To create lower resolution versions of the same sprite atlas for different platforms, create variant sprite atlases. A variant sprite atlas combines the same sprites and textures as the original sprite atlas, but the combined texture it creates has a lower resolution.
Follow these steps:
Create a sprite atlas as normal. Make sure its Type is set to Master. This sprite atlas is the parent sprite atlas.
Create another sprite atlas, then in its Inspector window set Type to Variant.
In the Inspector window of the variant sprite atlas, set Master Atlas to the parent sprite atlas you created in step 1. Either drag the parent sprite atlas from the Project window, or select the picker (⊙).
A variant sprite atlas combines the same sprites and textures as the parent asset. It doesn’t have its own Objects for Packing list, and Unity doesn’t create a sprite atlas asset for it in the Project window.
To select the size of the combined texture of the variant sprite atlas, set the Scale property. For example, set Scale to 0.5 to create a sprite atlas texture half the resolution of the parent sprite atlas.
Select Pack Preview to display the packed texture in the Preview window at the bottom of the Inspector window.
By default, Unity includes both the parent sprite atlas and the variant sprite atlas in your built project. This means Unity randomly chooses which sprite atlas to render with at runtime.
To avoid this, use any of the following approaches:
Important: If you disable Include in Build for both the parent sprite atlas and the variant sprite atlas, Unity includes no textures for the sprites and textures, and the sprites that use the texture are invisible.