Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Tyler Boley" 
<tyler@t...> wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "J Michael
> Sullivan" <michael@h...> wrote:
> snip...
> 
> > Dan Margulis' seminal book "Professional Photoshop" pretty much
> debunks the need 
> > for 16-bit.
> 
> http://www.brucelindbloom.com/index.html?DanMargulis.html
> 
> I'll take Lindbloom over Margulis any day. Many have much to offer
> including Dan, this would be one area others are far ahead,
> particularly regarding concerns members of this list may have.
> Tyler

More of the same ipse dixit fallacy.

Actually, Bruce Lindbloom admits that Dan Margulis' claim is based 
on a bogus challenge. One that involves taking a 16-bit image, 
converting it to 8-bits, then back to 16-bits, then doing your edits 
and comparing with a file converted to 8-bits and then edited.

As he says, anyone who took the challenge was baited and should be 
ashamed for not seeing it from the outset.

Why was this point left out of the discussion?! It was right there 
in the linked discussion.

Why leave out other experts, who clearly disagree? Like Fraser and 
Blatner, Kieran, etc. That makes the evidence selective.

If one understands what Bruce Lindbloom is saying -- quite clearly, 
BTW -- Dan Margulis' test has the same information on both sides.

By converting from 16-bits to 8-bits and then back to 16-bits, you 
knock out off the intervening values. You will only have every 
information for every 256th possible value. 0, 256, 512 . . . 
because everything from 0 to 255 is a 0 in 8-bits. Now, going 0 and 
then 256, when mapped back to 8-bits is the same as going 0 and then 
1.

As Lindbloom acknowledges, if you do not knock off the extra 
information in this way, Dan Margulis' challenge fails. Another 
oversight that's crucial.

The fair test is to take a 16-bit image. Make a copy. Convert the 
copy to 8-bits. Now, make the same editing changes to both images. 
This retains all of the information in the 16-bit image instead of 
truncating intervening values. You will find that visible 
posterization develops faster and more severely in the 8-bit image.

My practical experience is 100% congruent with the argument that 8-
bit images are more likely to posterize as I edit them than the 12-
bit images that DSLRs capture and the 12- to 16-bit images scanners 
capture.

I and others who work in 16-bits are not talking theory. Our very 
real experience is that there is more editing headroom with 
increased bit depth.

Cheers,

Mitch