I’m a bit lacking in experience with digital image processing but would like to undertake digitizing a lot of old family photographs (i.e., negative and positive film as well as paper prints). I have done some experimenting with GIMP and have been delighted by capability to improve the image quality over what can be seen on the originals.
My scanner Epson V600 Photo is able to produce what it calls either 24bit or 48bit color (also 8bit or 16bit grayscale). I’ve pretty well decided that 24bit color (8bit grayscale) is desired for the final product. This is based on the idea that it is sufficient for the general quality of the originals combined with more universal compatibility for a wide area of potential viewing products/devices that must remain unknown to me. Is this valid thinking?
GIMP now is capable of editing the 48bit color (16bit grayscale) images and I could easily create those with my scanner. I’m imagining that the added color depth could be beneficial during editing even if the final work product is converted back to 8bit. However, my imagination is lacking good depth of knowledge on this subject. What’s the best choice for scanning?
I’d scan in 48/16 bit and process them as such in GIMP – maybe even in 32 bit float precision. That way intermediate editing operations are less risky wrt. generating banding in the image. Especially with greyscale, 8 bit are not that much. It’s basically just 256 colors in the whole image.
I would even go a step further and save the result as a high bit depth and only export a copy as 8 bit. That way you still have the big files should you ever need them. Of course that would require more disk space.
I always try and capture as much data from the source as possible, whether it is shooting or scanning. I’d scan at 16 bits or more! You never know what you’ll need in the future, and this way you won’t have to scan again.
@houz’s advice is probably the best process. While you may not see a need for anything greater than 8-bit for final output, you’re right in thinking that intermediate operations done to the image will best be done with higher bit-depths.
This will give you the most leeway for pushing or pulling the tones around to suit your vision. Save any 8-bit result for a final export to, as you’ve already said, cover the widest devices for viewing it.
It’s no trouble, and is rather why we’re here in the first place!
[edit] - in fact, @houz had previously produced a nice graphic to illustrate what’s going on:
Only with subtle gradients like with the sky; helps prevent banding. Otherwise, 8-bit’s good enough for me and even sky banding can be eliminated with some cleanup work.
A nice/helpful diagram. Something I notice is the remark about color management in GIMP. I haven’t been aware of any notion of turning it on or off. How so?
I like the idea of this diagram. I’m definitely in favor of anything that shortens the learning curve for color management.
@houz, what was the original format in which you created this diagram? I’m finding the text in the .png tough to read at any magnification I’ve tried. Would you be willing to post the original?
When I scan negatives, I try to capture as much information as possible that goes into the editing process. Don’t forget that you can throw it away later, once your final result is there. Or you can keep it (for certain photos) to edit them later.
I described the essence of my process here:
So I would definitely recommend a high bit depth. I’m also considering to increase the resolution. Currently I use 3200 dpi (for medium format, 6x7) and it might be interesting to play with higher resolutions in order to do some oversampling and to finally achieve a better quality in a down-scaled export.
It might be obvious for most people on this forum but for the sake of completion color depth is often described as a total of all 3 channels. So 24-bit is actually 8-bit per channel and 48-bit means 16-bit.
Use GIMP 2.9.x and above for a GIMP that handles high bit depth and does color management. Hint: even if you import a low bit depth and color-profile-less image, you can set a higher bit depth and set a color profile in GIMP 2.9.x. Go to Image → Color Management → …
