I have a very simple task that I can't find a good solution for. I need to print a 4x6 photo image at exactly 3.5" x 5.5" with a 1/4" symmetrical border, with no cropping of the image whatsoever. From hours of experimenting I don't think this is possible with my printer (Canon MX850, essentially a PIXMA), Windows 7 picture viewer, or with my only image editing software (Paint Shop Pro X4).
You can't reduce a 4x6" image to 3.5x5.5" and keep the same aspect ratio without cropping. You'll need to either crop the image, compress the image in one direction, skip the borders entirely, or live with uneven borders. For example, you could reduce to 3.5x5.25", giving you 1/4" borders along the long sides and 3/8" borders on the short sides. Or, you could print at 3.5x5.25" with 1/4" borders all around, ending up with a 4x5.75" print.
Right, math says that that's not possible, because 6 ÷ 4 is 1.5, while 5.5 ÷ 3.5 is ~1.5714 — that is, they have a different aspect ratio. (That's the proportion between an images' height and width.)
You are going to have to crop, stretch (probably not a reasonable possibility without looking funny), or accept a non-symmetrical border.
This isn't the fault of your software or printer — it's harsh reality. In order to keep the same proportions, your border width will have to be proportional to the original aspect ratio. That is, if you add a 0.25" border to the long side, you'll have to use 1.5× that on the short side — 0.375". That will result in a 5.25" × 3.5" image, and 5.25 ÷ 3.5 is 1.5 — just like 6/4.
Or you could go the other way, with 0.25" on the short edge and a reduced 0.167" border on the long edge, for 5.5" × 3.67" — also the same proportion.
If the balanced border is more important than the size and you can't crop the image, consider cropping the print instead — a rotary paper trimmer is a great thing to have for all manner of reasons, and this might be a good one.