Liquid Crystal Display projectors are convenient, compact devices that transform the image on your computer screen or digital television into a large-scale image that a roomful of people can see. They're well suited to presenting digital data, because LCDs are built in pixels, the same way your computer or television screen is built. However, the projector's colors can drift off over time, distorting the look of your screen.
Pixels
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Your computer screen — and your television — is organized in pixels, tiny picture elements that can each display a range of color. The color of each pixel is created by adding together a red, green and blue signal to artificially create some other color. Your computer sends a digital signal to the red, green and blue, or RGB, parts of every pixel. These digital signals get converted to voltages that control the amount of red, green and blue light emitted from each pixel. The pattern of light from each pixel creates an image on the display.
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LCD Projectors
LCDs also consist of pixels laid out in a rectangular pattern. However, there's one big difference between your display screen's pixels and the LCD pixels: where each pixel of the display has red, green and blue sections, each pixel of the LCD only works for one color. Therefore, an LCD projector has three different LCDs within it: one designed just for red, one for green and one for blue.
Mechanism
The LCD projector has a very bright white light inside that goes through an arrangement of beamsplitters that separate the white into red, green and blue parts. Each separate color then goes to the LCD designed for that color, where it reflects or transmits through and gets put back together again with the other colors. Each LCD has the right color pattern to make the projected image look like a larger version of your computer or television screen.
Distorted Colors
Each of the RGB pixels on a display screen emits a specific set of light wavelengths; the red, green and blue each correspond to separate regions of the light spectrum. The colors in the LCD projector look good when they perfectly match the RGB of the pixels on your display. LCD projector designers try to make the beamsplitters — also called dichroics or dichroic mirrors — split the light into exactly the same set of red, green and blue wavelengths as the pixels on your computer screen. The problem is that age, heat, exposure to chemicals or other problems can mess up the beamsplitters, so the colors don't match your computer screen's colors, resulting in distorted colors.
Solution
Before you try to fix the problems yourself, be aware that opening up your LCD projector and messing with the guts will almost certainly void your warranty. If you're still up for trying, then open up the case of the projector to see two or three beamsplitters, which look like mirrors except that you can see a tinted image through them. Each manufacturer has its own way of holding the dichroics, so you may have to look up how to detach and take them out in a user's guide or the manufacturer's website. Slip in replacement dichroics and line them up so they send light to the right LCDs.
Warning
If your projector shows good colors in some areas of the image, and poor colors in other areas, there's probably a problem with one or more of the LCDs themselves. In these cases it's far more cost effective just to buy a new projector. Even if you can figure out which LCD is the problem and replace it, you'd have to line it up just perfectly with the other LCDs. That's not an easy job, especially without the right equipment, so it's probably not worth the trouble. There are some other problems that can cause variation in color quality across the image, but they're also pretty complicated to solve without specialized equipment.