How does a random scan display draw a picture?

By moving the beam directly from endpoint to endpoint along the lines only

By sweeping every scan line from top to bottom

By lighting each pixel stored in a frame buffer

By refreshing a fixed 60 Hz grid regardless of lines

What does a raster scan system store to hold the picture?

A frame buffer holding the intensity of every pixel

A display list of line-drawing commands

Only the endpoints of the lines

Equations of the geometric objects

Which statement about random scan is correct?

It needs little memory and gives smooth, high-resolution lines

It needs a large frame buffer and shows jaggies

It is cheap and ideal for shaded photo-like images

Its refresh time is independent of picture complexity

Why can a random scan display flicker?

The whole display list is redrawn 30-60 times/s, so a complex picture takes too long to redraw

The beam sweeps too fast over every pixel

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Random scan versus raster scan display

Short answer

Random scan draws pictures by moving the electron beam directly along line endpoints from a display list, giving high resolution but poor shading. Raster scan sweeps the beam row by row, setting each pixel from a frame buffer, enabling realistic images at a fixed resolution with jaggies.

Differentiate between random scan (vector) and raster scan display technologies.

A random scan (vector) display draws a picture as a set of straight line segments, moving the electron beam directly from one endpoint to the next. A raster scan display sweeps the beam over the whole screen row by row and turns each pixel on or off according to values stored in a frame buffer.

Point	Random scan (vector)	Raster scan
Drawing method	Beam moves only along the lines of the picture	Beam sweeps every scan line, left to right, top to bottom
Picture storage	Display list (line-drawing commands)	Frame buffer (intensity of every pixel)
Memory needed	Small, depends on number of lines	Large, depends on resolution and bits per pixel
Resolution	Very high, smooth lines	Limited by number of pixels; lines show staircase (jaggies)
Refresh	Redrawn 30 to 60 times/s from display list; flicker if picture is complex	Fixed rate (e.g. 60 Hz) independent of picture complexity
Filled areas and colours	Poor at shading, solid areas and many colours	Good at filled regions, shading, photo-like images
Cost	Costly	Cheap, mass produced (TV technology)
Animation / editing	Easy to modify lines in display list	Needs the frame buffer updated
Examples	Pen plotters, early CAD displays	Monitors, TVs, LCD/LED screens

Random scan:  A ------> B
                        |
              D <------ C      (beam jumps along lines)

Raster scan:  ->->->->->->->|   (beam sweeps each row,
              ->->->->->->->|    horizontal retrace
              ->->->->->->->|    between rows)

Raster scan has replaced random scan in almost all present systems because it displays realistic, shaded and coloured scenes cheaply.

✓ Answer checked by Claude Opus 5.5 (high effort)

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