JPH01231474A - Method for preventing baking of picture display tube - Google Patents

Abstract

PURPOSE:To prevent baking caused at a border with a blank part of a display plane simply by eliminating the deviation of the aspect ratio by the adjustment of deflection amplitude of a monitor display tube and eliminating the baking of the border of non-display part caused on the display screen based on the difference from the aspect ratio through the addition of an intermediate level signal. CONSTITUTION:In the case of displaying a picture signal having a signal waveform for one scanning line comprising a blanking period t1 and a video signal period t2 onto a display screen of a monitor with a different aspect ratio, when a slight deviation in the aspect ratio caused in displaying a converted output picture signal subject to scanning rate conversion with a simple ratio close to the difference from both the scanning rates is adjusted by more or less expanding/contracting the deflection amplitude of the monitor display screen, a blank period giving no display due to the difference between the flyback time t3 of the monitor and the blanking period t1 in the scanning period t1+t2 based on the difference from the aspect ratio of the picture signal and the monitor display screen is produced. Then an intermediate level signal with a proper period length taking the over scan of the monitor display screen into account is added to the nondisplay blank period. Thus, baking of a display screen fluorescent substance layer caused at the border of the blank part is prevented.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is useful for displaying images of other television systems with different aspect ratios on an image display tube that displays images of a particular television system, such as a so-called high-visibility display. This invention relates to an image display tube burn-in prevention method for preventing burn-in that occurs at the boundary between the display screen and the blank area, and in particular, a simple circuit is added to achieve the burn-in prevention effect. .

(Summary of the Invention) The present invention provides a method for displaying images of different aspect ratios using different scanning methods on an image display tube that displays images of a specific aspect ratio constructed using a specific scanning method. To solve the burn-in that occurs at the border, we convert the scanning method using a simple circuit configuration, slightly expand or contract the scanning amplitude to match the aspect ratio, and then apply a constant intermediate level or This can be easily and effectively prevented by adding an intermediate level image signal that gradually decreases as the distance from the image display section increases.

(Prior Art) This type of image display tube burn-in prevention became necessary only after so-called high-vision, which displays horizontally long images with an aspect ratio different from the conventional standard aspect ratio with double the number of scanning lines, was put into practical use. However, since high-definition itself is still in the preparation stage, there is no conventional technology for preventing this kind of burn-in.

Therefore, first of all, when displaying normal standard television images on a dedicated high-definition monitor, what kind of signal conversion should be performed to display images with different aspect ratios, and in that case, how should it be done? We will explain whether burn-in occurs on the display surface.

High-definition monitors have 30 counts per second and 1 scanning line.
125 with an aspect ratio of 16:9, and the monitor screen with such a configuration has a count of 3 times per second.
0, the number of scanning lines is 525 and the aspect ratio is 4:3 or 16
: It is possible to display 12 standard format television images by applying appropriate scanning format conversion, but the display screen in that case would look like the one shown in Figure 1 due to the difference in aspect ratio. Non-display areas remain black at both ends of the horizontally long display surface.

However, if a monitor display tube is used for a long period of time in the above-mentioned conditions, burn-in will occur at the boundary between the image display area and the non-display area, so to prevent such burn-in, it is necessary to It is necessary to constantly display an intermediate level signal and to alleviate the constant and significant difference in display brightness at the boundary, and therefore in the excited state of the display surface phosphor layer.

(Problem to be Solved by the Invention) When an image as shown in Figure 1 is displayed on the display surface of a monitor display tube driven by a predetermined scanning method, an intermediate level image signal is added to the non-display area. However, if the scanning method of the image signal used to display the image shown in Figure 1 is significantly different from the predetermined scanning method of the monitor, it is possible to display the intermediate level signal. Attachment is no longer a simple matter.

Here, we will explain what it means to display standard television images on a dedicated high-definition monitor.

One scanning line of a standard television image signal is as shown in Figure 2, and the number of scanning lines is less than half the number of high-definition scanning lines, so the period length of one scanning line is 63.55.
6. Since l/sec is more than twice the period length of the high-definition scanning line, the standard image signal can be displayed on a high-definition monitor as it is, but it is necessary to convert the scanning method. For example, the configuration shown in FIG. It is necessary to double the number of scanning lines by using an up-converter.

The upconverter shown in FIG. 3 has a relatively simple circuit configuration and is considered to be relatively easy to manufacture.

That is, an input standard image signal is guided to an A/D converter 1 and also to a phase-locked loop (PLL) circuit 2 to generate a clock signal with a frequency of 8f,c for the color subcarrier frequency fsc. A clock signal with a frequency of 4 fSc, which is down-converted by the frequency divider 3, is supplied to the A/D converter 1, and the digitized standard format image signal is guided to the scanning rate converter 4. The scanning rate converter 4 has a frequency of 4 fs.
The scanning rate of the input digitized image signal is doubled by supplying clock signals of both frequency c and frequency 8f, c, thereby converting the input digitized image signal into an output digitized image signal with twice the number of scanning lines. If the converted output image signal is returned to an analog signal by the D/A converter 5 and extracted, an image signal having a signal waveform for one scanning line as shown in FIG. 4 is obtained, and the scanning line period length is 31. Since .778 μsec is close to the scanning line period length of a high-definition image signal, 29.630 μsec, it can be displayed on a high-definition monitor. Since it is done in relation to each other, it is relatively simple and seems easy to manufacture.

However, as can be seen by comparing FIG. 5 showing the high-definition image signal waveform for one scanning line with FIG. 4, the scan rate conversion output image signal of the up-converter with the configuration shown in FIG. Due to the difference in the ratio between the image display period and the blanking period, the aspect ratio of the converted output image will not be the standard 4:3 or 12:9, but will be 15.2:9. .

Therefore, in order to accurately display a standard format image with an aspect ratio of 4:3, [1] Change the scan rate conversion rate to shorten the image display period.

[2] Adjust the deflection circuit that drives the monitor display tube to shorten the horizontal deflection amplitude.

You must choose one of the following.

[1] In order to change the scanning rate conversion rate, the up-converter should be configured as shown in FIG. 6, and the phase-locked loop (PLL) in the circuit configuration shown in FIG.
The frequency of the clock signal from circuit 2 is 20fsc,
Therefore, the clock signal with a frequency of 10 fsc from the frequency divider 3 is applied to the conversion output side of the scanning rate converter 4 and the D/A
In addition to supplying the clock signal to the converter 5, another frequency divider 6 is newly provided to reduce the clock signal frequency of 20 fsc from the PLL circuit 2.
A clock signal of 175 frequencies 4f, c is supplied to the conversion input side of the A/D converter 1 and the scanning rate converter 4.

As a result, the scanning rate converter 4 outputs the digital image signal manually generated at a clock frequency of 4fsc at a clock frequency of 10fsc, so as shown in FIG.
Scanning line period of high-definition monitor 31.778μse
The image display period of c is 26 and 32 in Fig. 4.
The converted output image is shortened from 8 p sec to 21.062 p sec and has an aspect ratio of 12:9, that is, 4:3, as shown in FIG. Therefore, the scanning line period of the high-definition image shown in FIG. 7 is 31.
Of the 778 μsec, the above-mentioned image display period is 21.06
2μsec and high-definition blanking period 4μsec
If an intermediate level image signal is added to the intermediate blank period of 2.633 μsec after subtracting 2.633 μsec to perform gray display, the significant difference in steady display brightness between the display surfaces before and after it will be alleviated, thereby reducing the occurrence of burn-in. problem will be resolved.

However, in the up-converter shown in Figure 6, the configuration of the clock frequency conversion circuit for scanning rate conversion is not only much more complicated than the circuit configuration shown in Figure 3, but also the clock frequency handled is much higher. A new problem arises in that the up-converter is much more difficult to manufacture than the up-converter with the configuration shown in FIG.

(Means for Solving the Problems) An object of the present invention is to adjust the aspect ratio of a converted output display image by adopting the above-mentioned (III) means of shortening the horizontal deflection amplitude by adjusting the deflection circuit. , blank areas that occur on the display screen due to the difference in aspect ratio when image signals with different scanning methods and aspect ratios are converted from one scanning method to another using a simple up-converter and displayed on a monitor with a specified scanning method and aspect ratio. An object of the present invention is to provide a method for preventing image burn-in in an image display tube, which can prevent burn-in from occurring at the boundaries of the image display tube.

That is, the image display tube burn-in prevention method of the present invention provides an image display tube having a display surface having a predetermined aspect ratio, which is driven by a deflection circuit configured to display an image having a predetermined aspect ratio. When displaying another image with a different aspect ratio, the deflection circuit maintains a constant intermediate level or the blanking period during the non-display period including the blanking period of the image signal constituting the image corresponding to the image display period by the deflection circuit. The present invention is characterized in that burn-in of the image display tube is prevented by displaying an intermediate level image signal that gradually decreases as the line erasing period approaches.

(Function) Therefore, if the burn-in prevention method of the present invention is implemented, when a standard image signal is displayed on a high-definition monitor after converting the scanning method using an up-converter with a simple circuit configuration, the horizontal deflection By simply adjusting the amplitude, an image with a predetermined aspect ratio can be easily displayed without causing burn-in.

(Example) The present invention will be described in detail below with reference to the drawings.

Now, when the aspect ratio of the converted output display image is adjusted by shortening the horizontal deflection amplitude by adjusting the deflection circuit (II) described above, the horizontal deflection waveform becomes as shown in FIG. 8.

As can be seen by comparing this horizontal deflection waveform with the signal waveform of the converted output image signal shown in Figure 4, which is obtained by converting the standard image signal by doubling the number of scanning lines using the up converter shown in Figure 3, the horizontal deflection waveform is The display image of a high-definition monitor when the deflection amplitude is shortened is as shown in Figure 9, and the 12:9 aspect ratio at the center of the display screen is
+0.33X 2 part is scanned by shortened horizontal deflection, the hatched parts at both ends are not scanned, and
A portion of 0.33 on both sides is scanned but becomes a non-display area where no image is displayed.

Therefore, in order to prevent burn-in at the boundary A between the image display area and the non-display area, as shown in FIG. I will do it. However, although the addition of such an intermediate level signal prevents the burn-in at the boundary A, a similar burn-in occurs at the boundary B between the non-display area and the non-scanning area. In this case, burn-in at boundary B cannot be prevented.

Moreover, the non-displayed area between boundaries A and B is
Corresponding to the folded end of the shortened ideal horizontal deflection waveform shown in ), the scanning width is further shortened due to the distortion of the deflection waveform end as shown in FIG. Therefore, it cannot be expected to have a large effect in preventing burn-in. In other words, if there is distortion at the end of the deflection waveform, the non-display area between the boundaries A and B in the display image shown in FIG. Addition of an intermediate level signal cannot be expected to have a mitigating effect on the significant difference in the excitation of the phosphor layer.

However, in general, the display surface of the monitor is 7~
The 10% overscan prevents the folded end of the deflection from appearing on the display screen even if the deflection amplitude changes slightly. Therefore, the video signal area in the image signal waveform for one scanning line shown in Fig. 2 Not all images appear on the display screen.

Therefore, even when displaying a standard television image on the display surface of a high-definition monitor, there should be no problem even if overscan is performed so that both ends of the deflection are off the display surface. Therefore, if there is distortion in the deflection waveform at the horizontal deflection end as described above, and if overscan is performed by, for example, 7%, the image signal waveform for one scanning line with an intermediate level signal added to the non-display area will be As shown in FIG. 12, since the width of the intermediate level display area is widened, the above-mentioned problem of reduced anti-burning effect due to deflection waveform distortion is solved.

The display screen when the image signal shown in FIG. 12 with 7% overscan as described above is displayed on a high-definition monitor is as shown in FIG. 13.
Compared to 2, the non-display area is wider by 0.807,
A sufficient anti-seizing effect can be expected.

Therefore, if the level range of the image signal is set to 0 to 1.0, the average level is expected to be 0.5, and if the image signal level added to the non-display area is set to about 0.5, it will be different from the image display area. It appears that burn-in at boundary A can be prevented.

However, the additional signal level of 0.5 is too high for the 0 level of the non-scanned portion, and it is impossible to prevent burn-in at the boundary B. Therefore, the additional signal level at the boundary B with the non-scanned area must be lowered to about 0.3, and an image signal having a signal waveform as shown in FIG. 14 is added to the non-display area.

An example of a circuit configuration in which the above-mentioned signal addition is performed in the up-converter having the configuration shown in Fig. 3 is shown in the first example.
It is shown in Figure 5. As shown, the addition of the intermediate level signal in the up-converter shown in the third diagram is performed at a frequency of 4f8. The digital image signal from the A/D converter 1, which is operated by the clock signal of The simplest and most preferable method is to add the additional signal from the additional signal generator 9 operated by the signal to the 0 level section and then supply it to the scanning rate converter 4. It should be noted that the image signal when the intermediate level signal is added is not in the state shown in FIG. The signal section is cut off according to the overscan ratio. Further, the additional signal generator 9 can be easily configured with a counter and a read-only memory.

Adding an intermediate level signal by combining the blanking circuit 7, adder 8 and additional signal generator 9 as described above is as follows:
Output side of scanning rate converter 4 or D/A converter 5
This can also be done on the output side.

In the above explanation, we have described an example of displaying television images in the standard format, that is, the NTSC format, with a number of scanning lines of 525 and a count of 30 per second on a high-definition monitor. When displaying images using other scanning methods, such as 625, SECAM output type with 50 counts per second, or PAL type television images, the intermediate By adding a level signal, it is possible to prevent burn-in occurring at the border of the non-display area. That is, generally the first
As shown in Figure 6, when an image signal having a signal waveform for one scanning line consisting of a blanking period tl and a video signal period t2 is displayed on the display screen of a monitor with a different aspect ratio, the difference in scanning rate between the two If you adjust the slight deviation in the aspect ratio that occurs when displaying a converted output image signal that has been subjected to scan rate conversion with a simple approximate ratio, by slightly expanding or contracting the deflection amplitude of the monitor display surface, the difference between the image signal and the monitor display surface can be adjusted. Based on the difference in the aspect ratio of Although there will be a blank period,
In the present invention, in this non-display blank period, the 14th period has an appropriate period length that takes into account the overscan of the monitor display surface.
The intermediate level signal shown is added to prevent burn-in of the display surface phosphor layer at the boundaries of the blank space.

Furthermore, as shown in FIG. 18, the blank areas that occur on the display surface due to the difference in aspect ratio between the monitor display surface and the image signal occur only on one side of the image display area where the video signal is displayed. It is also possible to perform similar burn-in prevention by displaying an additional signal in the blank space.

(Effects of the Invention) As is clear from the above description, according to the present invention, when displaying a standard television image on the display screen of a high-definition monitor, for example, the scanning format can be converted using an up-converter with a simple configuration. However, the aspect ratio shift caused by the deflection amplitude of the monitor display tube caused the problem that the aspect ratio of the displayed image would shift, and it was necessary to use a complicated up-converter to display the image with the correct aspect ratio. By simply adding an intermediate level signal, we can solve the problem by removing the burn-in at the border of the non-display area that occurs on the display surface based on the difference in aspect ratio between the display surface and the displayed image. This can be effectively prevented by using an up-converter with an easy-to-manufacture configuration, which is a special effect.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a display screen displaying a standard television image on a high-definition monitor display screen, and Fig. 2 is a waveform showing an example of a signal waveform for one scanning line of a standard television image signal. Fig. 3 is a block diagram showing an example of a simple configuration of an up-converter for converting the scanning method, and Fig. 4 is a signal of one scanning portion of an image signal whose scanning method has been converted by the up-converter shown in Fig. 3. A waveform diagram showing an example of a waveform. Figure 5 is a waveform diagram showing an example of a signal waveform for one scanning line of a high-definition image signal. Figure 6 is an example of a complicated configuration of an up-converter for scanning method conversion. Block diagram; Figure 7 is a signal waveform diagram showing an example in which an intermediate level signal is added to the image signal whose scanning method has been converted by the up-converter shown in Figure 6; Figure 8 is an example of the deflection waveform of a high-definition monitor display tube. FIG. 9 is a diagram showing an example of a display screen in which an intermediate level signal is added to the image signal waveform shown in FIG. 4 and the aspect ratio is corrected. FIG. 10 is a waveform diagram showing the image signal waveform shown in FIG. A signal waveform diagram showing an example of adding an intermediate level signal; Figures 11 (a) and 11) are waveform diagrams showing examples of an ideal deflection waveform and an actual deflection waveform, respectively; Figure 12 is an image of the image shown in Figure 4. 13 is a signal waveform diagram showing an example in which a part of the video signal in the signal waveform is removed and an intermediate level signal is added; FIG. 13 is a line diagram showing an example of a display screen displaying the image signal waveform shown in FIG. 12; FIG. FIG. 15 is a signal waveform diagram showing an example of an intermediate level signal added to the image signal waveform shown in FIG. Fig. 16 is a waveform diagram showing the signal waveform for one scanning line of a general television image signal, Fig. 17 is a signal waveform diagram showing an example in which an intermediate level signal is added to the image signal waveform shown in Fig. 16, and Fig. 18 2 is a diagram showing another example of a display screen of a scanning method converted output image signal to which an intermediate level signal is added; FIG. 1...A/D converter 2...Phase locked loop (PLL) circuit 3.6...
Frequency divider 4...Scanning rate converter 5...D/A converter 7...Blanking circuit

Claims (1)

[Claims] 1. Displaying another image with an aspect ratio different from the predetermined aspect ratio on an image display tube having a display surface with the predetermined aspect ratio, which is driven by a deflection circuit configured to display an image with a predetermined aspect ratio. In doing so, an intermediate level that is constant during a non-display period including a blanking period of the image signal constituting the other image corresponding to the image display period by the deflection circuit, or an intermediate level that gradually decreases as it approaches the blanking period. 1. A method for preventing image display tube burn-in, characterized in that image display tube burn-in is prevented by displaying an image signal.