JPH066707A - On-screen display device - Google Patents

Abstract

PURPOSE:To obtain an on-screen display device for generating a character pattern signal synchronizing with an inputted video signal by mutually switching a video signal and a character pattern signal whose scanning frequency is changed from that of the video signal at prescribed timing and outputting a switched signal. CONSTITUTION:A control part 3 inputs an instruction 14 from a microcomputer or the like and outputs a character signal generating control signal 16 to a character generation part 1. The generation part 1 outputs the picture element data of a character pattern by a prescribed clock signal based upon the signal 16. A frequency conversion part 2 stores the inputted picture element data, reads the stored picture element data by a prescribed clock signal synchronously with the scanning frequency of an inputted video signal based upon a frequency converting control signal 15 outputted from the control part 3 and forms a character pattern signal 17 obtained by frequency conversion such as up conversion or down conversion. A video switch part 4 properly switches a video signal 10 and the signal 71 based upon a timing control signal 12 outputted from the control part 3 and outputs an on-screen video signal 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-screen display device for frequency-converting a character signal or the like generated by a character generator according to the scanning frequency of an input video signal and superimposing it on the video signal.

[0002]

2. Description of the Related Art Video signals of personal computers and the like employ various check frequencies. For example, an MSX personal computer has a horizontal scanning frequency of 15.75 kHz, a business personal computer has a frequency of about 24 to 31.5 kHz, and a personal computer for graphic use such as CAD has a frequency of 36 kHz or more.
FIG. 3 is a block diagram showing a conventional on-screen method. Reference numeral 20 is a character generation unit such as a character generator, and 4 is a video switch unit such as an analog switch. The operation will be described. A conventional character generator 20 generates a character pattern signal in synchronization with a sync signal 11 of an input video signal 10. The video switch unit 4 receives the character pattern signal and the input video signal 10 and switches the input video signal based on the timing control signal 12 output from the character generation unit 20 so that the character pattern signal is output. The on-screen video signal 13 in the superimposed state is obtained. However, if a character generator developed according to the MSX standard is used as the character generator, on-screen display can be performed in correspondence with a video signal having a horizontal scanning frequency of 15.75 kHz. Therefore, the conventional on-screen method cannot generate a character pattern signal synchronized with the input video signal for a video signal other than the horizontal scanning frequency of 15.75 kHz, and the on-screen display can be performed. There wasn't.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is an on-screen display device for generating a character pattern signal or the like for on-screen synchronized with video signals of various scanning frequencies. The purpose is to provide.

[0004]

In order to achieve the above object, a character generator for generating a character signal composed of a pattern signal and pixel data of the pattern signal are stored based on a control signal, and the pixel data is stored. A conversion unit for converting the scanning frequency by reading in synchronization with the input video signal, and outputting a control signal for controlling the generation of the character signal to the character generation unit, and based on the synchronization signal of the input video signal, From the input video signal and the conversion unit, a control unit that outputs a control signal for a write operation and a read operation to the conversion unit and further outputs a timing control signal for switching a video signal to the switch unit. It consists of a video switch section that outputs a video signal by switching the switch for the character pattern signal with a different scanning frequency to be output.

[0005]

With the above construction, the character generator outputs a character pattern signal of a predetermined scanning frequency, and the converter inputs and stores the pixel data of the character pattern signal, and stores it in the input video signal. By synchronously outputting a character pattern signal based on a predetermined clock signal, the character pattern signal is frequency-converted into a character pattern signal having a scanning frequency synchronized with the video signal.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An on-screen display device according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of an on-screen display device according to the present invention. Reference numeral 1 is a character generator that generates a character signal or the like composed of a pattern signal. Reference numeral 2 synchronizes the character pattern signal with the video signal 10 by inputting and storing the pixel data of the character pattern signal and outputting the character pattern signal based on a predetermined clock signal in synchronization with the input video signal. The frequency conversion unit converts the character pattern signal 17 having the scanning frequency. A frequency conversion unit 3 outputs a character signal generation control signal 16 to the character generation unit 1 and controls the writing operation and the reading operation to the frequency conversion unit 2 based on the synchronizing signal 11 of the input video signal 10. Is a control unit for outputting a control signal 15 for video and a timing control signal 12 for switching a video signal to the video switch unit 4. Reference numeral 4 indicates the character pattern signal 1 by switching the input video signal 10 and the character pattern signal 17 output by the frequency conversion unit 2.
7 is a video switch unit for outputting an on-screen video signal 13 on which 7 is superimposed.

The operation will be described. FIG. 2 is a flowchart showing the operation of the on-screen display device according to the present invention. The control unit 3 gives an instruction 1 from a microcomputer that controls the system.
4 is input, and at the same time, the character generation unit 1 is instructed by the character signal generation control signal 16 such as a character type, a display position, a character size, and a character color (STP1).
The character generator 1 outputs pixel data of a character pattern based on the character signal generation control signal 16 with a predetermined clock signal (STP2). The frequency converter 2 receives and stores the pixel data (STP3), and the controller 3
Based on the frequency conversion control signal 15 output by the CPU, the pixel data to be stored is read out by a predetermined clock signal in synchronization with the scanning frequency of the input video signal, thereby performing a frequency conversion such as up-conversion or down-conversion character pattern. The signal 17 is generated (STP4). The video switch unit 4 receives the input video signal 10 and the frequency-converted character pattern signal 17, and switches the two types of inputs appropriately based on the timing control signal 12 output from the control unit 3 to generate an on-screen video signal. 13 is output (STP5).

[0008]

Since the on-screen signal can be supplied corresponding to the video source of various scanning frequencies, it can be applied to the on-screen display device such as a multimedia personal computer. Since the pixel data output from the character generator can be directly stored and frequency converted, an AD conversion circuit or the like is not necessary, and frequency conversion can be realized by a small-scale circuit as compared with the case of frequency converting an image signal. .

[Brief description of drawings]

FIG. 1 is a block diagram of an on-screen display device according to the present invention.

FIG. 2 is a flowchart showing the operation of the on-screen display device according to the present invention.

FIG. 3 is a block diagram showing a conventional on-screen method.

[Explanation of symbols]

 1 Character Generator 2 Frequency Converter 3 Controller 4 Video Switch 10 Video Signal 11 Sync Signal 12 Timing Control Signal 13 On-Screen Video Signal 14 Instruction 15 Frequency Conversion Control Signal 16 Character Signal Generation Control Signal 17 Character Pattern Signal 20 Conventional character generator

Claims (2)

[Claims] 1. A character generating means for generating a character pattern signal synchronized with a synchronizing signal of an input video signal, and inputting the input video signal and the character pattern signal,
By switching the switch at a predetermined timing,
An on-screen display device comprising: a switching unit that outputs one of the two types of signals. 2. A character generator for generating a character signal composed of a pattern signal, and storing pixel data of the pattern signal based on a control signal and reading the pixel data in synchronization with an input video signal. A conversion unit that converts the scanning frequency and a control signal that controls the generation of the character signal are output to the character generation unit, and write and read operations are performed on the conversion unit based on the synchronization signal of the input video signal. Control signal for outputting a timing control signal for switching the video signal to the video switch section, and a character pattern signal in which the input video signal and the scanning frequency output from the conversion section are changed. The on-screen display device according to claim 1, further comprising a video switch unit that switches a switch to output a video signal. .