Mike Russell wrote:
[snip
Bart, is this in linear gamma space? It sounds as if you speak from experience, and have an example of an image that shows posterization, or sharpening artifacts, that are present after an 8 bit correction, but absent in a similar 16 bit correction. If this is the case (and you are not working in linear gamma space), I am still questing for such an example image.
I have recently been doing some testing to see how safely I can work in 8-bit rather than 16-bit after a raw conversion. In summary, if I am careful with the settings, (in ACR 3.x), I can normally JUST get away with 8-bit. But only just.
Normally, I can get a good histogram and no posterisation in Photoshop. I rarely have to do significant global corrections in Photoshop if I take enough care in ACR. (If I did, I might query my ACR settings, and try again). If I do LOCAL changes, however, they are likely to be more dramatic than would a global one, and looking at the local histogram where I’ve done such edits I sometimes see the histogram breaking up into spikes. On recent pictures, I haven’t actually seen bad results from this when printed at A3, but if I did much more with those local areas in Photoshop, (or perhaps if they were larger areas), I think I would. (I really need 9-bits for comfort!)
Although I have previously been working at 16-bits, I am trying to work at 8-bits instead. (For a few reasons, such as size, speed, filters, etc). I think if I got posterisation in local areas, as a result of local edits, I might go back to ACR and do another raw conversion suitable for that local area so that I could get a good 8-bit result in Photoshop, then combine the two conversions.
This is still a bit tentative. I intend to run at 8-bit for a while, and keep monitoring things closely just in case.
—
Barry Pearson
http://www.barry.pearson.name/photography/ http://www.birdsandanimals.info/