I have a miniDV to DVD project that is going to be projected with 4:3 LCD-projectors

It's been shot on XL1 in 16:9 (no, we're not going to discuss about the quality of this mode this time ;).

I have four options to do the letterboxing:

1) Before mpeg-encoding in premiere e.g. with Canopus PiP-plugin
2) during the encoding process in tmpgenc
3) let the DVD player do it
4) flatten the picture in the projector

Which one of these would give the best picture quality? Or is there a significant difference at all?

4.

that will yield the best results, no loss of resolution.

If the image size adjustment works digitally, it has to lose resolution, right?

It's hard to believe that the projectors would resize the picture optically.

Hopefully I'm wrong.

If you know your output to be 4:3 you will get the best quality
in 1 & 2 or 4. The last one (4) is only true if it is a optical effect
with the lens, otherwise the preference goes to 1 & 2 because
there you will have the full source image to work with and the
best routines to process them (instead of having to do it real-
time (speed over quality).

I know TMPGEnc resize is pretty good. Can't talk about Canopus
one.

However if you ALSO want to use it on anamorphic TV's or
projectos then the only thing to do is let your DVD player do
the downscaling, so that your anamorphic viewings will use
anamorphic.

I have responed to your other thread (http://www.dvinfo.net/conf/showthread.php?s=&threadid=7360)