Frame Buffer And Video Controller
This article show the complete knowledge about frame buffer and video controller both are used in computer graphics video controller and display devices.
A fixed area of the system memory is reserved for the frame buffer, and the video controller is given direct access to the frame-buffer memory. Frarne-buffer locations, and the corresponding screen positions, are referenced in Cartesian coordinates.
A 1024×1024 elements requires 2^20 squre raster or 1048 ,576 memory bits in a single bit plane.
VIDEO DISPLAY DEVICES
The primary output device in a graphics system is a video monitor The operation of most video monitors is based on the standard cathode-ray tube (CRT) basic operation of,a CRT. A beam of electrons (cathode rays), emitted by an electron gun, passes through focusing and deflection systems that direct the beam toward specified positions on the phosphomted screen. The phosphor then emits a small spot of light at each position contacted by the electron beam. Because the light emitted by the phosphor fades very rapidly, some method is needed for maintaining the screen picture.
The primary output device in a graphics system is a monitor.
There are some examples of display devices
- Cathode-Ray Tube(CRT)
- Color CRT Monitor
- Liquid crystal display(LCD)
- Light Emitting Diode(LED)
- Direct View Storage Tubes(DVST)
- Plasma Display
- 3D Display
Raster scan display is the most common type of display used in CTR television and monitor in a raster scan display the electron beam is swept across the screen one row at a time from top to bottom as the beam is swept across the road the beam intensity is return on and off to create a pattern of illuminated spots
Picture definition is stored in a memory area called the refresh buffer or frame buffer
The refresh buffer holds the set of intensity values for all the screen points is Tod intensity values are are then try and from the refresh buffer and pointed on the screen one row at a time
Fig. Raster scan system display object as a set of discrete points across each lineRefreshing has two types
- horizontal Ratracing
- vertical Ratracing
When operated as a random-scan display unit, a CRT has the electron beam directed only to the parts of the screen where a picture is to be drawn. Randomscan monitors draw a picture one line at a time and for this reason are also referred to as vector displays The component lines of a picture can be drawn and refreshed by a random-scan system
A pen plotter operates in a similar way and is an example of a random-scan, hard-copy device.
Video Controller & Display Processor
A special-purpose processor , called the video controller or display controller, is used to control the operation of the display device. the frame buffer can be anywhere in the system memory, and the video controller accesses the frame buffer to refresh the screen.
A number of other operations can be performed by the video controller, besides the basic refreshing operations. For various applications, the video controller can retrieve pixel intensities from different memory areas on different refresh cycles
Fig. Basic video controller refresh operations