Re: [Gimp-user] Subtracting an image from another image.

[Ofnuts <ofnuts laposte net>]

On 08/10/14 21:26, GreenFeather wrote:
> Hi, I'm fairly new to GIMP. I need help.
>
> Let's say, I have a base image. Then another image which is comprised of the
> base image and a transparent layer of blue, but is merged into one layer.
> How can I subtract the base image from the other image, resulting in a layer
> of blue?
>
> Here, I'll show what is needed in my case.
>
> I have my base image, here
> <http://gimp.1065349.n5.nabble.com/file/n43846/Arcanist_Costume_-_F.jpg>
>
>   and here is the other image, which is the base image plus a rainbow layer
> <http://gimp.1065349.n5.nabble.com/file/n43846/Rainbow_ark_female.jpg>
>
> As I said before, the second image is one layer, and I can't click undo
> because that image isn't originally mine.
>
> How would I subtract the base image from the second image that leaves me
> with a rainbow gradient layer, that looks something like this
> <http://gimp.1065349.n5.nabble.com/file/n43846/Rainbow.jpg> (image not to
> scale) (note, this is just an example and I can't use this one because it
> does not match the exact shades of the seconds image, which is what I need)
>
> Help please.

This coloring is usually applied using some form of multiplication:

final=original X colors

so to get back at the colors:

colors= final / original

So in Gimp:

- Load rainbow-ed image
- Load original image as a layer over it
- Put original image layer in "Divide" mode

Result not perfect, due to overflow/clipping...