What is raster scan and random scan displays? explain in detail?
Answers
Raster Display System:
In some graphics systems a separate processor is used to interpret the commands in the display file. Such a processor is known as display processor. Display processor access the display information, processes it once during every refresh cycle.
In the raster scan display systems, the purpose of display processor is to free the CPU from the graphics routine task. Here, the display processor is provided with separate memory area. The main task of the display processor is to digitize a picture definition
Bigg BossCheck out this once.given in an application program into a set of pixel-intensity values for storage in the frame buffer. This digitization process is known as scan conversion.
Display processors are also designed to perform a number of additional operations these operations include:
· Generating various line styles( dashed, dotted or solid)
· Display color areas
· Performing certain transformations
· Manipulations on displayed objects.
Random Scan Display:
The architecture of a random scan display system with display processor. This architecture is similar to the display processor based raster system architecture except the frame buffer. In random scan display no local memory is provided for scan conversion algorithms, since that functionality is typically implemented using PLAs (Programmable Logical Arrays) or microcode.
In random scan displays, the display processor has its own instruction set and instruction address register. Hence it is also called Display Processing Unit ( DPU) or Graphics Controller. It performs instruction fetch, decode and execute cycles found in any computer. To provide a flicker free display, the display processor has to execute its program 30 to 60 times per second. The program executed by the display processor and the graphics package reside in the main memory. The main memory is shared by the general CPU and the display processor.
Explanation:
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. The word rastercomes from the Latin word rastrum (a rake), which is derived from radere (to scrape); see also rastrum, an instrument for drawing musical staff lines. The pattern left by the lines of a rake, when drawn straight, resembles the parallel lines of a raster: this line-by-line scanning is what creates a raster. .
Random scan monitors draw a picture one line at a time and for this reason are also referred to as vector displays (or stroke-writing or calligraphic displays).The component lines of a picture can be drawn and refreshed by a random-scan system in any specified order .