Best for detailed images, photographs, and complex graphics.
Best for precise lines and curves; less suited for complex images.
Memory Usage
High; requires substantial memory for pixel data.
Low; uses less memory as only drawing commands are stored.
Performance
Can be demanding on hardware for high resolutions and detailed images.
Efficient for line drawing but less effective for detailed textures.
Advantages
High detail and color range; versatile for various content types.
Line accuracy; lower memory requirements.
Disadvantages
Requires large frame buffers; performance can be impacted by high resolution.
Limited detail and color range; issues with image persistence and flicker.
Raster-scan Displays
The electron beam is swept across the screen one row at a time from top to bottom.
As it moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots.
This scanning process is called refreshing. Each complete scanning of a screen is normally called a frame.
The refreshing rate, called the frame rate, is normally 60 to 80 frames per second, or described as 60 Hz to 80 Hz.
Picture definition is stored in a memory area called the frame buffer.
This frame buffer stores the intensity values for all the screen points. Each screen point is called a pixel (picture element).
Property of raster scan is Aspect ratio, which defined as number of pixel columns divided by number of scan lines that can be displayed by the system.
Case 1: In case of black and white systems
On black and white systems, the frame buffer storing the values of the pixels is called a bitmap.
Each entry in the bitmap is a 1-bit data which determine the on (1) and off (0) of the intensity of the pixel.
Case 2: In case of color systems
On color systems, the frame buffer storing the values of the pixels is called a pixmap (Though now a days many graphics libraries name it as bitmap too).
Each entry in the pixmap occupies a number of bits to represent the color of the pixel. For a true color display, the number of bits for each entry is 24 (8 bits per red/green/blue channel, each channel 28=256 levels of intensity value, ie. 256 voltage settings for each of the red/green/blue electron guns).
Random-Scan Displays
When operated as a random-scan display unit, a CRT has the electron beam directed only to those parts of the screen where a picture is to be displayed.
Pictures are generated as line drawings, with the electron beam tracing out the component lines one after the other.
For this reason, random-scan monitors are also referred to as vector displays (or stroke writing displays or calligraphic displays).
The component lines of a picture can be drawn and refreshed by a random-scan system in any specified order A pen plotter operates in a similar way and is an example of a random-scan, hard-copy device.
Refresh rate on a random-scan system depends on the number of lines to be displayed on that system.
Picture definition is now stored as a set of line-drawing commands in an area of memory referred to as the display list, refresh display file, vector file, or display program
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.
Random-scan displays are designed to draw all the component lines of a picture 30 to 60 times each second, with up to 100,000 “short” lines in the display list.
When a small set of lines is to be displayed, each refresh cycle is delayed avoiding very high refresh rates, which could burn out the phosphor.
