Making an emissive masked texture using Gimp

[KT Kingsley]

I can breeze through the process of making an alpha layer to use as an emissive mask on a texture in Corel Paint, but I'm not familiar with Gimp and I can't figure out how to do it there.

Can someone either explain, in simple steps, as if for a complete beginner, how, starting with a base texture, to do this in Gimp, or point me to a decent tutorial?

[Fritigern Gothly]

The simple answer is that transparent or black pixels will not glow. Any other color will glow in that specific color.

So all parts that you do NOT wish to glow should be made either black or transparent.

Personally, I like to load the source texture, create a new layer to work on, and when I am happy with the result I merge the two layers, then export to PNG. Using a new file name of course so as not to overwrite anything which I may need later.

And done, one emissive mask to be imported into SL.

[KT Kingsley]

Yup, that's how I do it too. But how would I do it in Gimp?

[Fritigern Gothly]

 

 

[Quarrel Kukulcan]

6 hours ago, KT Kingsley said:

Yup, that's how I do it too. But how would I do it in Gimp?

Your emission mask will be your alpha layer, which normally gets used for transparency but gets used for emission level instead when you want that feature active. (SL can't do both custom emission and custom translucency at the same time with one texture.)

1. Add an alpha channel to your image layer if it doesn't have one (Layer -> Transparency -> Add Alpha Channel).
2. Add a mask (Layer -> Mask -> Add Layer Mask..., then select the most logical default mask to start editing from). You should see a second micro-thumbnail appear in your Layers toolbox.
3. Edit the mask like any other grayscale image.

You can change whether you're editing the image or the mask for that layer by left-clicking the appropriate micro-thumbnail.

To see the mask itself, rather than the image with the mask applied, Alt-left-click the mask thumbnail. (It'll turn green.)

To see the image without the mask, Ctrl-left-click the mask thumbnail. (It'll turn red.)

It'll be a little confusing at first, since both options toggle but one takes precedence. And you can also control these things in the main Layer menu or the layer's right-click menu.

[KT Kingsley]

Thank you, @Fritigern Gothly, I've just taken a quick scan of that tutorial, and it looks very promising: clear, direct and hardly any ums and errs either.

@Quarrel Kukulcan, I've just tried that and it all starts to make sense now. Many thanks.