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Fixing App Store Connect screenshot errors: wrong dimensions and alpha channels

#ios #swift #appstore #indiedev

App Store Connect usually gives you two kinds of screenshot errors: the dimensions are wrong, or the file has an alpha channel. Both are quick to check from the terminal on a Mac before you upload anything.

1. Check dimensions and alpha with sips

sips ships with macOS:

for f in *.png; do
  sips -g pixelWidth -g pixelHeight -g hasAlpha "$f" | tr '\n' ' '; echo
done
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Compare the output with Apple's screenshot specifications. A few common portrait sizes:

  • iPhone 6.3" (required slot): 1206 × 2622 or 1179 × 2556
  • iPhone 6.9": 1320 × 2868
  • iPhone Duo outer: 1398 × 2034
  • iPhone Duo inner: 2007 × 2853

For landscape, swap width and height. If the numbers match but Connect still complains, you're probably dropping the file into the wrong device slot, or the orientation doesn't match the rest of the set.

2. Remove the alpha channel

Screenshots exported from design tools often keep an alpha channel even when every pixel is opaque. App Store Connect rejects these.

The simplest fix that keeps PNG is to flatten onto a solid background with ImageMagick:

magick input.png -background white -alpha remove -alpha off output.png
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Or convert to JPEG with sips, since JPEG can't store alpha at all:

sips -s format jpeg -s formatOptions 95 input.png --out output.jpg
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Run the sips -g hasAlpha check again afterwards. It should print hasAlpha: no.

3. Don't fix dimensions by stretching

If a file is the wrong size, resizing it to fit distorts your UI, and the Duo sizes have aspect ratios no regular iPhone shares. Capture again on the right simulator or device, or rebuild the layout for that ratio. Guideline 2.3.3 also expects screenshots to show the app accurately, so a stretched capture is a risk on its own.

4. Count your files

You can upload up to 10 screenshots per device size. An export folder with 12 files won't upload cleanly.

Quick checklist

  • [ ] Right pixel size for the slot, in the right orientation
  • [ ] hasAlpha: no on every file
  • [ ] PNG or JPEG
  • [ ] 10 files or fewer per device size
  • [ ] Real captures of the app, not stretched

I build DuoShot, which exports opaque PNG/JPEG screenshots at these sizes. The checks above don't depend on any tool, though. I also keep a full sizes reference up to date.

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