A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems.
Several processing units: Contains a special purpose processor, called video controller or display controller.
Video controller: A fixed area of the system memory is reserved for the frame buffer, and the video controller is given access to the framebuffer memory.
- Tow registers are used to store the coordinates of the screen pixels.
- The value is stored in the frame buffer for this pixel position is then retrieved and used to set the intensity of the CRT beam Initially the x register is set to 0 and the y register is set to ymax.
- Then the x register is incremented by 1, and the process repeated for the next pixel on the top scan line.
Computer Graphics is the manipulation of the image in a pictorial manner. The rendering can be done in this manipulation and creation of the new image and hence computer graphics is used. Even a raster scan is an important aspect when it comes to computer graphics.
Raster Scan Displays are the most common type of graphics monitor which employs CRT. It is based on television technology.
- In the Raster scan system, the electron beam is used as a fixed path on the screen. The electron bean starts from the top left corner of the screen and follows the horizontal path until it reaches the end of the line. This defines a scan line. During the scan, the intensity of the beam is modulated according to the pattern of the desired image along the line.
- After reaching the right corner of the screen, the beam is switched off and it is moved back to the left edge/point of the new row as the new starting point. This defines horizontal retrace.
- Picture definition is positioned in a memory area which is technically known as Frame Buffer. This memory area holds up the set of intense values for all the screen points. Stored intensity values are then retrieved from the frame buffer and used to display images on the screen.
- Now the scanning is continued until it reaches the bottom right corner of the screen. After it reaches the bottom right corner of the screen it defines one scan is completed. Each screen point is known as a pixel.
- After one scan is completed the electron beam is re-positioned at the top left corner of the screen for the next scan. The repositioning process of the electron beam bottom right corner to top left corner is referred to as vertical retrace.
The diagram is represented as follows:
- Cost for raster scan devices is cheaper/low.
- Doesn’t require an intelligent electron beam.
- Used for animation purposes.
- Low resolution.
- Requires more memory.
- Electron beam coordinated to the whole screen not exclusively to those parts of the screen where the picture is to be drawn.