JP2685511B2 - Color band characteristic improvement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital television receiver, and more particularly to ensuring quantization accuracy of a carrier color signal in an automatic saturation adjustment circuit (ACC) and preventing resolution deterioration. The present invention relates to a preferable color band characteristic improving system.

[Conventional technology]

The digital television receiver converts the demodulated baseband composite video signal into a digital signal by the A / D converter, performs all signal processing by digital processing, and finally, converts it into an analog signal by the D / A converter. Return and display. Its features are simplification of adjustment, reduction of adjustment error (variation) and reduction of change with time (drift), and further various signal processing can be performed without degrading the characteristics of the video signal.

FIG. 2 shows a block diagram of the video system in a conventionally known general digital television receiver (deflecting the deflection system and the audio system), mainly the A / D converter 3, Y / It is composed of a C separation circuit 4, an ACC circuit 6, a luminance processing circuit 5, a chromaticity processing circuit 7, a matrix circuit 8 and a D / A converter 9.

First, the demodulated baseband video signal (composite signal) is supplied to the input terminal IN and is converted into a digital signal by the A / D converter 3. The converted video signal of the digital signal is supplied to the Y / C separation circuit 4, and the luminance signal Y and the carrier color signal C are separated. The separated Y signal and C signal are separately processed. The Y signal is input to the brightness processing circuit 5 and subjected to processing such as contour compensation and contrast adjustment. Further, the C signal is input to the ACC circuit 6 and the amplitude of the signal is controlled so as to follow the magnitude of the burst signal. The above-mentioned control is indispensable to the television receiver because the amplitude of the C signal is likely to change due to the reception characteristics (for example, the influence of multipath), and the signal processing is performed. The ACC-processed C signal is input to the chromaticity processing circuit 7, where color demodulation is performed.

FIG. 3 shows the ACC described in JP-A-62-224182.
It is a block diagram showing an example of a circuit. The carrier color signal C is input to the burst detection register 10 and the multiplier 17, respectively. The burst detector 10 detects burst values one after another in each horizontal cycle. First, the detected burst value is
Add to subtractor 11. The previously smoothed burst value is subtracted from the burst value detected by the subtracter 11. The output signal of the subtractor 11 is added to the multiplier 12, where
The output is multiplied by 1 / K. The 1 / K multiplied signal is added by the adder 13 to the previously smoothed burst value. Adder 13
Is output as a newly smoothed burst value from
Input to the divider 14 and the latch 15. The output signal of the latch 15 is applied to the subtractor 11 and the adder 13 as the previously smoothed burst value, and the same signal processing as described above is performed. The smoothing function of the smoothing circuit 16 increases as the value of K increases. On the other hand, the divider 14 outputs a value obtained by dividing the reference burst value by the smoothed burst value. The output of the divider is input to the multiplier 17, is multiplied by the carrier color signal, and outputs the carrier color signal whose amplitude is accurately compensated.

The output signals processed by the luminance processing circuit 5 and the chromaticity processing circuit 7 are both input to the matrix circuit 8 to obtain R, G, B three primary color signals. Then, the R, G, B signals are converted into analog signals by the D / A converter 9 and guided to the output terminals OUTα, β, γ.

In the signal processing described above, in order to process this characteristic without deteriorating, a quantization accuracy of 8 to 9 bits is required, and a sample rate of about 14 MHz (f sc) is desired.
Therefore, in a normal digital television, as shown in FIG. 2, a baseband video signal is sampled at 4f sc (f sc: subcarrier frequency) and quantization of 8 bits is performed.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, when the reception condition changes, for example, when the frequency characteristic deteriorates in the transmission line, the gain control of the carrier color signal that follows the burst signal level is performed. Becomes worse. According to the broadcast standard, the color burst amplitude is 0.2 for a 1V _{P_P} video signal.
Since it is defined as 86V _{P_P} , if the video signal quantization is 8 bits, the number of quantization levels of the burst signal is about 73 levels. Now, if ACC control of 15 dB is enabled, the number of quantization levels of burst signals will be about 13 levels, and deterioration due to quantization noise becomes a problem. In the above conventional example, the quantization of the burst value provides some relaxation, but the quantization accuracy for the carrier color signal is not sufficiently taken into consideration, and the accuracy of the quantization is insufficient when the ACC control amount increases. Therefore, there is a problem in that color unevenness occurs, or the saturation is displayed differently between the received channels. Further, even if the number of quantization bits of the video signal is increased in advance to secure the quantization accuracy of the carrier color signal, the circuit scale becomes large.

An object of the present invention is to ensure the quantization accuracy for the carrier color signal without increasing the number of quantization bits of the video signal.

[Means for solving the problem]

The above purpose is to provide a circuit for compensating the color band component of the video signal according to the level of the burst value before converting the demodulated baseband composite video signal into a digital amount, and providing the target video signal to this circuit. This is achieved by setting the multiplexed carrier color signals to almost a predetermined value by passing them.

[Action]

The color band compensation circuit, which is newly installed before the A / D conversion circuit, operates so as to bring the video signal whose color band level has changed to a substantially predetermined level. As a result, even if the carrier color signal component is greatly attenuated by the reflection of the antenna system, etc., its level is roughly corrected, and when it is quantized, it becomes a state close to the standard signal level, so it is digital. AC
The amount of C is very small, and the quantization accuracy can be secured. In addition, the compensated video signal improves not only the color component but also the high-frequency component of the luminance, so that the resolution is prevented from lowering.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is a block diagram showing the configuration of a color band component characteristic improving system according to an embodiment of the present invention.

Reference numeral 1 is a characteristic group having various kinds of compensation characteristics, and is a circuit for adding compensation according to the deterioration state of the color band component of the received video signal. Reference numeral 2 is a control signal generation circuit for selecting a color band compensation characteristic from the composite video signal supplied to the input terminal IN, for example, a burst detector.
20, rectifier circuit 21, low-pass filter (LPF) 22, A / D converter 2
It is composed of an averaging circuit 24 and a hysteresis circuit 25.
3 is an A / D converter for converting an analog composite video signal into a digital amount, 4 is a Y / C separation circuit for separating a luminance signal Y and a carrier color signal C from the video signal, 5 is a luminance processing circuit, 6 Is an ACC that controls the carrier color signal C to a predetermined level
A circuit, 7 is a chromaticity processing circuit for performing processing such as color demodulation, 8 is a matrix circuit for generating three primary color signals from a luminance signal and color signals, and 9 is a digital signal for converting a digital signal back to an analog signal.
A converter.

The video signal of the composite demodulated to the base band is supplied to the input terminal IN, and is input to the color band compensation characteristic group circuit 1 and the control signal generation circuit 2.

First, the video signal input to the color band compensation characteristic group circuit 1 is the control signal CTL which is the most suitable compensation characteristic among the various types of characteristics prepared in advance according to the state of deterioration of the color band component. Is selected (for example, a characteristic is selected by a multiplexer), the compensation is performed, and the output is performed. In this embodiment, in order to simplify the explanation, there are eight types of compensation characteristics in consideration of the control signal generating circuit 2 described later.

The tendency of the compensation characteristics prepared in advance is as follows.
The one shown in FIG. 4 is suitable. In this characteristic, for example, the compensation requiring the intermediate level between (a) and (b) is finely adjusted again in the ACC circuit 6.
Therefore, the compensation characteristic selected by the color band compensation characteristic group circuit 1 may be such that the ACC circuit 6 later can ensure the quantization accuracy of the carrier color signal. If the control range of ACC is from -3dB to + 3dB, it is sufficient to prepare compensation characteristics in 3dB steps.

Next, the analog video signal compensated by the color band compensation characteristic group circuit 1 is input to the A / D converter 3 and converted into a digital amount. The video signal converted into digital amount is Y / C
It is input to the separation circuit 4 and separated into a luminance signal Y and a carrier color signal C. The Y signal is input to the brightness processing circuit 5 and is subjected to signal processing such as contour compensation. The C signal is input to the ACC circuit 6, compensated to a predetermined level, and then supplied to the chromaticity processing circuit 7. The processing in the ACC circuit 6 may be basically the same as that of the conventional technique, but the control range of the compensation is narrower than that of the conventional technique, so that more accurate compensation is possible. The chromaticity processing circuit 7 performs color demodulation to obtain I and Q or (RY) and (BY) signals. The output signals processed by the luminance processing circuit 5 and the chromaticity processing circuit 7 are both supplied to the matrix circuit 8 to obtain R, G, B three primary color signals. Then, the R, G, B signals are returned to analog signals by the D / A converter 9 and led to the output terminals OUTα, β, γ.

By the way, in the NTSC composite signal, as shown in FIG. 5, a burst (color synchronization) signal and a carrier color signal are superimposed on a luminance signal. When the amplitude of the NTSC composite signal is terminated with 75Ω, it is defined as 1V _{P_P} , of which the burst level is defined as 0.285V _{P_P} . However, depending on the reception situation, the burst level often fluctuates with respect to the specified one. Since the fluctuation amount of the burst level is equal to the fluctuation amount of the color band component, it is necessary to accurately detect the burst level. 2 is a block diagram of an example for detecting the burst level from the video signal.

First, in the burst detector 20, a burst gate is applied to the video signal, and only burst signals as shown in FIG. 6 are sequentially extracted for each horizontal period. Next, the extracted burst signal is added to the rectification circuit 21, and signal processing of full-wave rectification or half-wave rectification is performed to shape it into the signal shown in FIG. The output signal of the rectifier circuit 21 is a low pass filter (LP
F) Enter in 22. In LPF22, by setting the cutoff frequency to several hundred KHz, for the rectified burst signal,
Smoothing is applied to obtain a flat burst (amplitude) value as shown in FIG. At this time, the burst value is proportional to the magnitude of the carrier color signal. Therefore, the obtained burst value is added to the A / D converter 23 to be quantized into n bits. However, here, there are eight types of color band compensation characteristics, and n ≧ 3. A / D converter 23
A sample rate of 63.5 μs is sufficient for the horizontal (H) period. The output signal of the A / D converter 23 has a field period (V−
It is supplied to the averaging circuit 24 for averaging in a cycle.
The purpose of averaging is to prevent burst values from being quantized one after another in H-cycles, but to prevent the digital amount of the burst values from changing within one field due to the influence of noise or the like. Therefore, at the output of the averaging circuit 24, 3-bit digital data proportional to the size of the received burst signal is smoothed for each field and obtained one after another.
That is, the smoothed 3-bit digital data serves as a control signal. Further, here, the smoothed signal is input to the hysteresis circuit 25 so as to have a hysteresis characteristic. The purpose of operation of the hysteresis circuit 25 is to stabilize the switching of characteristics in the color band compensation characteristic group circuit. That is, since the color band compensation characteristic prepared in advance does not change continuously but changes discretely, the operation becomes unstable when the averaged burst value reaches the boundary level at which the characteristic is switched. This is to prevent this. Therefore,
At the output of the hysteresis circuit 25, a control signal CTL for selecting a characteristic to be color band compensated is obtained and supplied to the color band compensation characteristic group circuit 1.

According to the present embodiment, before the digital processing of the received video signal is performed, rough deterioration is added to the color band component by analog processing, so that the A / D converter for quantizing the video signal ACC without increasing the number of quantization bits
It is possible to secure the quantization accuracy in and to realize a highly accurate digital ACC. Further, the deterioration of the resolution due to the deterioration of the color band component is also improved.

〔The invention's effect〕

According to the present invention, since the color band component based on the burst signal level is previously compensated before the composite video signal is quantized, the attenuated video signal can be made to have a substantially predetermined level. The quantization accuracy of the color signal obtained by Y / C separation after A / D conversion is secured, the effect of preventing changes in saturation due to the quantization accuracy and the prevention of resolution deterioration due to deterioration of color band components effective.

[Brief description of the drawings]

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a video system in a general digital television receiver, and FIG. 3 is a block diagram showing an example of an ACC circuit.
FIG. 4 is a diagram showing an example of color band compensation characteristics according to the present invention, FIG. 5 is a diagram showing a specified NTSC composite signal, and FIG. 6 is a waveform diagram in which a burst signal is extracted. 1 ... Color band compensation characteristic group circuit, 2 ... Control signal generation circuit, 3,23 ... A / D converter, 4 ... Y / C separation circuit, 5 ... Luminance processing circuit, 6 ... Automatic color Degree adjustment (ACC) circuit, 7 ...
Chromaticity processing circuit, 8 ... Matrix circuit, 9 ... D / A converter, 10, 20 ... Burst detector, 16 ... Smoothing circuit, 17 ...
… Multiplier, 21 …… Rectifier circuit, 22 …… Low pass filter (LPF), 24 …… Averaging circuit, 25 …… Hysteresis circuit, C …… Carrier color signal, Y …… Luminance signal, CTL …… Control signal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 62-264789 (JP, A) JP 63-102485 (JP, A) JP 60-3293 (JP, A) JP 60- 167589 (JP, A) JP-A 1-212990 (JP, A) JP-A 60-10892 (JP, A) Actually developed Shou 58-149875 (JP, U)

Claims (2)

(57) [Claims] 1. An A / D converter for converting a composite video signal demodulated to baseband into a digital signal, and a Y / C separation for separating the video signal converted into a digital signal into a luminance signal and a carrier color signal. A luminance processing circuit that performs predetermined digital signal processing on the separated luminance signal, an ACC circuit that performs ACC processing on the separated carrier color signal, and a predetermined digital signal processing on the ACC processed carrier color signal. A chromaticity processing circuit to perform, a matrix circuit for converting the luminance signal and the color signal processed by the luminance processing circuit and the color processing circuit into three primary color signals, and converting the three primary color signals into analog signals.
In a color band characteristic improving system in a digital television receiver having a D / A converter, a plurality of discretely varying types for compensating frequency components in the vicinity of the color width carrier frequency in the composite video signal A color band compensation characteristic group circuit in which compensation characteristics are preset is provided in the preceding stage of the A / D converter, and one corresponding to the burst level detected from the composite video signal among the plurality of types of compensation characteristics A color band characteristic improvement method characterized by selecting and compensating the composite video signal. 2. When the control range of the ACC circuit is ± ndB, the plurality of types of compensation characteristics are set to compensation characteristics in mdB (m ≦ n) steps. The color band characteristic improvement method described in.