Shadows in Gimp.

[erdrix]

Does any one have any idea how to make a mask overlay that looks like a forest canopy shadow in gimp?

Usually when I import a map in I'll make a new layer from visible. I then darken that layer and then use the free-form mask tool with feathered edges to draw out where I want brighter ares and then delete that section so the brighter original picture is visible.

I want to do the same thing but make it look like light is shining through the forest canopy above. So, I'm thinking of some kind of template that could be applied that can be reused for any forest maps. I'm not good enough with gimp to figure out how to do something like that.

[Midgardsormr]

I'm not a Gimp user, but I can provide some general pointers. I think I'd find an image somewhere looking up through the trees—a Google image search for "forest canopy" turns up several likely candidates in the first page. Then I'd use some kind of threshold or contrast control to turn it into a black-and-white matte and scale it so that it fits nicely over the map. Change the blend mode to darken or multiply, then adjust the opacity until it looks nice. Maybe add a bit of a blur on it to soften the shadows. Then I'd make a copy of that layer, tint it green, and mask it out entirely. Then I'd find another, similar image and do the same thing, but use it on to punch out the mask of the green-tinted version, to give it a little bit of transmitted green light from the leaves, again adjusting the opacity to taste.

In Photoshop I'd use adjustment layers with the canopy image as a mask, but I am not sure if Gimp has adjustment layers.

[erdrix]

That totally worked! Thanks!

[Midgardsormr]

You're welcome!

Another popular technique to help with lighting is to make a layer that's filled with 50% gray and set it to the overlay blend mode. This blend mode makes 50% gray transparent, but anything above that level works as if it were screened, and anything below it works as if it were multiplied. So if you use the burn and dodge tools on the invisible gray layer, you'll be able to lighten or darken the underlying pixels without actually changing them. Use a low opacity on soft dodge/burn brushes for best results.