On Thursday 25 October 2007 10:18, norman wrote:
> 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
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.
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