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Posted: May 28, 2000
Written by: Tuan "Solace" Nguyen
Each individual pixel on the screen is made up of 3 dots -- red, green and blue (RGB). By controlling the intensity on each specific beam, it is possible to create the entire spectrum of colors. If one pixel needs to be purple, the guns will intensify the blue and red phosphor dots. The beam intensity can be changed to adjust tone of color, contrast and brightness.
But what if the light from one pixel leaks onto another pixel or the beam crosses pixel? Then you get a nasty blurry image with color tears. How do manufacturers prevent this? They use masking technology.
Invar Shadow Mask
Masking technology is used to prevent the a pixel's glow from leaking over to another pixel -- producing off-color images and blurriness. The most common type of mask is the Invar shadow mask. The Invar part is a type of metal alloy that has a virtually zero expansion factor when heated -- you don't want your holes getting larger and smaller. And besides, frequent expansion and contraction over time causes cracks.
The shadow mask is basically a thin layer of metal alloy with thousands upon thousands of perforated holes. These holes align with the pixels on the phosphorous screen. The mask assures that the electron beam strikes its intended pixel and no other at the same time.
There are drawbacks to using shadow mask technology. Over time, the mask will curve because of the constant heating and cooling from the electron beam. Because of this, images will eventually become blurry at the corners. This is why a nickel/iron mixture called Invar is used. Another drawback of shadow masks are that they are curved at the corners to compensate for the beam sweep or a warped image will appear. This is why "perfect flats" are never based on shadow masks.