Bit depth = levels of gradient?

Started 2 months ago | Discussions thread
knickerhawk Veteran Member • Posts: 6,262
I think you're getting misleading/unhelpful advice here

filmrescue wrote:

I've been searching around to find some sort of chart or list that tells me how many levels of gradient there is for different single channel bit depths but I'm not having a lot of luck. Can anyone fill me in or link me to the info I'm looking for. I'd like to see from 2 all the way up to 20 or so.

Your problem isn't about too much noise in the deep shadows limiting the dynamic range of the image. Indeed, more noise would actually reduce the appearance of posterization/banding that you're seeing. And since you're scanning negatives and presumably inverting them to positives, most of the image noise should be present in the highlights, not the shadows, of the output image. The dithering effect of the noise should actually mask posterization, not make it worse.  Noise is NOT the enemy here!

What's really happening is that the low contrast scans you're performing require significant tonal adjustments in your photo editor. Since you need to invert, pretty much any subsequent contrast adjustment is going to induce posterization in your (positive) highlights ESPECIALLY if there wasn't much noise to dither away the tonal transitional borders. If, in addition, those edits are done in 8-bit mode (even if the image has not been saved to JPEG),  you're absolutely guaranteed to get posterization in the lighter tones due to quantization errors introduced by the editor during the tonal adjustment. The better strategy here rather than going out and buying a new camera might be to scan/shoot the negatives twice - once exposing for the highlights and once exposing for the shadows - and then layering/merging in post.

Good luck.

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