Make a 100" Screen for under $100

Evan Powell, May 26, 2006

Color Accuracy

Color accuracy is one of the hardest aspects of screen performance to get right. Even professionally made screens can introduce subtle color shifts in the reflected image. So we were not surprised to find that our DIY screen was lacking in color neutrality. In normal daylight it looks pure white, of course. But we discovered that the particular brand of seamless paper that we used is comparatively inefficient at reflecting blue light, so the result is an image that manifests a subtle yellowish bias. On the other hand, the Grayhawk is essentially neutral, and reflects more accurately what is coming from the projector.

Since the purpose of this exercise is to see how good we can make our quick n' easy DIY screen look, we boosted the blue gain and bias on the projector to compensate for the screen's inaccuracy. The result was that color balance was normalized on our DIY screen. Meanwhile, the Grayhawk accurately reflected the excess blue that the projector was actually delivering. You can see this color shift in the following test shot, with our DIY screen on the left and the Grayhawk on the right. Notice the stone building has a slightly colder tone on the right:

The next image below shows the same effect of the DIY screen's color bias on flesh tones and water. The Stewart Grayhawk is still on the right, and it is showing us what the projector is delivering--an excessively blue image. However, since our cheapo DIY screen can't reflect blue as efficiently as it can yellow, it compensates for the excess blue coming from the projector, and the image comes out looking properly balanced:

Note of Caution: There are numerous brands of 53" seamless roll paper on the market, and they come in many different colors. Some brands offer two or more varieties of "white". You can expect each of these products to have some sort of color error, but it may or may not be the same bias toward yellow that we see in this particular brand. Some might exaggerate blue or green, or even possibly red. We used the RPS Super-White Background Paper (#SB-1251) for this test. However, we don't know for sure how consistent even the RPS Super-White is from one batch to the next. But the good news is that on most home theater projectors, you can adjust the relative strength of the color components in the signal to compensate for whatever bias your screen may have.

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