Radius color to transparency overlay

[jayhova]

I'm trying to create a sort of overhead circular glow effect. Imagine looking down on a lamp from overhead and seeing a yellow or white glow that falls off with distance. I would like to lay this over an existing image of a map. I would the effect to be transparent Strongly colorizing the map at the center of the effect and falling off toward the edge of the effect like a radiant gradient. I'm far from a GIMP expert.

[Blighty]

There are various ways to do this, depending on the effect you want. One way is to use a light beam brush (sample attached). Unzip and place the .gbr in the brushes folder of your user profile.
C:/Users/YourName/AppData/Roaming/Gimp/2.10/brushes
Refresh the brushes or restart Gimp.
Create a new transparent layer above your map.
Set the foreground colour.
Select the light beam brush and set the brush size.
Paint on the transparent layer (a single click in the position you want).
Reduce the opacity of this layer (say to 50%).

There are many light beam brushes on the internet. Many are in photoshop .abr format that work in Gimp.

If you want a more uniform layer, create a new layer with the colour of your choice. Create a layer mask for this layer and apply a radial white-to-black gradient on the mask. This is similar to a vignette. The standard vignette will darken the outside portions of an image, you want to lighten the centre.

[rich2005]

The spotlight brushes are usually very good. If you want to try your hand at using basic Gimp 2.10 tools this little video demo.





direct link https://youtu.be/f2Rtv4_F0Ks duration 3 and a half minutes

Once it is set up, just play around with opacities, layer modes, maybe apply a colour curve to the copied area of the map.