I have been given an impossible task:
Take a picture image (jpg) at 1422 x 1067 px with 100 dpi and scale it to 86400 x 29376 px (that's equivalent to 34ft x 100ft or 30.5 meters x 10.36 meters)
Unfortunately there are times when a boss requests the impossible from their employee. This is one of those times.
More specifically it was requested that "there be no pixelation (at a viewing distance of 2 feet (0.6 meters)."
The easy (and right) answer is: It can't be done.
But that doesn't mean you can't make the best of an awful situation. So what I'm looking for are techniques, or software solutions that specialize in this sort of huge scaling.
I have heard of something in the past that blows up and image using circles. Granted, it doesn't look great from close up but from a greater viewing distance it looks more held together (like pointillism).
I don't think there is a clear answer, which is why I was hesitant asking here. So I was wondering if this could be transformed into a wiki, because I'm sure I'm not the first or last to be looking up information regarding this sort of scaling.
I would take a different approach to this, because the task is like wishing for the moon. There's no unicorn filter in Photoshop yet. (And I'm surprised nobody has so far pointed out that Photoshop's pixel limit for a PSD is 30,000 in either dimension, so 86,400 would only be achievable by slicing the image into separate files and enlarging those.)
The problem here is human, more than technical. Your boss has a particular display problem in mind. He/she thinks that the solution is an impossibly small initial image scaled to an insanely number of pixels. We know that's going to look awful, and you don't want your company or your boss to look bad because that won't help anybody.
My response, when I get something like this from a client, is to talk over the actual situation, find out what problem they are trying to solve and then come up with a solution that will work. Make no mistake, you can only do this with a live conversation. Memos, texts, emails are not likely to work. This also requires, on your part, complete sincerity, tact, creative thinking and persistence, in about that order of importance. Sometimes you have to work through some huffing and puffing from the other party, who doesn't want to look foolish or ignorant. (That's where tact and your own sincerity of purpose to find the best possible solution will help enormously. When the other party realizes they're not being made wrong, they don't have to insist on being right.)
Do what Marc suggests and run some tests with a portion of the image so you have something to "show and tell." But don't use this as a club to beat the boss into submission. You have to be on his side.
Keep asking questions until you completely understand the challenge your boss is up against, then come up with the right solution. If you make it seem like his/her idea, so much the better.
As you probably know, the viewing distance of two feet is ludicrous. If people were going to view whatever this is from two feet, it wouldn't need to be 34 feet tall. When people get up close to something that big, they're used to seeing image issues.
From a reasonable distance (20 plus feet?), Scott has the right idea. Depending on the photo, the Illustrator solution is quite elegant. The file size will be manageable and, with a little work, the result can be surprisingly photographic. If you haven't used it much before, spend some time playing with the live trace settings — they can interact in surprising ways.
If you have to suffer through the PS solution (that file is going to kill you!), do yourself a favor and use an action. I've found the best results with increments of no more than 20% (whether reduction or enlargement). For more modest scaling I have actions set up to go either up or down in increments of 5%, 5 times, with the fifth time doing an unsharp mask. The smaller your scaling increments, the better PS is at guessing the new pixels. Since you're going so far up, you could set you action to do 5 or 10% maybe 15 times and then manually do the unsharp so you can more finely control it.
I used to know of a stand alone app that did this sort of thing a decade or so ago (fractal something or other). As I understand it, Adobe bought that technology or something similar and rolled it into Photoshop. If anyone can confirm I'd be interested to know. It certainly does a better job these days than it used to.