I'm about to begin submitting to Alamy.  I have an EOS 10D, which is 6.3 megapixel and produces tiffs about 15 megabytes in size.  Alamy requires 48 megabytes.  I have found that I need to interpolate to roughly 5000 by 3300 pixels.

Will this pass QC at Alamy?  What uprezing routine do you use--bicubic, multistage bicubic, or Qimage (or something similar)?

Do interpolated photos sell well?

They sell. But I can't say I can't say whether they sell well or not. Nothing to compare with.

As for interpolation ... my camera produces images of about 17mb and I interpolate them up to just over Alamy's 48mb minimum using Phototshop 7. I'd advise you use ONLY the bicubic option (the other two are faster but give markedly inferior results) and do it in 10% steps as I believe that this gives even better results.

I've made this process into an 'action' on one of the F keys, so it's pretty much automated.

Thanks, gang.  I'll use QImage to uprez.  My informal tests show that it produces sharper results even with sharpening turned off.

I am quite confused about some agencies REQUIRING upsizing.  This seems to contradict good photo editing, since upsizing can degrade an image.

Does anyone understand the reasoning behind this?

No idea ... ours not to reason why   

I'm about to begin submitting to Alamy.  I have an EOS 10D, which is 6.3 megapixel and produces tiffs about 15 megabytes in size.  Alamy requires 48 megabytes.  I have found that I need to interpolate to roughly 5000 by 3300 pixels.

Will this pass QC at Alamy?  What uprezing routine do you use--bicubic, multistage bicubic, or Qimage (or something similar)?

Do interpolated photos sell well?

TLR Image Resizer Action for Photoshop is your friend http://www.thelightsrightstudio.com/photoshop-tools.htm and best of all, it's free. It is a Godsend....I live by it!