The cathode ray tube when operates as a random scan display device directs the beam of an electron only to those areas of the screen where display or a picture has to be drawn.Random scan monitors are used to draw a picture in one line at a time and are thus also referred to as vector displays.Image source: Basic working of random scan display It can draw and refresh lines on the screen of a picture in any sequence not particularly specific. It is also termed as vector display, as it displays or draws a picture in the form of one line at a time. In Random Scan Display a beam of the electron is directed only to the screen areas where any picture has to be displayed or drawn on the screen. This all happens faster than any human eye can perceive. Then, the even lines are printed in between the odd lines before the odd lines fade away. First, the odd lines are printed on the graphics screen. Refreshing of raster scan displays is carried out at the rate of 60 to 80 frames per second.Ī TV video signal is graphically interlaced, which means every full screen of information is made up of two separate fields which include the odd field and even field. This is referred to as a full color or true color system. The raster graphics system of high quality contains 24 bits per pixel in the frame buffer.The amount of information each pixel represents is known as the color depth of the image.The quality of this image is determined by the number of pixels which is termed as the resolution of the image. The image formed through this raster scan is known as a raster image.The values stored in the buffer are then fetched and traced over scan lines one by one on the screen. The buffer in a raster scan is that area that is responsible for containing intensity of the various points on the screen.The picture is then stored in an area of memory which is referred to as the frame buffer or refresh buffer.This motion is referred to as Vertical retrace. As a particular frame ends, the beam of electron moves to the left top corner of the screen to move to another frame.This motion is known as Horizontal retrace. When each scan of the line is refreshed it returns to the left side of the screen. As the beam of electron moves through each row, its intensity is alternatively turned on and off which helps to create a pattern of spots that are illuminated.It moves from top to bottom considering one row at a time. In this system, a beam of an electron is moved across the screen.Image source: Basic working of Raster Scan Raster can be explained as a rectangular collection of dots or points plotted.Īn image is subdivided into various horizontal lines which are referred to as scan lines which are then further divided into different pixels which helps in the processing of an image. Submitted by Monika Sharma, on April 07, 2020 Computer Graphics | Raster Scan and Random Scan Display: In this tutorial, we are going to learn about the Raster Scan and Random Scan Display in Computer Graphics, these Scanning methods, and we will also learn each of them in detail.
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