JPH03185985A - Picture display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Purpose of the Invention (Industrial Application Field) The present invention converts a high-definition broadcasting image signal having an aspect ratio of 16:9 to a general NTV image signal having an aspect ratio of 4:3.
The present invention relates to an image display device that displays images on a TSC television screen.

(Prior Art) As is well known, television broadcasting in recent years includes cable-based CATV in addition to conventional terrestrial broadcasting.
(Cable television) As the diversification progresses, such as broadcasting and satellite broadcasting using satellites, IDTV
(Inblue But Definition Television)
Developments such as HDTV and HDTV (Extemporaneous Definition Television) are promoting higher image quality. In particular, high-definition broadcasting using satellites has more than twice the number of scanning lines as the NTSC signal, which is the conventional broadcasting signal, and is expected to change television broadcasting in the future, not only in the broadcasting industry but also in the Indian and foreign industries. , is attracting attention from various quarters.

By the way, this high-definition broadcast is not compatible with the NTSC signal that has been broadcast in the past, so it cannot be received by commonly used television receivers. Therefore, in order to receive high-definition broadcasts, a new television receiver for high-definition broadcasts must be prepared. For this reason, there is a strong demand for the development of a converter that can display high-quality broadcast images on commonly used NTSC television receivers.

The major difference between high-definition broadcasting and conventional broadcasting using the NTSC system is that NTSC has 525 scanning lines and an aspect ratio of 4:3, while high-definition broadcasting has 1125 scanning lines and an aspect ratio of 4:3. The ratio is 16:9. Therefore, consider a case where a high-definition broadcasting screen with an aspect ratio of 16:9 is displayed on a screen with an aspect ratio of 4:3. That is, as shown in FIG. 4, if the entire horizontal direction of a 16:9 screen is displayed in the horizontal direction of a 4:3 screen,
The center part of the 4:3 screen becomes the image display part G, and above and below there are parts MA without image information (hereinafter referred to as mask parts).

Since this mask portion MA is originally a portion unrelated to image information, the brightness and hue can be freely set. For example, if we set the mask area MA to a state where the brightness is O and there is no color, there will always be a brightness difference between the image display area G and the mask area MA on the screen, and this brightness difference will reach the white peak level at the maximum. This is the difference between the black level and the black level.

Therefore, if images whose brightness is close to the white peak level are continuously displayed on the image display section G of the screen, burn-in will occur on the cathode ray tube at the boundary between the image display section G and the mask section MA. When image information with an aspect ratio of 4:3 is displayed later, a problem arises in that the brightness and hue change along the boundary line.

Therefore, in order to solve this problem, conventionally, the mask area MA is set to an intermediate level between the white peak level and the black level, and the brightness difference between the image display area G and the mask area MA is at the self-peak level even if the luminance difference between the image display area G and the mask area MA is The difference between the black level and the black level is set to half, so that burn-in is less likely to occur. However, when image information is actually displayed on the image display section G, when an image close to the white peak level is displayed, the brightness of the mask section MA decreases, and conversely, when an image close to the black level is displayed, the brightness of the mask section MA decreases. A phenomenon occurs in which the brightness of the image increases.

This phenomenon occurs because an automatic beam current control circuit called ABL provided in the image display device operates.

That is, the brightness of the image displayed on the cathode ray tube is controlled by changing the beam current, and as shown in FIG. 5, the brightness can be increased by increasing the beam current. However, in practice, if the brightness is increased beyond a certain level, the focus will be blurred and burn-in will occur on the cathode ray tube, so when the above automatic beam current control circuit receives an image signal with a certain level of brightness, the beam current is controlled to be smaller. This is because the beam current is controlled so that the brightness of the screen is lowered and the brightness of the screen has a relationship as shown in FIG. 6 with respect to the image signal level.

For this reason, when the image signal level increases, the beam current is lowered, which lowers the brightness, and low-luminance areas become lower.Conversely, when the image signal level decreases, the beam current increases, which increases the brightness and reduces the brightness. The lower part will move in the higher direction. In other words, if the displayed image is a bright image, the brightness will be lowered and the brightness of the mask area MA will be lowered, and conversely, if the displayed image is a dark image, the brightness will be increased and the brightness of the masked area MA will be increased. Become. Therefore, even if the level of the mask portion MA output to the cathode ray tube is kept constant, the brightness of the mask portion MA will also change in accordance with changes in the brightness of the displayed image.

(Problems to be Solved by the Invention) As described above, in the conventional image display system that attempts to display image information having a predetermined aspect ratio on screens having different aspect ratios, the brightness of the mask portion on the screen is As the brightness of the image display area changes, the difference in brightness between the mask area and the image display area increases, so no matter how much you set the mask area to an intermediate level between the self-peak level and the black level, the CRT's Burn-in becomes more likely to occur, and
The problem is that the brightness of the mask part fluctuates, making it difficult to see the screen.

Therefore, the present invention has been made in consideration of the above circumstances, and when image information having a predetermined aspect ratio is displayed on a screen having a different aspect ratio, it is possible to prevent image burn-in from occurring on the cathode ray tube and to display an image that is easy to view. The object of the present invention is to provide an extremely good image display device that can display images.

[Structure of the Invention] (Means for Solving the Problems) An image display device according to the present invention displays an image signal in a format compatible with display on a first screen having a predetermined aspect ratio on the first screen. The object is to supply a predetermined mask level to a mask portion that is displayed on a second screen having an aspect ratio different from that of the second screen, and where no image is displayed using an image signal on the second screen. The averaging means averages the image signal, and the coefficient means multiplies the output signal of the averaging means by a predetermined coefficient to generate a mask level. It is configured to provide an input/output characteristic that outputs a mask level that keeps the brightness of the mask portion constant even when the brightness of the mask portion is maintained constant.

(Function) According to the above configuration, the brightness of the mask portion can be kept constant even if the image signal level changes.
It is possible to reduce the risk of burn-in on the cathode ray tube and to display images that are easy to view.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, reference numeral 11 denotes an input terminal to which a digitized image signal with an aspect ratio of 16:9 for high-definition broadcasting is supplied.

The image signal supplied to this input terminal 11 is transmitted to the selector 1
2, and is supplied to one input terminal of the adder circuit 13.
is supplied to one input end of the

This adder circuit 13 has its output connected to the other input terminal of the adder circuit 13 via a latch circuit 14, and adds the image signal supplied to the input terminal 11 and the output signal of the latch circuit 14. It is multiplied by a coefficient of 1/2 and output. The latch circuit 14 also has a clock input terminal 15.
The output of the adder circuit 13 is latched based on the latch clock VCK supplied to the adder circuit 13, and is output to the adder circuit 13. Therefore, the latch circuit 14 generates a signal obtained by averaging the image signals supplied to the input terminal 11.

The averaged signal output from the latch circuit 14 is
It is supplied to the coefficient circuit 16. This coefficient circuit 16 is composed of, for example, a ROM (read-only memory), and generates a mask level to be supplied to the mask portion MA of the screen by multiplying a manually input signal by a predetermined coefficient. 2
It has input/output characteristics as shown in the figure. Here, the characteristic shown in FIG. 6 earlier is B-f(V)+BS, where the image signal level is v1 bright and B1 offset is BS, and the characteristic shown in FIG. If the output is M, then M = -a·f (V) +, b. However, a and b are constants. Therefore, by appropriately setting the constants a and b, the mask level output from the coefficient circuit 16 can have characteristics opposite to the brightness change controlled by the automatic beam current control circuit according to the image signal level. This makes it possible to keep the brightness on the screen constant even if the image signal level changes. The output M of the coefficient circuit 16 is supplied to the other input terminal of the selector 12 as a level setting value of the mask section MA.

Here, the selector 12 derives the mask level that is the output of the coefficient circuit 16 when the mask control signal MASK supplied to the control terminal 17 is at H level, and
The image signal supplied to the input terminal 11 when SK is at L level is derived. In this case, the latch clock VCK and mask control signal 0 MASK are generated at a timing corresponding to an image period of one vertical period of the image signal, as shown in FIG. In this way, the image signal or mask level derived from the selector 12 is supplied to a D/A (digital/analog) conversion circuit 18, converted into an analog image signal, and supplied to a display device 19 such as a cathode ray tube. The image is then displayed.

Therefore, according to the configuration of the above embodiment, the mask portion M on the screen is determined based on the average value of the input image signals.
Since the mask level supplied to A is changed so that a constant brightness can be obtained even if the image signal level changes, burn-in on the cathode ray tube is less likely to occur, and
It becomes possible to display an image that is easy to see. Furthermore, although the coefficient circuit 16 is constructed of a ROM in the above embodiment, it can also be constructed of, for example, a microprocessor.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] As detailed above, according to the present invention, when image information having a predetermined aspect ratio is displayed on a screen having a different aspect ratio, burn-in on the cathode ray tube is less likely to occur, and it is easier to see. An extremely good image display device capable of displaying images can be provided.

[Brief explanation of drawings]

FIG. 1 is a timing diagram for explaining an actual production of an image display device according to the present invention, and FIG. 4 shows a state in which an image with an aspect ratio of 16:9 is displayed on a screen with an aspect ratio of 4:3. 5 is a characteristic diagram showing the relationship between beam current and brightness, and FIG. 6 is a characteristic diagram showing the relationship between image signal level and brightness. 11...Input terminal, 12...Selector, 13...
Addition circuit, 14... Latch circuit, 15... Clock input terminal 2, 6... Coefficient circuit, 7... Control terminal, 8... D/A conversion circuit, 9... Display circuit.

Claims (1)

[Claims] Displaying an image signal in a format compatible with display on a first screen having a predetermined aspect ratio on a second screen having an aspect ratio different from that of the first screen, and displaying the image signal on the second screen. In the image display device that supplies a predetermined mask level to a mask portion in which an image is not displayed by the image signal, an averaging means for averaging the image signal, and a predetermined value for the output signal of the averaging means are provided. coefficient means for multiplying by a coefficient to generate the mask level; input/output for outputting to the coefficient means a mask level that maintains the brightness of the mask portion constant even if the image signal level changes; An image display device characterized in that it is configured to give characteristics.