Scanning digital prints at 24bit or 48bit?

Question

I have thousands of digital prints I plan on scanning, restoring in Lightroom, and then cataloging. I have an Epson V600 scanner and plenty of raw computing power.

I plan on scanning at 600dpi to tiff but trying to decide between 24bit or 48bit. On one hand 48bit is of course better and allows for theoretical better editing when I'm restoring any at the cost of significant more storage use. I'm fine scanning at 48bit as long as it will actually allow for improved quality/editing. If they were negatives I'd choose 48bit in a heartbeat since the benefit (even small) would be clear. But in my case, almost all of these scans will be roughly 4x6 most of which were printed in the 70s, 80s, and 90s (some are older prints).

The prints such as the ones from the 90s at least were taken I imagine mostly on throw away cameras and printed at drug stores, so my thinking is if I scan at 48bit is it attempting to scan more detail than actually exists? If so, would I be able to scan at 24bit without any loss of quality when scanning those types of digital prints?

Update - Incase it's relevant, wanted to note most of these photos are being borrowed from family members so I only have one time to scan them and attempting to future proof the files incase future generations want to print or use on higher quality screens. The higher bit in this case would make sense if there is even a chance that it results in a higher quality file for either editing, viewing or printing. But I want to make sure I'm not scanning data that doesn't exist. For instance if scanning these in 16/48 would be the same as if I scanned in 8/24 and later simply converted to the higher bit then it wouldn't make sense to scan higher now since in would just be extra fake data the computer is generating. But if scanning at the higher is able to capture more data even for these drug store 4x6 digital prints then will do so. To note they are roughly 73MB each. If I convert to a zip tiff then 64mb if zip tiff with the lower bit then its only 21MB. I use SSD drives storage on my Mac (and traditional drives for backup and online backup). So would ideally like the drastically smaller file size but not at the cost of losing actual data in the images if that makes sense?

Answer 1

My notions are that scanning as 48 bits won't hurt the result, but it will waste time and effort and storage space. Arguably might help slides, but it won't help prints. Print paper does not have it to give.

A printed magazine image has a dynamic range well less than 2.0, maybe about half of that (1.7). The blackest ink still reflects some light, the white paper is not all that bright, and the difference is relatively small. Photographic color prints have a dynamic range of maybe 1.8, certainly not exceeding 2.0, for same reason, even if a bit brighter paper. Film negatives might have a range up near 2.8 (but we don't view negatives). Slides can be greater, extremes perhaps up towards 3.5, so dynamic range becomes important, but not likely even near 4.0. These are not precise numbers.

Scanners and cameras do have typically at least 12 bits today (36 bits), because the extreme shift of adding gamma needs it. And this does help when scanning slides. But prints really don't need 16 bit output. Yes, 16 bits might help preserve radical correction shifts, maybe possible in slides, but not likely in prints (prints have already been corrected once, they don't need that much work).

We don't have opportunity to see 16 bits, our monitors and printers are 8 bits. All JPG files are 8 bits too (meaning 24 bit color).

If you might print double size copies, the 600 dpi might help (some, but the color prints really don't have that much detail to give either). Even copies of color prints scanned at 600 dpi and printed double size at 300 dpi will be visibily degraded some (but 600 dpi is a good try for double size). Grayscale might have slightly more detail than color (especially old contact prints). If printing original size copies, 300 dpi is plenty. No way to use more if printing original size. If not printing copies, video monitors are not large enough to even need 300 dpi (but an archive surely should be 300 dpi, for unknown future printing). If making Ken Burns style movies, then 300 dpi could allow zooming on small areas.

You say you have thousands of prints to scan, which is a big job, suggesting that before starting, the work deserves your spending a bit of time experimenting briefly with the various methods considered, at least scanning a few prints the different ways, to see if the methods actually do help your results. This testing should include actually printing a few of the scanned copies, to examine that result too, it's an important part of the process. You should believe those results that you can see yourself, meaning you ought to be able to actually detect and see that which you claim helps.