Bit depth = levels of gradient?

Started 2 months ago | Discussions thread
OP filmrescue Contributing Member • Posts: 802
Re: Bit depth = levels of gradient?

J A C S wrote:

filmrescue wrote:

Another poster suggested that the reason I sometimes get banding is because of noise and not because of bit depth when capturing very low contrast B&W negatives with a DSLR. I'm not fully understanding that though. The banding goes away when I scan it with an actual film scanner at 16 bit but maybe he's right and that's not a bit depth issue.

Why don't you post some scans. Who knows what your scanner is doing under the hood. It might not use your bits efficiently or it might convert to low quality JPEGs, etc.

My own scans show enough grain to think that posterization should not be a problem but on some of them, I do see posterization. Most likely a poor conversion (Nikon Coolscan 4000ED if I remember well, 14 bit).

BTW, the tonal range calculations are valid at a reference resolution for the highest frequencies only, roughly speaking. In large low frequency areas, like sky, etc., the extra bits might help.

Thanks Jacs...I'll try to do that tomorrow when that computer is back on the network here.  I think I'm maybe worrying about it too much though because as another poster brought my attention to that with the extremely low contrast negatives that we're capturing, noise is overwhelming everything anyway when we try to bring things up to normal values and banding is only a small issue in comparison and relatively rare. It might be coming from something different than I thought it was.

We're just in the market for a new capture camera now so I was hoping to strike off the list one of the issues we sometimes see because we finally have a budget for something decent...up to 25,000 USD or so but if I can do it for a much smaller dollar amount I'll want to do that. The big dollars come with the 16 bit camera systems.
BTW...this needs to be done with a camera and not a scanner for a number of different reasons. To low contrast to marquee the frame, sometimes too dense for a scanner to see through the film and sometimes we need to capture film while it's under water...long explanation for that.

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