Digital BW, The Print

With all due respect, you are wrong here.  A two point linear curve 
is exactly the same as a Levels adjust with no gamma slider tweak.  
Someone speculated that PS uses a different curve subroutine for 
Levels than Curves, which doesn't make sense, but is of course 
possible, but that would be the only reason one would be more 
destructive than the other.  That a Curve adjust is preferable does 
have merit, especially since you can usually apply just one 
adjustment curve instead of two (after Levels a curve adjust is 
usually required).  The reason to use Levels is generally to expand 
your data to fill the entire tonal range, not to clip your data, and 
it is easier to do this in levels since you see the entire tonal 
range in the histogram and can easily set your black and white points 
accordingly.

Just out of curiousity, how do you think Levels works in PS?  
Mathematically you shift your data to allign your black point and 
then scale the data so your white point comes out right (or visa-
vera).  The simplest way to do this is with a linear curve adjust.  

A four point "s-curve" will not be the same as a Levels end point 
adjust, but a linear Curve adjust with appropriate  endpoints will be 
identical. 

mark


--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Jon Zax 
<lotus@i...> wrote:
> While it's possible to get very similar results from using the 
curves 
> dialogue and the levels dialogue, they are not the same and do not 
> function the same.
> 
> When you pull in the white point slider in the levels dialogue, you 
> are clipping all the data above the slider.
> 
> If you do not move the end points in the curves dialogue and 
increase 
> the contrast,say, with a traditional "s" curve you are reassigning 
> values in the
> image but not clipping any.
> 
> There is a difference and curves is much less destructive than 
levels.
> 
> That said, the notion that a combed histogram is bad is much too 
much 
> overstated, and generally speaking the problems attributed to them 
> arise from
> other issues.
> 
> J.Z.