On Thu, 20 May 2004 12:52:56 -0500 David Riecks wrote: >This reduction in posterization is a result of the "dithering" that is >introduced when you move from 16-bit to 8-bit in Photoshop. > >I posted a set of instructions yesterday, that you can use to test and see the >results. Most likely you could have done your manipulations, seen the >posterization, converted to 16-bit, then done a second conversion back to >8 bit >and the posterization would have disappeared. This doesn't prove that >taking an >8-bit image into 16-bit makes for better image manipulation, it simply means >that the dithering introduced is helping to smooth out the tonal transitions.
I don't find this works David. I opened a new RGB 8 bit document & filled it diagonally with a black to white grad. Then 1) I did a very steep S shaped curve increasing midtone contrast across the centre of the image. Saved & closed. 2) I converted the same original file to 16 bit, did the same curve, back to 8 bit, saved & closed. There is mild but clear banding in the mid grey transitions both on screen & print on the file from 1) but not on 2). So then I took the file that had remained in 8 bit throughout, opened it, converted to 16 bit, converted to 8 bit, saved. I couldn't see any change. Did it again adding 1 pixel to the size, still couldn't see any difference, the banding appeared unchanged by any dithering. I still believe in the virtues of 16 bit for major tweaking! David Hoffman -- __________________________________________________________ David Hoffman Photo Library <http://www.hoffmanphotos.com> phone +44 (0)20 8981 5041 fax +44 (0)20 8980 2041 =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
