Digital BW, The Print

* -----Original Message-----
* From: Mark Hahn [mailto:markhahn2000@yahoo.com] 
* Sent: Monday, September 29, 2003 8:58 PM
* To: DigitalBlackandWhiteThePrint@yahoogroups.com
* Subject: Re: [Digital BW] New Photoshop CS -- aka Photoshop 8
* 
* 
* Not really... at least if you agree that the human eye can't 
* distinguish between more than 16 million colors.  The real problem 
* with 8 bits per channel is with the fixed precision math that is 
* performed for each adjustment... you get rounding errors which become 
* cumulative and destructive.  This is much reduced when calculations 
* are done in 16 bit mode.
* 
* mark
* 
* PS  I am working on an image editing package that works at a fixed 64 
* bit depth per channel and maintains butter smooth tones through out 
* any number of adjustments... but it runs way slower than PhotoShop;)
* 
Mark,

I think that 256 shades of gray are probably more than adequate for B&W
printing but as you note, adjusting an 8-bit file causes that number to
drop. Fortunately we can actually lose quite a bit and still come up with a
good print. I suspect that as few as 100 shades of gray may be acceptable in
some images but it is very easy to fall below an acceptable threshold if you
are not careful.

With the 65,536 shades of gray available in a 16-bit file the chances of
having it visually degrade during Photoshop adjustments is greatly reduced
to say the least. Although I imagine if you try hard enough you will still
get things out of whack!

At 64 bit or 18,446,744,073,709,551,616 shades of gray you are probably way
beyond what is needed. In all honesty I wonder if we couldn't do just fine
with say 12-bit or 4096 shades of gray. In any case you don't need more that
your scanner or digital camera can output and this has been in the 10 to
14-bit range.

It is interesting to note that even when you scan 10 to 14-bit data to a
16-bit file you can lose image data if you do not spread that data over the
full 16-bit range before you start applying gamma or curve adjustments. In
other words you need to set your black and white points in levels first and
seperately before any other adjustments.

Martin Wesley
http://www.carolyn.cc/Guests/MartinWesley/pages/MW_01.html
http://www.borderless-photos.de/guests.html