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Why App Store preview videos matter

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Tranquil mountain lake at dawn with distant snow-capped peaks.

App Store Connect can reject a screenshot with this message: "Images can't contain alpha channels or transparencies."

This is easy to miss because the image can look completely normal. The problem is not always a visible transparent area. It can be the exported file format itself.

Why It Happens

Apple accepts App Store screenshots in .jpeg, .jpg, and .png formats, but screenshots must be flat images with no transparency.

PNG is the risky one. A PNG can include an alpha channel even when every visible pixel appears opaque. If the exported screenshot keeps that alpha channel, App Store Connect can reject it.

The Simple Fix

For App Store screenshots, export a flattened image:

  • Use .jpg or .jpeg when you do not need transparency.

  • If you export PNG, make sure it is a 24-bit RGB PNG with no alpha channel.

  • Always draw the background first, then place the screenshot or device frame on top.

JPEG is the simplest safe default because it cannot contain an alpha channel.

How FrameOS Handles This

FrameOS exports screenshots as a fully rendered canvas, including the chosen App Store size, background colour or gradient, padding, corners, and shadow.

For screenshot exports, FrameOS writes the final image as a high-quality .jpg. That keeps the output compatible with App Store Connect and avoids the hidden alpha channel problem that can happen with PNG exports.

Reference