JPS6258797A - Video printer - Google Patents

Abstract

PURPOSE:To attain light printing even when an input level is low by applying gain correction to an input signal and applying AGC control. CONSTITUTION:In selecting a video signal by an analog switch 1, a changeover switch 2 inputting switchingly a gain lock signal and a video signal is switched to the position of a terminal (b). The inputted video signal is separated into a chrominance signal C and a luminance signal Y via a Y/C separation circuit 3. After the luminance signal Y is subject to DC recovery by a clamp circuit 7, the result is converted into a value of (a mean value between DC recovery voltage + luminance signal) while being integrated by an integration circuit 8 and the result is inputted to a comparator 9. A reference voltage is set to the comparator 9 by a variable resistor VR1 and when the luminance signal level after the integration is lower than the reference value, the comparator output (AGC voltage) goes to H level. The AGC voltage corresponds to each RGB signal connected to output terminals of changeover switches 6a, 6b, 6c and becomes a control voltage controlling the amplification factor of R/G/B amplifier sections 10a, 10b, 10c.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a video printer that inputs output signals from a video camera, electronic still camera, etc. and prints out the output signals.

(Prior Art) Conventionally, video cameras and the like have been provided with RGB and genlock input terminals, and by connecting these terminals to input terminals provided on a video printer, a video printer can print out a video screen. provided. Further, this type of video printer can input only a video signal, and these two types of signals are inputted selectively.

(Problem that the invention attempts to solve) However, in this kind of video printer.

Conventionally, there has been no means for correcting the gain of the input signal in the printer itself.

For this purpose, the level of the output signal is corrected using a video camera, electronic still camera, etc., and then input into a single video printer. However, such a video printer system has a problem in that when the level of the input RGB signals is low, the print is very dark.

(Means for Solving the Problems) The present invention provides a video printer to which an RGB signal and a genlock signal or a video signal is input, in which the genlock signal or the video signal is manually switched and separated in luminance. .

An AGC voltage proportional to the luminance signal level after separation is created, and this AGC voltage is used to adjust the gain of the RGB signal or the video signal converted into the RGB signal.

(Function) The genlock signal or video signal is switched input,
Based on the luminance-separated luminance signal, it is converted into an AGC voltage that controls the amplification degree of the RGB amplification section. This AG
C voltage is the input signal (RGB signal or video signal)
If the level is low, the RGB gain is increased to amplify the signal level to a level that allows bright printing.

(Example) Two examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows a video printer according to the present invention, and this video printer is capable of inputting two systems, one for inputting RGB signals and a genlock signal, and the other for inputting a video signal.

These two input systems are switched by operating the analog switch 1. In this example, this analog switch 1
When the output level is "H" level, the RGB signal and genlock signal input is selected, and when the output level is "L" level, the video signal input is selected.

When a video signal is selected by this analog switch 1, a changeover switch 2 for switching input between a genlock signal and a video signal is switched to the terminal side. The input video signal is converted into a chroma signal (C) via the Y/C separation circuit 3.
and a luminance signal (Y). The chroma signal is input to the chroma demodulation circuit 4, where the color difference signals (R-Y, G
-Y, B-Y), the matrix circuit 5
Then, the signals are mixed with the luminance signal (Y) separated by the Y/C separation circuit 3 and converted into R, G, and B signals, respectively, and the corresponding color signal changeover switches 6a and 6b.

It is input to the terminal side of 6C. This changeover switch 6
On the a terminal side, which is the other input terminal of a, 6b, and 6c, R
The GB signal is directly input. Also,
These changeover switches 6a.

The input terminals 6b and 6c can be switched between terminal a and terminal A by operating the analog switch 1.

The luminance signal (Y) is DC-regenerated by a clamp circuit 7, then integrated by an integration circuit 8, converted to a value of (DC regeneration voltage+average value of the brightness signal), and inputted to a comparator 9. A reference voltage is set in this comparator 9 by a volume VR, and when the luminance signal level after the integration is lower than this reference voltage, the comparator outputs (
AGC voltage) becomes rHJ level. This AGC voltage is.

This corresponds to each of the RGB signals connected to the output terminal sides of the changeover switches 6a, 6b, and 6c.

This becomes a control voltage that controls the amplification factors of the R amplifying section 10a, the G amplifying section 10b, and the B amplifying section 10C.

The RGB signals after automatic gain adjustment in these amplifiers 10a, 10b, and 10C are as follows.

Clamp circuits 11a, llb, llc and A/
D:1 is digitally converted via inverters 12a, 12b, and 1.2c and sent to subsequent processing circuits (not shown).

FIG. 2 shows specific circuits of the amplifying sections 10a, 10b, and 10c.

Note that although the following explanation will be limited to the R amplifying section 10a, the configuration and operation of the other amplifying sections 10b' and 10c are the same as that of the R amplifying section 10a.

In Fig. 2, the R signal is DC-cut by a capacitor C, biased by resistors R+ and Rz, and input to a transistor Q, whose collector side is connected to a differential amplifier consisting of a transistor Q2 and a transistor Q. The transistor Q is provided on the common emitter side, and constitutes a constant current circuit configured to supply a constant current value determined by a resistor R3 connected to the emitter side of the transistor Q.

The AGC voltage is input to the base of one transistor Q2 constituting the differential amplifier, superimposed on the voltage defined by the volume VR, while the other transistor Q3 is connected to the base by the resistors Ra and Rs. Fixed bias. Then, from the collector side of this transistor Q3, a transistor Q4 and bias resistors Rh, R
It is output via an inverting amplifier circuit configured by q.

In such an R amplifying section 10a, if the input signal level is high, the luminance signal (Y) level is also high, so that the A
The GC voltage is also high, while the AGC voltage is low when the input signal level is low. Therefore, the transistor Q2
The base bias of is.

When the input signal level is high, the bias value is set high, and when the input signal level is low, the bias value is set low. now.

If the emitter currents of the transistor Q2 and the transistor Q3 are iEZ+ iE3+ and the collector current of the F transistor Q3 is ic+, then the linear equations (11, (2+) hold true.

i tt + i I! :l=constant...(1) ip
s#1cff...(2) Therefore, AGC
When the voltage is high, the emitter current i of transistor Q2
Because there is a lot of IT flowing.

Emitter current i of transistor Q3! 3 decreases, and the gain output from the transistor Q decreases. On the other hand, when the AGC voltage is low, the emitter current ftz of transistor Q2 decreases and the emitter current it+ of transistor Q increases, so the gain output from transistor Q increases.

(Effects of the Invention) As described above, according to the present invention, a single video printer connected to a video camera, electronic still camera, etc.
The gain of the input signal can be corrected, and AGC
Since it is controlled, it is possible to print brightly even when the input level is low.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a video printer according to the present invention, and FIG. 2 is a circuit diagram illustrating an RGB amplification section in FIG. 1. 3...Y/C separation circuit 7...Clamp circuit 8.
・Integrator circuit 9 ・Comparator 10a・
...R amplification section 10b...G amplification section 10c...
B amplifier section

Claims (1)

[Claims] 1) In a video printer to which an RGB signal and a genlock signal are input or a video signal is input, the genlock signal or the video signal is switched input and the luminance is separated, and an AGC voltage proportional to the luminance signal level after the separation is applied. A video printer characterized in that the AGC voltage is used for gain adjustment of the RGB signal or the video signal converted into the RGB signal.