Digital BW, The Print

Martin,

Can't you set the black and white points in curves just as well 
(along the x axis)?  Is there a difference between using levels to do 
this and constraining the x axis in curves?  I thought a discussion 
earlier this summer established that levels tends to degrade the 
image much more than a curve adjustment.

Steve

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Martin Wesley" 
<mwesley250@e...> wrote:
> * -----Original Message-----
> * From: Mark Hahn [mailto:markhahn2000@y...] 
> * 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