iPhone Duo wallpapers

At 2752 × 2752 it is the only size in either pack that covers both of the Duo’s screens with no upscaling at all. A phone scales a wallpaper to fill the screen and crops whatever hangs over, so the square loses about 31 per cent of its width on each panel and none of its height.

Do not use the phone file. It is the obvious pick and the wrong one. The Duo unfolds to 1878 pixels across and the 19.5:9 phone wallpaper is 1320 wide, so it has to be stretched 1.42 times to fill that screen. Upscaling is the one thing these packs exist to avoid: every file is rendered straight to its native size in code, and blowing one up throws that away and puts the banding back into the gradient.

Why nothing matches exactly is worth knowing before you download a Duo wallpaper from anyone. Apple describes the two screens as sharing an aspect ratio, and they nearly do, but not quite: unfolded works out at 1.4217 to 1 and the cover at 1.4549, a difference of 2.3 per cent. No single image is native on both. Every Duo wallpaper, including the ones that came on the phone, is being cropped on at least one of the two panels.

Scale to fill and crop the overflow, which is what the phone does with a wallpaper. Anything stretched is the file being blown up past the size it was drawn at.

1878 × 2732, and it is being drawn now. The width is the unfolded screen’s own, so nothing is ever stretched. The height is a choice rather than a calculation: the two panels are 2.3 per cent apart in shape, so a sliver has to come off one of them whatever the file measures, and this puts it on the unfolded screen rather than the cover, because a folding phone spends most of its life shut. Either way it is about two per cent, against the 31 the square file costs today.

It goes into every pack that already ships, free, to everyone who has already bought one. That is what future sizes included means here, and it is the reason to buy a pack rather than a single file.