what bit depth to use?

DS
Posted By
Doug Smith
Dec 3, 2006
Views
329
Replies
1
Status
Closed
Hi,
I am scanning photos using a Nikon Coolscan IV which can scan in 8-bit or 12-bit.
It has been suggested to me to scan in 12-bit, do some overall colour corrections such as fixing exposure, highlights and shadows, then resample the photo down to 8-bit.
However, I also have a lot of color runs from bad film processing and I’m using the heal and patch tool extensively. Should I do these corrections in 12-bit or 8-bit. I’m using PS 7.

thanks

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B
bmoag
Dec 3, 2006
Although this will likely change in CS3 most Photoshop filters, plug-ins and many other processes only work at 8 bit depth. To my recollection PS7 has little or no functionality at greater than 8 bit color depths. You can scan at higher than 8 bit color depths but I am of the opinion that this adds almost nothing, and can be deleterious, for most users. If a print is your final aim many forget that prints live in a less than 8 bit world that may or may not conform to the printer manufacturer’s specified gamut and that paper surfaces and ambient light also affect this process. The printed image cannot reproduce the inbetween tones that greater than 8 bit color depths yield. The software for the printing process will arbitrarily convert your greater than 8 bit image algorithmically to what the printer can handle. Otherwise you have to convert to 8 bit color prior to printing and finish processing the image in 8 bit color if you want predictable printing results.
This is never likely to change because of the physical properties of the media involved. Including eyeballs.
So if you scan at 12 bits and then convert to 8 bits for processing do you necessarily have a better image then if you scanned in 8 bits to begin with? Ideally yes, but the ideal and the real are not the same. Anyway, are you scanning for you and your family or for posterity? I do not believe that there is anything practical to be gained for most people using greater than 8 bit color depths other than some smoother looking histograms, longer processing times, limited processing options and tremendously greater storage requirements (most of which will be recording digital zeros).
Its your call.

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