Differentiate between Raster scan and Random scan?

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written 7.9 years ago by

teamques10 ★ 68k

Raster Scan methods have increasingly become the dominant technology since about 1975.

These methods use the TV type raster scan.

The growth in the use of such methods has been dependent on rapidly decreasing memory prices and on the availability of cheap scan generating hardware from the TV industry.

The screen is coated with discrete dots of phosphor, usually called pixels, laid out in a rectangular array.

The image is then determined by how each pixel is intensified.

The representation of the image used in servicing the refresh system is thus an area of memory holding a value for each pixel.

This memory area holding the image representation is called the frame buffer.

Random Scan Display

Random scan displays, often termed vector Vector, Stroke, and Line drawing displays, came first and are still used in some applications. Here the characters are also made of sequences of strokes (or short lines).

The electron gun of a CRT illuminates straight lines in any order.

The display processor repeatedly reads a variable 'display file' defining a sequence of X,Y coordinate pairs and brightness or color values, and converts these to voltages controlling the electron gun.

Base of difference	Raster scan system	Random scan system
Electron Beam	The electron beam is swept across the screen, one row at a time, from top to bottom.	The electron beam is directed only to the parts of screen where a picture is to be drawn.
Resolution	Its resolution is poor because raster system in contrast produces zig-zag lines that are plotted as discrete point sets.	Its resolution is good because this system produces smooth lines drawings because CRT beam directly follows the line path.
Picture Definition	Picture definition is stored as a set of intensity values for all screen points, called pixels in a refresh buffer area.	Picture definition is stored as a set of line drawing instructions in a display file.
Realistic Display	The capability of this system to store intensity values for pixel makes it well suited for the realistic display of scenes contain shadow and color pattern.	These system are designed for line-drawing and can't display realistic shaded scenes.
Draw an Image	Screen points / pixels are used to draw an image.	Mathematical functions are used to draw an image.

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