JPS62114387A - Video recorder - Google Patents

Abstract

PURPOSE:To obtain an image with high quality by performing a recording applying a few amount of emphasis on a video signal having a large amount of noise, and a large amount of emphasis on the video signal having a few amount of noise. CONSTITUTION:A HPF21a consists of a capacitor and a resistor, and separates the high frequency component of a luminance signal Y at a clamping circuit 7. And a limiter 21b consists of a differential amplifier and takes out only a low level component out of an inputted high frequency component. Also, the gain of a gain control circuit 21c is controlled with the output voltage signal of an output from a noise component detection circuit 20, and it is controlled with the output voltage signal of a DC detection circuit 20, and the gain becomes low when a DC output voltage signal is at a high level and it becomes high when the DC output voltage signal is at a low level.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a device for recording video signals on a magnetic recording medium such as a magnetic tape, and more specifically, to an apparatus for recording video signals on a magnetic recording medium such as a magnetic tape. The present invention relates to a video recording device equipped with a video signal processing circuit for recording.

[Conventional technology]

FIG. 5 is a block diagram showing an example of a video recording circuit of a conventional color VTR. In the figure, a TV broadcast signal received by antenna (1) is tuned by tuner (2),
It is converted to an intermediate frequency and amplified by a video intermediate frequency amplifier (3), detected by a video detector (4) to become a video signal, and amplified by a video amplifier (5).

The luminance signal Y of this video signal is separated by the LPF (6), the sync signal is clamped by the clamp circuit (7), and the high frequency component is emphasized by the pre-emphasis circuit (8).
After the spikes of the pre-emphasized luminance signal Y are suppressed by the white/dark clipping circuit (9), it is converted into an FM signal by the FM modulation circuit αQ.

On the other hand, the chroma signal C of the video signal has a BP of 3 to 4 MHz.
After being extracted at Ft13 and subjected to predetermined signal processing at the color marking signal processing circuit (to), the above Ft is extracted at the mixer lJυ.
It is mixed with the M-modulated luminance signal Y and sent to the recording amplifier 114.
) and is recorded on the video track of the magnetic recording tape tll by the magnetic head 4.

[Problem that the invention seeks to solve]

The video recording circuit of a conventional VTR is configured as described above. In the case of a recording tape in which the width of the video track recorded in the α frame was 58 μm, a reproduced image with a practically sufficient N ratio of 87 was obtained.

However, as the recording and playback time becomes longer, the width of the video trunk becomes narrower, and the width of the video trunk for home use is approximately 19 mm.
The mainstream is µm. For this reason, the video signal level during playback is approximately 1/3 of that when the video track width is 58 μm, and there is a problem in that the 87N ratio of the playback image decreases accordingly.

The present invention has been made to solve these problems, and aims to provide a video recording device that can produce high-quality reproduced images even when reproduced from a narrow video trunk.

[Means to resolve the gap]

The video recording device according to the present invention includes a means for detecting the amount of noise in a video signal and is provided before a pre-emphasis circuit, and controls the amount of emphasis to change from small to large depending on the detected amount of noise. It is characterized in that it is equipped with a non-linear emphasis circuit.

[Effect]

In the non-linear emphasis circuit according to the present invention, when a video signal has a large amount of noise, a small amount of emphasis is applied, and conversely, when a video signal has a small amount of noise, a large amount of emphasis is applied when recording.
The details of the reproduced image are improved and a high-quality reproduced image can be obtained.

[Embodiments of the invention]

FIG. 1 is a block diagram of an embodiment of the present invention, and the same reference numerals as in FIG. 5 indicate the same parts. In the figure, (1) is a noise component detection circuit that detects the amount of noise in a video signal. υ is a nonlinear emphasis circuit whose emphasis amount is controlled by the amount of detected noise, and (a) is a buffer amplifier.

The noise component detection circuit (7) separates a random noise component in the high frequency range from the output video signal of the video amplifier (5) using the HP F (20a), amplifies it using the noise amplifier (20b), and then separates the random noise component in the high frequency range from the output video signal of the video amplifier (5). 20C) to perform amplitude detection and output a DC detection signal with a level corresponding to the amount of noise. The luminance signal Y may include video signals in a high frequency range apart from noise components, but it may contain video signals in the high frequency range, such as large-area images such as the sky or ocean when receiving weak electric field TVi waves. The noise in the flat areas may have a high noise level, but it does not change much when receiving that channel. However, by appropriately selecting the threshold level and time constant of the noise detector (20C), it is possible to distinguish between the noise component and the high frequency component of the video signal and extract only the noise component. In this way, the noise component detection circuit (1) outputs a high level DC voltage signal when the luminance signal Y contains a lot of random noise, and when the luminance signal Y contains little random noise, the S/N When the voltage is good, a low level DC voltage signal is output.

Is Figure 2 a nonlinear emphasis circuit? FIG. 3, which is a block diagram of an example of υ, is a circuit diagram showing a specific example of its configuration. In the figure, HP F (2ia) is a bypass filter consisting of a capacitor and a resistor and having a cutoff frequency of 5 to 6 MHz, which separates high frequency components of the luminance signal Y of the clamp circuit (7). The limiter circuit (2tb) is composed of a differential amplifier, and extracts only low-level components from the input high-frequency components. Gain control circuit (
21c), the gain is controlled by the output voltage signal of the noise component detection circuit (1), and the gain is small when the DC output voltage signal is at a high level, and the gain is large when the DC output voltage signal is at a low level.

The mixer (21d) receives the luminance signal Y of the clamp circuit (7).
The output signal of the gain control circuit (21c) is added to and output to the buffer amplifier. In this case, the luminance signal Y of the clamp circuit (7) and the output signal of the gain control circuit (21c) are in opposite phase, so T(
The luminance signal Y from which the high frequency noise component separated by P F (2ta) has been canceled is sent to the pre-emphasis circuit (8
) is output.

The noise component detection circuit (4) controls the gain of the gain control circuit (2IC) depending on the amount of random noise contained in the luminance signal Y, as described above. Figure 4 is a diagram showing the emphasis characteristics of the non-linear emphasis circuit t21), where the solid line shows the emphasis characteristics when the amount of noise in the luminance signal Y is small, and the dashed-dotted line shows the emphasis characteristics when the amount of noise is large. .

In other words, noise in the flat portion of the image that is visually noticeable in the input luminance signal Y is concentrated in the low level of high frequency components, so this noise component is
Take out with F (21a) and limiter circuit (2xb),
The structure is such that the amount of emphasis is changed depending on the level of the input video signal and the amount of noise, and the phase is reversed and superimposed on the input luminance signal Y to cancel the noise component.As a result, the details of the reproduced image are improved. and the quality of the played image will improve.

On the other hand, if the amount of emphasis is kept constant regardless of the level of the input luminance signal Y, if the S/N ratio of the input luminance signal Y is poor, the image quality will improve due to the increase in details, and the S The deterioration of the /N ratio becomes noticeable, and the quality of the reproduced image deteriorates. In such a case, the emphasis amount is reduced to suppress the 8/N deterioration and improve the image quality in a condensed manner.

In the above embodiment, the noise component detection circuit (a) is an HPF
(20a) and an amplitude detector (20c), but the A
It is also possible to use a signal such as GCm pressure that is an index of 87H of the input video signal.

Furthermore, the amount of emphasis applied by the non-linear emphasis circuit (c) can be changed using an electronic switch so that when the input video signal is at a high level, a certain amount of emphasis is applied, and when the input video signal is at a low level, the amount of emphasis is zero. good.

Further, in the above embodiment, a case where a TV scratch signal is recorded is shown, but it is clear that similar effects can be obtained even when applied to video recording by a video camera and video recording during dubbing.

〔Effect of the invention〕

The present invention is a video recording device equipped with means for detecting the noise level of an input luminance signal, and a nonlinear emphasis circuit that adjusts the amount of emphasis from small to large according to the detected noise level. Therefore, when a magnetically recorded signal is reproduced by this device, a high-quality reproduced image with improved detail can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a block circuit diagram of an example of a nonlinear emphasis circuit constituting this embodiment, and FIG. 3 is a circuit diagram showing a specific example of its configuration. Figure 4 is a characteristic diagram of this non-linear emphasis circuit, and Figure 5 is a block circuit diagram of an example of a conventional video recording device. ...Noise component detection circuit, (b)...Nonlinear emphasis circuit, (21a)...Bypass filter, (21b)...Limiter circuit, (21C')...
...gain control circuit, (21d)...adder. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) It is configured to perform pre-emphasis on the luminance signal of the input video signal, then perform FM modulation, add the chroma signal of the video signal that has been subjected to predetermined signal processing, and record it on the magnetic recording medium. In the video recording device, a means for detecting the amount of noise in the input video signal and a means provided before the pre-emphasis circuit are provided, and when the amount of noise in the detected input video signal is small, the amount of emphasis is large; 1. A video recording device comprising: a non-linear emphasis circuit that controls the amount of emphasis to be small when the amount is large. (2) comprising a noise component detection circuit that detects the amount of noise contained in the high frequency component of the luminance signal of the input video signal;
2. The video recording apparatus according to claim 1, wherein the amount of emphasis of the nonlinear emphasis circuit is controlled to be small or large in accordance with the level of the detection signal. (3) A switch is provided that operates depending on the level of the input video signal, and the nonlinear emphasis circuit is configured to apply a predetermined amount of emphasis only when the input video signal level exceeds a predetermined value. A video recording device according to claim 1.