Sharpening for print output and resizing
I have taken some photos for family and they would like to print the photos for a frame. I am trying to work out what would be the best size that they could get different sizes of to get 6x4, 7x5, 8x6 etc. Not sure if I would need to do three sizes for each photo or I can do one at the biggest size. They will more than likely be printed at a photo place such as Boots.
Also, when sharpening for print, what do people use? Unsharp mask or something like the output display sharpener by NIK set to paper output? And if I sharpen at the biggest size will the image still look ok at 6x4 or "oversharpened"?
Many thanks, getting a bit confused!
I'm just an amateur and I print at home on an A4 inkjet printer. Unfortunately, I think for optimum quality you probably need to process the image with the particular printing process in mind. I'm not sure, but Boots may use real photographic paper which will have somewhat different characteristics to an inkjet printer.
Having said that I can tell you what I usually do, but you need to work out what suits you and your printing - it may not necessarily be exactly the same.
I generally resize images so that they can be printed at 300ppi to give the exact size I want. After resizing, I sharpen with Unsharp Mask at something like radius 0.3, amount 1.0 (or 100%), threshold 0. However, the amount needs to be selected for the image. For portraits I may use less than 1.0 (or even no sharpening if that is more flattering), while for some subjects I may increase it to 2.0 or more. If you print at a smaller size (e.g. at 600ppi, giving half the size), the image will not appear oversharpened, in fact it will appear slightly under sharpened in my experience.
In conclusion, I'd suggest you do a bit of trial and error. It is worth wasting a few prints to get it right. So, print the same image with no sharpening, some sharpening and thirdly, with more sharpening, and see what looks best. The important thing is to keep a detailed record of what you have done and the sharpening parameters used. You'll soon get an idea of what level of sharpening you like best.
Just another point, I find that images sharpened to my taste for printing look oversharpened when viewed on screen at 100%. I usually view them at 50% to get a better idea of whether the sharpening is about right (but that may also depend on the software used for viewing the images - which has its own effects on the sharpness).