---

Apple App Store will reject your binary if the app icon or any screenshot asset contains an alpha channel. The rejection message is usually:

Invalid Image Path - No image found at the path referenced under key ‘CFBundleIcons’… ERROR ITMS-90717: “Invalid App Store Icon. The App Store Icon in the asset catalog… can’t be transparent nor contain an alpha channel.”

You need every PNG flattened to plain RGB before uploading. Here’s how.

Background: Why Apple Rejects Alpha

iOS app icons are framed by the system with a fixed rounded-square mask. If your PNG has transparency, that mask combines with your alpha channel in unpredictable ways — dark halos, fringes, mismatched corner radii. App Store Connect refuses the upload to avoid the whole class of bug.

Screenshots have a different reason: Apple’s marketing pipeline scales and recompresses them, and alpha pre-multiplication can introduce artefacts. So the same rule applies — opaque RGB only.

Method 1: Python with Pillow (cross-platform, batch-friendly)

The most reliable approach. Pillow handles edge cases like palette PNGs (P mode) with a transparency chunk, which sips doesn’t always catch.

python3 -m pip install --user Pillow

Then a one-shot script:

from PIL import Image
import os

paths = [
    "icon-1024.png",
    "screenshot-01.png",
    "screenshot-02.png",
]

for p in paths:
    img = Image.open(p)
    has_alpha = (
        img.mode in ("RGBA", "LA")
        or (img.mode == "P" and "transparency" in img.info)
    )
    if not has_alpha:
        print(f"skipped (no alpha): {p}")
        continue
    if img.mode != "RGBA":
        img = img.convert("RGBA")
    # Composite onto white so transparent pixels become opaque white.
    bg = Image.new("RGB", img.size, (255, 255, 255))
    bg.paste(img, mask=img.split()[-1])
    bg.save(p, format="PNG", optimize=True)
    print(f"flattened: {p}")

Verify afterwards:

from PIL import Image
img = Image.open("icon-1024.png")
print(img.mode)  # Should print "RGB", not "RGBA"

If mode is still RGBA, the file wasn’t rewritten — check write permissions.

Method 2: sips (macOS, no install)

Built into macOS. Works for simple RGBA PNGs but the syntax is unintuitive:

sips -s format png \
     -s formatOptions normal \
     --setProperty hasAlpha no \
     input.png \
     --out output.png

In practice the --setProperty hasAlpha no flag is unreliable across macOS versions. A more dependable trick is to round-trip through JPEG, which has no alpha by definition, then back to PNG:

sips -s format jpeg -s formatOptions 100 input.png --out /tmp/tmp.jpg
sips -s format png /tmp/tmp.jpg --out output.png
rm /tmp/tmp.jpg

JPEG at quality 100 is visually lossless for app-store assets. Transparent pixels become white.

Method 3: ImageMagick (if installed)

One-liner per file:

magick input.png -background white -alpha remove -alpha off output.png

Batch over a folder:

for f in *.png; do
  magick "$f" -background white -alpha remove -alpha off "$f"
done

The -alpha remove flag composites against -background white; -alpha off strips the channel entirely so the saved PNG has no alpha sample type.

Verifying the Result

Before uploading, confirm none of your assets still have alpha:

python3 -c "
from PIL import Image
import sys, glob
for p in glob.glob('*.png'):
    m = Image.open(p).mode
    print(f'{m:5s}  {p}')
"

Every line should read RGB. Anything showing RGBA, LA, or P with transparency will be rejected by App Store Connect.

Gotcha: What “White” Means in Your Design

All three methods composite transparent pixels onto white. If your icon was designed with transparency over a coloured backdrop, the result will read very differently after flattening:

• An icon designed on a coloured app-screen mockup → bake the colour into the icon first, then strip alpha.
• A screenshot with a transparent status-bar area → that area becomes white, which usually looks fine on iOS submissions.

If you need a non-white flatten colour (e.g. your brand colour), change the background tuple in the Pillow script — Image.new("RGB", img.size, (255, 255, 255)) becomes (R, G, B) of your choice.

Why This Isn’t an Android Problem

Google Play accepts PNGs with alpha for both icons and screenshots, so this is purely an Apple constraint. If you ship a cross-platform asset pipeline, keep the alpha-channel originals around for the Play Store listing and only flatten on the iOS submission path.