JPH0748849B2 - Television signal band compression device - Google Patents

Description

The present invention relates to a band compression device for television signals.

[Conventional technology]

As a conventional method for band-compressing a television signal, there is, for example, a MUSE method developed for high-definition transmission.

First, in order to facilitate understanding of the present invention, the principle of band compression will be described with reference to the drawings.

FIGS. 4A to 4D are explanatory diagrams showing the principle of band compression by comparing the conventional method with the present invention.

In FIG. 4A, the horizontal axis represents the time frequency f (Hz), and the vertical axis represents the vertical spatial frequency ν (piece). If the signal is a field frequency f _{S of} a television and a 2: 1 interlaced scanning signal of ν _s scanning lines, the sampling frequency of the interlaced scanning is located at (f _S / 2, ν _S / 2). Since carrier I ^* appears, it is possible to transmit only half the area surrounded by the origin ~ (0, ν _S / 2) ~ I ^* ~ (f _s / 2,0). A band-limited signal is transmitted in the area shown in FIG.

However, as in the case of the method in which the interlaced scanning signal is converted into the progressive scanning signal on the receiving side, it is only the transmission path that has to be limited to the above-mentioned area. As shown in, the space is spatiotemporally band-limited to either the area of W + I or E + I in accordance with the movement of the image.
On the receiving side, this signal is adaptively restored to enable transmission of the area of W + A + D in the entire system. (For example, Japanese Patent Application No. 58-224398, television signal conversion system).

On the other hand, in FIG. 4 (C), the vertical axis represents the vertical spatial frequency ν
(Book), the horizontal axis is the horizontal spatial frequency μ (MHz). (Μ _S
When a signal is sampled by a carrier S ^* having a frequency of / 2, ν _S / 2), the origin ~ (0, ν _S /
2) ~ S ^* ~ (ν _S / 2,0) Since only half the area enclosed by the area can be used, it is normally possible to spatially limit the area to the + and + areas and then sample with the carrier S ^* . To do. At this time, the components in the K region can be returned to the K region by sampling, so the signal is band-limited to the horizontal spatial frequency band of μ _S / 4 or less and only the K and K regions are transmitted. You can correctly restore the components of the black and white regions.

In this way, a signal having a horizontal spatial frequency band of μ _S / 2 can be band-compressed to a transmission frequency band of μ _C = μ _S / 4.

By combining the method of FIG. 4 (B) and the method of (C),
Further, band compression of the signal is possible. That is, in FIG. 4 (D), the band is spatially limited to either the source + region or the source + region in advance in accordance with the image, and then sampling is performed by the carrier S ^* , and the sampling is performed. The signal is band-limited to the transmission frequency band μ _C = μ _S / 4 and transmitted. At this time, the above-mentioned spatial band limitation is
If it is the area of Si, the area of Service + Si is transmitted as it is.
In the case of the service area, the service area is folded back to the service area and the service area (returned) is transmitted.

If this signal is adaptively restored on the receiving side, it is possible to transmit the area of ++++ in the transmission path of the transmission frequency band μ _C = μ _s / 4 in the entire system.

The above is the principle of band compression in the present invention. Switching of the spatial band limitation is performed, for example, by detecting the amount of high frequency components of the horizontal frequency band from the image signal, that is, the amount of components included in the S region, and when there are many components included in the S region, When a region is selected and a high frequency component of the vertical frequency band, that is, a large amount of components are included in the region of Si, it is sufficient to select the region of + S.

FIG. 5 (A) shows an example of a pattern (pattern) in the case of sampling by the carrier S ^* .

The position to be sampled is shifted by 1/2 of the interval between sampling points for each scanning line.

A 2: 1 interlaced signal is generally used for transmission of a television signal, and the sampling pattern of this signal is shown in FIG. 5 (B).

In the figure, if the solid line is the odd field, the dotted line is the even field signal. In other words, this corresponds to inverting the phase of the carrier of the sampling frequency for each field and sampling.

This method is known as field offset sampling, and when a signal is expressed in a three-dimensional space-time frequency domain as shown in FIG. 5 (C), the spectrum of the carrier S ^* to be sampled appears at three points. . In this case, the spectrum of the carrier S ^* on the f-ν plane is 2:
1 Appears in the same position as Carrier I ^* due to interlacing.

FIGS. 6A to 6D are layout diagrams of transmission areas by band compression.

The filter which spatially band-limits the source region in FIG. 4 (D) has a pass band in the region shown by hatching in FIG. 6 (A). A filter having this pass band can be realized by progressive scanning, but cannot be realized by a 2: 1 interlaced signal because of carrier I ^* due to interlacing.

This can be realized with a filter having a pass band in the region shown by hatching in FIG. 6 (B). This passband is the spatial frequency in the time direction
Since it is cut off at f _S / 4, the motion component of the image signal is cut off.

Therefore, the motion of the image signal is detected in the interlaced signal, and if there is a motion component, the signal of the signal component in the region of FIG. The band may be limited to the area of. This corresponds to band limitation as shown in FIG. 6 (C). That is,
Simply pass a filter having a horizontal spatial frequency transmission band μ _C.

The pass band shown in FIG. 6 (B) can be modified as shown in FIG. 6 (D), which is advantageous for motion detection.
That is, in this case, since the entire area of the f-ν plane is the pass band in the band where the horizontal spatial frequency is μ ₁ or less, the motion detection can be easily performed by performing the motion detection from this band.

[Problems to be solved by the invention]

To summarize the above explanation of the principle, there have been conventionally used methods such as MUSE to perform offset sampling of a television signal to perform band compression. However, in these methods, a spatial transmittable area is not available. Vertical spatial frequency ν _S / 2 and horizontal spatial frequency μ _S / 2 of sampling frequency signal S ^*
It was limited to less than half the area surrounded by.

Therefore, the object of the present invention is to adapt the way of using the spatial frequency region corresponding to the transmission signal component to the image and switch and use it to loosen the above-mentioned 1/2 or less area limitation and widen the transmittable region. It is an object of the present invention to provide a television signal band compression device capable of performing the above.

[Means for solving problems]

In order to achieve such an object, in the present invention, in a band compression device for a television signal, one of a region having a high vertical spatial frequency and a region having a high horizontal spatial frequency, or both of the components of an image signal included in both regions. Presence / absence is detected, and based on the result, whether or not to insert the component outside the transmission band of the transmission line included in the image signal in the region of the transmission line and in the region of high vertical spatial frequency is adaptively switched. To do so.

That is, according to the present invention, in a television signal band compression apparatus for band-compressing a television signal by an interlacing operation by changing the phase for each field period, a low frequency range of the vertical spatial frequency (ν). Is a pass band (area A + C in FIG. 1), and a low frequency region of the horizontal spatial frequency (μ) is a pass band (first space filter 2 in FIG. 2). A second filter (LPF1 in FIG. 2) defined as a region A + B in the figure and a shared frequency band (region in FIG. 1) commonly included in the pass bands of the first and second filters. First, based on A), the amount of high frequency band components (region D in FIG. 1) in the vertical direction is detected.
And a second detecting means (second area detecting circuit 7 in FIG. 2) for detecting the amount of the high frequency band component (area E in FIG. 1) in the horizontal direction based on the shared frequency band. 2) E area detection circuit 8) and third detection means (motion detection circuit 6 in FIG. 2) for detecting the amount of motion component of the image.
And when the amount of the motion component or the high frequency band component in the vertical direction is large, the passing signal is taken out from the second filter, while when the amount of the high frequency band component in the horizontal direction is large, the first filter is obtained. It is provided with a selection means (switcher 3 and judgment circuit 9 in FIG. 2) for taking out the passing signal from the wave filter.

[Action]

Therefore, according to the present invention, when a television signal is band-compressed and transmitted by a transmission line having a predetermined narrow frequency band, the component of the television signal is a region having a high vertical spatial frequency and a horizontal spatial frequency. It is possible to correctly restore even the components in the high frequency region of the original image signal by determining whether or not it is included in the high region, adaptively switching the filter, band-compressing and transmitting.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail and specifically with reference to the drawings.

FIGS. 1 (A) and 1 (B) are layout diagrams showing a transmission region of an embodiment according to the present invention.

As a television signal, for example, the number ν of scanning lines is 1125.
It is assumed that the book is a 2: 1 interlaced signal having a field frequency f of 60 Hz and has a band of 24 MHz.

In FIG. 1 (A), the area of A + C corresponds to the pass band of FIG. 6 (B), and the area of A + B corresponds to the pass band of FIG. 6 (C).

If this signal is subjected to field offset sampling in which the phase is changed for each field cycle with a carrier signal S ^* having a sampling frequency of 24 MHz for μ _S / 2 MHz and 1125/2 for ν _s lines, it is shown in FIG. The area of C in) is folded back to the area of B.

In this way, the transmission band is 12MHz for still images.
(Corresponding to μ _S / 4), it is possible to adapt and transmit the area of A + B + C in FIG. 1 (A).

Moreover, in this case, even if the signal components of the D and E regions indicated by the dotted lines are detected instead of detecting the signal components of the B and C regions, respectively, the spectrum of the image is generally natural in the spatial frequency domain. Because it has a wide spread,
It is unlikely that a large error will occur in switching the band limitation. In this way, since the areas D and E are always in the area A to be transmitted, the B of the transmitted signal can be transmitted to the receiving side without further multiplexing the signal for switching.
The areas C and C can be correctly restored.

In addition, as shown in FIG. 1 (B), the motion detection is well known as a component appearing in the vicinity of 15 Hz of f _S / 4 due to the correlation between frames. Can be detected with.

In this case, the spatial band limitation is A + B in FIG.
In the case of the area (1), that is, the area (G) in FIG. 6C, the area G in FIG.

In the case where the band limitation is the area A + C, the area F in FIGS. 6B to 1B is the pass band. F
The region of is folded back by the sampling frequency signal S ^* (I ^* ) to generate a component in the region of F ′, but even if F and F ′ are combined, only half of the region of H used for motion detection is used. Since it cannot be used, the sensitivity of the motion detection on the receiving side is somewhat lowered, but this level can be easily compensated by adding a device to the motion detection circuit.

FIGS. 2A and 2B are block diagrams showing the configuration of an embodiment according to the present invention.

FIG. 2A is a block diagram of an embodiment of the encoder.

In FIG. 2 (A), 1 and 5 are a low-pass filter (LPF) for limiting the transmission band within the band, 2 is a space-time filter, 3 is a switch, 4 is a switch, and 6 Is a motion detection circuit, 7 is a D area detection circuit for detecting an area component having a high vertical spatial frequency, 8 is an E area detection circuit for detecting an area component having a high horizontal spatial frequency, and 9 is a determination circuit.

The switching device 3 for switching between the LPF 1 and the space-time filter 2 for selecting the region of band limitation is provided by the region detection circuits 7 and 8 for detecting the amount of signal components in the regions D and E of FIG. In addition to the output signals Y and Z, switching is performed by the output signal of the determination circuit 9 based on the output signal X from the motion detection circuit 6 which indicates the presence / absence of image motion obtained by the motion detection circuit 6.

If the motion component of the image is large, the switch 3 falls to the LPF1 side regardless of the values of the output signals Y and Z from the D and E area detection circuits 7 and 8. Space-time filter 2 is the sixth
It is a two-dimensional space-time filter having a pass band in the area A + C in FIG. 1B, that is, FIG. The filters of the D area detection circuit 7 and the E area detection circuit 8 are three-dimensional space-time filters. The configurations of these filters are well known and will not be described. Similarly, the configuration of the motion detection circuit 6 is well known.

The determination by the determination circuit 9 is performed as follows, for example. First, as described above, if the amount of the motion component X from the motion detection circuit 6 is larger than an appropriate value, the switching device regardless of the component Y from the D area detection circuit 7 and the component Z from the E area detection circuit 8. 3 is connected to the LPF1 side. When the amount of the motion component X is small and Y <Z, or when Z is larger than an appropriate certain value, or when Y is smaller than an appropriate certain value, the space-time filter 2 is connected. X, Y and Z
When is opposite to the above condition, it is connected to the LPF1 side. This switching is performed for each pixel.

The signal switched by the switch 3 is transferred to the carrier S by the switch 4.
Field offset sampling by ^* , LPF5
Is limited to the transmission band μ _C of the transmission path and is sent out as a transmission signal.

FIG. 2B is a block diagram of an embodiment of the decoder. In FIG. 2 (B), 11 and 13 are low-pass filters (LPF) that pass signals in the transmission line band, 12 is a switch for field offset sampling, 14 is a space-time filter, and 15 is A switch, 16 is a motion detection circuit, 17 is a D area detection circuit for detecting an area with a high vertical spatial frequency, 18 is an E area detection circuit for detecting an area with a high horizontal spatial frequency, and 19 is a determination circuit.

The transmitted signal is band-limited by the switch S12 by the carrier S ^* after being band-limited to the transmission band μ _C of the transmission line by the LPF 11 for removing noise. A band limiting circuit that is configured by the LPF13 to the determination circuit 19 and that adaptively operates according to the components included in the image signal.
The band limitation adapted to the image signal is performed, and the original image signal is restored. The operations of the LPF 13 to the determination circuit 19 are exactly the same as in the encoder.

FIGS. 3 (A) and 3 (B) are layout diagrams showing transmission areas of another embodiment according to the present invention.

FIG. 3A is a layout diagram of another embodiment of the transmission area when the band limitation of FIG. 6D is used.

In the figure, a signal in the 20 MHz band is used as a carrier S of μ _S / 2 = 24 MHz.
It is compressed to a transmission band of 12 MHz by sampling with ^* , but in the band of μ ₁ = 4 MHz or less, the entire pass band is the field frequency f and the number of scanning lines ν, so use this band. Motion can be detected on the receiving side with the same sensitivity as on the transmitting side. Further, the position of the area D is different from the case of FIG. 1 (A), but FIG. 1 (A)
Of course, the same position as is also good. It may be easier to realize the circuit by using the region at the position shown in FIG.

FIG. 3B is a layout diagram of another embodiment of the transmission area when the band limitation of FIG. 6D is used.

By sampling with a carrier S ^* of μ _S = 37 MHz, a signal having a band of 30 MHz can be compressed and transmitted in a band of 18.5 MHz (μ _S / 2).

Setting μ _S = 37 MHz is advantageous when the encoder and the decoder are composed of digital circuits with a clock frequency of 74 MHz. Of course, if μ _{S of the} carrier S ^* is lowered below 37 MHz, the same 30 MHz signal band can be transmitted in a narrower transmission band.

The present invention is not limited to the above-mentioned number of scanning lines of 1125, a field frequency of 60 Hz, a television signal by interlace of 2: 1 as well as other types of television signals, for example, the number of scanning lines is 525 and the field frequency is It can also be used for band compression transmission of a 60 Hz, 2: 1 interlaced signal, or an interlaced signal with 625 scanning lines and a field frequency of 50 Hz, 2: 1.

Further, the band compression rate can be further increased by using the present invention in combination with another band compression method, for example, a method of folding a component signal in a high region in a gap in the time-frequency domain performed by MUSE or the like.

〔The invention's effect〕

As is apparent from the above, according to the present invention, in the television band compression method by the conventional offset sampling, up to half the area surrounded by the vertical spatial frequency and the horizontal spatial frequency of the sampling frequency carrier signal. What could only be transmitted can be transmitted up to 3/4 of the above-mentioned area by adapting the spatial frequency domain to the signal components of the image and using them properly.

[Brief description of drawings]

1 (A) and 1 (B) are layout diagrams showing a transmission area of an embodiment according to the present invention, and FIGS. 2 (A) and 2 (B) are block diagrams showing a configuration of an embodiment according to the present invention. 3 (A) and 3 (B) are layout diagrams showing the transmission area of another embodiment according to the present invention, and FIGS. 4 (A) to (D) are band compression principles in comparison with the conventional one and the present invention. 5A to 5C are explanatory diagrams of offset subsampling, and FIGS. 6A to 6D are layout diagrams showing transmission areas by band compression. 1,5,11,13 …… Low-pass filter (LPF), 2,14 …… Spatiotemporal filter, 3,15 …… Switcher, 4,12 …… Switch, 6,16 …… Motion detection circuit, 7,17 ... D area detection circuit, 8,18 ... E area detection circuit, 9,19..judgment circuit.

Claims (1)

[Claims] 1. A television signal band compression apparatus for band-compressing a television signal by an interlacing operation by changing the phase for each field period and sampling the low-frequency region of a vertical spatial frequency as a pass band. A first filter, a second filter having a low spatial frequency band in the horizontal direction as a pass band, and a common shared pass band of the first and second filters First detecting means for detecting the amount of the high frequency band component in the vertical direction based on the frequency band, and second detecting means for detecting the amount of the high frequency band component in the horizontal direction based on the shared frequency band, Third detecting means for detecting the amount of the motion component of the image; and a passing signal from the second filter when the amount of the motion component or the high frequency band component in the vertical direction is large. Out, while the television signal band compressor when the amount of the high-frequency band component is large, characterized by comprising a selection means for taking out the passage signal from said first slag Namiki in the horizontal direction.