JPH07298208A - Letter box picture detector - Google Patents

Abstract

PURPOSE:To provide a letter box picture detector in which the presence of a non-picture part is precisely discriminated even from a video signal with sag and the letter box pain is discriminated with high precision. CONSTITUTION:The detector is provided with 1st detection means 16d, 16g detecting a DC level of a low horizontal frequency component, 2nd detection means 16e, 16h detecting a high horizontal frequency component from the video signal, 3rd detection means 16f, 16i detecting a vertical high frequency component from the video signal, and a discrimination means 16j discriminating the presence of a non-picture part from the video signal based on the results of detection by the 1st to 3rd detection means 16d, 16g, 16e, 16h, 16f, 16i.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video display system capable of displaying video signals having different aspect ratios, and more particularly to improvement of a letterbox screen detection device for determining the letterbox screen.

[0002]

2. Description of the Related Art As is well known, in the NTSC system, the aspect ratio of a video signal is regulated to 4: 3.
Among package software such as R (video tape recorder) and laser disk, there are many commercially available software whose aspect ratio of the video signal is wider than 4: 3. This kind of video software has a letterbox screen with black non-image parts inserted at the top and bottom of the screen, and the image part is 4:
The aspect ratio is horizontally longer than 3.

For example, a wide T having an aspect ratio of 16: 9
When viewing horizontally oriented software on a V (television) receiver, it is possible to enjoy a more powerful image by stretching vertically and effectively using the screen. However, in the case of receiving image software with an aspect ratio of 4: 3 on a wide TV receiver, if the image is displayed as it is, the pattern stretched in the lateral direction due to the difference in aspect ratio. in this case,
By compressing and displaying the image in the horizontal direction, it is possible to prevent the pattern from being stretched in the horizontal direction.

Therefore, conventionally, means has been developed for controlling the horizontal and vertical amplitudes of a television receiver according to the aspect ratio of video software. For example, Japanese Patent Application No. 63-1
No. 93779, a blanking (non-image portion) width is detected by operating a clock counter in a period in which a luminance signal level is lower than a predetermined DC voltage, and if a vertical synchronizing signal exists in the blanking period, no image is generated. A method for detecting a letterbox screen, which is designed to be certified as a department, is shown.

By the way, as described above, in the letter box software, there is a blanking period (no image portion) above and below. However, there is no regulation about the luminance signal level during the non-image portion period, and there are various variations. When actually examining various image software of letterbox screen, the luminance signal level in the non-image part period is 1
Many have gone up to around 5 (IRE). N
The black level in the TSC system is 5 in the broadcasting standard.
Since it is (IRE), this is a signal brighter than the black level.

On the other hand, even with image software having an aspect ratio of 4: 3, the luminance signal level naturally lowers to the black level on a dark screen. Therefore, if the letterbox screen is simply determined from the luminance signal level, erroneous determination is likely to occur. For example, on a wide TV screen, originally, as shown in FIG.
When the image displayed as shown in (a) and having an aspect ratio of 4: 3 is mistakenly determined to be a letter box image and the vertical amplitude is widened, as shown in FIG. The upper and lower edges are missing and cannot be seen. If the letterbox image is erroneously determined to be an image having an aspect ratio of 4: 3, the display screen cannot be effectively used.

In the letterbox signal shown in FIG. 9A, the vertical synchronizing period is z, the vertical blanking period is y,
The non-image part is s and t. And, in general, when the time constant is insufficient in the AC (alternating current) coupling circuit,
Sag occurs as shown in (c). That is, the letter
Upper and lower non-image parts s and t of box signal, vertical blanking period y
, The DC voltage level monotonously increases, and in the image part, it monotonically decreases. If the waveform of this letter box signal is simply sliced by a DC voltage, the non-image portion s and t will be crossed depending on the slice level shown by the broken line in FIG. Cannot be detected accurately.

However, since such a sag may be generated in the signal source of the VTR or the laser disk device, the television receiver may not be able to cope with it. Therefore, there is a demand for an apparatus that accurately determines the presence or absence of the non-image areas s and t even with a signal waveform with a sag and controls the vertical amplitude or the horizontal amplitude.

[0009]

As described above, in the conventional letterbox screen detecting means, the presence or absence of the non-image part at the top and bottom of the screen is determined only from the signal level.
There is a problem that erroneous determination is likely to occur. There is also a strong demand to be able to accurately determine the presence or absence of a non-image portion even with a video signal with a sag.

Therefore, the present invention has been made in consideration of the above circumstances, and it is possible to accurately determine the presence or absence of a non-image portion even in a video signal with a sag, and it is possible to perform the determination of a letterbox screen with high accuracy. An object is to provide a good letterbox screen detection device.

[0011]

A letterbox screen detecting apparatus according to the present invention comprises first detecting means for detecting a direct current level of a low frequency component of a horizontal frequency from a video signal, and high frequency range of a horizontal frequency from a video signal. No image of the video signal based on the second detection means for detecting the component, the third detection means for detecting the high-frequency component in the vertical direction from the video signal, and the detection results of the first to third detection means. A determination means for determining the presence or absence of a copy is provided.

[0012]

According to the above structure, the presence or absence of the non-image portion is determined based on the DC level of the horizontal low frequency component of the video signal, the horizontal high frequency component and the vertical high frequency component.
Even with a video signal with a sag, the presence or absence of a non-image portion can be accurately determined, and the letterbox screen can be determined with high accuracy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a schematic configuration of a wide TV receiver described in this embodiment. That is, the video signal supplied to the input terminal 11 is supplied to the Y / C (luminance signal / color signal) separation circuit 12 and separated into a luminance signal and a color signal. The color signal is demodulated by the color demodulation circuit 13 and then supplied to the switching circuit 14 together with the luminance signal. Further, the luminance signal output from the Y / C separation circuit 12 and the color signal demodulated by the color demodulation circuit 13 are both supplied to the horizontal compression circuit 15 and subjected to horizontal compression processing, and then the switching circuit 14 Is supplied to.

Further, the video signal supplied to the input terminal 11 is supplied to a signal determination circuit 16 which will be described in detail later to determine whether it is a letterbox screen, that is, whether there is a non-image portion at the top and bottom of the screen. Whether or not is detected. Then, the switching circuit 14 is based on the detection signal output from the signal determination circuit 16 and the luminance signal output from the Y / C separation circuit 12 and the color signal demodulated by the color demodulation circuit 13 and the horizontal compression. Switching control is performed so that the luminance signal and the color signal output from the circuit 15 are selectively guided to the display device 17 having a wide screen configuration, such as a CRT (cathode ray tube).

Further, the video signal supplied to the input terminal 11 is supplied to the sync detection circuit 18 to detect vertical and horizontal sync signals. The vertical and horizontal synchronization signals detected by the synchronization detection circuit 18 are supplied to the vertical deflection circuit 19 and the horizontal deflection circuit 20, respectively, and the display device 17 is displayed.
Is used to control the display operation of. In this case, the horizontal deflection circuit 19 controls the vertical deflection operation based on the detection signal output from the signal determination circuit 16.

That is, in this wide TV receiver, the signal determination circuit 16 automatically determines whether or not the video signal supplied to the input terminal 11 is a letterbox screen, and based on the determination result, By controlling the compression processing in the horizontal direction and the vertical deflection processing, the input video signal can be displayed on the display device 17 in the best mode.

Here, FIG. 2 shows the details of the signal discriminating circuit 16. That is, the video signal supplied to the input terminal 11 is supplied to the A / D (analog / digital) conversion circuit 16b via the addition circuit 16a and converted into a digital signal. The video signal converted into the digital signal is added to the addition circuit 16a via the clamp control circuit 16c.
And a horizontal LPF (low-pass filter) 16d and a horizontal BPF8 band-pass filter) 16e.
And the vertical BPF 16f. Of these, the clamp control circuit 16c compares the pedestal DC (direct current) level of the video signal with a reference level, for example, and supplies a DC offset level based on the comparison result to the addition circuit 16a, thereby the pedestal of the video signal. D
The C level is controlled to be constant.

The horizontal LPF 16d extracts the luminance signal by removing the color carrier contained in the video signal. The luminance signal extracted by the horizontal LPF 16d is supplied to the DC value detection circuit 16g, and its DC level is compared with a predetermined threshold level to detect the level of the threshold level. The horizontal BPF 16e uses the color carrier band as a pass band. Therefore, the horizontal high frequency component of the color carrier or the luminance signal in the input video signal is detected by the horizontal BPF 16e, and the detection result is binarized by the non-linear circuit 16h to detect the presence or absence thereof. The presence / absence of the component that has passed through the vertical BPF 16f is also detected by being binarized by the nonlinear circuit 16i.

The detection signals output from the DC value detection circuit 16g and the non-linear circuits 16h and 16i are
It is supplied to the discrimination circuit 16j. This discrimination circuit 16j is
The presence / absence of a non-image portion in a predetermined scanning line is determined based on the DC detection value by the DC value detection circuit 16g and the presence / absence of the horizontal BPF component and the vertical BPF component output from the non-linear circuits 16h and 16i. Output terminal 16k
Is output via. The clock generation circuit 21
Generates a clock signal CK necessary for digital signal processing in the signal determination circuit 16 based on the synchronization signal separated from the video signal by the synchronization detection circuit 18. Further, the vertical timing generation circuit 22 includes a synchronization detection circuit 18
As shown in FIG. 9B, a signal that becomes H (high) level in a period corresponding to the non-image portions s and t of the letterbox video signal is generated based on the synchronization signal output from
It is output to the discrimination circuit 16j.

FIG. 3 shows details of the vertical BPF 16f. That is, the digitized video signal output from the A / D conversion circuit 16b is input to the input terminal 16f.
Two 1H delay circuits 16f connected in series via 1
By 2, 16f3, each horizontal line is sequentially delayed. The video signal supplied to the input terminal 16f1 and the video signal output from the 1H delay circuit 16f3 have a coefficient circuit 16f having an input / output gain of -1/4.
4,16f5. In addition, the 1H delay circuit 16f
The video signal output from 2 is supplied to the coefficient circuit 16f6 whose input / output gain is 1/2. The outputs of these coefficient circuits 16f4, 16f5, 16f6 are added to the adder circuit 1
The vertical high frequency component of the video signal is extracted by the addition by 6f7, and is taken out from the output terminal 16f8.

FIG. 4 shows the input / output characteristics of the nonlinear circuits 16h and 16i. That is, the nonlinear circuits 16h, 1
6i outputs a predetermined constant level when the input amplitude level exceeds a predetermined value, and binarizes the input signal. The nonlinear circuits 16h and 16i
Are different characteristics. In the non-image portion, although there is a DC offset of the luminance signal, there is no color carrier component or horizontal high-frequency component and vertical high-frequency component of the luminance signal. Therefore, by detecting the presence or absence of these components, the non-image portion The accuracy of detection can be improved.

FIG. 5 shows another example of the signal discrimination circuit 16. When the same parts as those in FIG. 2 are described with the same reference numerals, the digitized video signal output from the A / D conversion circuit 16b is supplied to the time BPF 16l. This time BPF 16l is configured as shown in FIG. That is, the digitized video signal supplied to the input terminal 16l1 is subtracted from the signal delayed by the frame delay circuit 16l3 by the frame delay circuit 16l3 by the arithmetic circuit 16l2, whereby the 1-frame difference signal. Is generated.

That is, the change in the image during one frame is extracted as the inter-frame difference signal from the arithmetic circuit 1613, and the inter-frame difference signal is output from the output terminal 1615 via the absolute value circuit 25. Taken out. in short,
In the time BPF 16l, a change in the input video signal in the time direction is detected, and the detection result is binarized by the non-linear circuit 16m and is led to the discrimination circuit 16j.

When the upper and lower parts of the screen are the non-image part, there is no change in the time direction, so no signal is extracted from the non-linear circuit 16m. In the case of the image portion, the movement of the pattern is detected by the time BPF 16l, binarized by the non-linear circuit 16m, and supplied to the discrimination circuit 16j. In this case, when binarizing in the nonlinear circuit 16m,
The threshold value is set so as not to respond to noise mixed in the video signal.

The discriminating circuit 16j discriminates the non-image portion based on the outputs of the DC value detecting circuit 16g and the non-linear circuits 16h, 16i and 16m. Several means can be considered for the discrimination of the non-image portion in the discrimination circuit 16j. First, as a first means, the output DC level of the horizontal LPF 16d is the DC value detection circuit 16g.
Is less than or equal to the threshold level of and the horizontal BPF component,
When neither the vertical BPF component nor the time BPF component is detected, it is determined as a non-image portion.

The second means is the DC value detection circuit 16
Two of V1 and V2 (V1 <V2) are set as the threshold level of g, and when the output DC level of the horizontal LPF 16d is V1 or less, it is determined that there is no image portion. Also,
If the output DC level of the horizontal LPF 16d exceeds V1 and is V2 or less and none of the outputs of the nonlinear circuits 16h, 16i, 16m is in a non-state, it is determined that there is a non-image portion. Furthermore, the output DC level of the horizontal LPF 16d is V2.
When it exceeds, it is determined to be an image portion.

Here, when a video signal waveform having vertical sag as shown in FIG. 9C is input, the first means sets the threshold value to a level at which the vertical sag does not respond, for example, FIG. False detection can be prevented by setting the level indicated by the alternate long and short dash line in (c). Even if there is a vertical sag, there is no horizontal high frequency component of the chrominance carrier or the luminance signal, so the output of the non-linear circuit 16h is in a non-state. Further, even in the range of the non-image portion, there is no vertical high frequency component, so that the output of the non-linear circuit 16i is in a non-state. Furthermore, since no change in the time direction is detected, the output of the non-linear circuit 16m is also in a non-state. Therefore, the discrimination circuit 16j can discriminate the non-image portion. Horizontal BPF16
Even if not all of e, the vertical BPF 16f, and the time BPF 16l are provided, the detection accuracy can be improved.

FIG. 7 shows the details of the vertical deflection circuit 19 shown in FIG. That is, the vertical synchronizing signal that is synchronously separated by the synchronous detecting circuit 18 is supplied to the vertical oscillating circuit 19a to generate a sawtooth wave signal that is synchronous with the vertical synchronizing signal. The sawtooth wave signal output from the vertical oscillation circuit 19a is supplied to the vertical drive circuit 19b for waveform shaping and amplification, further amplified by the vertical output circuit 19c, and supplied to the vertical deflection coil 19d. The feedback circuit 19e is designed to maintain the linearity of the sawtooth wave signal.
The output signal of the vertical output circuit 19c is supplied to the vertical drive circuit 19
Negative feedback to b.

In the vertical deflection circuit 19 shown in FIG. 7, when the signal determination circuit 16 determines that there are no image portions above and below the video signal, the vertical deflection circuit 1 is detected by the detection signal.
By controlling the feedback circuit 19e or the vertical drive circuit 19b of No. 9, the vertical amplitude of the video signal is expanded. In this case, the signal discriminating circuit 16 may once control the enlargement of the vertical amplitude via a microcomputer (not shown). When it is determined that the non-image portion does not exist, the vertical amplitude is controlled so that the upper and lower parts of the image do not protrude from the display surface, as shown in FIG. 8A or 8C. The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

[0030]

As described above in detail, according to the present invention,
It is possible to provide a very good letterbox screen detection device capable of accurately determining the presence or absence of a non-image portion even with a video signal with a sag and capable of highly accurately determining a letterbox screen.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a letterbox screen detection device according to the present invention.

FIG. 2 is a block configuration diagram showing details of a signal determination circuit in the embodiment.

FIG. 3 is a block configuration diagram showing details of a vertical BPF of the signal determination circuit.

FIG. 4 is a diagram showing input / output characteristics of a non-linear circuit of the signal determination circuit.

FIG. 5 is a block configuration diagram showing another example of the signal determination circuit.

FIG. 6 is a block configuration diagram showing details of a time BPF in another example of the signal determination circuit.

FIG. 7 is a block configuration diagram showing details of a vertical deflection circuit in the embodiment.

FIG. 8 is a diagram shown for explaining various display forms when a video signal having an aspect ratio of 4: 3 is displayed on a wide TV receiver.

FIG. 9 is a waveform diagram shown to explain a video signal of a letterbox screen and its sag.

[Explanation of symbols]

11 ... Input terminal, 12 ... Y / C separation circuit, 13 ... Color demodulation circuit, 14 ... Switching circuit, 15 ... Horizontal compression circuit, 16 ... Letterbox detection circuit, 17 ... Display device, 18 ... Sync detection circuit, 19 ... Vertical deflection circuit, 20 ... Horizontal deflection circuit, 2
1 ... Clock generation circuit, 22 ... Vertical timing generation circuit.

Claims (5)

[Claims] 1. A first detecting means for detecting a DC level of a low frequency component of a horizontal frequency from a video signal, and a second detecting means for detecting a high frequency component of a horizontal frequency from the video signal.
Third detection means for detecting a high-frequency component in the vertical direction from the video signal, and determination means for determining the presence or absence of a non-image portion of the video signal based on the detection results of the first to third detection means. A letterbox screen detection device comprising: 2. The third detection means includes a plurality of delay means for delaying the video signal by a predetermined time and a plurality of delay means for amplifying an input signal and an output signal of each of the plurality of delay means with a predetermined gain. 2. The letterbox screen detection device according to claim 1, further comprising: coefficient means and addition means for adding output signals of the plurality of coefficient means. 3. The letterbox screen detection according to claim 1, further comprising control means for controlling a horizontal amplitude or a vertical amplitude of the video signal based on the determination result of the determination means. apparatus. 4. A fourth detection means for detecting a high frequency component of a time frequency from the video signal is provided, and the determination means comprises:
The letterbox screen detection device according to claim 1, wherein the presence or absence of a non-image portion of the video signal is determined based on the detection results of the first to fourth detection means. 5. The fourth detecting means comprises a generating means for generating an inter-frame difference signal of the video signal, and an absolute value means for taking an absolute value of an output of the generating means. The letterbox screen detection device according to claim 3.