Video Display Devices - Movingtrend
Cathode Ray Tube (CRT)
CRT is a common video display device.
it emits a beam of electrons, which passes through focusing and deflection systems, and hits on the screen which is phosphor-coated.
number of pixels display on a CRT screen is called resolution.
It is a common methodology for color CRT display. Different small colored-light spots emit by different phosphors. These spots when combines form a range of colors.
Drawback of shadow-mask Methodology
Lights emitted by the phosphor fades rapidly, so there is need to redraw the picture repeatedly.
There are two types of redrawing techniques.
electron beam moves across each row, and the intensity of the beam is turned on and off, this created pattern of illuminated spot which is called refreshing. Refreshing is also called a scanning process.
Scanning of a full screen is called frame.
refreshing rate called the frame rate, which is 60 to 80 frames per second or described as 60 HZ to 80 HZ.
each screen point is called a pixel. It is called a picture element.
it is the area of a memory which used to store the definition of a picture. That area called a frame buffer.
Black and white system
On black and white system
the frame buffer storing the value of pixel is called a bitmap. On and off determine the intensity of the data.
Pixmap is storing the value of the pixels. Each entry in the pixmap occupies a number of bits to represent color.
True color display:
3 bytes which is equal to 24 bits, 8 bits for each color red, green, blue. 2^8 = 256
That value shows the intensity of the colors.
Random-Scan (vector display)
Electron beam directed to the parts of the screen where the picture is to be drawn. Picture definition is stored in in a refresh buffer in memory. Random has higher resolution than the raster scan, and it cannot display the realistic shaded scenes.