My goodness, you're fast.  Thank you.  I'll have to go back over this to see which things are left for me to do once I'm done with class for today!  I see from the timing script that (after N=50, or 150 InterpolatedImage initializations), we're down to an average of 0.25s, 0.5s, 0.25s, and 0.04s for the cases of padding from a CF, image, image specified with filename, and no padding at all.  And I had found that these silly noise images take longer to turn into an InterpolatedImage than some realistic galaxies, so the situation should be better with something realistic.