Is it possible to apply a curves transformation to part of an image?

[ianpwilliams]

I have a wide field image of M31. I would like to apply a mask to the galaxy itself to protect it, and then increase the colours of the rest of the image using Curves Transformation, to try to bring out the different colours of the stars. Is that possible?

[Alejandro Tombolini]

Yes!. See for example this processing example.

Saludos, Alejandro

[ianpwilliams]

Thanks, but really I need a resource that can tell me how to do it, rather than the names of the steps, as I'm very new to all this!

[pfile]

well, you basically want to generate a star mask, apply that to the image, then adjust the saturation curve in the CurvesTransformation tool. make sure when the mask is applied that the background appears red and the stars are black. if not, invert the mask. red means the mask is protecting that stuff.

rob

[ianpwilliams]

But if I apply a mask that doesn't protect the stars (which is what I want), then won't that also protect the galaxy (which is not what I want)? I was thinking that if I created a mask that protected the galaxy, then I could apply the curves transformation to the rest of the image (background and stars), and it wouldn't matter that it would be affecting the background as well as the stars, because the background is black.

[Alejandro Tombolini]

Maybe you better start here, it is explained how to use masks.

But if I apply a mask that doesn't protect the stars

Check that the mask is enabled (not only applied)

Hope this helps

Saludos, Alejandro.

[ianpwilliams]

Thanks, I'll give that a try.