JPH02241286A - Chrominate signal processing circuit - Google Patents

Abstract

PURPOSE:To emphasize the contour of color to a carrier chrominance signal and to decrease the spreading of color in a reproduced picture by supplying an output signal from a differentiator, which differentiates an output signal from a filter, as a gain control signal to a variable gain amplifier. CONSTITUTION:A low-pass filter LPF 5 has a zero point in a frequency 2sc and has a filter characteristic to attenuate more than a central frequency fsc. In a differentiator 6, only a contour part is extracted by differentiating the output signal of the LPF 5 and taken out as a signal only in the starting part and ending part of a burst waveform. The output signal of this differentiator 6 is supplied as the gain control signal to the input end of again control. Thus, the gain of a variable gain amplifier 2 is made high in the starting part of the burst waveform, reversely made low in the ending part and fixed in the other part. Accordingly, in the variable gain amplifier 2, the contour part of the carrier chrominance signal can be emphasized and the spreading of the color can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a color signal processing circuit used in a video tape recorder (hereinafter referred to as a VTR) or the like.

(Prior art) In the television standard system based on the NTSC system, the color signal has a frequency of 3.58 MHz (hereinafter referred to as fs).
The chrominance subcarrier of 3.58 MHz is amplitude-modulated to produce a carrier chrominance signal, and the carrier chrominance signal whose band is limited to ±0.5 MH7 centered around 3.58 MH and a luminance signal having a band of about 4 MHz are combined. The data is multiplexed and transmitted.

Therefore, the band of the carrier color signal is f,. ±0.5MH2
The horizontal resolution of the demodulated color signal is inferior to that of the luminance signal.

Furthermore, if the received television signal is subjected to signal processing such as frequency conversion and recorded on magnetic tape using a home VTR, for example, the horizontal resolution of the signal obtained by playing back this signal becomes increasingly worse. When viewing this reproduced signal on a television screen, the colors ooze out from the front and back of the image, so-called color blurring becomes noticeable.

(Problem to be Solved by the Invention) In order to fundamentally solve the above-mentioned color bleeding, it would be sufficient to widen the recording band of color signals when recording signals on magnetic tape. This is difficult to achieve in home VTRs that record by superimposing them on luminance signals, because the recording bandwidth is limited and standards must be changed.

For these reasons, it has conventionally been difficult to effectively improve color bleeding, which causes blurred color outlines.

The present invention has been proposed to solve these problems, and is a color signal processing circuit that can reduce color blur in reproduced images by emphasizing color outlines with respect to carrier color signals. The purpose is to provide

[Structure of the Invention] (Means for Solving the Problems) In order to achieve this object, the color signal processing circuit according to the present invention has a gain controlled based on a gain control signal, and amplifies an input carrier color signal. A variable gain amplifier for outputting, a detector for detecting the carrier color signal, a filter for filtering a signal having a frequency equal to or higher than the frequency of the carrier color signal among the output signals from the detector, and an output signal from the filter. , and an output signal from the differentiator is supplied as a gain control signal to the variable gain amplifier.

(Function) According to the above-described configuration, after detecting the carrier color signal, the contour portion of the carrier color signal can be extracted by passing it through a filter. By roughly differentiating the output signal of the filter and supplying it as a gain control signal to the variable gain amplifier, the gain can be increased at the rising edge of the chrominance signal, and conversely, the gain can be decreased at the falling edge, resulting in variable gain. A carrier color signal with color blur removed can be extracted from the amplifier.

(Example) Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing one embodiment of a color signal processing circuit according to the present invention.

In this figure, a carrier color signal obtained by separating a received television signal by a color signal separation circuit of a VTR, for example, is input to an input terminal 1, and is supplied to a variable gain amplifier 2. This carrier color signal has a center frequency fsc (Fig. 2 (A
)reference).

The carrier color signal applied to the input terminal 1 first passes through a variable gain amplifier 2 and appears on the output line of this amplifier 2. The signal that has passed through this variable gain amplifier 2 is shown in Fig. 2 (E
).

Point E on the output line of the variable gain amplifier 2 and the gain control input terminal (point D) of the variable gain amplifier 2 are connected by a loop 3, and this loop 3 is connected to a detector 4, a low-pass filter 5, and below. , LPF5) and a differentiator 6.

In the detector 4, the waveform of FIG. 2(E) is double-wave rectified, and L
It is supplied to PF5. FIG. 2(B) shows the double-wave rectified waveform appearing at the output end (8 points) of this detector 4.

As shown in FIG. 3, the LPF 5 has a frequency of 2f.

has a zero point at and a frequency f,. It has filter characteristics that attenuate the above. The above double-wave rectified waveform is ideally 2
f8. In fact, it should be around and this harmonic only frequency. Since nearby components also remain, an LPF 5 having the characteristics shown in FIG. 3 is used.

By passing through this LPF 5, an output waveform as shown in FIG. 2(C) is obtained at its output end (0 point), and this output signal is supplied to the next stage differentiator 6.

The differentiator 6 differentiates the output signal of the LPF 5 to extract only the outline of the signal that appears at point E, resulting in the rise of a burst waveform like the output waveform at point D shown in Figure 2 (D). Only the falling part and falling part are extracted as a signal.

The output signal of the differentiator 6 is supplied as a gain control signal to the gain control input terminal, so that the gain of the variable gain amplifier 2 becomes high in the rising part of the burst waveform, becomes low in the falling part of the burst waveform, and vice versa. It is constant in the part. Therefore, in the variable gain amplifier 2, the contour portion of the carrier color signal is emphasized, and a carrier color signal with reduced color fringing can be extracted from the output terminal 7.

Note that the signal on the output side of the variable gain amplifier 2 is not detected by the detector 4, but the carrier color signal input to the variable gain amplifier 2 is detected by the detector 4, and after passing through the LPF 5 and the differentiator 6, It may also be supplied to the gain control input terminal of the variable gain amplifier 2.

[Effects of the Invention] As explained above, according to the present invention, when recording and reproducing television signals on a VTR, etc., it is possible to effectively eliminate color blurring in reproduced images that tends to occur due to the narrow frequency band of the carrier color signal. It is possible to provide high-quality images.

Further, the color signal processing circuit according to the present invention has a simple circuit configuration and is advantageous in terms of cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the color signal processing circuit according to the present invention, FIG. 2 is an operation waveform diagram at each point of the color signal processing circuit shown in FIG. 1, and FIG. 3 is a block diagram showing the color signal processing circuit shown in FIG. 1. FIG. 3 is a characteristic diagram of a low-pass filter used in a processing circuit. 1... Input terminal 2... Variable gain amplifier 4
...Detector 5...Low pass filter 6
... Differentiator

Claims (1)

[Claims] a variable gain amplifier whose gain is controlled based on a gain control signal and which amplifies and outputs the input carrier color signal; a detector which detects the carrier color signal; and a detector which detects the carrier color signal of the output signal from this detector. It has a filter that filters a signal higher than the frequency of the signal, and a differentiator that differentiates the output signal from the filter, and the output signal from the differentiator is supplied as a gain control signal to the variable gain amplifier. A color signal processing circuit characterized by: