Saving 16bpc to JPG - first convert to 8bpc?

Forum|Forum|9 years ago
January 27, 2017
2 replies
3506 views

I'm sorry if this is well known but I've only just noticed that if I save a flattened 16bpc image directly to JPG then no dithering is applied to the 8 bit conversion, even though I have the 'Use Dither' option checked in Color Settings. Is there another setting somewhere to enable dithering on saving a 16bpc image at 8bpc? Otherwise, the solution looks like converting to 8bpc mode prior to saving the JPG....i.e. an extra operation in the workflow.

Normally I want to enable dithering when converting down to 8bpc, so as to retain a bit of extra shadow detail and reduce perceived banding. It might explain some of the effects I've noticed that, up until now, I'd blamed on JPG artefacts.

dither

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Randy Hufford

Community Expert

Yes you have to change file to 8bit before saving as jpeg

Trevor.Dennis

Community Expert

Randy, they made saving directly JPG from higher bit depths a JDI feature with CS5 (I think). Are you saying that using that feature does not work as well as doing it step by step?

richardj21724418Author

Known Participant

Yes, it looks like saving directly to JPG from 16-bit was a JDI feature with CS5, but I can't see mention that it included dither.

It's easy enough to test. Simply draw a gentle grey scale grad in 16-bit mode and save to JPG.

Now change to 8-bit mode (with dither enabled in color settings) and save that to JPG. The difference between the two JPGs should be pretty obvious.

D Fosse

Community Expert

Jpeg compression in itself creates color banding in soft gradients. That's most likely where the banding comes from - unless you can demonstrate that converting to 8 bit prior to saving as jpeg eliminates it.

richardj21724418Author

Known Participant

Yes, when I pixel peep I can clearly see that banding is eliminated (or at least it's dither distributed by the lower order bits) if I drop down to 8-bit before saving as JPG. It's how I spotted this effect in the first place. If I drop to 8-bit mode with dither disabled the screen looks remarkably like the JPG image saved from 16-bit mode!

It's not something I was aware of before. I'd naively assume Photoshop would dither down to 8-bits when saving to JPG. Still learning something new every day.

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