In looking at ads for several different front projectors, I've noticed several specifications for resolution. Native, maximum, and compatible.... Can anyone shed some light (!) on the differences? Can you notice a difference between using the native and a compatible (HD 720p or 1080i)?

How do they show a 16:9 picture if the "native" resolution is not in that ratio? Bands top and bottom?

Thanks in advance for your comments.

Martin, lets use a projector that has a 720p "native resolution". What that means is that it has 720 pixels(picture elements)counting vertically. To be able to show a complete picture all 720 have to be used. If the source material is 720 then of course there's no problem. If the source material is 480(standard DVDs and standard definition TV)the projector has to mathematically calculate and interpolate extra pixels to fill all the 720. This doesn't increase the resolution to what a "real" 720 input would offer, it just makes the picture complete. So the 720 projector would be "compatible" with a 480 input. It would also be compatible with a 1080 input(the "maximum resolution")and it would in that case have to scale the 1080 pixels down to fit the 720 screen, so it wouldn't have the full resolution possible with the 1080 input.

So, that projector would be "compatible" with 480 and 1080 inputs(in addition to 720, of course)and would be able to process a "maximum resolution" of 1080.

This "scaling" (basically a digital zoom in or out) is where chips from companies like Faroujda or Genesis (now Silicon <something>) come in. The quality of the digital scaler varies quite a bit from one projector to the next...

... and THAT is where the complicated "where should I scale up to native resolution -- in the player, the receiver, or the projector" comes in when you go to plan and set up the system.

DVDs are 480... 480i, I guess. A progressive player can convert that to 480p, and an upscaling player can convert that to 720p or 1080i.

Some receivers can upscale as well. Most can't.

Nearly all projectors can upscale.

When you watch a DVD, you "know" what the resolution is going to be coming out the DVD, and you "know" that the projector is only going to display at its native resolution. Scaling is going to happen if they are different -- the challenge is to figure out where to scale.

Having the projector do all the work is often the easiest since you can feed different resolution signals in from different sources (VCR, regular TV, HDTV, DVD) and let the projector figure out what to scale up and down. Some projectors (the Sony PL51, for example) are reputed to do a crappy job of scaling analog inputs up, although they scale digital inputs (HDMI) just fine.

The fun never stops

Lots of great advice here.

In short, most projectors will always output at their native resolution, regardless of whether you feed it less or more. It will just scale/convert it to native.

I have a projector that is 720p native, but like others mentioned, can handle 1080i. I asked a similar question a while back about which would be better, 720p or 1080i (that was back before I had the projector, so I couldn't test it). Anyway, from a standard DVD, I have let both the DVD player and the projector both "upconvert" from the 480i to 720p and 1080i. All in all, I find that the 1080i is no better looking than 720p. It was also explained to me that 1080i is sending the same amount of information as 720p, and from a standard 480i DVD source, I can say that this statement seems to be true in real life tests as well.

HD-DVD or Blu-Ray may be better at 1080i over 720p, but if the projector can only output 720p, I would think that this would be ideal to set up at.

SO I would stick with the native resolution. Even 720p is a lot better than 480i. Plus, most things that can send a 720p signal natively themselves (not a DVD player upconverting) is hi-def, so there is a lot less compression, less artifacts, and obviously higher detail, so there is even more than just more lines of resolution at play here.

Have fun!