JPH0361396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvement of image quality when a signal C/N is defective in a decoder of a MUSE type television receiver or the like.

[Conventional technology]

Research and development of high-definition television is nearing the stage of practical use. MUSE (Multiple Sub-Nyquist
The Sampling Encoding method is a method developed by the Japan Broadcasting Corporation, which encodes high-definition television signals with a baseband bandwidth of approximately 30 MHz to approximately 8M
Bandwidth compression to Hz bandwidth. The television receiver performs A/D conversion on the MUSE baseband signal input to the decoder, then performs digital signal processing to separate it into a Y signal and two color signals ( _CW , _CN signals), which are then D/A converted. Output. The digital signal processing includes various processing such as frequency band expansion, color signal separation, and time axis expansion, but there is no special processing for signal processing in the case of C/N failure.

[Problem that the invention seeks to solve]

If the C/N is poor, the color image becomes particularly difficult to see because the color signal is compressed by 1/4 time and the color sense.

In view of the above circumstances, an object of the present invention is to provide C/C/
It is an object of the present invention to provide a color killer that transmits only the Y signal in the case of an N defect so that the image does not become difficult to see.

[Means for solving problems]

In the color killer of the present invention, each level detection circuit in the horizontal synchronization detection section, which is composed of circuits for front-stage level detection, rear-stage level detection, and slope detection circuits of the HD waveform, has a sample value of the HD waveform determined based on a standard level with respect to a reference level. A means for outputting a judgment signal when the fluctuation range is exceeded is provided, and an error flag circuit for generating an error flag signal when the judgment signal is received from at least one of the level detection circuits is provided, and the color signal processing system is followed by an error flag circuit. , and a selector that sets the color signal output to zero when the error flag signal is input.

[Effect]

According to the present invention, in a horizontal synchronization detection section that detects a horizontal synchronization signal from an HD waveform, fluctuations in the levels of the previous and subsequent stages of the HD waveform with respect to a reference level are grasped as corresponding to the C/N, and in the case of a defective C/N. , the color signal display is stopped. Therefore, in this case, although the image has no color, it is easy to see and the viewer can recognize sufficient information.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Figure 1 includes color killer
FIG. 2 is a schematic configuration diagram of a MUSE baseband signal decoder.

The MUSE baseband signal is converted into a digital signal 101 by the A/D converter 1, and the interpolation filter 2 expands the band compression to the original signal band. At this time, the interpolation filter 2 is time-compressed and multiplexed color signal (C signal) and luminance signal (Y signal).
signal). Y signal is D/A
The converter 8a outputs it as an analog Y signal.
On the other hand, the C signal is separated into a wideband color signal (C _W signal) and a narrowband color signal (C _N signal) by the color processing circuit 6, and each is sent to the D/A via selectors 7a and 7b.
Analog C _W signal, guided by converters 8b and 8c,
Output as C _N signal.

The selectors 7a and 7b have two input terminals A and B, and an error flag signal 402 from a horizontal synchronization detecting section (HD detecting section) 4, which will be described later, is input to the select terminal (S terminal). When the error flag signal 402 is low, it is switched to the A input terminal, and when it is high, it is switched to the B input terminal. Therefore, the error flag signal 40
2 is high, the output of the color processing circuit 6 is not transmitted, and the inputs of the D/A converters 8b and 8c are zero,
The analog _CW signal and _CN signal become zero.

Digital signal 1 which is the output of A/D converter 1
01 is also led to the synchronization separation/clock recovery system. The frame pulse detection circuit 3 generates a frame pulse 301, and the HD detection section 4 generates a frame pulse 301.
Digital signal 101 and the frame pulse 30
1 and input HD pulse (horizontal sync pulse)
401 and an error flag signal 402 are generated.
The HD pulse 401 is input to the PLL circuit 5, and the PLL circuit 5 reproduces a system clock synchronized with the HD pulse 401. Error flag signal 40
As described above, 2 switches the A side of the selectors 7a and 7b connected to the color processing circuit 6 to conduction and the B side to zero output.

Next, details of the HD detection section 4 will be explained with reference to FIG. The HD waveform shown in Fig. 3 (displayed as an analog wave for ease of understanding) is divided into three parts centered around the sharply changing part, and level and slope detection is performed. The front stage level detection is l
4 points in the section, subsequent level detection at 5 points in the n section, and slope detection at 3 points in the m section.

As shown in FIG. 2, the HD converter 4 includes a front-stage level detection circuit 41, a rear-stage level detection circuit 42, a slope detection circuit 45, and an error flag circuit 46. Each of the level detection circuits 41 and 42 inputs the digital signal 101 and the frame pulse 301, and detects l sections of the HD waveform within a variation range from the reference level determined for each level detection circuit 41 and 42, respectively.
It is detected whether each point in the n interval is included. Third
In the figure, the permissible fluctuation level width for both the first and second stages is commonly α. This level width is determined by level width setting circuits 43 and 44. Since the HD waveform is inverted line by line as shown in FIG. 3, the level detection circuits 41 and 42 can handle each line by inverting the numerical value at each point based on the input frame pulse 301. .

If each point in the front and rear stages is all within the range of variation from the reference level, the slope detection circuit 45 detects the slope, and if it meets the regulations, generates the HD pulse 401. 4 points in the first section l, 5 points in the second section n
If any one of the points exceeds the fluctuation range, the HD pulse 401 will not be generated as described above, but the error flag circuit 46 will generate the error flag signal 4.
02 stands. The error flag circuit 46 performs an OR operation on the signals 41a and 42a as shown. This error flag signal 402 is sent to selectors 7a and 7b.

In addition, in the conventional HD detection section, the front stage level detection circuit and the rear stage level detection circuit do not consider the level fluctuation range, but calculate the average value of each point in the front stage and the rear stage, and when the average value meets the regulations, , the inclination is detected.

〔Effect of the invention〕

As explained in detail above, in the present invention, HD
It detects whether each point in the front and rear stages of the waveform falls within the fluctuation range set for the specified level. If even one point does not fall within the range, the color signal is changed by outputting zero output from the selector that follows the color processing circuit. Set to zero. In other words, when noise is present in the MUSE baseband signal, the circuit of the present invention operates as a color killer by checking the data at the front and rear stages of the HD waveform to correspond to the C/N size. .

In this way, although the color of the image disappears, the information can be sufficiently recognized as a black and white image that is easy to see. It is especially effective when the main content is character/numeric information.

[Brief explanation of drawings]

1 and 2 are circuit block diagrams of one embodiment of the present invention, and FIG. 3 is a diagram showing HD waveforms. 1...A/D converter, 2...Interpolation filter, 3
... Frame pulse detection circuit, 4 ... HD detection section, 5 ... PLL circuit, 6 ... Color processing circuit, 7a,
7b...Selector, 8a, 8b, 8c...D/A
Converter, 41, 42... HD front/back stage level detection circuit, 43, 44... Fluctuation level width setting circuit,
45...Tilt detection circuit, 46...Error flag circuit.

Claims (1)

[Claims] 1. In a MUSE television receiver, each level detection circuit in the horizontal synchronization detection section, which consists of the HD waveform front-stage level detection, rear-stage level detection, and tilt detection circuits, detects that the sample value of the HD waveform is determined relative to the reference level. A means for outputting a judgment signal when a specified fluctuation range is exceeded is provided, and an error flag circuit for generating an error flag signal when the judgment signal is received from at least one of the level detection circuits, and an error flag circuit subsequent to the color signal processing system. and a selector that sets the color signal output to zero when the error flag signal is input.