Try reading this: The Art Of The Up-Res
(sorry the figures are a bit bad because of the way the magazine converted my supplied CMYK files :~(
Bottom line, you can easily do a 200% upsample with most digital captures. It takes some special techniques to optimize the images. If the starting image is technically excellent (exposure, focus, sharpness, etc.) you may be able to go up 400%. Just remember that as you upsample the image, you upsample any defects as well. You should do retouching AFTER
you upsample, not before. I also suggest starting the upsampling in Camera Raw with proper capture sharpening and do any additional upsampling in Photoshop after the ACR upsampling. Some cameras don't offer any additional upsampling in the Workflow Options setting in ACR. In that case stick to Photoshop.
Jeff, I found your article very informative, but I have always uprezz'd to 300 ppi for my ipf5000 using the "bicubic smoother" option as the final step in PS after cropping, if needed, to output size, followed by output sharpening.
Unless I'm missing something, ACR 6.3 has no choice of bicubic algorithms in Workflow Options, so I assume it uses standard "bicubic" mode. Also, ACR's crop tool has no linear or aspect ratio settings I can find which makes it essentially useless to me, and if I crop later, having resampled first in ACR, have to resample again in PS for printing. So set me straight here, por favor!
Also, what's your current take on incremental sharpening? Your (rather dated!) article addressed the point, but I got the impression subsequently that the development of the "bicubic smoother" upsampling algorithm eclipsed that. What's your current opinion here?
Thanks for sharing your wisdom,