 Objective Objective  Basic Techniques Basic Techniques - Beam Penetration methodBeam Penetration method - The Shadow - Mask method.The Shadow - Mask method.  Beam Penetration : How it Works ? Beam Penetration : How it Works ?  Shadow Mask: How it Works ? Shadow Mask: How it Works ?

 This was one the earlier CRTs to produce color displays. Coating phosphors of different compounds can produce different colored pictures. But the basic problem of graphics is not to produce a picture of a predetermined color, but to produce color pictures, with the color characteristics chosen at run time. Back

 There are two popular techniques for producing color displays with a CRT are: 1. Beam-penetration method 2. Shadow-mask method Back

phosphor  Two layers of phosphor (red and green) are coated onto the inside of the CRT screen.  The display color depends on haw far the electron beam penetrates into the phosphor layers.

 The speed of the electrons, and the screen color at any point, is controlled by the beam acceleration voltage.

The beam penetration method:  Used with random scan monitors  Only four colors are possible (red, green, orange, and yellow).  Quality of pictures is not as good as with other methods. Back

The color CRT has: phosphor  Three color phosphor dots (red, green and blue) at each point on the screen electron guns  Three electron guns, each controlling the display of red, green and blue light.

 We obtain color variations by varying the intensity levels of the three electron beam. Shadow mask methods are:  Used in raster scan system (including color TV) RGB  Designed as RGB monitors.

 High quality raster graphics system have 24 bits per pixel in the frame buffer (a full color system or a true color system). BACK