JPH07298201A - Letter box picture detector - Google Patents

Abstract

PURPOSE:To discriminate a letter box picture with high precision by detecting a vertical correlation of a video signal whose image has a non-picture part at its upper and lower position and detecting a timewise change in the correlation so as to discriminate precisely the presence of the non-picture part even from a video signal with sag. CONSTITUTION:A video signal fed to an input terminal 11 is given to a letter box detection circuit 16, in which whether or not a non-picture part is in existence in upper and lower positions of a pattern is detected. Then a changeover circuit 14 is controlled to provide a luminance signal outputted from a Y/C separation circuit 12 and a chrominance signal subjected to demodulation processing in a chrominance demodulation circuit 13 or a luminance signal and a chrominance signal outputted from a horizontal compression circuit 15 selectively to a display device 17. Furthermore, the video signal fed to the input terminal 11 is given to a synchronization detection circuit 18, in which a vertical synchronizing signal and a horizontal synchronizing signal are detected. The synchronizing signals are respectively fed to a vertical deflection circuit 19 and a horizontal deflection circuit 20, the signals are used to control the display operation of the display device 17.

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, a pattern as shown in FIG. 9 (b) is obtained. 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.

Here, in the letterbox signal shown in FIG. 10A, the vertical synchronizing period is z, the vertical blanking period is y, and the non-image portion is s and t. And, in general, AC
If the time constant is insufficient in the (AC) coupling circuit,
A sag occurs as indicated by 0 (c). That is, the DC voltage level monotonically increases in the upper and lower non-image portions s and t of the letter box signal and the vertical blanking period y, and monotonically decreases in the image portion. When the waveform of this letterbox signal is simply sliced by a DC voltage, the non-image areas s and t may be removed depending on the slice level shown by the broken line in FIG.
Since the period is crossed, it becomes impossible to accurately detect the non-image portions s and t.

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 a correlation detecting means for detecting the presence or absence of vertical correlation of a video signal, and a time direction of a detection signal outputted from the correlation detecting means. And a control means for controlling the horizontal amplitude or the vertical amplitude of the video signal based on the detection result of the time change detecting means.

[0012]

According to the above-mentioned structure, in the video signal to which the non-image portions are added at the top and bottom, there is a correlation in the vertical direction of the top and bottom non-image portions, and this correlation is stable in the time direction. Therefore, by detecting the correlation of the video signal in the vertical direction and detecting the change of the correlation in the time direction, it is possible to accurately determine the presence or absence of a no-image portion even in the video signal with a sag, and the letterbox screen can be determined with high accuracy. You will be able to do it in.

[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 has a letterbox detection circuit 16 whose details will be described later.
To detect whether it is a letterbox screen, that is, whether there is a non-image portion at the top and bottom of the screen.
Then, the switching circuit 14, based on the detection signal output from the letterbox detection circuit 16, the luminance signal output from the Y / C separation circuit 12, the color signal demodulated by the color demodulation circuit 13, and the horizontal signal. The luminance signal and the chrominance signal output from the compression circuit 15 are converted into, for example, C of a wide screen configuration.
Display device 1 consisting of RT (cathode ray tube) etc.
The switching control is performed so as to selectively lead to 7.

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 letterbox detection circuit 16.

That is, in this wide TV receiver, the letterbox detection 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. 2A shows a detailed structure of the letter box detection circuit 16. That is,
The video signal supplied to the input terminal 11 is supplied to the correlation detection circuit 22 via the delay circuit 21 and directly to the correlation detection circuit 22. This delay circuit 21
Is to delay the video signal by n (natural number) horizontal scanning period. Further, the correlation detection circuit 22 uses the input terminal 11
The video signal directly supplied via the delay circuit 21 and the video signal value supplied via the delay circuit 21 are compared to detect the correlation between the two video signals or the correlation between the scanning lines.

The correlation detection signal output from the correlation detection circuit 22 is supplied to the determination circuit 24 via the time direction change detection circuit 23 and directly to the determination circuit 24. The time direction change detection circuit 23 detects whether the correlation detection signal output from the correlation detection circuit 22 is changing in the time direction, or whether the presence or absence of correlation for each scanning line is changing in the time direction. . The determination circuit 24 includes the correlation detection circuit 22 and the time direction change detection circuit 2.
The presence or absence of upper and lower non-image portions of the input video signal is determined by receiving each output of No. 3.

Here, FIG. 2B shows the internal configuration of the correlation detection circuit 22 and the connection relationship with other blocks. That is, the correlation detection circuit 22 includes a subtraction circuit 22a, an absolute value circuit 22b, and a non-linear circuit 22c. Of these, the subtraction circuit 22a takes the difference between the video signal directly supplied via the input terminal 11 and the video signal output from the delay circuit 21, and supplies the difference signal to the absolute value circuit 22b. . Absolute value circuit 22b
Then, the absolute value of the difference signal is generated and output to the nonlinear circuit 22c. The non-linear circuit 22c, as shown in FIG.
It has an input / output characteristic that outputs a constant value when the input signal exceeds a certain value.

FIG. 4 shows the details of the time direction change detection circuit 23. That is, the correlation detection signal output from the correlation detection circuit 22 is the three frame delay circuits 23b, 23 connected in series via the input terminal 23a.
c and 23d are sequentially transferred. Each of the frame delay circuits 23b, 23c, 23d includes a subtraction circuit 23.
The difference between the input and the output is taken by e, 23f and 23g. Then, the outputs of the subtraction circuits 23e, 23f, 23g pass through the absolute value circuits 23h, 23i, 23j and the non-linear circuits 23k, 23l, 23m, respectively, and are then OR-operated by the OR circuit 23n to pass through the output terminal 23o. It is supplied to the determination circuit 24.

The correlation detection signal output from the correlation detection circuit 22 is supplied to the frame delay circuit 23b via the input terminal 23a and delayed by one frame period.
The one frame delayed correlation detection signal output from the frame delay circuit 23b is delayed by one frame by the frame delay circuit 23c, and further, the frame delay circuit 23d.
Then, it is delayed by one frame. That is, with respect to the correlation detection signal supplied to the input terminal 23a, the frame delay circuit 23
b is a frame delay circuit 23 for a signal delayed by one frame.
c outputs a 2-frame delay signal, and the frame delay circuit 23d outputs a 3-frame delay signal.

The subtracting circuit 23e has an input terminal 23.
The difference between the correlation detection signal directly supplied from a and the one-frame delayed correlation detection signal output from the frame delay circuit 23b is calculated, and the difference signal is output to the absolute value circuit 23h. . The absolute value circuit 23h generates an absolute value signal of the difference signal and outputs it to the non-linear circuit 23k. The non-linear circuit 23k has an input / output characteristic as shown in FIG. 5, and binarizes the input absolute value signal and outputs it to the OR circuit 23n. The input / output characteristic shown in FIG. 5 is obtained by cutting the output that does not reach the constant value of the input / output characteristic shown in FIG.

Further, the other absolute value circuits 23i and 23j and the non-linear circuits 23l and 23m have the same construction as the above-mentioned absolute value circuit 23h and the non-linear circuit 23k, and perform the same operation, so that the description thereof will be omitted. .

When the correlation detection signal supplied to the input terminal 23a does not change in the time direction, the nonlinear circuit 23
The output of k becomes L level. Therefore, when the correlation detection signal does not change continuously for 3 frames, the output of the OR circuit 23n becomes L level. However, when the correlation detection signal changes between any one of the three continuous frames, the output of the OR circuit 23n becomes H level.

First, the correlation detection circuit 2 shown in FIG.
In 2, it is possible to detect the presence / absence of vertical high-frequency components before and after the vertical synchronization signal and the presence / absence of vertical high-frequency components at the boundary between the non-image portion and the image portion. This vertical high frequency component does not change in the time direction on the letter box screen,
In a video signal with an aspect ratio of 4: 3, a change in the time direction is seen along with a change in the image, so this change can be detected by the time direction change detection circuit 23. Then, the decision circuit 24 decides that the vertical high-frequency component exists in a predetermined period, and when this component does not change in the time direction, it is a letterbox signal.

Even when a video signal with a sag as shown in FIG. 10C is input, the vertical high frequency signal output from the subtraction circuit 22a in FIG. 2B is the absolute value circuit 2
By being supplied to 2b, it is detected as an output of a peak value as shown in FIG. 10 (b). That is, even if there is a vertical sag, the correlation between scanning lines is maintained, so that the boundary between the non-image portion and the image portion can be detected.

FIG. 6 shows the letterbox detection circuit 16 described above.
Another example of is shown. That is, the video signal supplied to the input terminal 11 is supplied via the nH delay circuit (n: natural number) 25 to one input terminal of the subtraction circuit 26a that constitutes the correlation detection circuit 26, and at the same time, the direct subtraction circuit 26a.
Is supplied to the other input end of the. This nH delay circuit 2
Reference numeral 5 delays the video signal by n (natural number) horizontal scanning period. Then, the subtraction circuit 26a subtracts the video signal supplied via the nH delay circuit 25 from the video signal directly supplied via the input terminal 11.

The subtraction signal output from the subtraction circuit 26a passes through the H-BPF (horizontal band pass filter) 26b and the non-linear circuit 26c, and the time direction change detection circuit 2 is detected.
H-LPF while being output to one input terminal of
(Horizontal low-pass filter) 26d and non-linear circuit 26e
Is output to the other input terminal of the time direction change detection circuit 27 via. Then, the output of the time direction change detection circuit 27 is output terminal 28 as a determination signal of the letterbox screen.
Taken from. The area a shown in FIG. 7 is HL
Shows the vertical-horizontal frequency characteristics of the output signal of PF26d,
A region b shown in FIG. 7 shows the vertical-horizontal frequency characteristic of the output signal of the H-BPF 26b.

In the configuration shown in FIG. 6, the change in the color carrier component and the change in the luminance signal can be detected through the different nonlinear circuits 26c and 26e, and the change in the time direction can be detected, thereby improving the detection accuracy. be able to. Generally, since the modulation degree of the color signal is low and the amplitude of the color carrier component is small, the input / output characteristic of the nonlinear circuit 26c receiving the output signal of the H-BPF 26b is set as shown by the broken line a or the one-dot chain line b in FIG. However, the detection sensitivity can be increased.

FIG. 8 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. 8, when the letter box detection circuit 16 determines that there are no image areas above and below the video signal, the detection signal causes the feedback circuit 19e of the vertical deflection circuit 19 or the vertical circuit. By controlling the drive circuit 19b, the vertical amplitude of the video signal is expanded. The position of the image portion can be detected from the vertical high-frequency signals (k) and (l) existing before and after the vertical synchronizing signal as shown in FIG. 10B, whereby the vertical amplitude can fill the effective display screen. Can be expanded to. When it is determined that the non-image portion does not exist, the vertical amplitude is controlled so that the upper and lower portions of the image do not protrude from the display surface, as shown in FIG. 9A or 9C. 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.

[0032]

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 letterbox detection circuit in the embodiment.

FIG. 3 is a diagram showing input / output characteristics of an absolute value circuit that constitutes a correlation detection circuit of the letterbox detection circuit.

FIG. 4 is a block configuration diagram showing details of a time-direction change detection circuit of the letterbox detection circuit.

FIG. 5 is a diagram showing input / output characteristics of a non-linear circuit of the same time direction change detection circuit.

FIG. 6 is a block diagram showing another example of the letterbox detection circuit.

FIG. 7 is a diagram showing a frequency characteristic of a filter forming a correlation detection circuit in another example of the letterbox detection circuit.

FIG. 8 is a block configuration diagram showing details of a vertical deflection circuit in the embodiment.

FIG. 9 is a diagram for explaining various display forms when a video signal having an aspect ratio of 4: 3 is displayed on a wide TV receiver.

FIG. 10 is a waveform diagram shown for explaining 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
DESCRIPTION OF SYMBOLS 1 ... Delay circuit, 22 ... Correlation detection circuit, 23 ... Time direction change detection circuit, 24 ... Judgment circuit, 25 ... nH delay circuit, 2
6 ... Correlation detection circuit, 27 ... Time direction change detection circuit, 28
… Output terminal.

Claims (4)

[Claims] 1. Correlation detecting means for detecting the presence or absence of vertical correlation of a video signal, time change detecting means for detecting the presence or absence of change in the time direction of a detection signal output from this correlation detecting means, and this time A letterbox screen detection device comprising: a control unit that controls the horizontal amplitude or the vertical amplitude of the video signal based on the detection result of the change detection unit. 2. The correlation detecting means delays the input video signal by a predetermined number of horizontal lines, and a difference between the video signal delayed by the delay means and the input video signal. The input means exceeds the predetermined value, and the absolute value means for generating the absolute value of the difference signal output from this arithmetic means and the absolute value signal output from this absolute value means are supplied. 2. The letterbox screen detection device according to claim 1, further comprising: a non-linear means having an input / output characteristic in which an output is a constant value. 3. The time change detection means includes a plurality of delay means for delaying a detection signal output from the correlation detection means by a predetermined time, and a difference between an input signal and an output signal of each of the plurality of delay means. The plurality of calculating means, the plurality of absolute value means for generating the absolute value of each difference signal output from the plurality of calculating means, and the respective absolute value signals output from the plurality of absolute value means are 2 respectively. 2. The letterbox screen detection device according to claim 1, further comprising a plurality of non-linear means for digitizing, and a gate means for detecting that the signals output from the plurality of non-linear means coincide with each other. . 4. The correlation detecting means delays the input video signal by a predetermined number of horizontal lines, and a difference between the video signal delayed by the delay means and the input video signal. , A first filter for extracting a color carrier component from the difference signal output from the calculator, and a color carrier component output from the first filter are supplied. A first non-linear means having an input / output characteristic in which the output becomes a constant value when the value exceeds the value, a second filter for extracting a luminance signal component from the difference signal output from the arithmetic means, and a second filter A second non-linear means for supplying an output luminance signal component and having an input / output characteristic in which the output becomes a constant value when the input exceeds a predetermined value; Over 2. The letterbox screen detection device according to claim 1, wherein the presence or absence of a change in the time direction of each signal output from the second non-linear means is detected.