JPS63136790A - Transmission system for component video signal - Google Patents

Abstract

PURPOSE:To reduce crosstalk from a chrominance signal C to a luminance signal Y by using a signal inputted at the input side of a signal processing circuit as a signal which is in linear relation in terms of level to the gradation of a display picture at least with respect to the luminance signal. CONSTITUTION:A nonlinear correction circuit GAMMAY8 for the luminance signal is provided to the sender side so as to reduce the effect of noise in a transmission line and a nonlinear inverted correction circuit GAMMAY<-9>9 is provided for the luminance signal only to the reception side to restore the correction. In a picture display device at the reception side having a nonlinear in the relation between brightness and input signal such as a CRT, a conventional gamma correction 16 compensating the nonlinearity is executed. Since the nonlinearity correction is less with respect to the chrominance signal, the nonlinear correction circuit GAMMAC6 for reducing the effect of noise in the transmission line is inserted before a signal processing circuit of a MUSE encoder 7. Thus, the crosstalk from the chrominance signal C to the luminance signal Y is reduced.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a component transmission method for color television signals, and is particularly suitable for a MUSE signal transmission method (time axis compression multiplex sub-sampling transmission method for high-vision). It is related to.

(Prior Art) It has been known to perform nonlinear processing on a transmission signal in order to reduce the influence of noise on a transmission path.

In television signals, gamma correction to compensate for the nonlinearity of the image display cathode ray tube (CRT) on the receiving side is generally performed on the transmitting side to reduce the cost of the receivers used.
This helps reduce the influence of noise on the transmission line.

However, at the same time, the noise on the color signal is transferred to the luminance signal, making the noise noticeable.

(Problems to be Solved by the Invention) When transmitting a color television signal, three primary color image signals R and G are obtained from a signal source.

Normally, B is not transmitted in its original form, but is converted into a luminance signal Y and a color signal C through matrix processing and then transmitted. At this time, the luminance signal Y is intended to transmit only information regarding the luminance of the subject, and the color signal C is intended to transmit only information regarding the color of the subject, so even if the color signal C changes, the luminance signal If the Y signal level is constant, the brightness of the image displayed on the image display device should remain constant without changing.This is called the constant brightness principle, and transmission that satisfies this principle is called constant brightness. It's called transmission.

However, in reality, gamma correction to compensate for CRT nonlinearity on the receiving side is performed on the transmitting side, and then the above-mentioned matrix processing is performed before transmission. A portion of the signal Y is converted into a portion of the color signal C and is transmitted. Therefore, when the transmission band of the color signal C is restricted and its high-frequency components are attenuated, some of the luminance signals converted to the color signal C are also attenuated, and the reproducibility of the signal level of the reproduced luminance signal Y deteriorates. Also, due to narrowband transmission, noise on the color signal C is transferred to the luminance signal Y, resulting in a disadvantage that the noise is noticeable. This failure of the constant luminance principle can occur simply by converting the three primary color signals without gamma correction into a luminance signal Y and a color signal C, and narrowing the transmission band of the color signal after YC separation. Matrix processing causes more significant deterioration of the luminance signal.

In order to avoid this, the conventional constant brightness transmission method avoids gamma correction on the transmitting side, and
As described in the specification of No. 9989 "Color Image Display System", when a wideband high-definition color television image signal is transmitted with an insufficient transmission bandwidth, the reduction in brightness level reproducibility in the receiving device is separately compensated for. This ensures high quality playback.

However, this method is insufficient because it does not take into consideration the deterioration caused by the transfer of noise on the color signal of the transmission system to the luminance signal.

Therefore, the purpose of the transmission system of the present invention is to improve the above-mentioned drawbacks and provide a component video signal transmission system that eliminates the influence of noise on the transmission path while retaining the advantages of the constant brightness transmission system described above. be.

(Means for Solving the Problems) In order to achieve this object, the transmission system of the present invention, when transmitting component video signals, uses The signal input to each of the signal processing circuits is characterized in that, at least regarding the luminance signal, the signal is in a linear relationship in level with the gradation of the display image displayed on the receiving side.

Further, in a preferred embodiment of the present invention, in the component video signal transmission method, the three primary color signals are converted into a luminance signal and a color signal by a matrix circuit on the transmitting side, and the converted luminance signal and color signal are inverted on the receiving side. When the inverse conversion is performed by a matrix circuit, the transmitted signal is subjected to nonlinear correction and nonlinear inverse correction only between the matrix circuit on the transmitting side and the inverse matrix circuit on the receiving side.

(Examples) The present invention will be described in detail below by way of examples with reference to the accompanying drawings.

The transmission method of the present invention is applied to MUSE (Multiple Sub-Ny) related to high-definition television signal transmission method.
FIG. 1 shows a schematic block diagram of an embodiment applied to the quistSampling (Encoding) transmission system.

The MUSE transmission method is a method for effectively compressing and transmitting wideband high-definition television signals, and is a multiple subsampling transmission method using offset subsampling between frames and fields. For example, the applicant's patent application No. 60-125049 6 "Time axis compression multiplex sub-sample transmission system", Japanese Patent Application No. 1986-10
Please refer to No. 6132, “Multiple subsample transmission system”.

The gamma inverse correction circuit (γ-1) l shown in Figure 1 performs γ correction on the transmitting side to compensate for the nonlinearity of the CRT on the receiving side in normal color television signal transmission. This is to achieve the above-mentioned constant brightness transmission by returning the R, G, and B input signals, and is the input for a system where the input signal of the display device and the luminance of the display device are in a linear relationship, such as a gas discharge display panel. This is not necessary for signals.

As described in the claims, the gist of the transmission system of the present invention is, for example, in a transmission system having the system shown in FIG. a signal processing circuit consisting of a band-limiting filter LPF (Y)3 for luminance signals, a band-limiting filter LPF (CI)4 for wide-band chrominance signals, and a band-limiting filter LPF (Cm)5 for narrow-band chrominance signals; Signal processing circuit of MUSE encoder 7, MU
Signal processing circuit of SE decoder 10, band-limiting filter for luminance signal LPF (Y) 12, band-limiting filter for wide-band chrominance signal LPF (CI) 13, band-limiting filter for narrow-band chrominance signal LPF (Cz ) 14 and an inverse matrix processing circuit MTX-'15, the signals input to each of the signal processing circuits are processed to determine the level of the display image displayed on the receiving side, at least with respect to the luminance signal. The goal is to create a signal that has a linear relationship with the key in terms of level. In other words, the transmission system may be constructed so that the luminance signal having the linear relationship is always present on the input side of each of the signal processing circuits.

This means that at least the nonlinear correction regarding the luminance signal and the nonlinear inverse correction thereof need to be closed between the respective signal processing circuits.

Figure 1 shows a nonlinear correction circuit rv8 for only the luminance signal provided on the transmitting side to reduce the influence of noise on the transmission path, and a nonlinear reverse correction circuit rv8 for only the luminance signal provided on the receiving side to restore the correction. '9 is exactly that, M U 'S R
The signal processing circuit of the encoder 7 and the signal processing circuit of the MUSE decoder 10 are closed. The restored three primary color signals obtained after the inverse matrix processing circuit MTX-'15 are Normal gamma correction γ1 to compensate for nonlinearity
6, and there is no need to perform gamma correction for devices with linear characteristics such as gas discharge display panels.

In the example shown in the first figure, since less nonlinear correction is required for the color signal C, a nonlinear correction circuit 1'c6 is inserted in front of the signal processing circuit of the MUSE encoder 7 to reduce the influence of noise on the transmission path. There is.

If the signal processing accuracy of the signal processing circuit is sufficiently high, it is better to perform nonlinear correction after the signal processing circuit of the MUSF and encoder 7, similarly to the luminance signal Y.

The characteristics of this nonlinear correction for the transmission path are significantly different between the luminance signal Y and the chrominance signal C, and the characteristics of the correction of the luminance signal Y are significantly different from the conventional gamma correction on the camera side (see Figure 2 (a)). However, the correction of the color signal C is as shown in Fig. 2 (b
), it is better to have an rc shape that is almost a straight line with a slope in the part with extremely low saturation.

The reason for doing this is that when a CRT is used as the image display device on the receiving side as shown in the first diagram, it is impossible for the gamma correction circuit γ16 to completely compensate for its nonlinearity. Crosstalk to the luminance signal Y occurs on the CRT. This is particularly noticeable in the highly saturated portions of the color signal, so it is desirable to have a good S/N ratio for the color signal C in the highly saturated portions. Therefore, the characteristics of the color signal nonlinear correction circuit rc6 are of a higher level, as shown in FIG. 2(b), unlike the characteristics of the nonlinear correction circuit r'y8 for transmission of the luminance signal Y, as shown in FIG. 2(a). It is better not to have sections with progressively lower slopes.

Note that the MUSE encoder and decoder shown in Figure 1 are usually constructed using a digital system, so in actual circuits, A/Ds are installed on the input and output sides of each.

A D/A converter is inserted.

Further, when the configuration shown in FIG. 1 is adopted, the signal processing of the MUSE encoder and decoder is performed in the linear level space for the luminance signal Y, which is extremely important in the following respect. That is, in the MUSE method, at least two types of spatial filters are used and switched depending on the content of the image, for example, whether it is a still image or a moving image. In this case, if there is no linear relationship between the level of the electrical signal and the display level on the display device, the narrower the passband width of the spatial filter will lower the peak level even if the average level of the electrical signal is the same (high-frequency cutoff). Therefore, the displayed average level of the signals that have passed through the two types of filters fluctuates. In reality, the display characteristic of a CRT is a curve of the square or higher power, so blurred parts of a moving image become dark, which causes the image to become unstable when switching between moving images and still images.

The embodiments in which the method of the present invention is applied to the MUSE transmission method related to the high-definition television signal transmission method have been described above, but the transmission method of the present invention is not limited to this. It should be noted that the present invention is applicable to all transmission systems in which a system having a linear relationship in level with the gradation of a display image may be established at the input end of each signal processing circuit.

(Effects of the Invention) By adopting the transmission method of the present invention, crosstalk from color signal C to luminance signal Y is reduced in the transmission of color television signals, and it is consistent with the visual conspicuousness of transmission line noise. Transmission methods can be created.

In addition, since there is a linear relationship between the electrical signal and the display on the image display device, the transmission band of the color signal can be narrower than before, and the influence of transmission line noise is reduced, and as with the MUSE transmission method, it is possible to Even if different spatial filters are used, the discontinuity in switching between moving images and still images can be reduced.

[Brief explanation of the drawing]

FIG. 1 shows a schematic block diagram of an embodiment in which the transmission method of the present invention is applied to the MUSE transmission method, and FIG. 2 shows a correction curve of a nonlinear correction circuit for a transmission line used in an embodiment related to the present invention. Luminance signal bone 1'y (a) and color signal molecule C (b)
and is shown. 1... Gamma inverse correction circuit 2... Matrix circuit 3.12... LPF for luminance signal 4.13... LPF for wideband color signal 5.14... LPF for narrowband color signal 6.11 ...Transmission color signal nonlinear correction and inverse correction circuit 7...MUSE encoder 8.9...Transmission luminance signal nonlinear correction and inverse correction circuit 10...MUSE decoder 15...Inverse matrix circuit 16.・・Gamma correction circuit

Claims (1)

[Claims] 1. When transmitting a component video signal, on the input side of each signal processing circuit on the transmitting side and receiving side that constitute the transmission system, the signal input to each signal processing circuit,
A component video signal transmission system characterized in that at least a luminance signal is a signal that has a linear relationship in level with the gradation of a display image displayed on a receiving side. 2. In the component video signal transmission method, the three primary color signals are converted into luminance signals and color signals by a matrix circuit on the transmitting side, and the converted luminance signals and color signals are inversely converted by an inverse matrix circuit on the receiving side. In the component video according to claim 1, the transmission signal is nonlinearly corrected and nonlinearly inversely corrected only between the matrix circuit on the transmitting side and the inverse matrix circuit on the receiving side. Signal transmission method. 3. The component video signal transmission system according to claim 2, wherein the nonlinear correction is correction based on individual characteristics for each of the luminance signal and the color signal. 4. The component according to claim 2 or 3, wherein the nonlinear correction is a correction having a characteristic curve with a slope on the high side of the signal level that is gentler than a slope on the low side of the signal level. Video signal transmission method. 5. A patent characterized in that the nonlinear correction of the color signal is a correction having a characteristic curve that has a smaller difference in slope between the high side and the low side of the signal level compared to the nonlinear correction of the luminance signal. A component video signal transmission system according to any one of claims 2 to 4.