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     áòèé÷ :: Filmscanners
Filmscanners mailing list archive (filmscanners@halftone.co.uk)

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Re: filmscanners: Colors in Neutral Gray



On Tue, 27 Feb 2001 15:17:24 +1030  Mark Thomas (markthom@camtech.net.au) 
wrote:

> Is this really true?  I have encountered images where playing with RGB 
> curves has just made me feel like I am drowning (perhaps just in my 
> personal pool of insufficient knowledge!)

It's not easy, but it does get easier and quicker to do, with experience. 90% 
of the problem is identifying what is wrong - what colour the error is and 
which tones it affects. This *does* get hard if there are a compound mixture of 
defects, eg wrong colour temp + crossed curves.

Frankly the best thing to do is to spend time playing with it. Deadlines help 
concentrate the mind too:)

Often software provides different ways to control much the same thing, eg PS 
adjust levels, adjust curves, adjust colour balance all provide a different UI 
to the same fundamental parameter, gamma of the individual channels. The trick 
is largely knowing which set of controls is appropriate and when. The right 
ones make matters easier.

For instance : say you have a simple case of a pic being too cool because it 
was taken in light which was too blue. You /could/ fix this entirely by 
dragging curves around or setting the levels of each channel differently, but 
it's a far simpler operation to use levels just to set levels (assume auto 
levels does not help with this).

However it's much easier to use Adjust colour balance. My personal way of 
dealing with this is to try and take out the most obvious error first, which 
usually means increasing yellow/decreasing blue. However there is usually a 
secondary shift which also needs dealing with by moving the cyan-red slider 
toward red. It can be magenta-green though.

You should never use all 3 sliders, 2 max. If you feel tempted to, you're doing 
something wrong with the others.

A curious thing I've noticed is that when colour has been successfully 
corrected, the sliders always line up diagonally if there's a 2 channel error. 
This is a useful shortcut guide once you are sure which channels need 
correcting. Mid greys in the pic make life much easier here.


> If it really was that easy, why would we need colour filters (eg for 
> tungsten lighting on daylight film)?  

It can be done, though the error is rather gross with slide film because of 
its contrasty nature. I have 'rescued' daylight Kodachrome exposed via tungsten 
with no filter with no obvious ill effects. It's easy with colour neg, and a 
main reason I have swapped to it + scanning is the refreshing ability to be 
able to take colour pics in almost any lighting conditions  without filters.

Regards 

Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner info & 
comparisons




 




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