16-bit vs. 8-bit

The 16-bit Advantage

I recently got a question from a client:

I am looking into having some high-quality scans made from my transparencies, and there are some choices involved, mainly 8 bit vs.16 bit. The vendor’s web site said an 8 bit scan would look just as good to the human eye as the 16 bit scan, at much less cost. Don’t know much about this kind of thing, do you think the 16 bit scan is necessary at almost twice the price?

My answer:

With current imaging technology, the choice of 8- vs. 16-bit has to do with maintaining quality when editing/manipulating the file. If you're going straight from capture to print, without editing, 16-bit won't be a benefit.

However, when adjustments are made to any file, such as color or contrast changes, and even sharpening, 16-bit allows much greater “headroom” before the image starts to degrade from the changes. This is due to the fact that a mathematical description of color in 16-bit contains much more data than an 8-bit description (65,536 levels in 16-bit vs. 256 levels in 8-bit). Note that Photoshop's 16-bit mode is not truly 16-bit, but close enough; that's outside the scope of this article.

An example of image degradation problems would be visible bands in what should be a smooth gradient, such as a blue sky. Adjustments to a smooth blue sky in 8-bit will start to break down the image and reveal banding or posterization more than if working in 16-bit.

The only exception to this is for images that go straight from capture to print with no editing at all. An example would be someone shooting digital JPG and outputting directly to a printer, which is common for wedding and portrait photographers. (The current JPG standard does not support 16-bit color depth.)

So if you feel that some of your images won’t need much adjusting in Photoshop, or you have images where you’re not concerned with quality, it might be ok to work in 8-bit.

However, a professional workflow requires capturing the maximum amount of data possible from the beginning, and working with as much data as possible throughout the image editing workflow.