random scan display in computer graphics | random scan display advantages and disadvantages
In this video we will learn about random scan display in computer graphics.
Basic concept:
In random scan display the electron beam is directed to the area on screen only where the picture is to be drawn.
Random scan display are also known as vector display or stroke-writing or calligraphic display.
The reason its also called vector display is because random scan display draws the picture one line at a time.
Refresh Buffer:
Refresh rate on a random-scan system depends on the number of lines to be displayed.
The picture definition is stored as a set of line drawing commands in an area of memory called the refresh display file.
The refresh display file is also called the display list or simply the refresh buffer.
To display a specified picture, the system cycles through the set of commands in the display file, drawing each component line in turn.
After all line-drawing commands have been processed, the system cycles back to the first line command in the list.
The refresh rate of random scan display is 30 to 60 frames per second(fps).
For example if we want to display and maintain a picture of a triangle ABC on the screen then the display list will have commands like this:
Draw a line from A to B
Draw a line from B to C
Draw a line from C to A.
Advantages of Random scan display
Random scan display have higher resolution compared to raster scan display as the picture is stored as line drawing instructions rather than intensity values.
It produces smooth line drawing.
It also requires less memory as we are storing information about only the picture to be drawn rather than information about full screen.
DISADVANTAGES OF RANDOM SCAN DISPLAY
We cannot draw realistic images like with different shades.
There is limitation to the colors that can be drawn for example when we draw images with beam penetration display its actually random scan display and we can draw only maximum 4 colors which are based on how deep the beam penetrates the phosphor layer.
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