Displaying or capturing a video image line by line. Computer monitors and TVs use this method whereby electrons are beamed (scanned) onto the phosphor coating on the screen a line at a time from left to right starting at the top-left corner.
in random scan display the electron beam directly draws the points/lines.the crt tube directly illuminates the points/lines and the image is displayed
Application of Raster scan display: Basically it is used in Plotters. and mainly more like....Printers,,,,
raster scan display -based on television technology.where as random scan display based on hard copy devices.raster scan display cannot directly pass electron beam through the scan line..but random scan directed the beam toward the scan line.
Raster-scan Display Processor :- One way to set up the orangyation of a raster system containing a separate display processor,sometimes referred to as a graphics controller or a display coprocessor.the purpose of the displays processor is to free the CPU from the graphics chores. In addition to the system memory, a separate display-processor memory area can also be provided.A major task of the display processor is digitizing a picture definition given in an application program into a set of pixel-intensity values for storage in the frame buffer. This digitization process is called scan conversion.Display processors are also designed to perform a number of additional operations. These functions include generating various line styles, displaying color areas, and performing certain transformations and manipulations on displayed objects. Also, display processors are typically designed to interface with interactive input devices, such as a mouse.
Raster-scan system:-1)raster displays have less resolutio. 2)the lines producced are ziz-zag as the plotted values are discrete.3)high degree realism is achived in picture with the aid of advanced shading and hidden surface technique.4)decreasing memory costs have made raster systems popular.Random scan system:-1)random displays have high resolutions since the picture definition is stored as a set of line drawing commands and not as a set of intensity values. 2)smooth lines are produced as the electron beam directly follows the line path.3)realism is difficult to achieve.4)random-scan system's are generally costlier.
Raster scan, or raster scanning: is the pattern of image detection and reconstruction in television, and is the pattern of image storage and transmission used in most computer image systems. The word raster comes from the Latin word for a rake, as the pattern left by a rake resembles the parallel lines of a scanning raster. Picture element: In a raster scan, an image is cut up into successive samples called pixels, or picture elements, along scan lines. Each scan line can be transmitted as it is read from the detector, as in television systems, or can be stored as a row of pixel values in an array in a computer system. On a television receiver or computer monitor, the scan line is turned back to a line across an image, in the same order. After each scan line, the position of the scan line is advanced, typically downward across the image in a process known as vertical scanning, and a next scan line is detected, transmitted, stored, retrieved, or displayed. This ordering of pixels by rows is known as raster order, or raster scan order.
Raster scan, or raster scanning: is the pattern of image detection and reconstruction in television, and is the pattern of image storage and transmission used in most computer image systems. The word raster comes from the Latin word for a rake, as the pattern left by a rake resembles the parallel lines of a scanning raster. Picture element:In a raster scan, an image is cut up into successive samples called pixels, or picture elements, along scan lines. Each scan line can be transmitted as it is read from the detector, as in television systems, or can be stored as a row of pixel values in an array in a computer system. On a television receiver or computer monitor, the scan line is turned back to a line across an image, in the same order. After each scan line, the position of the scan line is advanced, typically downward across the image in a process known as vertical scanning, and a next scan line is detected, transmitted, stored, retrieved, or displayed. This ordering of pixels by rows is known as raster order, or raster scan order.
The Raster scan system is a scanning technique in which the electrons sweep from top to bottom and from left to right. The intensity is turned on or off to light and unlight the pixel. The beam is swept back and forth from the left to the right across the screen. When the beam is moved from the left to the right, it is ON. The beam is OFF, when it is moved from the right to the left. When the beam reaches the bottom of the screen, it is made OFF and rapidly retraced back to the top left to start again. A display produced in this way is called raster scan display.
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In Raster scan display electron beam swept across the screen one row at a time from top to bottom.when reaches the bottom scan starts again from top.It produce a zig zag lines.
Display File is a memory area which stores picture definition as a set of line drawing commands.Video controller interprets these commands and produces actual image on the screen.Display File in random scan system is comparable to frame buffer in raster scan system, on the basis of their functions.
Raster-scan system:-1)raster displays have less resolution.2)the lines produced are ziz-zag as the plotted values are discrete.3)high degree realism is achived in picture with the aid of advanced shading and hidden surface technique.4)decreasing memory costs have made raster systems popular.5)In this case, the electron beam is swept across the screen, one row at a time from top to bottom.6)Picture definition is stored in a memory area called the refresh buffer/frame buffer.7)Refreshing on raster scan displays is carried out at the rate of 60 to 80 frames/second. Random scan system:-1)random displays have high resolutions since the picture definition is stored as a set of line drawing commands and not as a set of intensity values.2)smooth lines are produced as the electron beam directly follows the line path.3)realism is difficult to achieve.4)random-scan system's are generally costlier.5)Here CRT has the electron beam directly only to the parts of the screen where a picture is to be drawn.6)Picture definition is stored as a set of line drawing commands in an area of memory referred to as refresh display file.7)Random scan systems are designed to draw all the component lines of a picture 30 to 60 times each second.
Raster-scan:-q1) Raster displays have less resolution.q2) The lines producced are ziz-zag as the plotted values are discrete.q3) High degree realism is achived in picture with the aid of advanced shading and hidden surface technique.q4) Decreasing memory costs have made raster systems popular.Random scan:-q1) Random displays have high resolutions since the picture definition is stored as a set of line drawing commands and not as a set of intensity values.q2) Smooth lines are produced as the electron beam directly follows the line path.q3) Realism is difficult to achieve.q4) Random-scan system's are generally costlier.