I don't use any primitive... i just use the pix_draw to show the image on screen (i saw this in the first patch of the "04.pix" files).
try and use a [pix_texture] + geo combination. in addition to the resizing you will also get a nice increase in performance.
on a somewhat related note: i have made, but not committed, a [projector] geo that takes pixel sizes as arguments [projector 640 480]. it might help some people out to use an object that works with pixel dimensions rather than the somewhat unknown GL dimensions (meters? furlongs? acres?). it also has an 'auto' mode to fill the gemwin with the image, which has been a much requested feature. the object needs a bit more testing and tweaking before it gets added to the CVS.
cgc