Digital BW, The Print

on 8/11/01 12:31 PM, mwesley250@... wrote:

>> Sorry Martin, I see my reply to you was merely redundant to your
> question. I
>> think my answer was based upon remembering that in the past I've
> found it
>> useful to slap a "false" set of curves on an image to aid in
> creating an
>> alpha mask from one of the channels.
> 
> I think by doing this you get the illusion that you are adding
> something to the file but in reality you are just pushing arround the
> original scan data. It might be useful for final quality but have to
> try it out.
> 
> "False"set of curves for alpha mask?? I'm not following you.
> 
> Martin

By "false" I mean that they are not really corrective for the image, but
they are just for accomplishing a specific task, then tossed.

For instance, if you want to take a color channel and dupe it to make a
mask, your channels will be different depending on what layer is active at
the time, and what adjustment layers are active above it.

While there is a lot you can do to any channel just by treating it like a
grayscale image, and working on it directly, with adjustment layers you can
alter it before you even start to work on it. Curves was but one example.

Say you have a head with wispy hair you want to make a mask for. Which
channel will be better (more contrast) to work from may depend on the color
of the persons skin, and hair, and the color of the background. Rather than
just working with the best channel of the image before any adjustments are
made, you could add an adjustment layer of some sort, to accentuate the
difference between the subject and background color. Take the case of
Caucasian skin and blond hair against a red background. There may or may not
be good luminosity contrast between subject and background due to lighting,
but as subject and foreground are both comprised predominantly of red, there
will not be a lot of separation due to color contrast. A preliminary
selective color move, or an increase in saturation, on the image might give
you a better channel to start making your mask from.

So, when you work on a color channel directly, you only have grayscale tools
available to you, but if you work on a color channel through the image
itself (the composite channel), you have a broader tool set to work with.

Todd