(Repost I made to similar question at Projector Central)
First thing you need to know is that there are two sides to resolution.
The first side is how much resolution is being broadcast or made available to you. It could be anything really. 1024x768, 720x640, 1280x1024, 1920x1080, 1280x720, 800x600, etc., etc., etc. It sounds crazy, but it really doesn't matter that much. All that you need to know is that there is a lot of 'mumbo-jumbo' ways for video to get to your display device.
FOUR formats are the most popular:
480i, 480p, 720p, and 1080i
480i is (more or less) 720x480 lines of data shown 30 complete frames a second. It actually is made up of 60 half frames a second and the 'i' on the end means interlaced. (Google it for great info) This is regular television which we've had for years. It is also what comes out of a DVD player normally.
480p is (more or less) 720x480 lines of data shown 60 complete frames a second. The 'p' on the end means progressive. (Google again) This often comes out of sub $100.00 DVD players and provides a better image than 480i does. Very common with DVD, but not much else uses it.
720p is 1280x720 pixels. Abut a million individual elements shown 60 times a second. Just like above except about twice the resolution. It is one of two standards for broadcast HDTV right now.
1080i is 1920x1080 pixels. About two million individual elements shown 30 times a second. The other HDTV broadcast standard.
~~~~~~~~~~~~~~~~~~~~~~PART 2~~~~~~~~~~~~~~~~~~~~
Now, you know these standards - how do these apply to your display?
Well, modern displays have a specific resolution. A certain number of pixels. Common sizes are 853x480, 1024x768, 1280x720, 1365x768, and 1920x1080.
Your display has that many pixels the day you buy it and when you throw it away, 250 years from now, it will STILL have that many pixels. It won't have more, it won't have less. So, the resolution of the display you purchase has an effect on the quality of the image you will be able to project.
It does NOT limit your ability to project those images!
It affects the QUALITY of those images.
So, if we take the 4805, which is a 853x480 pixel projector. It has about half a million pixels available to it to display 480i and 480p which both have 480 lines. It does a great job with that. But, when you feed it HDTV, it has to throw away pixels. 1280x720 (720p) does not equal 853x480. So, for the 4805 to show a 720p image, it must effectively remove half a million pixels. Or, half the image!
This sounds crazy, but it does a remarkably good job at it. Due to this removal of pixels though, it requires you to back up a bit more from the screen to have a similar viewing effect as if you were looking at a higher resolution display.
If we take another projector, like the Sanyo Z3, we are given 1280x720 pixels to work with on that projector. It takes 480i, and 480p and must ADD data to get it to fill the 1280x720 pixels available to it. It may not always do a great job with this conversion, but it does the job alright. Where it really shines is when given a 720p signal, it can reproduce that pretty much identically and it looks awesome. Once again, when give more pixels, like a 1080i signal (1920x1080) it must throw out half the pixels to get it to fit on the 1280x720 matrix available.
There are really no new home theater projectors that won't accept standard video broadcasts. There are some computer resolutions that home theater projectors can't handle if you hook your desktop PC up to it. But, they can usually handle the 'standard' computer resolutions. Most notably: 1024x768 which is a good standard to begin with if you do this.
Once you know that there are two halves to projecting an image, it can help you realize that you want a higher resolution projector if you plan to watch a lot of higher resolution material. The lower resolution projectors are great, but may limit the length of time you will keep the projector, especially as you upgrade to higher resolution sources over time. Those will include HD discs, and more and more HD broadcasts.... oh, and HD gaming. The future is HD, and 1280x720 projectors will be about the minimum.
