JPH06250624A - Screen display controller - Google Patents

Abstract

PURPOSE:To automatically change over a moving picture and a still picture. CONSTITUTION:When a moving picture signal on the NTSC standard, etc., is inputted from the outside of a work station or a personal computer, its pedestal level is stabilized to 0V by means of a well-known clamping circuit 1. A peak holding circuit 2 is composed of a capacitor and holds the maximum value of the level of the moving picture signal within the effective section of data. A comparator 4 compares the maximum value with a prescribed value and when the maximum value is larger than the prescribed value, detects the input of the moving picture signal from the outside. On the other hand, when the maximum value is smaller than the prescribed value, the comparator detects the stoppage of the input of the moving picture signal from the out side. Consequently, a moving picture selecting signal MOVON-P is changed over to a high level or a low level and a vertical synchronizing frequency and a horizontal synchronizing frequency are changed to those for a moving picture or a still picture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screen display control device for displaying moving images and still images on a display device provided in a workstation or a personal computer.

[0002]

2. Description of the Related Art In a workstation or personal computer, in order to show the processing result to an operator,
It is equipped with a display device such as a CRT (cathode ray tube) or a liquid crystal display device. On such a display device, not only data and the like are displayed as still images, but also moving images are displayed by input of external signals. FIG. 2 is a block diagram of the CRT display device. As shown in FIG. 2, the CRT comprises a phosphor screen 101 coated with a phosphor, a deflection system 103 for deflecting an electron beam 102, and a neck portion 105 for holding an electron gun 104.

In FIG. 2, an electron beam 102 emitted from an electron gun 104 is changed in its traveling direction by a deflection system 103,
A light emission phenomenon occurs at each pixel on the screen when it hits the phosphor screen 101. FIG. 3 is a front view of the CRT of FIG. The deflection system 103 shown in FIG. 2 is provided with electrodes in the horizontal and vertical directions, and when a sawtooth voltage is applied to these electrodes, the electron beam 102 is moved left and right on the phosphor screen 101 as shown in FIG. Moved up and down. The scanning in which the electron beam 102 is moved in the left-right direction at this time is called horizontal scanning, and the lines appearing on the screen by the horizontal scanning are called scanning lines. Further, scanning in which scanning lines are gradually shifted from the top to the bottom of the screen is called vertical scanning.

Therefore, by synchronizing these horizontal scanning and vertical scanning with the data output to the electron beam 102, a predetermined image can be displayed on the screen. This display control is performed by the CRT control unit described below. FIG. 4 is a schematic configuration diagram of a conventional CRT control unit. As shown in FIG. 4, the CRT control unit includes a crystal oscillator 7
1, D / A converter 72, and CRT controller 7
3 and 3. The crystal oscillator 71 oscillates with a clock (dot clock) corresponding to one dot on the CRT 74. The D / A converter 72 outputs each data of red (R), green (G), and blue (B) in synchronization with the dot clock oscillated by the crystal oscillator 71. The electron gun 104 shown in FIG.
Outputs an electron beam 102 having an intensity corresponding to this data.

The CRT controller 73 is a crystal oscillator 7
1 generates a horizontal synchronizing signal and a vertical synchronizing signal from the dot clock. The horizontal synchronizing signal indicates the start of horizontal screen display on the CRT screen. Also, the vertical sync signal is
The start of screen display in the vertical direction on the CRT screen is shown, and the switching timing of one screen (frame) is shown. The frequency of this switching is called the frame frequency. When the frame frequency is low, the display of characters and the like on the screen will appear to flicker, and conversely when the frame frequency is high, the flicker will be reduced. Therefore, it is necessary to increase the frame frequency in order to improve the display quality of the CRT. Therefore, when displaying data such as processing results as a still image on a workstation or personal computer, the vertical frequency is 70 Hz.
Is set to.

However, when displaying a moving image on a workstation or a personal computer by inputting an external signal, the vertical frequency must be 60 Hz. For example, a movie like a television
Although the frame frequency is 30 Hz, as is well known, the interlace system is adopted, and one frame is composed of two fields, an odd field and an even field, so the vertical synchronizing frequency is doubled to 60 Hz. still,
When displaying a moving image on a workstation or personal computer, a non-interlaced method is often used. In such a non-interlace system, a frame is generated for each of the odd field and the even field of the interlace system by signal interpolation, and each frame is displayed in synchronization with a vertical synchronizing signal of 60 Hz. Conventionally, such switching of the vertical synchronizing frequency is manually performed by an operator such as a workstation.

FIG. 5 is a schematic configuration diagram of a conventional CRT control unit capable of displaying a moving image. That is, as shown in FIG. 5, in addition to a crystal oscillator 71 that generates a horizontal synchronizing signal and a vertical synchronizing signal for displaying internal data of a workstation or a personal computer, a moving image for externally input is displayed. A crystal oscillator 81 for generating a horizontal synchronizing signal and a vertical synchronizing signal is provided. Then, the selection circuit 82 switches the clock output from the crystal oscillator 71 or 81. Therefore, the movie selection signal MOVON-
Input P to the flip-flop 83. Then, the flip-flop 83 receives the current vertical synchronization signal VSYN.
The moving picture selection signal MOVON-P is output to the selection circuit 82 at the CP output timing. As a result, the video selection signal MOVO
When a moving image input from the outside is selected by NP, 60 Hz corresponding to the clock from the crystal oscillator 81
Vertical sync signal and a horizontal sync signal of 15750 Hz are generated. On the other hand, when the display of internal data of the workstation or the like is selected, the vertical synchronizing signal of 70 Hz and 18375 corresponding to the clock from the crystal oscillator 71 are selected.
A horizontal synchronizing signal of Hz is generated.

[0008]

However, the above-mentioned conventional technique has the following problems. That is, there is a problem that the operator's burden increases because the operator has to switch between the moving image display and the still image display. In addition, the operator may make an error in setting. For example, if a moving image is displayed when the vertical synchronizing frequency is 70 Hz, or a still image is displayed when the vertical synchronizing frequency is 60 Hz, the screen display is not performed at all. There was a problem that it became unusable or abnormal. The present invention has been made in view of the above points, and an object of the present invention is to provide a screen display control device that automatically switches between moving image display and still image display without depending on the operator. To do.

[0009]

A screen display control device of the present invention is a peak hold circuit for holding a maximum value of a level of a moving picture signal inputted from the outside, and a level held in the peak hold circuit is for the moving picture. It is characterized by comprising a comparator which detects the input of a moving image signal and outputs an instruction to select a moving image display by determining whether or not the signal is higher than a pedestal level by a predetermined value or more.

[0010]

In the screen display control device of the present invention, the NT is supplied from the outside of the workstation or personal computer.
When a moving image signal of SC standard or the like is input, the pedestal level of the moving image signal is stabilized to 0V by a known clamp circuit. The peak hold circuit is composed of a capacitor or the like and holds the maximum value of the signal level in the data valid section of the moving image signal. The comparator compares this maximum value with a predetermined value, and if the maximum value is greater than or equal to the predetermined value, it detects that a moving image signal has been input from the outside. On the other hand, if the maximum value is smaller than the predetermined value, it is detected that the moving image signal is not input from the outside. As a result, the vertical synchronizing frequency and the horizontal synchronizing frequency are switched to those for moving images or still images.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the screen display control device of the present invention. The illustrated device comprises a clamp circuit 1, a peak hold circuit 2, a reset circuit 3, a comparator 4, a flip-flop 5, and the like. The clamp circuit 1 inputs a moving image signal input from the outside. The moving image signal is an analog signal and conforms to the NTSC standard. That is, as shown in FIG. 6, the moving image signal includes a sync pulse 21, a pedestal level 22, and a data valid section 2.
It consists of three. The sync pulse 21 is a pulse corresponding to a horizontal sync signal. The pedestal level 22 serves as a reference for the black level of the image. Image data is included in the data valid section 23. The clamp circuit 1 stabilizes the signal level so that the pedestal level 22 of the moving image signal is always 0V.

The peak hold circuit 2 detects the maximum value of the image data and holds the maximum value until the reset circuit 3 resets it. The reset circuit 3 resets the peak hold circuit 2 at the timing of generation of the vertical synchronizing signal when the moving image display is selected. Therefore, the maximum value held in the peak hold circuit 2 is the maximum value from the generation of one vertical synchronizing signal to the generation of the next vertical synchronizing signal. The comparator 4 compares the maximum value of the image data held in the peak hold circuit 2 with a predetermined value. Then, when the maximum value of the image data is equal to or larger than the predetermined value, it is determined that the moving image signal is input from the outside. On the other hand, when the maximum value of the image data is smaller than the predetermined value, it is determined that the moving image signal is not input from the outside. The flip-flop 5 stores whether to select the moving image display, and corresponds to the flip-flop 83 shown in FIG.

FIG. 7 is a circuit diagram showing an example of a peak hold circuit and the like. The illustrated peak hold circuit includes a comparator 31, a diode 32, a capacitor 33 and the like. The reset circuit 3 includes a transistor 34, an AND circuit 35, and the like. The transistor 34 is used as a switch, and the video selection signal MOVON-P and the vertical synchronization signal
Turns on when both VSYNC-P are high level. When the transistor 34 is off, the output voltage of the comparator 31 remains held by the capacitor 33.
The voltage held by the capacitor 33 is input to the counter input terminal of the comparator 31. Therefore, the comparator 31 applies the level voltage of the image data to the capacitor 33 via the diode 32 only when the voltage level of the image data input to the positive input terminal is higher than the voltage held by the capacitor 33. That is, the comparator 3
1 does not output the level voltage of the image data when the level voltage of the image data input to the positive input terminal is lower than the voltage held by the capacitor 33. For this reason,
As shown in FIG. 8, the capacitor 33 holds the maximum level voltage of the image data.

That is, if the image data as shown in FIG. 8A is input, the output from the peak hold circuit 2 shows the maximum value of the past image data as shown in FIG. 8B. . The upper limit of this maximum value is, for example, 1V. When a reset signal as shown in FIG. 8C is input by the reset circuit 3, the electric charge accumulated in the capacitor 33 of the peak hold circuit 2 is discharged through the transistor 34, so that the maximum value becomes 0V. Will be reset.
Then, thereafter, similarly, the maximum value of the past image data is held.

Next, the operation of the above-mentioned device will be described. FIG. 9 is a time chart explaining the operation when a moving image signal is input. When a moving image signal as shown in FIG. 9A is input to the workstation or personal computer, it is sent to the CRT 74 and also input to the clamp circuit 1 of the screen display control device shown in FIG. The clamp circuit 1 stabilizes the pedestal level 22 of the moving image signal shown in FIG. 6 to 0V, and inputs this moving image signal to the peak hold circuit 2. The peak hold circuit 2 holds and outputs the maximum value of the image data. This output waveform is as shown in FIG. 9B and is input to the comparator 4. The comparator 4 compares the maximum value of the image data with a predetermined voltage value (for example, 0.1 V), and when it exceeds the predetermined voltage value, outputs a high level signal to the flip-flop 5 as shown in FIG. 9C. . The flip-flop 5 is shown in FIG.
It is set to "1" at the rising timing of the current vertical synchronizing signal VSYNC-P as shown in (d). This allows
As shown in FIG. 9E, the moving image selection signal MOVON-P output from the flip-flop 5 becomes high level. As a result, in FIG. 5, the crystal oscillator 8 is selected by the selection circuit 82.
The clock from 1 is selected, and the CRT controller 73
In this way, a vertical synchronizing signal of 60 Hz and a horizontal synchronizing signal of 15750 Hz are generated.

On the other hand, FIG. 10 shows the operation when no moving image signal is input. If no video signal is input to the workstation or personal computer,
As shown in 0 (a), the level of the image data in the data valid section 23 does not rise and remains almost 0V. Therefore, as shown in FIG. 10B, the peak hold circuit 2
The maximum value of the voltage held at is approximately 0V. As a result, the output of the comparator 4 becomes low level as shown in FIG. As a result, the flip-flop 5 is reset to "0" at the current rising timing of the vertical synchronizing signal of 60 Hz, and the moving image selection signal MOVON-P is returned to the low level as shown in FIG. As a result, the clock from the crystal oscillator 71 is selected by the selection circuit 82, and the CRT controller 73 generates a vertical synchronizing signal of 70 Hz and a horizontal synchronizing signal of 18375 Hz. As a result, the data from the inside of the workstation or personal computer is displayed as a still image.

When a moving image signal from the outside is input again to the workstation or personal computer, the level of the image data in the data valid section 23 rises, as shown in FIG. 9 (a). Therefore, as shown in FIG. 9B, the maximum value of the voltage held in the peak hold circuit 2 exceeds 0.1V. As a result, as shown in FIG. 9 (c), the output of the comparator 4 becomes high level, and the flip-flop 5 is set to "1" at the timing of the current vertical synchronizing signal of 70 Hz shown in FIG. 9 (d). It As a result, as shown in FIG.
The video selection signal MOVON-P is set to high level again. As a result, the clock from the crystal oscillator 81 is selected by the selection circuit 82, and the CRT controller 73 generates a vertical synchronizing signal of 60 Hz and a horizontal synchronizing signal of 15750 Hz. As a result, the moving image based on the moving image signal from the outside is displayed again on the CRT.

FIG. 11 shows the reset operation of the peak hold circuit. As shown in FIG. 11A, when the output of the peak hold circuit 2 becomes 0.1 V or higher, the output of the comparator 4 becomes high level as shown in FIG. 11B. Then, as shown in FIG. 11C, when the vertical sync signal VSYNC-P rises and the comparator output shown in FIG. 11B is at a high level, the moving image selection signal MOVON-P is at a low level. If it is, it is switched to high level.

On the other hand, as shown in FIG. 11E, the reset signal output from the reset circuit 3 is a vertical synchronizing signal.
Same as VSYNC-P. This reset signal is shown in FIG.
As shown in (d), it is output only when the moving image selection signal MOVON-P is at high level. As a result, the peak hold circuit 2 is reset every time the vertical synchronizing signal is generated while the moving image signal is being input to the workstation or the like. Therefore, the peak hold circuit 2 always holds the maximum value of the image data after the rising timing of the vertical synchronizing signal generated immediately before. As a result, if the moving image signal does not come in, the maximum value of the image data held in the peak hold circuit 2 is certainly smaller than 0.1V. This ensures that the display on the CRT is switched from the moving image display to the still image display.

As described above, the switching between the display of the moving image and the still image can be automatically performed by detecting the level of the moving image signal input from the outside by the peak hold circuit 2 and the comparator 4 without depending on the operator. it can. It should be noted that, in the above-described embodiment, the case where the moving image signal of the NTSC standard is input and the moving image is displayed has been described. It can also be applied to the case of inputting a standard moving image signal to display a moving image.

[0021]

As described above, according to the screen display control device of the present invention, the level of the moving image signal input from the outside is detected and the vertical synchronizing frequency and the horizontal synchronizing frequency are switched. Even if the operator does not manually switch between display and still image display, the display can be automatically switched. Therefore, it is possible to reduce the operational burden on the operator and prevent erroneous operations.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a screen display control device of the present invention.

FIG. 2 is an explanatory diagram of a configuration of a CRT display device.

FIG. 3 is a front view of the CRT shown in FIG.

FIG. 4 is a block diagram showing an example of a CRT display control unit.

FIG. 5 is a block diagram showing another example of a CRT display control unit.

FIG. 6 is an explanatory diagram of a moving image signal.

FIG. 7 is a circuit diagram showing an example of a peak hold circuit and the like.

FIG. 8 is a time chart explaining the operation of the peak hold circuit.

FIG. 9 is a time chart illustrating an operation when a moving image signal is input.

FIG. 10 is a time chart illustrating an operation when a moving image signal is not input.

FIG. 11 is a time chart explaining the operation of the peak hold circuit at the time of resetting.

[Explanation of symbols]

 1 Clamp circuit 2 Peak hold circuit 3 Reset circuit 4 Comparator 5 Flip-flop

Claims (1)

[Claims] 1. A peak hold circuit for holding a maximum value of a level of a moving image signal input from the outside, and whether or not the level held by the peak hold circuit is higher than a pedestal level of the moving image signal by a predetermined value or more. A screen display control device comprising: a comparator that detects an input of a moving image signal and outputs an instruction to select a moving image display.