character image is reproduced on a cathode ray display tube using a video signal from an image pickup tube, and the reproduced character image is projected onto a photosensitive material for printing. This paper relates to a video signal compensation method in a machine.

FIG. 1 is a schematic diagram showing an example of a CRT phototypesetting machine, in which a character image on a dial 2 illuminated by a light source 1 is projected and accumulated on an image pickup tube 3, and the character image is sent to a video signal circuit 4. Through the cathode ray display tube 5 (hereinafter simply
(CRT). This reproduced image is photographed on a photosensitive material 7 via an optical system 6, and desired characters are printed.

Incidentally, conventionally, the video signal circuit 4 has generally been constructed using a capacitor coupling method.

However, in such a capacitor-coupled circuit, due to the effect of the low-frequency cutoff characteristic, the signal waveform actually supplied to the CRT for the image pickup tube output signal 8 shown in FIG. 2A, for example, is as shown in FIG. 2B. As shown, there was a tendency to deviate toward the reference value E ₀ or less with the passage of time. Therefore, if such a signal is waveform-shaped at a certain slice level 9, the final signal obtained will be a signal with different pulse widths for inputs of the same width, as shown in Figure 2C. However, if the CRT is driven by this signal, it becomes impossible to reproduce characters with the desired line width.

The present invention provides a video signal compensation system designed to solve the conventional problems as described above. By correcting or shaping the signal, a desired signal can always be obtained.

The system according to the present invention will be explained below based on the drawings.

FIG. 3 is a diagram showing an embodiment of a circuit that realizes the method of the present invention, and FIG. 4 is a diagram showing signal waveforms at each point in FIG. Display as A.

In FIG. 3, 21 is an input amplifier for facilitating signal processing in the subsequent stage, 22 is a low-pass filter, 23 is a diode, 24 is an emitter follower circuit for compensating the voltage drop of the diode and converting impedance, and 25 is an adder circuit. , 26 are comparators. In this circuit of Fig. 3, Fig. 4A
When a video signal A=E ₀ +v ₀ (t) as shown in FIG. 4 is input, the output signal B of the amplifier 21 is as shown in FIG.
As shown in , B=E ₁ −α{E ₀ +v ₀ (t)},
The output signal C of the low-pass filter 22 is the signal B
, that is, C=E ₁ −αE ₀ . Therefore, the output signal D of the emitter follower circuit 24 is D=E ₁ -αE ₀ -Vbe.

If the envelope of the portion of the video signal A that deviates below the reference value E ₀ is E ₀ −V(t) as shown in the figure, then the envelope of the corresponding output signal B is E ₁
−α{E ₀ −V(t)}.

Since the output signal D is supplied to one end E of the capacitor 27 via a resistor and the output signal B of the amplifier 21 is also supplied via the diode 23, the capacitor 27 receives the two signals D. The higher potential of and B is accumulated sequentially, and the signal E is equal to the change in the envelope of the signal B with respect to the output signal D, that is, αV
(t) becomes a superimposed signal. Therefore, as shown in FIG.
(t), and the signal G input to the adder circuit 25 via the variable dividing resistor 29 with the dividing ratio β becomes αV(t)·1/β.

In addition to the above-mentioned signal G, a level adjustment potential -E ₂ is input to the adder circuit 25, and the output signal C=E ₁ -αE ₀ of the above-mentioned low-pass filter 22 is inputted to another input terminal with a gain of 1. /γ is input. Therefore, the output signal H of the adder circuit 25 is H=-{1/γ(E ₁ −αE ₀ )−E ₂ +1/β・αV(t)}=E ₂ −1/γ・E ₁ +1/γ・αE ₀ −1/β・αV(t).

Therefore, the circuit constants are set so that α=β=γ, and E ₂ −1/α·E ₁ =M (0<M<v ₀ (t)max), that is, E ₂ = M+1/
If the level adjustment potential -E ₂ is adjusted so that α·E ₁ is obtained, the output signal H becomes H=M+E ₀ -V(t).

As shown in FIG. 4H, the output signal H is always higher by a constant potential M than the reference potential of the input video signal A, that is, the envelope E ₀ −V(t) on the negative side of the signal A described above. In addition to being a signal that maintains its state, it also contains components specific to the input amplifier 21, that is, "E ₁ " or "α" that constitutes the signal B.
The signal is completely unaffected by

Therefore, when the video signal A is waveform-shaped using the signal H as a slice level as in the circuit shown in FIG. The desired character signal is always obtained regardless of the character signal.

Next, an embodiment different from the embodiment described above using the circuit of FIG. 3 will be explained based on FIG. 5.

In FIG. 5, 21 to 24 and 27 to 29 are the same as those in FIG. 3, so a description thereof will be omitted.
50 is an adder circuit for adding the output signal G of the variable dividing resistor 29 and the original video signal A.

By the way, as mentioned above, if the variable dividing resistor 29 is adjusted and the circuit constant is set so that α=β, the signal G becomes G=αV(t)・1/β=V(t) becomes.

That is, the signal G at this time is a signal corresponding to the envelope of the portion of the original video signal A that deviates below the reference value _E0 .

Therefore, the output signal J of the adder circuit 50 is a signal obtained by increasing the video signal A shown in FIG. 4A by V(t), that is, the desired character signal included in the video signal A itself. ing.

Then, the desired character signal obtained as explained above based on FIG. 3 or FIG.
By using a video signal for driving a CRT, it becomes possible to accurately reproduce a desired character image.

Various methods of the present invention have been described above based on specific circuit examples, but in short, the present invention relates to a compensation method for a video signal input via capacitor coupling,
Based on the output signal of the output signal and the signal supplied from the amplifier 21 via the diode 23, a deviation component signal from the reference value of the video signal is detected, and according to the detected deviation component signal, By correcting the original video signal or varying the slice level for waveform shaping, it is possible to compensate for deviation of the level of the video signal supplied via the capacitor coupling in the direction below the reference value. This is how it was done. As a result, in the case of the embodiment, a desired character signal can always be obtained, which is a great effect.

In the above explanation, the output video signal of the image pickup tube is
Although we have described the case of a phototypesetting machine that reproduces character images by applying voltage to a CRT, the application of the video signal compensation method of the present invention is not limited to this, and the reference voltage This method can be widely applied when extracting a desired signal from a signal that fluctuates.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a CRT phototypesetting machine, FIG. 2 is a diagram showing an example of input/output signal waveforms of the video signal circuit 4 in FIG. FIG. 4 is a diagram showing an embodiment of the circuit, and is a diagram showing signal waveforms at points A, B, C, etc. in FIG. 3. FIG. 5 is a diagram showing a different example of the circuit. 2... Dial, 3... Image pickup tube, 4... Video signal circuit, 5... Cathode ray tube, 21... Input amplifier, 2
2...Low pass filter, 25...Addition circuit, 2
6... Comparator, 50... Addition circuit.

Claims (1)

[Claims] 1. A compensation system for a video signal input via capacitor coupling, which includes an amplifier 21 that multiplies the input video signal by -α, and a low-pass filter that cuts high frequency components of the output signal of the amplifier 21. 22, and a deviation component signal detected based on the output signal of the low-pass filter 22 and the signal supplied from the amplifier 21 via the diode 23 is supplied, and a signal of 1/β of the signal is detected. A variable dividing resistor 29 and 1/1 of the output signal of the low-pass filter 22.
γ, a detection signal from the variable dividing resistor 29, and an adder circuit 25 that adds the level adjustment potential supplied from the outside; and a waveform shaping of the input video signal using the output signal of the adder circuit 25 as a slice level. Comparator 2
6, and the values of α, β, and γ are α=
A video signal compensation method characterized by setting β=γ. 2. A compensation system for a video signal input via capacitor coupling, which includes an amplifier 21 that multiplies the input video signal by -α, a low-pass filter 22 that cuts high-frequency components of the output signal of the amplifier 21, and the low-pass filter A variable dividing resistor 29 is supplied with a deviation component signal detected based on the output signal of 22 and the signal supplied from the amplifier 21 via the diode 23, and detects a signal of 1/β of the signal; a detection signal from the variable dividing resistor 29, and
A video signal compensation system comprising: an adder circuit 50 for adding the input video signals; and the values of α and β are set to α=β.