Start with a master asset
Use a square master at 1024 × 1024 pixels or larger. Keep the editable source separate from final PNG exports so you can revise color, spacing, and artwork without degrading the image.
Keep the visual subject away from the edges. Fine text, thin outlines, and edge-to-edge details often lose clarity after platform masks and small-size rendering.
Handle transparency deliberately
The App Store marketing icon is an opaque square PNG. Submit square artwork and let the operating system apply its own presentation mask.
If the source contains transparency, choose a deliberate background before exporting. Test the result on light and dark wallpapers; a faint halo is easier to correct in the master than after export.
Final checks
Confirm the source is square, inspect the result at 64 px and 32 px, remove accidental transparent pixels, and archive both master and exports. Generate each platform size from the master rather than enlarging a previous export.