Best way for quality enlargement from a scan?

[dkf10425]

What is the best way to enlarge a scanned photo? I want the best possible quality. Should I scan at a high resolution then with resample image unchecked lower it until I get to the correct print size? Or should I scan at the resolution I am going to print then use Fractals?

Edit: I forgot to add that I am asking this in the context of a photo that will be scanned, restored, then enlarged.

[mistermonday]

Your starting point should be to decide what the largest size print you will make (lets say it will be 8 x 12"). Your goal would be to scan the image at a resolution that will give you 8" x 300 PPI = 2400 pixels BY 12" x 300 PPI = 3600 Pixels. Now here is where the size of the image you are scanning comes in to the calculation. If you are scanning a 4 x 6" photo, in order to generate 2400 pixels on the 4 " side, you will need to scan at 600 ppi. This will also give you 6 x 600 ppi = 3600 pixels.
Similarly, if you are scanning a 35mm slide or negative (these are only 1 x 1.5"), you will need to scan at 2400 ppi.
If you have an odd size photo and the math doesn't work out to a normal scanner setting, always go up to the next higher resolution because you can always throw away pixels.
Now what if your scanner is not able to achieve the resolution you need for the quality and size final print you want. Well, then you need to size up the image. However, note that when you upsize an image you are manufacturing pixels through interpolation - its never as good as having the right amount to begin with.
Regards, Murray

[dkf10425]

Thanks! That's what I thought, I just wanted to be sure.

[OlProfBear]

It was suggested, somewhere on the Web (possibly even here) that it might be best to enlarge pictures in steps of about 10% at a time. I've never verified it for sure. My procedure has always been to prefer powers of 2 if at all possible, but that could be a fallacy of mine ...

Might be worth a try to see if doing it in small increments produces a more pleasing result than a one-time upsize.

[Dave.Cox]

I would not attempt to enlarge in multiple steps, as that increases the number of errors that are introduced. If you must enlarge, I usually prefer the Bicubic smoother setting, and enlarge in one step. Sometimes you can reduce some distortions by reducing in multple steps, but I find that their are other better ways to do that as well. If you can scan at the correct resolution to match your print, then that is the best way. The instructions that mistermonday posted above are right on.

[saby]

it depends on whata scanner U use, ccd scanner: set the maximum dpi what the scanner optically senses at 100% of the image, photomultiplier (drum) scanner: set the printing percentage size of the original at maximum dpi, if I've to enlarge it, I use the photoshop image size to set it 110% recorded into an action, and play it several times, it's ok for me to enlarge image by 80%, for any further enlargement I use the photozoompro at B-spline and Lanczos functions