Monday, March 19, 2007

What to Look for When Buying a Home Theater Projector

This is just a basic overview for the beginner. It is not very technical and is put in laymans terms. You can skip this post and just look at my picks instead. Here is some other good information for beginners.

  • Lumens is the measure of brightness of a projector. Most home theter projectors have around 300-350 calibrated. Manufactuer specs are notoriously high and should be iignored. Lumens determine how large your picture can be without looking dim and whether the image will be bright enough to watch with some daylight. Check out the review sites below for more detal on each projector.

  • Contrast Ratio is the difference between the lightest light and the darkest dark in an image(Also, remember, that manufactuer contrast specifications are often inflated. ). For real life purposes, it is how dark the blacks look in your image. Are they black or are they dark grey. The ligher the blacks the more the image will look washed out. The darker the blacks the more the colors and the image will "pop." Contrast is probably the most important quality of a projector. A 480p projector with a high contrast ratio will look much better than a 720p projector with a terrible contrast ratio. For example here is a image of with a low contrast ratio (lowered due to light shining on the screen).

  • Now compare it to a image with a high contrast ratio and tell me which image you would rather watch?

  • Resolution is the specification most recongizable to the average buyer. It means the number of pixels that make up an image. 480p is 848 by 480. 720p is 1280 by 720. 1080p is 1920 by 1080. For a DVD (which is 720 by 480) resolution is irrelevent if you are sitting 2x screen widths or more from the image (this is subject to how good your vision is ). If you sit closer than this distance, you will see "screen door effect." This will make the image look as if you are watching it through a screen door with tiny lines criscrossing the picture. Below is an example.

    So if you want to sit closer and not see screen door effect, get a higher resolution projector. 1.4 screen widths for 720p and 1x for 1080. Again these are averages and it will all depend on your eyesight. higher resolution for HDTV will give you much greater detail and will make a very big difference while watching HDTV. 480p projectors will still look very very good however.

  • Shadow Detail is, not surprisingly, the amout of detail you can see in dark areas of scene. The opposite if shadow detail is "black crush" in which all the shadows look like black blobs. The top image below has little shadow detail, while the bottom image has a lot of shadow detail. You can see how much of the image is simply lost when shadow detail is low

  • Color Accuracy is how accurate the colors look compared to perfectly calibrated color. If the color is not accurate, for example, yellow will have a lot of green in it, and skin tones could look too red or even green. Some projectors have accurate color out of the box and others need to calibrated with an calibration disk such as The Avia Guide to Home Theater. You can also get an ISF Calibration specialist to calibrate the color for you, but this costs hundreds of dollars. Here is an example of an image that has more green than it should ("green push") and below it a properly calibrated image:

  • Connectors are the sockets on the back of the projector to which you hook cables from your video sources. Digital connectors include DVI and HDMI (they are identical perfomance wise although HDMI can accomidate longer cables). Analog conenctors include component, s-video, and composite. S-video and composite should be avoided if possible. Usually a projector will have one of each conenctor. Use digital connectors if possible, but analog component is nearly as good.

  • Throw is the distance from the projector to the wall. A long throw projector needs a longer throw to make the same size image as a short throw projector. Whether you want one or the other depends on the size of your room. Here is an excellent calculator to determine how big a picture will be from any distance on any projector.

  • Lens shift is the ability of a projector to move the image on the wall without distorting it. This feature allows you to have much more flexibility in where you place the projector. Most LCD projectors have this function and most DLP projectors under $3000 do not as it is cheaper to implement on LCDs. Projectors can be tilted to move the image, but that results in the side of the image not being straight up and down. It can be fixed with a feature called "digital keystone", but that reduces resolution. A small amount of keystone is probably ok for the average user.

  • Zoom is self explanatory. A larger zoom enables more placement flexibility in a room. Most LCD manufacturers have put larger a larger zoom into their projectors.


krishna akella said...

thanks man, good detailing about projectors,thank u very much

David said...

Sure. I wrote this 5 years ago but the same concepts are still true.

David said...
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