JPH06267190A - Image reproducing device - Google Patents

Abstract

PURPOSE:To provide an image reproducing device capable of preventing the occurrence of a zero-cross in the level limit output of an image signal even when amplitude fluctuation exists in the image signal read from a recording medium and preventing the occurrence of a black rapture due to excess modulation. CONSTITUTION:The image reproducing device level limits for the FM modulated image siqnal SH read from the recording medium 11 to perform FM demodulation processing. This device is provided with a generation means 19 generating a control signal E1 dealing with the amplitude fluctuation of the image signal SH read from the recording medium 11 and an amplifier means 20 whose gain is varied based on the control signal E1 generated by the generation means 19 and amplifying the image signal SH read from the recording medium 11 so that the amplitude fluctuation causing the zero-cross when the image signal SH is level limited is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an image reproducing apparatus for reproducing an image signal recorded on a recording medium such as a magnetic tape.

[0002]

2. Description of the Related Art As is well known, image reproduction processing in a VTR (video tape recorder) or the like is performed by means shown in FIG. That is, the image signal read from the magnetic tape 11 by the reproducing head 12 is supplied to the reproducing amplifier circuit 14 via the rotary transformer 13 and amplified. In this case, the image signal S _H obtained from the reproduction amplifying circuit 14 has a large amplitude variation as shown in FIG.

The amplitude fluctuation of the image signal S _H causes the image signal, which has undergone the amplitude fluctuation at the time of recording the image signal, to be recorded on the magnetic tape 11 as it is, or the signal loss at the time of reproduction, that is, the magnetic tape 11 itself. It is caused by loss of high frequency output due to the tape running system. Therefore, when the image signal S _H output from the reproduction amplifier circuit 14 is supplied to the limiter circuit 15 and is level-limited by the level indicated by the alternate long and short dash line in FIG. 4A, the output signal S _H of the limiter circuit 15 is output. _As shown in FIG. 4B, _L causes a lack of zero cross points and causes overmodulation when the image signal S _H undergoes large amplitude fluctuations.

When the output signal S _L of the limiter circuit 15 is supplied to the FM demodulation circuit 16 and demodulated,
The demodulated signal S _D is distorted as shown in FIG. Therefore, when the demodulation signal S _D output from the FM demodulation circuit 16 is passed through the de-emphasis circuit 17, the signal S _V finally obtained from the output terminal 18 includes the signal S _V shown in FIG.
As shown in (d), a reversal phenomenon occurs, and noise called blackish noise appears on the reproduction screen.

[0005]

As described above, in the conventional image reproducing apparatus, since the image signal read from the recording medium has a large amplitude variation, a zero cross occurs in the output whose level is limited. However, there is a problem that blackening or blurring occurs due to overmodulation.

Therefore, the present invention has been made in consideration of the above circumstances, and even if the amplitude of the image signal read from the recording medium varies, zero cross does not occur in the level limited output of the image signal, It is an object of the present invention to provide an extremely good image reproducing device capable of preventing the occurrence of black and blur due to overmodulation.

[0007]

An image reproducing apparatus according to the present invention is intended for subjecting an FM-modulated image signal read from a recording medium to FM demodulation processing while limiting the level. Then, the generation means for generating a control signal corresponding to the amplitude fluctuation of the image signal read from the recording medium, and the gain variable based on the control signal generated by the generation means, the level limit to the image signal In order to remove the amplitude fluctuation that causes the zero cross when the above-mentioned procedure is performed, an amplifying means for amplifying the image signal read from the recording medium is provided.

[0008]

According to the above-mentioned structure, the amplification means whose gain is variable based on the control signal corresponding to the amplitude fluctuation of the image signal causes the zero cross when the level of the image signal is limited. Since the image signal read from the recording medium is amplified so as to eliminate the amplitude fluctuation,
Even if the image signal read from the recording medium has an amplitude variation, it is possible to prevent a zero cross from occurring in the level limited output of the image signal and prevent black and blur due to overmodulation.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. 1, the same parts as those in FIG. 3 are designated by the same reference numerals. That is, the image signal S _H output from the reproduction amplification circuit 14 and having a large amplitude variation as shown in FIG. 2A is supplied to the AM demodulation circuit 19 and the variable gain amplification circuit 20, respectively. . Among them, the AM demodulation circuit 19 is the reproduction amplification circuit 1
4 is to extract the peak on the positive side of the amplitude of the image signal S _H output from the image signal S _H , and as shown in FIG.
_{When the H} signal has a constant level in a region where there is no amplitude variation and the image signal S _{H has} an amplitude variation, the control voltage E ₁ having a level along the envelope on the positive side of the amplitude is generated.

Further, the variable gain amplifier circuit 20 has an AM
The gain is controlled based on the control voltage E ₁ output from the demodulation circuit 19, and the gain (amplification) increases as the control voltage E ₁ decreases from a constant level corresponding to a region where the amplitude of the image signal S _H does not vary. The rate will increase. Therefore, from the variable gain amplifier circuit 20, as shown in FIG. 2C, the image signal S _{H in the} region where a large amplitude variation occurs.
Is amplified, in other words, the image signal S _H1 from which the amplitude fluctuation that causes the zero cross when the level is limited by the limiter circuit 15 in the subsequent stage is removed is output. Therefore, in the limiter circuit 15, the occurrence of zero crossing that causes overmodulation is suppressed, the distortion of the signal SD after FM demodulation is reduced, and the reversal phenomenon can be suppressed on the reproduced screen to prevent the occurrence of black blurring. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

[0011]

As described above in detail, according to the present invention,
Provided is an extremely good image reproducing device capable of preventing the occurrence of black and blur due to overmodulation by preventing zero cross from occurring in the level limited output of the image signal even if the image signal read from the recording medium has amplitude fluctuation. can do.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of an image reproducing apparatus according to the present invention.

FIG. 2 is a waveform chart shown to explain the operation of the embodiment.

FIG. 3 is a block configuration diagram showing a conventional image reproducing device.

FIG. 4 is a waveform chart shown for explaining a problem of the conventional device.

[Explanation of symbols]

11 ... Magnetic tape, 12 ... Playback head, 13 ... Rotary transformer, 14 ... Playback amplification circuit, 15 ... Limiter circuit, 16 ... FM demodulation circuit, 17 ... De-emphasis circuit, 18 ... Output terminal, 19 ... AM demodulation circuit, 20 ... Variable gain amplifier circuit.

Claims (1)

[Claims] 1. An image reproducing apparatus for subjecting an FM-modulated image signal read from a recording medium to FM demodulation processing by limiting the level, wherein a control signal corresponding to an amplitude fluctuation of the image signal read from the recording medium. For changing the gain based on the control signal generated by the generation means for removing the amplitude fluctuation that causes a zero cross when the level of the image signal is limited. An image reproducing device comprising: an amplifying unit that amplifies an image signal read from the recording medium.