JPS5913479A - Magnetic video recording and reproducing device - Google Patents

Abstract

PURPOSE:To suppress the change of video contrast due to on/off of character display and to display characters clearly even if the white level with high luminance exists on the background of the characters, by connecting a slice circuit to slice only a higher potential part than that of a character signal to be added out of a video signal inputted to an adder to the titled device. CONSTITUTION:A character signal from a character signal generating circuit 1 is superposed at a sufficiently high level to a camera video output circuit 2 through a character signal output circuit 4 and the superposed signal is supplied to an electronic view finder 3 and a camera video signal. In the camera video signal, only the character part exists in the excess white level. When the slice circuit 6 is set up to 100% white level and the slice circuit is kept on status for a fixed period (a character frame part e.g.) including the excess characters by a switch 7, the video signal including an excess character signal within the fixed period is completely sliced to the white level and the sliced signal is inputted to the adder 5. If the addition level of the character signal is set up to 105%, the character can be clearly displayed even if the video signal on the background of the character is the white level with high luminance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a magnetic video recording and reproducing device, particularly a video tape recorder (abbreviated as VTR), which has a function of recording characters such as dates. Another object of the present invention is to provide an input video processing circuit that is most suitable for manual input to a character addition circuit in a device characterized in that a white character signal is output to an electronic bee finder of a camera. This type of method for calculating zero character ability can be configured as shown in FIG. 1, for example. That is, character signal generation circuit 1. Camera video output circuit 2. Electronic viewfinder circuit 3. 4. A character signal output circuit that outputs white characters to the electronic viewfinder. Furthermore, it is comprised of an addition circuit 5 that adds white characters to the camera video signal, and operates as follows.

One of the character signals generated by the character signal generation circuit 1 is superimposed on the camera video output circuit 2 by the character signal output circuit 4. The video signal on which the character signal has been superimposed is input to the electronic viewfinder 6 and the addition circuit 5, and a constant value (for example, 100 white level when a 1Vpp video signal is input) is input from the other output of the character signal. A character signal is added. However, the character signal superimposed on the camera video output circuit has different output impedance and video DC level depending on the camera, so the character signal must always be at a sufficiently high level to display sufficient white characters on the electronic viewfinder. Since output is required, the camera video signal input to the adder circuit 5 generally includes a character signal of the IOOS white level or higher. In addition circuit 5, 100
Character signals above the white level are passed through as is, so
The video auto gain control (abbreviated as AGC) will be overcast by excessive character signals, and the importance of character signals
There is a drawback that the contrast of the background camera video signal changes. In addition, the video signal is a constant addition value (I
There is also a drawback that if a level higher than the 100-inch white level (with respect to the Vp p video signal) becomes the background of a character, the character signal disappears.

The purpose of the present invention is to eliminate the above two drawbacks, to display white characters on the electronic bee finder of a camera, to display characters even when the background of the character part is high-intensity white, and to maintain a high level of video signal when the character signal is turned on/off. An object of the present invention is to provide an input video processing circuit that suppresses contrast changes.

In order to achieve the above object, in the present invention, a slicing circuit is added that slices only a portion of the video signal input to the adding circuit that has a higher potential than the character signal to be added.

FIG. 2 shows an embodiment of the present invention. Character signal generation circuit 1
．． A camera video output circuit 2+ is added to a slave finder circuit 31, a character signal output circuit 4, and an adder circuit 5, and a slice circuit 6 that slices the camera video signal input to the adder circuit 5 at about the character signal level; The switch 7 operates as follows.

The character signal obtained from the character signal generation circuit 1 is superimposed at a sufficiently high level from the character signal output circuit 4 to the camera video output circuit 2, and is supplied to the electronic P-finder 6 and the camera video signal. As mentioned above, in this camera video signal, only the text portion has an excessive white level, but the slice circuit 6 is set to a white level of 100, and the switch 7 is turned on only for a certain period including the text portion (for example, the text frame portion). In the case of a slice circuit, a video signal within a certain period of time including an excessively large character signal is sliced into 100 white levels and input to the adder circuit 5. If you set the addition level of the character signal to, for example, 105ch, you can create a video signal of the background of the characters! Even when the display is high-intensity white, characters can be displayed, and the video level input to the A (9) circuit (not shown) can be maintained almost constant before and after turning on and off the display of the character signal. It has become possible to sufficiently suppress changes in image contrast.

FIG. 6 shows a specific example, and FIG. 4 shows waveforms of each part thereof. The character signal e obtained from the character generation circuit 1 is q
is superimposed on camera video signal a to obtain video signal S. The video signal S contains an excessive white level as shown in FIG. 4, and is caused by the slice level determined by the base potential of the transistor q constituting the DCC level conversion slice circuit 6 using the emitter follower of q, for example, as shown in FIG. 4C. As shown (sliced at 100% white level).

At this time, the slice is performed only when the transistor q constituting the switch 7 is ON in response to the character frame signal f, and when it is OFF, the video signal passes through as is.

In this way, the video signal C sliced by the character frame portion passes through the transistor Qs that forms the clamp circuit, and then the transistor Q that forms the adder circuit.

q is input to the base of q, and a character signal of 105 white level is added again to obtain an output video signal d. Since the peak value of this signal hardly changes depending on the presence or absence of characters, it is possible to suppress changes in the contrast of the video due to the presence or absence of characters. Further, the signal of 100-white or higher in the character frame portion of the video signal d is sliced, and on the actual screen, only the character frame portion of the background of the characters is slightly reduced in brightness, making the characters easier to see.

As described above, according to the present invention, it is possible to display white characters on the camera's electronic vinyl viewfinder and to record character signals.
TR has the advantage of suppressing changes in image contrast due to character display on/off and making the characters easy to see even if there is a high brightness white level in the background of the characters.

[Brief explanation of the drawing]

FIG. 1 shows a system for adding camera images and characters in a magnetic video recording/reproducing device, which is the premise of the present invention. FIG. 2 shows a system for adding camera images and characters in a magnetic video recording/reproducing device according to the present invention. 3 are diagrams showing an example of an actual implementation circuit of the present invention, and FIG. 4 is a diagram showing video signal waveforms of each part in FIG. 3. Explanation of symbols 1 Character signal generation circuit 2 Camera video signal output circuit 3 Electronic and m-finder circuit 4 Character signal output circuit 5 Addition circuit 6 Slice circuit 7 Character frame switch circuit a Camera video signal b Video signal C of camera video terminal Video signal d of the slice circuit Output video signal e after jJn calculation Character signal f Character frame signal

Claims (1)

[Scope of Claims] 1) In a magnetic video recording and reproducing device having a character generation circuit and a circuit for adding a character output signal to a video signal, the video signal inputted to the addition circuit is placed at a higher potential than the character signal to be added. 1. A magnetic video recording and reproducing device characterized by having a slice circuit that fixes only a portion to a character signal potential. 2) The magnetic video recording and reproducing apparatus according to claim W1, wherein the slice circuit is operated only for a certain period of time including character signals.