Image control device for use in a video multiplexing system for superimposition of scalable video data streams upon a background video data stream

Abstract

An image control device for use in a computer system which includes a microprocessor, a bus coupled to the microprocessor, a video memory coupled to the bus and a display device. A write controller is also provided which is coupled to the bus and which controls writing of an image signal into the video memory by supplying a write address to the video memory. The write controller operates to change a range of the write address according to a plurality of write address parameters set by the microprocessor so that a memory area of the video memory into which the image signal is to be written is changed according to the range of the write address. Further, a size of an image represented by the image signal to be written into the video memory is changed. A read controller is also provided and is coupled to the bus for controlling reading of an image signal out of the video memory by supplying a read address to the video memory asynchronously with the writing into the video memory, and in synchronism with the synchronizing signal supplied to the display device along with the image signal read out of the video memory.

What is claimed is:  
     
       1. An image control device for use in a computer system having a microprocessor, a bus coupled to said microprocessor, a video memory coupled to said bus, and a display device, said image control device comprising: 
       write control means coupled to said bus for controlling the writing of an image signal into said video memory by supplying a write address to said video memory; and  
       first read control means coupled to said video memory and said display device, for controlling the reading of an image signal of a motion picture out of said video memory in synchronism with a synchronizing signal which is supplied to said display device along with said motion picture image signal; and  
       second read control means coupled to said video memory and said bus, for controlling the reading of an image signal out of said video memory while said first read control means executes the reading of said motion picture image signal.  
     
     
       2. An image control device in accordance with  claim 1 , further comprising: 
       a first output buffer, coupled to said video memory and said display device, for temporarily storing said motion picture image signal read out of said video memory before transferring said motion picture image signal to said display device; and  
       a second output buffer, coupled to said video memory and said bus, for temporarily storing said image signal read out of said video memory before transferring said image signal to said microprocessor.  
     
     
       3. A computer system comprising: 
       a microprocessor;  
       a bus coupled to said microprocessor;  
       a video memory coupled to said bus;  
       a display device;  
       write control means coupled to said bus for controlling line writing of an image signal into said memory be supplying a write address to said video memory;  
       first read control means coupled to said video memory and said display device, for controlling the reading of an image signal of a motion picture out of said video memory in synchronism with a synchronizing signal which is supplied to said display device along with said motion picture image signal; and  
       second read control means coupled to said video memory and said bus, for controlling the reading of an image signal out of said video memory while said first read control means executes the reading of said motion picture image signal.  
     
     
       4. A computer system in accordance with  claim 3 , further comprising: 
       a first output buffer, coupled to said video memory and said display device, for temporarily storing said motion picture image signal read out of said memory before transferring said motion picture image signal to said display device; and  
       a second output buffer, coupled to said video memory and said bus, for temporarily storing said image signal read out of said video memory before transferring said image signal to said microprocessor.  
     
     
       5. An image control device for use in a computer system having a video memory and a display device, the image control device comprising: 
       
         a write controller that controls writing of an image signal into the video memory through a first port of the video memory;  
       
       
         a first read controller that controls reading of a first image signal from a second port of the video memory according to a synchronizing signal so that the display device displays a first image based on the first image signal and the synchronizing signal; and  
       
       
         a second read controller that controls reading of a second image signal from a third port of the video memory while the first read controller executes the reading of the first image signal. 
       
     
     
       6. A computer system, comprising: 
       
         a video memory;  
       
       
         a display device;  
       
       
         a write controller that controls writing of an image signal into the video memory through a first port of the video memory;  
       
       
         a first read controller that controls reading of a first image signal from a second port of the video memory according to a synchronizing signal so that the display device displays a first image based on the first image signal and the synchronizing signal; and  
       
       
         a second read controller that controls reading of a second image signal from a third port of the video memory while the first read controller executes the reading of the first image signal. 
       
     
     
       7. An image processing device for use in a computer system having a display device, comprising: 
       
         a video memory;  
       
       
         a write controller that controls writing of an image signal into the video memory through a first port of the video memory;  
       
       
         a first read controller that controls reading of a first image signal from a second port of the video memory according to a synchronizing signal so that the display device displays a first image based on the first image signal and the synchronizing signal; and  
       
       
         a second read controller that controls reading of a second image signal from a third port of the video memory while the first read controller executes the reading of the first image signal. 
       
     
     
       8. A monitor, comprising: 
       
         a video memory;  
       
       
         a display device;  
       
       
         a write controller that controls writing of an image signal into the video memory through a first port of the video memory;  
       
       
         a first read controller that controls reading of a first image signal from a second port of the video memory according to a synchronizing signal so that the display device displays a first image based on the first image signal and the synchronizing signal; and  
       
       
         a second read controller that controls reading of a second image signal from a third port of the video memory while the first read controller executes the reading of the first image signal.