* Steven Woody <[EMAIL PROTECTED]>:
> Pasi Savolainen <[EMAIL PROTECTED]> writes:
>
>> * Steven Woody <[EMAIL PROTECTED]>:
>>>> See also: http://gimp-savvy.com/BOOK/index.html?node60.html
>>>
>>> when playing with level or curves, did you guys adjust each channel alone or
>>> the overall combined value?
>>
>> I often take them by channel. It really depends on how well your source
>> adjust image per-channel. My digicam, being pre-2000, tends to make blue
>> channel too weak, so it's 'white' point is much lower than red&blue.
>>
>> I can't really tell if operating on 'grand total' would produce same
>> result, it is a matter of convenience of knowing what is happening that
>> I'm after.
>>
>
> when i worked on individul channels, i always got color cast. i just can not
> image that how people working on channels can still keep color balance well
> sicne you can not do the r,g,b simultanously. any tips there?

This depends heavily on the image that's worked on.
Generally I'd say procedure is to go through r,g,b and adjust only black
and white point, leaving gamma (middle number) as it is. Most images
have about linear channels, only shifted+compressed in some way, so this
will get you mostly castless image (again, this is very taste-specific
operation and some people, of which I may be one, just don't see much
difference in some shades). When image has cast that I notice, I start
working with gamma sliders and try to achieve something that look a bit
like the anticolor of the cast.
For example if cast is blue, go to blue color and move gamma to the
right, making it smaller (the colorstrip will turn yellow). In case of
yellow cast one would move it to the left. etc.
Often after one cast is removed, another creeps up, so this is a game of
balance.
Turning preview on/off helps a lot, as does having a <Image>->Duplicate
around at all times.

Using color pickers and choosing black/grey/white colors from _really_
black grey and white spots will likely get you into a good start. They
just tend to clip whites/blacks too much, losing detail that way.

-- 
   Psi -- <http://www.iki.fi/pasi.savolainen>

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