How should I scan a very small 1939 black-and-white print to enlarge it to 5×7?
Asked 7/20/2016
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I have a sharp, glossy black-and-white photo from 1939 that is only about 1" × 1.25". I’d like to make a 5×7 enlargement. What scanning approach will give the best result from such a small print?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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Normally, the idea is that to print double size, you scan at 600 dpi and print at 300 dpi (for 2x).
Or to print triple size, you scan at 900 dpi, and print at 300 dpi (for 3x).
Anyway, that is the idea for printing enlarged copies.
However, prints really don't enlarge very well. One, prints are already enlarged, and two, print paper is simply only designed to be viewed by the eye, and they are NOT designed to be enlarged (film is designed to be enlarged). So reprinting original size is best, and good. 2x copies can be fair, and 3x is becoming objectionable, because prints really don't have the resolution to give. You can scan at 900 dpi, but the results just wont be that good (from prints). Scanning film enlarges pretty well larger, maybe 10x or 15x, but prints, not so much.
Old B&W contact prints (like yours, not enlarged) are an exception in some degree. These are sharper, and contain more fine detail. Triple size may be fair results after all.
Your 1x1.25 to 5x7 is 5.6x enlargement. That is 300x5.6 = 1680 dpi scan resolution to print 300 dpi. That is stretching it however. I wouldn't expect much result from more than 1200 dpi, if that. 1200 dpi would print 6x at 200 dpi. But it is still 6x.
I would scan it twice, at 1200 or 1600 dpi that you want, and also at 900 dpi for printing triple size that you may have to settle for, just in case.
Originally by user38978. Source · Licensed CC BY-SA 4.0
user38978
10y ago
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Because this is a print, not the original film, enlargement potential is limited. Prints have already been enlarged once and usually don’t contain enough detail for large, clean blow-ups. A 5×7 from a 1" × 1.25" print is roughly a 4–5× enlargement, so expect quality loss.
Best approach: scan at your scanner’s highest true optical (native) resolution, not an interpolated setting. As a rule of thumb, if you want to print at 300 dpi, scan at about the enlargement factor × 300 dpi. For a 4–5× enlargement, that suggests roughly 1200–1500 dpi minimum, but using the scanner’s highest true optical resolution may still help capture all available detail.
If possible, make multiple scans with the print rotated (for example 90° and 180°) and compare or combine them to reduce scanner artifacts. You may also need image editing afterward for tonal correction and cleanup.
If the original negative or film still exists, scanning that will produce far better enlargements than scanning the print.
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