It seems you would basically want an inverted copy of the blue channel with white regions being transparent. There are dozens of ways to accomplish this. I would propose the following:
Decompose you image to RGB components. In the new image, hide the red and green layers. Add a layermask to the blue layer, initialized to a "Grayscale copy of the layer". Fill the blue layer with black. OPTIONAL: Most orthochromatic film would respond to some extent to green, so repeat the last two steps on the green layer, make it visible, and set its opacity to a relatively low value (0-30%). This method is a bit crude, but should provide something not entirely unsuitable. A more accurate approach would probably entail applying appropriate curves to the different color channels. Quoting norman <[EMAIL PROTECTED]>: > 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. _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
