[Gimp-user] colour to black and white

[norman]

> > I would like to be able to produce a black and white negative image
> > from an ordinary colour image. The effect I would like to produce
> > would be to imitate what one would get if you took a colour,
> > positive transparency and made a contact print on to either
> > orthographic or lithographic film. Thus, blue would be black and
> > red would be clear and transparent. Have you any suggestions how to
> > approach this using the Gimp, please.
> >
> 
> Colors->Components->Decompose (elseqwhee if you are on gimp 2.2, b ut 
> still "decompose")
> 
> and pick only the "Hue"  channel.
> 
> You cna tehn use colors->curves, or colors-->levels to equate your 
> previous blue to black and your previous red to white.

Thank you for that. I cannot see a channel labelled as "Hue", perhaps I
am looking in the wrong place. I am using Gimp 2.4.0-rc3.

Would it then be possible to actually have the white areas transparent?
Norman