JPH0715619B2 - Display device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a character / character having a color lookup table.
The present invention relates to a graphic display device.

2. Related Art FIG. 4 shows an example of a conventional display device. Fourth
In the figure, 21 is a display memory that stores and repeatedly outputs an image signal, 22 is a color lookup table that converts the image signal from the display memory 21 into an actual color signal, and 24 is output from the color lookup table 22. A comparator that outputs a switching signal to the display signal switching circuit 23 when the color signal is compared with the contents stored in the color register 25 and they match, and 23 is a color look when the switching signal from the comparator 24 is not input. A display signal switching circuit that outputs a color signal from the up table 22 and uses another color signal input from the terminal 27 as a display signal when a switching signal is input. Reference numeral 26 is a control circuit for updating and controlling the contents of the display memory 21, the color lookup table 22 and the color register 25.

An image signal is stored in the display memory 21 with a relatively small number of bits per pixel (for example, 4 bits), so that 2 ⁴ = 16 colors can be designated per screen. However, the output of the display memory 21 does not indicate the color to be actually displayed, but the color to be actually displayed (for example, 4 bits for each of R, G, B is 12 bits in total) is stored in the color lookup table 22. The color signal corresponding to the output signal of the display memory 21 is supplied to the display signal switching circuit 23. Further, when the output color signal of the color lookup table 22 has a specific value, the other color signal (for example, the color signal indicating the background image) is used as the display signal instead of the color signal output from the color lookup table 22. Is performed. Therefore, the output of the color look-up table 22 is also supplied to the comparator 24 and compared with the value stored in the color register 25. If they match, a switching signal is output from the comparator 24 to the display signal switching circuit.
Is being supplied to 23. In addition, the color register 25 stores the values of the color signals corresponding to the positions where other color signals should be displayed in the control circuit 26.
It has been written by.

As shown in FIG. 4, the image signal stored in the display memory 21 is converted into a color signal to be actually displayed by the color look-up table 22 and supplied to the display signal switching circuit 23 and the comparator 24. . When the color signal from the color look-up table 22 and the content of the color register 25 do not match, the comparator 24 does not output the switching signal to the display signal switching circuit 23 and the color signal output from the color lookup table 22 becomes the display signal. When the output color signal of the color look-up table 22 and the content of the color register 25 match, a switching signal is output from the comparator 24, and another color signal supplied to the terminal 27 becomes a display signal.

Problems to be Solved by the Invention However, in the above-described conventional configuration, the comparator 24 has to compare values consisting of a large number of bits (for example, 12 bits), which causes a problem that the hardware becomes large. . In addition, in FIG. 4, the output color signal of the color lookup table 22 is configured to switch and output the other color signal corresponding to one value of the output color signal of the color lookup table 22. In order to switch and output other color signals corresponding to a plurality of values of, there is also a problem that a set of comparators and color registers corresponding to the number of the values is required.

In view of the above problems, it is an object of the present invention to provide a display device which has a simple structure and can switch and display a color signal based on a pixel signal of a display memory and another signal.

Means for Solving the Problems To achieve the above object, the present invention provides a display memory for storing an image signal, a color signal to be actually displayed corresponding to the image signal output from the display memory, and this color. A color lookup table storing a switching signal indicating which signal or another color signal should be used as a display signal, and an output color signal from the color lookup table or another color lookup table according to the switching signal output from the color lookup table. A display signal switching circuit for switching and outputting color signals,
A configuration including a switching signal indicating whether or not the color signal to be stored in the color look-up table is a color for which another color signal should be a display signal, and a control circuit for writing the color signal together with the color signal in the color look-up table Has become.

Operation According to the present invention, which has the above-described configuration, the control circuit should write the color signal corresponding to the image signal in the color lookup table, and at the same time, use the output color signal of the color lookup table or another color signal as the display signal. Is also written in the color look-up table. Then, the image signal read from the display memory is converted into a color signal to be actually displayed and a switching signal by a color lookup table, and the display signal switching circuit follows the switching signal to output a color lookup table or another color signal. Either is output as a display signal.

Examples The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a display device according to an embodiment of the present invention. In FIG. 1, 1 is a display memory for storing and outputting an image signal,
Reference numeral 2 is a color look-up table for converting an image signal output from the display memory 1 into a corresponding color signal and a switching signal. Reference numeral 3 is a color signal output from the color look-up table 2 according to the switching signal or applied to a terminal 4. A display signal switching circuit for switching and outputting any of the other color signals,
Reference numeral 5 is a control circuit for writing a color signal and a switching signal in the color lookup table 2.

FIG. 2 is a diagram showing an example of bit allocation of the color look-up table 2, and FIG. 3 is a flow chart showing an operation of a control circuit for writing a color signal and a switching signal in the color look-up table 2. .

The control circuit 5 first writes the color signal and the switching signal in the color lookup table 2. The color lookup table 2 is, for example, a memory of 16 columns × 13 bits, each column corresponds to an image signal from the display memory 1, and bit allocation in each column is as shown in FIG. Has become. As shown in FIG. 3, the control circuit 5 determines whether or not the color signal is a color for which another color signal is to be displayed (step 11), and if it is the color to be displayed, turns on the switching signal (step 11). 12) If not, the switching signal is turned off (step 13), and the color signal and the switching signal are written in the color lookup table 2 (step 14). The control circuit 5 is usually realized by program control using a microprocessor or the like, and it is extremely easy to realize the flowchart shown in FIG. The image signal output from the display memory 1 is converted into a corresponding color signal and a switching signal by the color lookup table 2, and the display signal switching circuit 3
Is supplied to. The display signal switching circuit 3 outputs another color signal as a display signal when the switching signal from the color lookup table 2 is on, and outputs the output color signal of the color lookup table 2 as a display signal when the switching signal is off.

Further, as shown in FIG. 3, the determination as to whether or not another color signal should be displayed is performed by program control, so that it can be easily realized even if there are a plurality of colors for which another color signal should be displayed.

According to the present invention, not only the color signal but also the switching signal is stored in the color look-up table. Therefore, the color signal based on the image signal stored in the display memory and another color signal can be switched and displayed. Very easy to achieve. Further, it is possible to easily realize a plurality of types of colors for displaying other color signals.

[Brief description of drawings]

FIG. 1 is a block diagram showing a display device according to an embodiment of the present invention, FIG. 2 is a table state diagram showing an example of bit allocation of a look-up table, and FIG. 3 is a control circuit in which color signals and FIG. 4 is a block diagram of a conventional display device, which is a flowchart showing an operation for writing a switching signal. 1 ... Display memory, 2 ... Look-up table, 3 ...
... Display signal switching circuit, 5 ... Control circuit.

Claims (1)

[Claims] 1. A display memory for storing and outputting an image signal, a color lookup table for storing and outputting a color signal and a switching signal corresponding to the image signal output from the display memory, and an output from the color lookup table. A display signal switching circuit for switching and outputting a color signal output from the color look-up table or another color signal based on the switching signal, and a control circuit for writing the color signal and the switching signal to the color look-up table. The control circuit turns on the switching signal when the color signal to be written in the color look-up table is a color for displaying another color, and turns off the switching signal when the color signal is not for displaying another color. A color signal and a switching signal are written in the color lookup table, and the color lookup table The image signal output from the display memory is converted into a corresponding color signal and a switching signal and supplied to the display signal switching circuit. The display signal switching circuit switches another color signal when the switching signal is on. When the signal is off, the color signal output from the color look-up table is output as a display signal, respectively.