JP2636872B2 - MUSE decoder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MUSE decoder that performs enhancement processing according to a noise level included in a slump signal period.

[Prior art] The MUSE decoder is currently in the commercial prototype stage, but the prototype MU
In the output stage of the SE decoder, a signal (enhancement signal) proportional to the high frequency component of the luminance signal is added to the three primary color signals and output in order to compensate for attenuation of the high frequency component of the three primary color signals. It is common to provide a circuit.

[Problem to be Solved by the Invention] The enhancement circuit of the MUSE decoder has a configuration in which a fixed ratio of the high frequency component of the luminance signal is added to the three primary color signals as an enhancement signal regardless of the level of noise.
That is, in the conventional prototype MUSE decoder, the enhancement amount determination circuit is composed of a simple coefficient circuit, and the output of the high-pass filter is multiplied by a coefficient, or a user who waits for image reproduction quality manually inputs the coefficient from the outside. It was only variable.

However, the video signal level is originally small at high frequencies, and when the high frequency is emphasized by the enhance signal, high-frequency noise is also emphasized at the same time. However, there is a problem that the noise level with respect to the noise tends to increase and the S / N ratio decreases.

On the other hand, Japanese Utility Model Application Laid-Open No. 61-57662 discloses an automatic image quality adjustment circuit which adjusts the image quality in accordance with noise during a blanking period without a video signal component. However, this one only controls the cutoff frequency of the frequency characteristic variable circuit according to the noise component of the received video signal, and it is not a MUSE decoder that demodulates Hi-Vision signals, but is based on the current standard of revisions It can be applied only to the corresponding demodulation circuit. In other words, this is completely unrelated to an enhancement circuit or the like that has an important significance in the demodulation process of the MUSE signal, and extracts a high-frequency component from the luminance signal demodulated from the MUSE signal, and extracts the extracted high-frequency component. It was clear that the technique was not related to the technique of varying the amount of enhanced components.

Also, Japanese Patent Application Laid-Open No. 61-168383 "High-definition television receiver" discloses that a MUSE signal has a clamp signal period including a clamp level signal having no video signal component. It could also be interpreted as suggesting the possibility of improving the reproduction quality of the Hi-Vision signal by adjusting the image quality according to the noise during the clamp signal period. However, this document does not disclose any method for quantitative detection of noise during a clamp signal period or a specific method of high-frequency emphasis according to the noise level, and the like, and does not disclose an enhancement amount control function according to the noise level. It was clear that a MUSE decoder with was not readily conceivable.

Japanese Patent Application Laid-Open No. 61-296881 "Television image quality improvement device" has a configuration in which a luminance signal and a chrominance signal are converted into three primary color signals by a matrix circuit, and a high frequency component of the luminance signal is added to each of the three primary color signals. Although this device is disclosed, this device quantitatively adds the high-frequency component of the luminance signal to the three primary color signals. Therefore, when the noise level is high, a large amount of the high-frequency component contained in the luminance signal is included. There is a problem that noise is added to the three primary color signals, sometimes resulting in an adverse effect of emphasizing high frequency noise instead of correcting high frequency attenuation.

It is an object of the present invention to provide a MUSE decoder that solves the above-described problem and, when noise is large, adjusts, for example, by reducing the amount of addition of an enhanced signal to improve the S / N ratio. .

Means for Solving the Problems In order to solve the above problems, the present invention provides a main part of a MUSE decoder that demodulates a MUSE signal to separate and output a luminance signal and a chrominance signal, and performs an inverse matrix operation on the output of the MUSE decoder. An inverse matrix circuit that generates three primary color signals, and a high-frequency component extracted from the luminance signal, a read-only memory that uses a noise level signal supplied from the outside as an upper address and the high-frequency component signal as a lower address, An enhancement signal generation circuit that reads out and outputs an enhancement signal obtained by performing an enhancement in inverse proportion to the noise level signal on the high-frequency component signal and an addition circuit that adds the enhancement signal to each of the three primary color signals; The clamp level signal is extracted from the MUSE signal, and the difference between adjacent samples of the clamp level signal is integrated over substantially the clamp period. , 1
A noise level detection circuit for setting a noise level in a field period, and a latch circuit for latching an output of the noise level detection circuit during a non-clamp period and supplying the noise level signal to the enhancement signal generation circuit. It is a feature.

[Operation] The MUSE signal includes a clamp level signal having a fixed level value in lines 563 and 1125 of the vertical blanking period as a transmission signal format. The change in the clamp level signal is detected as a representative value of the noise level in the transmission path during one field period, and the enhancement signal is corrected according to the detected noise level, thereby improving the S / N ratio.

Example An example of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing an embodiment of a MUSE decoder according to the present invention, and FIG. 2 is a diagram showing a main part of a transmission signal format of a MUSE signal.

The MUSE decoder shown in FIG. 1 includes a MUSE decoder main unit 10 for receiving a MUSE signal and demodulating three primary color signals, and other circuits. The digitized MUSE signal is converted into a luminance signal Y and a chrominance signal (here,
The signal is demodulated into a red color difference signal RY and a green color difference signal GY), and is inversely matrix-converted by a subsequent inverse matrix circuit 11 into three primary color signals R, G, and B of red, green, and blue. The enhancement signal 12a output by the enhancement signal generation circuit 12 is added to the addition circuit 13 to the three primary color signals R, G, B obtained by the inverse matrix conversion.

The enhancement signal generation circuit 12 is a main part of the MUSE decoder 10.
A high-frequency component is extracted from the luminance signal Y demodulated by the high-pass filter 121, and the extracted high-frequency component is determined by an enhancement amount determining circuit.
122, an appropriate enhancement amount is determined with reference to the noise level, and transmitted as the enhancement signal 12a. The three primary color signals R, G, and B to which the enhancement signal 12a has been added by the adding circuit 13 are converted into analog signals by a D / A converter (not shown) and sent to a display unit.

In the conventional prototype receiver, the enhancement amount determination circuit 122 is constituted by a simple coefficient circuit, and the high-pass filter
The output was merely multiplied by a factor, or the level of the factor was manually changed externally by looking at the image. On the other hand, in the present embodiment, as described below, the enhancement amount determination circuit 122 is configured to automatically change the enhancement amount depending on the noise situation of the MUSE signal and determine the optimum enhancement amount.

The MUSE signal is transmitted in accordance with the transmission signal format shown in FIG. 2, and a clamp level signal is included in lines 563 and 1125 in the vertical blanking period. The clamp level signal is 107 for each field as the line sample number.
To 480 (this period is called a clamp period), a fixed level value is transmitted on the transmission side. However, when receiving a MUSE signal including noise, the clamp level signal is not a constant level value when receiving. Therefore, in this embodiment, as a noise level detecting means, a difference between adjacent samples of a clamp level signal which is a sample signal is obtained, and an integrated value over the clamp period is detected as a nozzle level in one field period.

HD (horizontal synchronization), VD generated by MUSE decoder main unit 10
(Vertical synchronization) The timing generation circuit 23 for inputting a signal
Various necessary timing signals are generated, and the gate circuit 20, the noise level detection circuit 21, and the latch circuit 22 are operated by the output signals a, b, and c of the timing generation circuit 23. The gate circuit 20 extracts the clamp level signal from the input MUSE signal by opening the gate only during the clamp period including the clamp level signal. The noise level detection circuit 21 obtains a difference between adjacent samples of the clamp level signal in the one-dot difference circuit 211, and integrates each difference in the product-sum circuit 212. When all the differences in one clamp period have been obtained, the data of the product-sum circuit 212 is latched by the latch circuit 22 at the timing when the MUSE signal moves to the next line, and the product-sum circuit 212 is simultaneously cleared. The noise level signal 22a output from the latch circuit 22 is sent to the enhancement amount determination circuit 122 of the enhancement signal generation circuit 12.

The enhancement amount determination circuit 122 determines the optimum enhancement signal 12a based on the high-frequency component signal 121a extracted from the luminance signal Y by the high-pass filter 121 and the noise level signal 22a sent from the enhancement signal generation circuit 12. To determine. More specifically, the enhancement amount determination circuit 122 is formed of, for example, a ROM (read only memory), and uses the noise level signal 22a as an upper address and the high frequency component signal 121a as a lower address to store the contents of the written memory cell. Output as the enhancement signal 12a. However, a core characteristic is given to the noise level signal 22a, and only the upper bits of the latch circuit 22 are used as an address signal. When the noise level is high, the enhancement signal 12a is reduced to reduce the enhancement effect, thereby suppressing an increase in high frequency noise.

As described above, the MUSE decoder demodulates the MUSE signal and separates and outputs the luminance signal and the chrominance signal.
The output of 10 is subjected to an inverse matrix operation to generate three primary color signals R, G, B, and the enhanced signal 12a, which has been enhanced in inverse proportion to the noise level signal supplied from the outside, is converted to the three primary color signals R, G, B. While adding to each of them and performing enhancement processing, the clamp level signal is extracted from the MUSE signal,
The difference between adjacent samples of the clamp level signal is integrated over one clamp period to obtain a noise level for one field period, and this is latched during the non-clamp period to obtain the noise level signal 22a. A conventional MUSE that uses a high-frequency component of a luminance signal multiplied by a certain percentage as an enhancement signal regardless of the level of noise in the received signal when adding the enhancement signal for improvement
Unlike a decoder, it suppresses the enhancement effect for signals with large noise, suppresses the increase in noise due to high-frequency emphasis, and provides a sufficient enhancement effect for signals with small noise to increase unnecessary noise. A high-quality image can be obtained by high-frequency emphasis without accompanying. Therefore, S / S is effectively achieved by the enhancement process adapted to the amount of noise.
Since the N ratio can be improved, and the noise level signal obtained during the clamp period is latched and used by the next clamp period, the enhancement effect can be corrected in the field cycle, and fine S / N ratio improvement is possible.

[Effects of the Invention] As described above, according to the present invention, an output of a main part of a MUSE decoder that demodulates a MUSE signal and separates and outputs a luminance signal and a chrominance signal is subjected to an inverse matrix operation to generate three primary color signals. Further, from the luminance signal, a high-frequency component is extracted, and an enhanced signal that has been subjected to emphasis almost inversely proportional to a noise level signal supplied from the outside is read out. MUSE
A clamp level signal is extracted from the signal, and a difference between adjacent samples of the clamp level signal is integrated over a substantially clamp period to obtain a noise level for one field period. Therefore, when adding the enhancement signal to improve the high-frequency characteristics, regardless of the magnitude of the received signal noise, a signal obtained by multiplying the high-frequency component of the luminance signal by a fixed ratio is used as the enhancement signal. Unlike the conventional MUSE decoder that had been used, by using an enhanced signal that emphasized the high frequency component signal almost inversely proportional to the noise level signal,
Suppresses the enhancement effect for high-noise signals and suppresses the increase in noise due to high-frequency emphasis, while providing a sufficient enhancement effect for low-noise signals and high-frequency emphasis without increasing noise High-quality image, and therefore the S / N ratio can be effectively improved by the enhancement processing adapted to the amount of noise. Since the enhancement signal is read from the read-only memory with the signal as the lower address, the enhancement signal in which the high-frequency component signal is almost inversely proportional to the noise level signal, the high-frequency enhancement according to the storage content of the read-only memory By using only the upper bits of the read-only memory as address signals, noise level signals can be The core characteristics can be easily provided, and when the noise level is high, the enhancement signal can be reduced and the enhancement effect reduced to suppress the increase in high frequency noise. In addition, since the nozzle level signal obtained during the clamp period is latched and used until the next clamp period, the enhancement effect can be corrected in the field cycle, and fine S / N ratio improvement is possible. It has excellent effects such as certain effects.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of a MUSE decoder according to the present invention, and FIG. 2 is a diagram showing a main part of a transmission signal format of a MUSE signal. 10 MUSE decoder main part 11 Inverse matrix circuit 12 Enhancement signal generation circuit 121 High-pass filter 122 Enhancement amount determination circuit 13 Addition circuit 21 Noise level detection circuit 211 1 Dot difference circuit 212: Product-sum circuit 22: Latch circuit 23: Timing signal generation circuit

Claims (1)

(57) [Claims] 1. A main part of a MUSE decoder for demodulating a MUSE signal and separating and outputting a luminance signal and a chrominance signal, an inverse matrix circuit for performing an inverse matrix operation on an output of the MUSE decoder to generate three primary color signals, From a read-only memory that uses a noise level signal supplied from the outside as an upper address and the higher frequency component signal as a lower address, and is approximately inversely proportional to the noise level signal with respect to the high frequency component signal. An enhancement signal generation circuit that reads out and outputs an enhanced signal subjected to enhancement, an addition circuit that adds the enhancement signal to each of the three primary color signals, and a clamp level signal from the MUSE signal,
A noise level detection circuit that integrates a difference between adjacent samples of the clamp level signal substantially over a clamp period and sets a noise level during one field period, and latches an output of the noise level detection circuit during a non-clamp period; A latch circuit for supplying a noise level signal to the enhance signal generation circuit.