U of S | Mailing List Archive | alt-photo-process-l | Re: OT: 16 bit editing myth or reality?

Re: OT: 16 bit editing myth or reality?

On Dec 19, 2007, at 7:36 AM, Yves Gauvreau wrote:

What I basically say is this, if you take a normal multi megapixels image
and edit it such that it looks good in either 8 bit or 16 bit mode, a
"normal" human under "normal" viewing conditions wont be able to tell which
is which.
Not exactly. The point I was trying to make is that if you were to make a straight print without any adjustments whatsoever, you're right: no one would notice a difference. However, if any tonal adjustments are made, everything changes.

We've established that gaps in the histogram occur no matter what bit- depth you're working in. The main difference is that 16-bit has the capacity for exponentially more tonal values (256 times more than 8- bit, to be exact). This allows these gaps to very few and far between. 8-bit has much larger (and more) gaps after an adjustment. I've seen this in my own images on several occasions; believe me, this can happen during "normal" image preparation.

The image itself shouldn't have any gaps in its histogram immediately after capture. Only after making adjustments will these gaps materialize. So if you convert to 8-bit right away you're exposing yourself to the possibility of getting a poserized image. On the other hand, if you wait until just before printing to convert back to 8-bit (or even let the print driver do the conversion for you), the gaps in your histogram will be much smaller, leading to much smoother tonal transitions.

I suggest you carefully read the article I posted; it does a much better job explaining this than I can. Here's the link again:

Camden Hardy