Re: [Gimp-developer] suggestion for color to alpha

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Sven Neumann <sven@xxxxxxxx> writes:

> Hi,
> 
> "Branko Collin" <collin@xxxxxxxxx> writes:
> 
> > Does <image>/Select/By Color what you want?
> 
> I think Branko is right here. Color-To-Alpha is not suited for
> chroma-keying since it will remove all shades of blue from all
> colors in the image. Classic blue-boxing requires to clear only
> exactly the color defined as the blue-box background. This can
> easily be achieved using Select-By-Color with a small threshold
> followed by Clear.  

That works fine for opaque objects, but not for translucent ones.  For 
example, when you have someone with long hair you can see some of the
blue background through the hair, so the colour in those pixels is a
mixture of the hair colour and and the blue background.

Even with opaque objects you still have pixels along the edge of the
object where you get blue mixed in.  Using Select-by-Colour to remove
the blue leaves a blue fringe around the object. Select-by-Colour,
Grow, Feather, Clear works better, but you still have blue around the
object that should not be there.

Tim


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