Digital BW, The Print

Very informative post, thank you.
But basically, no easy way right?

1. Use a polariser
2. Use hue/sat / whatever conversion methods appropriate to get dark 
skies without posterisation
3. Darker (is PAINT) manually to darken

Right?  Pretty much what I've been doing, but its so da*n slow and 
I'm naff at it!

Oh well, practive makes and all that....

Steve



--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Anthony G. 
Atkielski" <anthony@a...> wrote:
> scrber writes:
> 
> > After 2-3 years of digital darkrooming and B&W printing I am 
still 
> > not happy with my methods to darken blue skies.
> 
> Take a snapshot, adjust curves to make the sky as dark as you 
require,
> take another snapshot, switch back to the first snapshot, then use 
the
> history brush or equivalent tool to brush the darkened sky back in.
> This has to be done by hand, unless the transition line between 
sky and
> the rest of the image is smooth and regular enough to allow you to 
apply
> a mask.
> 
> > I am familiar with the red filter / polariser filters on film
> > capture, but my efforts to successfully replicate this digitally 
> > have never been particularly fruitful.
> 
> It cannot be replicated digitally, because the necessary 
information is
> missing from the RGB image.  You need to use filters at the time of
> image capture.  Red filters can be partially simulated, although 
it may
> produce noise or posterization.  Polarization can only be 
simulated by
> modifying the image pixel-by-pixel.
> 
> > I have tried many channel mixer, hue/sat methods to convert
> > my digital colour images to B&W but all result in some sort
> > of posterisation or noise in the sky.  I cannot get a smooth
> > dark sky.
> 
> If the image has had less then 16 bits per channel at any time, 
you may
> see posterization if you make large modifications to the image.  
This
> cannot be avoided.  You need adequate bit depth to avoid 
posterization.
> 
> > Selective darkening also is very difficult if you are
> > really trying to go dark, the halos/  edges are almost
> > impossible to avoid.
> 
> Nevertheless, that's the way it is done.  Sometimes, if there is a 
sharp
> color or luminosity difference demarcating the transition to sky, 
you
> can use other tools to speed up the process, but it's still mostly 
long
> work by hand if you want the best results.
> 
> > Even after running neat image or selective bluring to remove sky 
> > noise I end up with clear banding in the sky as it gets darker.
> 
> You may have to manually smear and clone to reduce banding.  It 
will be
> hard to hide completely.
> 
> > Anyone want to share how you get those really dark / black skies
> > with me, any real way of doing this from a digital colour file?
> 
> Image files don't contain enough information for many types of
> filtering.  The best way is to use something like a polarizing 
filter at
> the moment of capture.  If you are lucky, there may be shortcuts 
for a
> given image, but very often it is a lot of hard work.
> 
> > I know this is slightly of topic but most of the 'retouching' or
> > editing forums are populated by colour gurus, this is really the 
> > knowledge base for B&W.
> 
> The principles are the same for both B&W and color, except that
> obviously any manipulations based on color are impossible in B&W 
(as
> opposed to merely difficult and often unsatisfactory in color), and
> there may be more of a tendency to posterization in B&W because 
you have
> only one channel instead of three (but if you work with 16-bit 
channels
> and the original image is clean, this should not be a problem).
> Isolating the sky with shortcuts is far harder in B&W, since 
intensity
> is the only possible clue for transitions, and sometimes not even 
that.