JPH0740722B2 - Digital signal processing circuit - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a digital signal processing circuit used in a digital television system.

[Technical background of the invention]

In recent years, with the progress of digital IC technology, it has been developed to digitize a television signal and perform various kinds of signal processing. In the case of a digital television signal, the storage delay means can be easily realized as compared with an analog television signal, data of one field (or frame) is accumulated in a memory, and various processes such as data addition, It is also possible to perform processing such as change.

When reproducing such a digital television signal,
It is better to switch the processing characteristics between the still image data processing and the moving image data processing, and perform appropriate processing according to the image content. For example, if there is image data that is transmitted in the 2: 1 interlace system, and if line interpolation is performed to increase the number of lines, a still image,
It is better to change the signal processing method depending on the moving image. When looking at the correlation of television signals, the correlation between fields is high for still images, and the correlation within the same field is higher for moving images than between fields. Therefore, when a signal for interpolation interpolation is made between horizontal scanning lines, an interpolation signal is made by using the signals of the current field and the previous field when it is a still image, and when it is a moving image, It is better to create an interpolation signal using a line signal.

FIG. 8 shows a circuit block for performing the above image processing. The current field signal applied to the input terminal 1 is supplied to the first field memory 2, the still image processing circuit 3, and the moving image processing circuit 4. The still image processing circuit 3 uses the current field signal and the previous field signal one field before to perform a process of increasing the spatial resolution. However, the output signal of the still image processing circuit 3 has good spatial resolution but low temporal resolution. In the moving image processing circuit 4, the line signal in the current field is used to increase the temporal resolution, but the spatial resolution of the output is low. Output signals of the still image processing circuit 3 and the moving image processing circuit 4 are supplied to the signal switching circuit 5. This circuit selects one of the signals according to the image content and outputs it to the output terminal 6
Derive to.

When the signal switching circuit 5 switches and selects a signal having a high spatial resolution and a signal having a high temporal resolution, a determination circuit for determining which to select is required.

As a method for the determination circuit to determine the image content (still image, moving image), there is a method using an inter-frame difference signal as a simple hardware configuration. That is, the inter-frame difference signal is judged as a threshold value, and if it is above the threshold value, it is judged as a moving image, and if it is below the threshold value, it is judged as a still image.

A processing circuit having such a determination circuit is shown in FIG.
The same parts as those in FIG. 8 are designated by the same reference numerals.

The output of the first field memory 2 is further supplied to the second field memory 7. Second field memory 7
And the current field signal are supplied to the inter-frame difference circuit 8. The output signal of the inter-frame difference circuit 8 is supplied to the threshold value judgment circuit 9 and is judged by the threshold value. Then, the determination signal from the threshold determination circuit 9 is supplied to the control terminal of the signal switching circuit 5.

The output of the inter-frame difference circuit 8 is small in the case of a still image because there is no change in data, and is large in the case of a moving image because there is a change in data. Therefore, the threshold value judgment circuit 9
Receives the output of the inter-frame difference circuit 8 and outputs a determination signal D as shown in FIG. If the inter-frame difference signal is higher than level A0, the moving image determination level D1 is output, and if it is lower than level A0, the still image determination level D0 is output.
As a result, the signal switching circuit 5 selects the output of the still image processing circuit 3 in the case of a still image and the output of the moving image processing circuit 4 in the case of a moving image.

[Problems of background technology]

As described above, when distinguishing between still images and moving images,
If the television signal data contains noise, the determination may be erroneous. In the case of a television receiver, if the received electric field strength decreases, the video signal
S / N decreases. In such a case, the noise level superimposed on the inter-frame difference signal also increases. The noise is almost uncorrelated between the frames, and although the complete still image is actually sent, the difference signal becomes large and the threshold value judgment circuit 9 moves the moving image. As a result, the probability of erroneous determination increases.

When noise is superimposed on a complete still image, the false determination is
It occurs randomly both temporally and spatially. As a result, on the screen, an image formed by a still image processed signal having a high spatial resolution and an image formed by a moving image processed signal having a low spatial resolution are randomly mixed and the image quality is deteriorated.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and provides a digital signal processing circuit capable of reducing misjudgment between a still image and a moving image even when the S / N of an input video signal is lowered. The purpose is to do.

[Outline of Invention]

The present invention, for example, as shown in FIG. 1, when the output of the still image processing circuit 22 is selected by the signal switching circuit 26,
The difference signal of the inter-frame difference circuit 26 increases due to the influence of noise, and the threshold value judgment circuit 28 accordingly changes the signal switching circuit 26.
This prevents the selection of (1) from being switched to the moving image processing circuit 22 side. In order to realize this, for example, an AGC voltage is introduced into the threshold value judgment circuit 28, and when the noise increases, the threshold value is varied by utilizing the fact that the AGC voltage also increases.

Example of Invention

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The signal received by the antenna 11 is transmitted to the tuner 12. From the tuner 12, the intermediate frequency signal of the desired channel is extracted,
The intermediate frequency signal supplied to the automatic gain control amplifier 13 and amplified here is detected by the video detection circuit 15 as a baseband video signal.

The automatic gain control amplifier 13 is an automatic gain control circuit (hereinafter referred to as AGC).
The gain is controlled by the AGC voltage from (referred to as a circuit) 14. The AGC circuit 14 monitors the output signal of the automatic gain control amplifier 13 and controls the gain of the automatic gain control amplifier 13 so that its level becomes constant.

Here, when the electric field strength is weak, the automatic gain control amplifier
Since the output signal level of 13 decreases, the AGC circuit 14 controls to increase the gain of the automatic gain control amplifier 13.

On the other hand, the output video signal of the video detection circuit 15 is converted into a digital video signal by the analog-digital converter 16,
It is supplied to the first field memory 21, the still image processing circuit 22, the moving image processing circuit 23, and the inter-frame difference circuit 25. The output of the first field memory 21 is supplied to the second field memory 24 and the still image processing circuit 22. The output of the second field memory 24 is an inter-frame difference circuit.
Supplied to 25. The high spatial resolution signal processed by the still image processing circuit 22 and the high temporal resolution signal processed by the moving image processing circuit 23 are supplied to the signal switching circuit 26,
Either one is selected and led to the output terminal 27.

The interframe difference signal from the interframe difference circuit 20 is supplied to the threshold value judgment circuit 28. Threshold judgment circuit 28
Controls the signal switching circuit 26 to select the output of the moving image processing circuit 23 when the inter-frame difference signal exceeds the threshold value, and the still image processing circuit when the inter-frame difference signal is below the threshold value. Control to select 22 outputs.

Here, in the present invention, the threshold judgment characteristic of the threshold judgment circuit 28 is controlled by the output of the AGC circuit 14.

The threshold value judgment circuit 28 is constructed, for example, as shown in FIG. The difference signal from the inter-frame difference circuit 25 is applied to the input terminal 28a and input to one of the comparison circuits 281. The output of the fixed threshold level setting circuit 283 is input to the other end of the comparison circuit 281 via the adder 282. Further, the adder 282 is connected to the A from the AGC circuit 14 via the terminal 28b.
The GC voltage is supplied.

In the above threshold judgment circuit 28, it is assumed that the AGC voltage is almost zero (the received electric field strength is sufficient). In this case, the interframe difference signal is compared to a fixed threshold level. Therefore, the determination signal D for still images and moving images is
As shown in FIG. 3A, it changes at the fixed threshold level A0.

Next, when the received electric field strength is weak and the AGC voltage increases, the increment is added to the fixed threshold level in the adder 282. Therefore, the threshold level A0 shifts to the threshold level A1 as shown in FIG. 3 (b). This means that even if the inter-frame difference signal increases due to noise, the probability of erroneously determining a still image as a moving image decreases.

FIG. 4 shows another embodiment of the threshold value judging circuit 28. In the case of this embodiment, the subtracting circuit 284 is connected to the input terminal 28a
It is provided between one input end of 281. The AGC voltage input terminal 28b is connected to the subtraction circuit 284 so that the AGC voltage is subtracted from the interframe difference signal. On the other hand, the output of the fixed threshold level setting circuit 283 is directly supplied to the other side of the comparison circuit 281. The characteristics of the threshold value judgment circuit 28 also change equivalently as shown in FIGS. 3A and 3B according to the change of the AGC voltage (change of the received electric field strength).

FIG. 5 shows still another embodiment of the threshold value judging circuit 28. In the case of this embodiment, the input terminal 28a to which the inter-frame difference signal is applied and the input terminal 28b to which the AGC voltage is applied are connected to the subtractor 285, and the output of the subtractor 285 is supplied to the non-linear conversion circuit 286. Is configured to. And
The output of the non-linear conversion circuit 286 is supplied as the determination signal D to the signal switching circuit 26 via the output terminal 28c.

In the case of the previous embodiment, the threshold value is set in a simple step shape, but as in the embodiment of FIG.
If is used, as shown in FIG. 6, it is possible to obtain the determination signal D that changes with inclination.

In Fig. 6 (a), the AGC voltage is small (the electric field strength is sufficient).
The determination signal in the case, FIG. 6B shows the threshold characteristic when the AGC voltage is large (weak electric field).

The non-linear circuit 286 may be an operational amplifier,
A read-only memory ROM may be used. When a ROM is used, the output of the subtractor 285 may be converted into address data, and the read data of the ROM may be determined by this address data. Therefore, by rewriting the contents of the ROM, it is possible to obtain an arbitrary threshold value characteristic.

As described above, when the non-linear circuit 286 is used, the signal switching circuit 26 simply inputs one of the input signals to the determination signal D.
A variable mixing circuit capable of changing the mixing ratio of both input signals may be used instead of switching according to That is, as shown in FIG. 7, the mixing ratio of the mixing circuit 30 is changed by the output of the threshold value judging circuit 28 using a non-linear circuit. The other parts are the same as those in the embodiment shown in FIG.

In the above description, the AGC voltage from the AGC circuit 14 is directly supplied to the threshold value judgment circuit 28, but depending on the polarity of the AGC voltage, it may be supplied via the inversion circuit, and the sensitivity is adjusted. Therefore, it may be supplied via a level conversion circuit.

Also, it is not always necessary to determine whether the video signal contains a lot of noise by the AGC voltage,
For example, noise may be detected using a signal portion having a known DC component such as a pedestal portion.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reduce the probability of erroneously determining a still image as a moving image even when the received electric field strength is reduced and the S / N of the video signal is reduced, and to obtain good image quality. It is possible to provide a digital signal processing circuit that contributes to

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a concrete example of the threshold value judging circuit of FIG. 1, and FIG. 3 is a diagram showing characteristics of the threshold value judging circuit. , FIG. 4 and FIG. 5 are circuit diagrams showing still another embodiment of the threshold value judging circuit, FIG. 6 is a diagram showing an example of characteristics of the circuit of FIG. 5, and FIG. Circuit diagrams showing other embodiments, FIG. 8 and FIG. 9 are circuit diagrams showing conventional still image and moving image processing circuits, respectively.
FIG. 10 is a characteristic diagram of the threshold value judgment circuit of FIG. 14 …… AGC circuit, 21,24 …… field memory, 22 …… still image processing circuit, 23 …… moving image processing circuit, 25 …… frame difference circuit, 26 …… signal switching circuit, 28 …… threshold Value judgment circuit, 30 ... Mixed circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuichi Ninomiya 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the broadcasting technology research institute of the Japan Broadcasting Corporation (72) Yoshimichi Otsuka 1-10 Kinuta, Setagaya-ku, Tokyo No. 11 Broadcasting Technology Institute of Japan Broadcasting Corporation (72) Inventor Yoshinori Izumi 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Broadcasting Technology Laboratory of Japan Broadcasting Association (72) Seiichi Koshi 1 Kinuta, Setagaya-ku, Tokyo (10) No. 10-11, Broadcasting Technology Research Institute, Japan Broadcasting Corporation (56) Reference JP-A-59-45770 (JP, A) JP-A-60-86988 (JP, A) JP-A-60-76885 (JP, A) )

Claims (6)

[Claims] 1. A still image processing circuit for obtaining a first video signal having a high spatial resolution for a still image, a moving image processing circuit for obtaining a second video signal having a high time resolution for a moving image, and A signal processing circuit provided with first and second video signals and deriving a third video signal using these first and second video signals based on a control signal. Means for obtaining an automatic gain control signal from the automatic gain control circuit as a noise detection signal, which is given to an amplifier for amplifying the output, and an inter-frame difference signal of the video signals input to the still image processing circuit and the moving image processing circuit. And a threshold for the inter-frame difference signal when the inter-frame difference signal and the noise detection signal are supplied and the noise detection signal indicates an increase in noise. A higher constant level, the resulting decision signal as said control signal third
And a threshold value judging circuit for supplying the video signal to the means for obtaining the video signal. 2. The threshold judgment circuit compares an output of a fixed threshold level setting circuit and the noise detection signal with an adder for comparing the output of the adder with the inter-frame difference signal. The digital signal processing circuit according to claim 1, further comprising a comparison circuit that obtains the determination signal. 3. The threshold value judgment circuit compares a subtracter for subtracting the noise detection signal from the inter-frame difference signal with an output of the subtractor and an output of a fixed threshold level setting circuit, The digital signal processing circuit according to claim 1, further comprising: a comparison circuit that obtains a determination signal. 4. The threshold value judgment circuit comprises a subtractor for subtracting the noise detection signal from the inter-frame difference signal, and a non-linear conversion circuit for receiving the output of the subtractor and varying the judgment signal. The digital signal processing circuit according to claim 1, wherein the digital signal processing circuit is a digital signal processing circuit. 5. The means for obtaining the third video signal selects the first video signal from the still image processing circuit at the first level of the determination signal and derives it as the third video signal. And a switching circuit that selects the second video signal from the moving image processing circuit at the second level of the determination signal and derives it as the third video signal. The digital signal processing circuit according to item 1. 6. The means for obtaining the third video signal changes the mixing ratio of the first and second video signals in response to a change in the level of the determination signal, and outputs the mixed output thereof. The digital signal processing circuit according to claim 1, wherein the digital signal processing circuit is a mixing circuit which is derived as a third video signal.