JPS6313488A - Chroma noise elimination circuit - Google Patents

Abstract

PURPOSE:To prevent color permeation without being averaged with a signal preceding one-hour by providing a means to selectively bypass a comb line filter to eliminate chroma noise. CONSTITUTION:A one shot multivibrator 20 generates a control pulse whose pulse width is equal to one-hour period corresponding to the outputs of counters 16 and 18 that are outputted in synchronism with scanning line signals corresponding to the upper end Iu and the lower end Id of a picture I. By means of this control pulse, the ON/OFF-state of analog switches 12 and 14 are converted, and the switch 12 is turned OFF while the switch 14 is turned ON. Accordingly, the scanning line signals corresponding to the upper end Iu and the lower end Id of the picture I are made bypassed through the comb line filter 10 by analog switch 14. As a result, the scanning line signals in a part where the color drastically changes are not averaged with the signals in one- houre period, and hence the color is prevented from permeating.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention is directed to an NTSC system that generates color television signals.
This invention relates to a chroma noise removal circuit in a decoder, etc.

[Conventional technology]

Generally, when a luminance signal, a color signal (chroma signal), and a synchronization signal are combined in an NTSC decoder or the like to generate a composite video signal, the chroma signal is passed through a chroma noise removal circuit consisting of a comb filter.

The comb filter consists of an IH delay line that delays a signal by an IH (one horizontal scanning line) period and a mixer. The signal is supplied to the second input terminal. Then, each horizontal scanning line signal is averaged with the horizontal scanning line signal before IH, and chroma noise is removed.

[Problem that the invention seeks to solve]

By the way, in parts of the screen where the colors change significantly, when the pre-IH signals are added, the colors may blur. In particular, when displaying a medical image from an electronic scope or the like with a frame provided on a part of the screen, color bleeding occurs in the horizontal direction, making it unsightly.

An object of the present invention is to prevent color blurring from occurring due to the influence of a comb filter in a portion of the screen where the color changes significantly in the ROMA noise removal circuit as described above.

[Means for solving problems]

The chroma noise removal circuit according to the invention includes an analog switch 12, 14 that bypasses the comb filter 10 in synchronization with a predetermined scan line signal.

[Effect]

According to the chroma noise removal circuit according to the present invention, the scanning line signal in the part where the color changes greatly is bypassed by the comb filter, so that it is not averaged with the signal before IH, and color bleeding is prevented. be done.

〔Example〕

An embodiment of the chroma noise removal circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an NTSC decoder having a chroma noise removal circuit according to this embodiment. The chroma signal is input to a comb filter 10. As described above, the comb filter 10 is composed of an IH delay line and a mixer, and each scanning line signal is averaged with the pre-IH signal to remove chroma noise. Comb filter 1
An output of 0 is provided via analog switch 12 to a first input terminal of mixer 22 . A chroma signal is also supplied to the first input terminal of the mixer 22 via an analog switch 14 that is interlocked with the analog switch 12 . A luminance signal and a synchronization signal are supplied to the second and third input terminals of the mixer 22. The mixer 22 outputs a decoded video signal.

The horizontal synchronization pulse H5ync is input to the clock input terminals of the counters 1B and 18. Vertical synchronization pulse v 5yn
c is input to the reset input terminals of counters 1B and 18. Counters 1B and 18 each have a horizontal synchronizing pulse H5
After counting ync by a predetermined number, an output is generated. The outputs of the counters 1B and 18 are supplied to the one-shot multivibrator 20, and the one-shot multivibrator 2
0 output signal and its inverted signal are respectively supplied to the control terminals of analog switches 14.12.

The operation of this embodiment will be explained. Here, we will explain a video in which image I obtained by an electronic scope is embedded in a predetermined area on the right side of the screen as shown in Figure 2.Normally, the color of the screen background is set to make image ■ stand out. The colors are quite different.

That is, the color of the screen changes greatly between the upper end Iu and the lower end Id of the electronic scope image I. Counter lB, 1
8, the number of scanning lines corresponding to the upper end 1u and lower end 1d is preset. When the vertical synchronizing pulse V5ync is supplied, the counter 16.18 outputs the horizontal synchronizing pulse H5y.
Start counting nc pulses. Therefore, counter 1
6.18 generates an output when the count value becomes O in synchronization with the scanning line signals corresponding to the upper end 1u and lower end Id. The time constant of the one-shot multi-bye break 20 is set to the IH period. Normally, the analog switch 12 is in a conductive state and the analog switch 14 is in a non-conductive state. Therefore, the chroma signal is normally supplied to the mixer 22 via the comb filter 10 and the analog switch 12. As a result, the chroma signal of each scanning line is averaged with the chroma signal before the IH period, and chroma noise is removed.

Then, the one-shot multi-by-break 20 generates a control pulse having a pulse width of the IH period in response to the output of the counter 16.18 which is output in synchronization with the scanning line signal corresponding to the upper end 1u and lower end 1d of the image I. This control pulse switches the conduction state of the analog switches 12, 14. The analog switch 12 becomes non-conductive, and the analog switch 14 becomes conductive. Therefore, the scanning line signals corresponding to the upper end 1u and lower end 1d of image (2) are bypassed through the comb filter 10 via the analog switch 14.

As a result, the scanning line signal of the part where the color changes greatly is I
The signal is not averaged with the signal before H, and color bleeding is prevented.

This invention is not limited to the embodiments described above and can be modified in various ways, and the specific configuration of the bypass means and the like is not limited to the examples described above. Also, the number of counters 1B and 18 is 2.
It is not limited to the number of scanning lines, but it is sufficient to provide the number corresponding to the number of scanning lines for which the square filter is to be bypassed.

〔Effect of the invention〕

As explained above, according to the present invention, by providing means for selectively bypassing the comb filter that removes chroma noise, the chroma signal is bypassed through the comb filter in areas where the color changes significantly, so that the IH Provided is a chroma noise removal circuit that is not averaged with the previous signal, prevents color bleeding, and provides a sharp image.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an NTSC decoder using an embodiment of the chroma noise removal circuit according to the present invention, and FIG. 2 is a diagram showing an example of a display screen. 10...Comb filter 12.14...Analog switch 16.18...Counter 20...One-shot multi-vibration break 22...Mixer

Claims (3)

[Claims] (1) A chroma noise removal circuit using a comb filter, characterized in that the chroma noise removal circuit includes means for bypassing the comb filter in synchronization with a predetermined scanning line signal. (2) The chroma noise removal circuit according to claim 1, wherein the bypass means bypasses the comb filter in synchronization with a scanning line signal of a portion where color changes. (3) The bypass means includes a first analog switch connected in series to the comb filter, a second analog switch connected in parallel to the comb filter, and a second analog switch connected to the comb filter in synchronization with a predetermined scanning line signal. 2. The chroma noise removal circuit according to claim 1, further comprising means for bringing the first analog switch into a non-conducting state and the second analog switch into a conducting state.