The image you can see above didn´t really have much colour information in it. Dusk was already gone, almost no blue was visible in the sky... so I decided to go for a black and white conversion. A basis analysis of the channels information showed that green and blue channels were too "flat", with very little contrast.
As a consequence, I applied a channels mix with the following values: R100%, G0%, B0%. I obtained the same result I would have got by decomposing the image into RGB layers, and then removing green and blue layers (no channels anymore).
To finish the edition, I applied a slight levels adjustment, to recover some texture in the clouds and to darken the islet, until it became just a silhouette.
Did you like this post? Then, you might want to check...
- Black and white with channels in GIMP
- Levels and curves with GIMP (book)
- Blanco y negro con The GIMP (book, in Spanish)