Why App Store Connect rejected your screenshot: IMAGE_ALPHA_NOT_ALLOWED

What actually triggers the error

A PNG file's IHDR header contains a one-byte color type that declares the pixel format for the whole file:

App Store Connect looks at that byte. If it says 4 or 6, the upload is rejected regardless of whether any pixel is actually transparent. That's why "but my screenshot has no transparency!" doesn't help: the file format says otherwise.

Where the alpha channel sneaks in

Almost every convenient export path writes RGBA (color type 6) by default:

• Figma and Sketch exports. Both write RGBA PNGs regardless of content.
• HTML canvas. canvas.toBlob('image/png') and toDataURL always emit RGBA, so any screenshot pipeline built on a browser or Electron canvas produces rejected files.
• Editing tools in between. A clean simulator capture that passes through Photoshop, Pixelmator, or a quick markup tool often comes out the other side as RGBA.
• Design templates with transparency. If your composition genuinely uses transparent regions, the export must be flattened onto a background before upload.

The fastest fix: in your browser, free

The Alpha Channel Fixer flattens your PNG and re-encodes it with a purpose-built encoder that writes color type 2 (RGB, no alpha), then parses its own output to prove the alpha channel is gone before you download. Your file never leaves your browser: no upload, no server, no account. Drop the rejected PNG, download the fixed one, re-upload to ASC.

Fix a PNG now

Manual fixes on macOS

Preview (no install)

1. Open the PNG in Preview.
2. File → Export.
3. Untick the Alpha checkbox and save.

Fine for one file; tedious for thirty screenshots across locales.

sips (built into macOS)

sips can convert to JPEG, which structurally cannot carry an alpha channel. ASC accepts JPEG screenshots:

sips -s format jpeg shot.png --out shot.jpg

Caveat: JPEG is lossy; crisp UI text can pick up compression artifacts.

ImageMagick (keeps PNG, batch-friendly)

magick shot.png -background black -alpha remove -alpha off shot-flat.png
# whole folder:
for f in *.png; do magick "$f" -background black -alpha remove -alpha off "flat-$f"; done

Swap black for whatever your composition's background color is; it only shows through where pixels were genuinely transparent.

In code (Core Graphics)

If you generate screenshots programmatically on Apple platforms, render into a bitmap context created without an alpha channel (CGImageAlphaInfo.noneSkipLast won't do for PNG export; draw into an opaque context and write RGB). The principle is the same everywhere: composite onto an opaque background, then encode a format that has no alpha channel to declare.

Verify before you re-upload

Don't trust the export dialog; check the file. Fast check with Python:

python3 -c "print('color type', open('shot.png','rb').read()[25])"
# 2 = RGB, good. 6 = RGBA, ASC will reject it.

Or drop the file into the free size checker, which reads the color type and validates the dimensions in the same pass.

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