Why an Aseprite sheet and image export can have different proportions

Aseprite can display sprites with non-square pixels, while exported PNGs are usually read as square-pixel grids. Applying the pixel ratio stretches geometry along one axis, whereas uniform export scaling changes both axes, so the two exports can differ without any lost pixels. The article's example uses a 12 by 21 source with a 2:1 pixel ratio, which becomes 24 by 21 square pixels and reaches 72 by 63 after a uniform scale of three. Its advice is to record stored dimensions, pixel ratio and export scale separately, and to compare a decoded frame from each export path. It also notes that changing PNG resolution metadata does not fix the geometry and that sheet exports may need a separate presentation copy.