JPH032312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a monochrome CRT display device, and relates to a video signal processing circuit that inputs multi-bit video data and outputs a video signal having gradations. .

(b) Prior Art Japanese Patent Publication No. 58-1786 discloses that when displaying a color image on a monochrome display monitor, the brightness of a portion corresponding to a predetermined color is changed, and the change in color is displayed as a change in brightness. A method is disclosed. However, in this conventional example, the configuration is simply to detect a predetermined color signal and apply brightness modulation, and there are three brightness levels: white, black, and an intermediate level.
There are only levels, and therefore, color changes cannot be fully expressed.

When displaying a monochrome image, generally only one bit of video data is allocated to one pixel of the display screen, but when displaying a color image, each of R, G, and B is usually allocated. It is equipped with a graphic video RAM that stores dot patterns for each primary color, or has an attribute memory that stores color control codes, and by combining it with the output of a character generator, one pixel on the display screen can be Multiple bits of video data are assigned to.

Therefore, as shown in FIG. 1, these multi-bit parallel video data output from an information processing device 1 such as a personal computer are input to a video signal processing circuit 2 , and this video data is subjected to DA conversion by a DA converter 3 . By doing so, it is possible to obtain a video signal S having a gradation according to the video data as shown in FIG.
When input to the video output circuit 6 of the monochrome display monitor 5 , the cathode ray tube 7 can faithfully display changes in color as changes in brightness.

However, in this type of configuration, as is clear from FIG. Furthermore, since underscanning is normally performed on monochrome display monitors, there is a problem in that noise and retrace lines are displayed during the blanking period. In conventional CRT display devices where the video data is 1 bit, the video signal has only two levels, white and black, so if you adjust the bright volume 8 and raise the black level K toward white, you can eliminate noise and retrace lines. However, if the video signal has gradation, if the black level K is raised toward white as shown by K' in Figure 1, the low level video signal SK in the black direction will increase to the black level K'. As a result, these parts are displayed uniformly in black and gradation cannot be displayed. Also, even if you compromise the gradation display to some extent and set it to the lowest level at which no noise is displayed, for example, the black level K'' in Figure 1, the blanking level will fluctuate due to temperature changes, etc. However, it still had the drawback of displaying noise.

(C) Purpose of the Invention The present invention aims to make it possible to display gradations on a monochrome display monitor, and to prevent the display of noise and retrace lines during the blanking period. The purpose is to suppress noise display caused by level fluctuations due to changes, etc.

(d) Structure of the Invention The present invention provides a plurality of input terminals for inputting multi-bit video data assigned to one pixel of a display screen, and a device connected to the plurality of input terminals for DA converting the video data. A detection circuit that detects input of video data corresponding to the lowest level of the gray level of the video signal in the black direction; , the level of the video signal is adjusted according to the detection signal of the detection circuit.
This configuration includes a level setting circuit that sets the level to a level lower than the lowest level in the black direction determined by the DA converter.

(E) Embodiment FIG. 3 is a circuit diagram showing an embodiment of the present invention, in which 91 to 94 indicate intensity I, red,
This is an input terminal for inputting 4-bit parallel video data consisting of data R, G, and B corresponding to the three primary colors of green and blue.
94, and an R-2R ladder resistance network 11 in which the output terminal of each electronic switch is connected to each input terminal, and each input terminal of the resistance network 11 is , are connected to resistors 111 to 114 whose ends for supplying a reference voltage are connected to power supply potential +B, respectively, and an output terminal of the resistor network 11 is connected to a bias resistor 12. The buffer 4 is composed of an emitter follower transistor 13 whose collector is connected to the power supply potential +B and an emitter resistor 14, and the output of the DA converter 3 is connected to the transistor 13.
The output terminal 15 of the buffer circuit 4 is connected to the video output circuit 6 of a monochrome display monitor 5 , as in the conventional example shown in FIG.

Further, an OR gate 16 which inputs each output of the electronic switches 101 to 104 is a detection circuit that detects that the input video data I, R, G, B are all "0", and 17 is a DA converter 3. A diode 1 as a switching element connected in the forward direction from the output side of the OR gate 16 to the output side of the OR gate 16.
8 and a level setting resistor 19 connected in series with this diode.
The electric switches 101 to 104 have their collectors grounded, for example, as shown in FIG.
It is composed of a PNP transistor 20, and by using the base as an input terminal and the emitter as an output terminal, when the video data is "0", it is connected to the ground potential, and when it is "1", it is connected to the reference potential.
A switching operation is performed so that the signal is input to the input terminal of the resistor network 11.

Next, the operation of this embodiment will be explained.

First, 4-bit video data I, R, G, B
is input to the input terminals 91 to 94, each of the electronic switches 101 to 104 turns on or off according to the input video data, and the resistor network 11
Input the ground potential or reference potential to each input terminal. Therefore, the resistor network 11 outputs an analog video signal S of gradation levels according to the input video data, which is impedance-converted by the buffer circuit 4 and output to the output terminal 15. For example, video data (I, R, G, B) is (0,
0,0,1)→(0,0,1,0)→(0,0,
If it changes in the order of 1, 1) → ... → (1, 1, 1, 1), a step-wave video signal is output in which the gradation level increases from black to white at equal intervals. be done. In this case, the output of the OR gate 16 is always "1", the diode 18 is in a cutoff state, and the level setting circuit 17 does not work.

However, in blanking period B, the video data is all "0", so in this case, OR
The output of gate 16 becomes "0", and diode 1
8 becomes conductive, and the level setting resistor 19 is inserted between the output terminal of the resistor network 11 and ground. Therefore, a level setting resistor 19 is connected in parallel to the combined resistance of the resistor network 11, and the blanking level BL is determined by the combined resistance of the resistor network 11 and the bias resistor 12, as shown in FIG. It is set to a level lower than the lowest level ML in the black direction of the gradation determined by . Therefore, bright volume 8
If the black level is set to the lowest level ML determined by the DA converter 3 by adjusting the Noise and retrace lines no longer appear on the display. Furthermore, if the resistance value of the level setting resistor 19 is appropriately selected and the difference between the blanking level BL and the lowest level ML is set to a certain degree large, even if level fluctuations occur due to temperature changes, the noise will remain at the black level. The following will not be displayed.

FIG. 5 is a circuit diagram showing another embodiment of the present invention, in which the input of the OR gate 16 is connected to the electronic switch 10.
The only difference from the embodiment shown in FIG. 3 is that the input terminals 1 to 104 are taken from the input side and that an electronic switch 21 is used instead of the diode 18, and the operation is the same.

Further, in the embodiments shown in FIGS. 3 and 5, a voltage addition type is used as the DA converter 3 , but a current addition type may be used as shown in FIG.
That is, in the embodiment of FIG.
Resistors 111 to 114 for supplying the reference voltage are not connected to the output side of 104, and therefore, when the video data is "0", the input terminal of the resistor network 11 is Although it is connected to ground potential, when the video data is "1", the input terminal of the resistor network 11 is in an open state. Therefore, in this case, the current value changes and DA conversion is performed depending on whether the electronic switches 101 to 104 are turned on or off, and the operation remains the same.

Incidentally, if noise is generated when the blanking level is changed by the level setting circuit 17 , it is effective to insert a capacitor 22 as shown by the broken line in FIG.

By the way, in the above-mentioned embodiment, the input terminals 91 to
Since the video data applied to 94 is video data for color images, color changes can be faithfully displayed as changes in brightness on a monochrome display monitor, but the input video data is not necessarily for color images. It is not necessary, and any video data that indicates a luminance gradation level in which a plurality of bits are assigned to one pixel on the display screen may be used.

(f) Effects of the Invention The video signal processing circuit of the present invention detects that video data corresponding to the lowest level of the gradation of the video signal in the black direction is input, and converts the level of the video signal at that time into the DA. Since the level is set lower than the lowest black level determined by the converter, it is possible to ensure that all gradations are displayed on a monochrome display monitor, and to prevent the display of noise and retrace lines during the blanking period. . Furthermore, even if level fluctuations occur due to temperature changes, it is possible to prevent noise display.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of a conventional CRT display device, Fig. 2 A and B are waveform diagrams of video signals, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 is an electronic FIGS. 5 and 6 are circuit diagrams showing a specific configuration of the switch, and FIGS. 5 and 6 are circuit diagrams showing other embodiments of the present invention. Explanation of main drawing numbers, 2 ...Video signal processing circuit,
3...DA converter, 4 ...Buffer circuit, 5 ...
Monochrome display monitor, 6...Video output circuit, 8...Bright volume, 11...R
−2R ladder resistance network, 16...OR gate, 1
7... Level setting circuit, 18... Diode, 1
9...Resistance for level setting, 101 to 104, 21
...Electronic switch.

Claims (1)

[Claims] 1 A plurality of input terminals for inputting video data of a plurality of bits assigned to one pixel of a display screen, and DA converting the video data connected to the plurality of input terminals to generate a video signal having gradations. a detection circuit for detecting input of video data corresponding to the lowest level in the black direction of the gradation of the video signal; and a detection signal of the detection circuit. and a level setting circuit for setting the level of the video signal to a level lower than the lowest level in the black direction determined by the DA converter.