Raster scans have a constant refresh rate while random scans do not. Random scan images are stored as vectors. ![]() Summary: A raster scan draws on the entire screen while a random scan does not. ![]() During Vertical and Horizontal retrace the electron beam is OFF and while scanning the scan line it is ON. Raster scanning is also the only technology that applies to newer display technologies like LCD and LED. For this separate display processor memory area is also provided. We continue this behavior until we reach the last scan line of our screen, the moment we reach the right end of last scan line we try to move back to the first scan line of the screen which is termed as Vertical retrace(dotted line). Raster Scan display Processor Sometimes also referred as graphics controller or a display coprocessor and its purpose is to free the CPU from the graphics operations. So moving from right to left to reach the scan line is called as horizontal retrace(Dashed Line). A raster scan display is a type of display technology used in computer monitors and televisions to create images and graphics. Now the electron ray/beam is kept ON while moving from left to right on scan line, but once it reaches to the right end of a scan line the electro beam is turned OFF until it reaches the left end of next scan line(This behavior is shown with dashed line in between scan lines). While scanning the scan line we refer to the frame buffer and accordingly we assign color to the screen pixels. The raster scan monitors make use of the whole screen for displaying the object while in random screen monitors the certain part of the screen is used where the electron beam is projected. Frame buffer is a special memory where we store the pixel intensity values(intensity values for all screen pixels). Our Electron beam starts from left top corner(1st scan line) and continues scanning the pixels on that scan line. At the end of each scan line, the electron beam returns to the left side of the screen to begin displaying the next scan line. Refreshing on raster-scan displays is carried out at the rate of 60 to 80 frames per second, although some systems are designed for higher refresh rates. Solid horizontal line in the diagram are called scan line. television monitor, it can be treated as if it were a random-scan display including its random-scan type light pen functions, which makes it possible to. The phosphor under each pixel within the screen is activated by electrons transmitted from the electronic gun, which rise rapidly to the maximum luminance and. pixel positions depends on the capability of the raster sys-tem. Let’s understand its working with the help of above mentioned diagram. A vector monitor, vector display, or calligraphic display is a display device used for computer graphics up through the 1970s. In Raster Scan Display we just don’t focus on a particular portion of screen where a line or character would be displayed instead here we scan the entire screen. In raster scan display at the end of one frame the electron beam returns to the left top corner of the screen to start the next frame is called vertical.
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