JPH0518518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a transmission method in which a television signal is subsampled and transmitted for the purpose of transmission band compression.

(Prior art) One of the methods for band compression of television signals is the multiple sub-sampling transmission method using offset subsampling between frames and between fields, such as MUSE (Multiple Sub-Nyquist
There is a current high-definition television signal multiplex sub-sampling transmission method called Sampling Encoding, which effectively achieves band compression.

However, in the case of the current multiplex sub-sample transmission system, there is a problem in detecting a moving image area, which is necessary for performing signal processing while distinguishing between moving image areas and still image areas. In other words, since the subsampling in the current method goes through one round every two frames, when performing motion detection, it is not possible to use the difference signal between one frame (there is no partner), and the difference signal between two frames must be used. First, motion detection was incomplete.

SUMMARY OF THE INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks and provide a complete
The present invention aims to provide a multiple subsample transmission system that can perform motion detection using interframe difference signals, and that not only simplifies the configuration of the receiver but also considerably improves the image quality.

In other words, the multiple subsample transmission method of the present invention is
A television signal subsampling transmission method in which an input television signal is sequentially subsampled with inter-field and inter-frame offsets and transmitted with band compression, and a received signal is subjected to motion-adaptive signal processing according to the motion of an image, the motion adaptive In order to obtain image motion information for digital signal processing from inter-frame difference signals of low frequency components that do not exceed the image frequency n, each of the inter-field offset subsampling and the inter-frame offset subsampling is Assuming the sub-sampling frequencies as _S1 and _S2 ,
Sequentially a band limit the input signal to a frequency band not exceeding frequency _S1 , b subsample its output at frequency _S1 , and c convert the subsampled output to frequency ( _S1 /
2), d subsampling its output at frequency _S2 = ( _S1 /2) + _o , and e subsampling its output at frequency ( _S2 /2) + o.
2) The transmission signal is prepared by limiting the band to a frequency band that does not exceed 2).

(Example) FIG. 4 shows a sampling pattern (luminance signal) of this method. The subsampling pattern is two frames in one order, which is exactly the same as that of the current high-definition television signal multiple subsampling method (MUSE method). 〇 mark, □ mark, ● mark, ■ mark,
The × marks are the 4nth, 4n+1, and 4nth, respectively.
The sub-sampling positions of the 4n+2nd and 4n+3rd fields and sampling points that are not transmitted are shown, respectively. Also, d in the figure is the sampling interval, and the sampling frequency is 1/d, which is 64.8M.
Corresponds to Hz. This method uses a combination of inter-field offset subsampling and inter-frame offset subsampling, and uses the former to reduce the resolution in the diagonal direction to reduce information by half.
In the latter case, information for one screen is transmitted over two frames over time, thereby reducing the information per frame by half.

By the way, when the signal transmitted after the above-mentioned signal processing on the transmitting side is played back on the receiving side, for a still image, a complete information signal is sent with two frames in one order, but in the case of a moving image, This relationship does not hold. Therefore, on the receiving side, field interpolation is performed to reproduce the necessary missing signals. Since a certain amount of visual blur is originally acceptable for moving images, it is desirable to transmit information with less information than for still images from the time of signal transmission, and to prevent the introduction of extra noise. Then, depending on the motion information, the transmitting side either switches between still image information (wider band) and moving image information (narrower band), or linearly mixes both information and transmits it, and the receiving side changes the transmitted image information. The motion information is detected from the signal and the signal is decoded.

In any case, it is necessary to detect motion information with higher accuracy from the transmitted image signal. However, as mentioned above, in the case of the current multiple subsample transmission method, sampling is performed once in two frames.
Since the motion information must be detected based on the difference between two frames, tracking of fast motion is insufficient.

Looking at the above relationship from another perspective, we get the following. If the sampling pattern in Figure 4 is sampled at 16 MHz with the band-limited pattern as shown in Figure 5 a, it will be within the transmission baseband (8 MHz or less, current high-definition television transmission), as shown in Figure 5 b. The high frequency components (8MHz-16MHz) of the signal are not folded back. Of course, at this time, in order to prevent the low-frequency component and the folded high-frequency component from overlapping, the two components are placed in an interleaved relationship (Japanese Patent Application No. 59
-30145 (see JP-A-60-176381)). A difference signal between one frame cannot be obtained from this signal format, and the aliased high-frequency component is removed using the two-frame signal (focusing on the opposite phase of the high-frequency component between adjacent frames due to frame offset subsampling). (cancellation), and only the low-frequency components have to be extracted to obtain motion information. That is, this is two-frame difference signal processing.

The proposed transmission method improves this point, and FIG. 1 shows an example of the encoding procedure. First of all
As shown in FIG. 1A, a signal band-limited to 24 MHz is subjected to inter-field offset sampling at a frequency of 24 MHz to obtain the frequency spectrum shown in FIG. 1A. Next, as shown in Figure 1b, the frequency components higher than 12MHz are filtered out using a low-pass filter, and the
Interframe offset sampling is performed at a frequency of 16 MHz as shown in Figure c. Then, the baseband component (0
A spectrum that does not include folded components (components that are inverted between frames) is obtained in the 0 to 4 MHz portion of ~8 MHz5. Therefore, for a signal having the spectrum shown in Fig. 1d that is transmitted every frame,
By applying 4MHz low-pass filter processing, a signal part without aliasing can be obtained, and this can be used to
An inter-frame difference signal can be determined.

The signal having the frequency spectrum shown in FIG. This is exactly the same as the decoding of the high-definition television signal multiple sampling transmission system (MUSE). However, according to the method of the present invention, since an accurate one-frame difference signal is obtained, the moving image area and the still image area can be accurately distinguished, decoding is easy, and the reproduced image has good image quality.

Furthermore, from a decoding standpoint, the signal at the stage shown in FIG. 1b corresponds to the stage at which interframe interpolation has been completed, but it does not include the 16 MHz component. This means that the 16MHz false signal component that occurs when a moving image area is mistakenly decoded as a still image area can be removed regardless of whether it is a moving image area or a still image area. This shows that the original information is not lost even if it is removed by processing with a low-pass filter that removes it. Even if a moving image area is determined to be a still image area and decoded, the 16MHz component, which causes the most interference, will not be generated, leading to a significant improvement in image quality.

A specific embodiment of the apparatus of the present invention will be described below with reference to FIGS. 2 and 3.

As for processing on the transmitting side, as shown in Figure 2a, (1) A/D converter 1 samples the input signal at 48.6MHz. The signal band is shown in Figure 3a. In the figure, the horizontal axis is the horizontal component H, and the vertical axis is the vertical component V, and this relationship holds true in FIG.

(2) As a process for the still image area, an inter-field prefilter 2 as shown in FIG. 3b is applied to remove high-frequency components in the diagonal direction of the screen.

(3) Perform field offset subsampling 5 at 24.8MHz. At this time, signals of 12.15 MHz or higher are folded back, and the signal band becomes as shown in Figure 3c.

(4) Next, perform sampling frequency conversion 6 from 24.8MHz to 32.4MHz. The signal band remains as shown in Figure 3c.

(5) For processing of the moving image area, the band is limited to 12MHz using the in-field prefilter 3 as shown in FIG. 3d.

(6) Next, subsampling 5 at 24.3MHz,
Since the band is limited to 12MHz in (5), there is no loopback and the signal band remains as shown in Figure 3d.

(7) Perform sampling frequency conversion 6 from 24.8MHz to 32.4MHz. The signal band remains as shown in FIG. 3d.

Here, in the processing of (6) and (7), since there is no change in the signal band, (7) may be obtained by performing sampling frequency conversion from 48.6 MHz to 32.4 MHz all at once from (5).

(8) Motion detection 4 is separately performed, and the absolute value of the one frame difference is subjected to nonlinear processing and the amount of motion is output.

(9) The still image system of (4) and the moving image system of (7) are linearly mixed 7 according to the amount of movement described above.

(10) Next, frame offset subsampling 8 is performed at 16.2MHz, but at this time, the third
Figure c is similar to Figure 3 e, and moving image Figure 3 d is looped back at 8.1 MHz, as shown in Figure 3 f. Third
Figure d12.The signal band is up to 15MHz, and there are no aliasing components below 4MHz. Therefore, by applying a 4MHz low-pass filter and taking the frame difference, reliable motion detection can be performed without aliasing. This part is the most important point of the present invention.

(11) Finally, perform D/A conversion 9 to create an analog signal. At this time, a transmission line filter is inserted to obtain a cosine roll-off characteristic at 8.1MHz, and the signal is sent to the transmission line.

On the receiving side, the process is reversed to that on the transmitting side, as shown in FIG. 2b.

(12) Resampling with A/D converter 1. At this time, the signal band for the still image system is as shown in FIG. 3e, and the signal band for the moving image system is as shown in FIG. 3f.

(13) In the still image system, pixels that are not sampled in the interframe interpolation 11 are replaced with the signal from one frame before, and the folding in FIG. 3e is returned as in FIG. 3c.

(14) Perform sampling frequency conversion 13 from 82.4MHz to 24.3MHz. The signal band remains as shown in FIG. 3c.

(15) The interfield interpolation filter 14 returns the aliasing components to their original values. The signal band is shown in Figure 3b.

(16) For the moving image system, field interpolation 12 is performed to return the aliased component in Figure 3 f to Figure 3 d.

(17) Perform sampling frequency conversion 13 from 32.4MHz to 48.6MHz. The signal band remains as shown in Figure 3d.

(18) Next, motion detection 4 is performed. Here, the signal
Bandwidth is limited to 4MHz, frame differences are taken, and nonlinear processing is performed on this to calculate the amount of motion.

(19) Linear mixing 7 of the still image processing system and the moving image processing system is performed according to the amount of motion.

(20) Finally, perform D/A conversion 9 to obtain an analog signal. The signal band at this time is the third in the still image system.
In Figure b and Figure 3 D for the moving image, the part that has moved slightly is in the middle of the two.

(Effects of the Invention) According to the transmission method of the present invention, in a transmission method using inter-field and inter-frame offset subsamples, the difference between one frame can be used to detect a moving area, so the detection accuracy is improved and the configuration is simple. It is.

Furthermore, even if a mistake is made in detecting a moving area, there is an advantage that, as mentioned above, this will not cause significant deterioration in image quality.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the frequency spectrum of each stage of the encoder procedure of a television signal (luminance signal) according to the transmission method of the present invention, and Fig. 2 is a diagram showing the decoding and encoding configurations of transmitting side a and receiving side b according to the transmission method of the present invention. FIG. 3 is a diagram showing the band characteristics of each stage of decoding and encoding in FIG. 2, FIG.
The figure shows a frequency spectrum when the sample pattern of FIG. 4 is sampled at 16MHz. 1...A/D converter, 4...Motion detection, 2...Inter-field prefilter, 3...Intra-field prefilter, 5...Field offset subsampling (24.3MHz), 6...Frequency conversion (24.3MHz→
32.4MHz), 7...Linear mixing, 8...Frame offset subsampling (16.2MHz), 9...D/A
Converter, 10...Transmission line filter, 11...Interpolation between frames, 12...Interpolation within fields, 13...Frequency conversion (32.4MHz→24.3MHz), 14...Interpolation between fields.

Claims (1)

[Claims] 1. Television signal subsampling transmission in which an input television signal is sequentially subsampled with inter-field and inter-frame offsets, band-compressed and transmitted, and a received signal is subjected to motion-adaptive signal processing according to the movement of an image. In this method, in order to obtain the motion information of the image for the motion-adaptive signal processing from the inter-frame difference signal of a low frequency component that does not exceed the frequency n of the image, the inter-field offset subsampling and the inter-frame Let the subsampling frequencies of each offset subsampling be _S1 and _S2 ,
Sequentially a band limit the input signal to a frequency band not exceeding frequency _S1 , b subsample its output at frequency _S1 , and c convert the subsampled output to frequency ( _S1 /
2), d subsampling its output at frequency _S2 = ( _S1 /2) + _o , and e subsampling its output at frequency ( _S2 /2) + o.
2) A multiple subsampling transmission method characterized by preparing a transmission signal by restricting the frequency band to a frequency band not exceeding 2). 2. Sampling frequency _S1 of the inter-field offset subsampling and sampling frequency of the inter-frame offset subsampling
The multiplex subsampling transmission system according to claim 1, characterized in that the ratio with _S2 is 3:2. 3. When decoding the transmission signal on the receiving side, the component of the sampling frequency _S2 of the interframe offset subsampling is removed after performing interframe interpolation. The multiple subsampling transmission method described in Section 2.