How to export using Photoshop

When you're ready to export your finished project, toggle the visibility of the Legend.

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Once you've toggled off the Legend, click on File > Export > Export As...

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A window will pop up and give you options for exporting your file, we want a transparent .png with the dimensions of 1024 by 1024 px(pixels).

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After that you will be prompted to name and save your file to a specific location, for an easier time I suggest already having your file path set up.
The file path should look something like this: [Folder w/ name of your mod]\guis\textures\pd2\skilltree_2

Once we're at our desired sub folder name your file icons_atlas_2.texture and click save.

Now we can place our folder with our pathway to the finished icons in the mod_overrides folder.
The pathway to the folder will look this: C:\SteamLibrary\steamapps\common\PAYDAY 2\assets\mod_overrides