Photoshop CS2 - Blowing scans up with as little loss of quality as possible

Question

What's the best way to make a file that you can blow up into a big poster, say 10 by 20 feet, for example, without the image being too blurry?
I plan to scan in some drawings I did on 8.5x11", colour them in Photoshop CS2, and then make a file so that you can print it out as a big poster, like the 10 by 20 feet example above. I would like the printout to be sharp (as little loss of quality as possible).
What's the best way to do this?
Which dpi should I scan the pictures in, so I can blow them up big?
Which file type should I save the working file, and the file I'm going to print them out?
Please advise. Thank you.

Answer 1

What are your specifics (how high is the resolution of the scans, how many pixels do you have in the image you want to print)?
There are some tools out there for doing just that kind of thing, but you have to realize that there are limits - no software yet can invent detail where none exists.
Starting with very CLEAN image information, a product called Perfect Resize (which used to be called Genuine Fractals) is pretty good at this, as it finds "edges" in the image and tries to preserve them.  I have a beautiful 24 x 30 inch print I made from an old Canon D30 capture (just 3 megapixels) upsampled with Perfect Resize and it stands up even to close inspection.
But the good news is that people don't usually scrutinize giant prints from too closely.  A rule of thumb is that viewing distance will typically be no closer than about the long dimension of the image (e.g., 20 feet in your case).
OnOne Software has a trial version of Perfect Resize available (chances are you'll only need the standard edition).  Alternatively, if you'd like to post a small part of an image you're considering blowing up, I'll be happy to run it through Perfect Resize and post the result so you can see.  Here's a small example using one of my own images:
Original:
Upsampled 400% in each dimension (this forum software may mess up the display but you should be able to copy and paste it into Photoshop or a viewer app):
-Noel