I'm looking for advice on what are the best techniques to use Qimage Ultimate to upsample a photo and export it as a JPEG. Recently I was asked for one of my photos to make a life-size cutout of the requestor's daughter. In my photo she is 3469 pixels tall, and I figure the print was going to run about 4'9" long / tall, so natively that's only about 61 ppi. Generally I'd assume and advise that anyone serious enough to have a 24" photo printer and roll paper should probably be left to do final file prep however is best, but based on the requests I got, the time urgency, and my sense from the discussion, the guy with the printer was just somebody with access to the printer who was printing for a friend as a last-minute thing. So I:
(1) opened the TIFF from the raw converter in Qimage Ultimate,
(2) in the HQ Sharpening field I set the radius to I think 4 and the % to I think 100, and
(3) did a Save As... and then in the Output Options box checked Resample (Fusion) box and set the length to 17100 pixels.

My most basic question is sharpening: is that radius applicable to the resampled 17100 pixel length (what I wanted) or the original 3469 pixel length (for which a radius of 4 would be really high)? Is there some way to do post-resampling sharpening, other than saving the file with resampling, then opening the resampled file and sharpen it, and save it as a third version?

Also, is there some recommended or preferred resampling procedure when the goal is to output a file?

Thanks!

P.S.
I don't have Gigapixel AI and it won't even run on my old computer. Also, Qimage's resampling is fine for my own needs and the sizes I can print. So really, my choice was between Qimage and Affinity Photo.

You're probably better off just letting Qimage do what it was designed to do by printing to file.  Switch to print to file mode and set up your paper size to what you want (around 24 x 60 inches) at 300 PPI.  Then when Qimage prints to file, it'll create a 24x60 photo at 300 PPI and it'll calculate the necessary sharpening at that level.

Regards,
Mike

When printing, Qimage will use the selected interpolation method.  I would stick with fusion as it is the best for photos.  It is the best balance between sharpness and and detail: it doesn't try to oversharpen or "create" detail which can cause weird artifacts.

Regards,
Mike