Open Blender, quick File > Import > FBX and navigate to the assets folder of your project.
Find the fbx file for the game object you wish to add an emissive to.
Click the UV Editing tab, select Open in the UV window, and browse to the associated albedo file for your game object / fbx.
On the right hand side, click the checker board looking icon which represents texture.
There is another checkerboard icon underneath “Brush”, click it and select the texture we’ve imported.
Switching to the Texture Paint tab and back to the UV Editing tab takes us from “Object Mode” to “Edit Mode”.
You may have the option after adding the texture to just use the drop down and change the mode.
If we highlight the area we want to make emissive, we’ll see it also selected on the UV window.
If I zoom in, I can get a good idea of the borders of the selection.
Now that I know what I need to modify, I’ll open Krita and work on it from there.
In Krita I don’t have a highlight, but I know where it is.
I’ve zoomed in real tight on the area to be changed.
I’ll use the box selection tool to select the correct area, as close to the pixel as I can.
Fill bucket didn’t give me the result I wanted, so I simply switched to brush and filled it in with white.
After all, I have a selection that keeps me from going out of bounds.
We’ll click Layers > New > Copy Selection to New Layer.
We’ll also add another layer for the background of black.
We need to deselect off of our magic tool, and then we can fill our black background, move the layer below our white section layer, and then save as a png file appropriately named with emission.
Last, we open up Unity and assign our new emission map texture to the material assigned to our game object.
If we like, we can change the color with the Unity color picker.