Apple doesn’t allow alpha to be in the app icons and if you try to submit an app without removing Alpha channel from images you will get following error
ERROR ITMS-90717: "Invalid App Store Icon. The App Store Icon in the asset catalog in 'Energy saving game.app' can't be transparent nor contain an alpha channel."
What is Alpha channels?
Alpha channels are masks through which you can display images. The alpha channel is an 8-bit channel, which means it has 256 levels of gray from 0 (black) to 255 (white).
To remove this, there are many tools you can use including Mac Preview app, Photoshop, Gimphy etc. The simplest way to remove alpha from app icon is by using Mac Preview app. Follow the steps below:
Open the app icon you would like to edit.
Press Command-Shift-S to create a copy of the image then press Command-S to Save
Deselect the “Alpha” checkbox option below image format, then select folder you would like to save the image in.
Then rename the image to remove copy from filename (including the space). This will overwrite your original image, but if you don’t want to replace it, rename the image name to something else.
Click Save and ‘Replace’ to confirm you want to overwrite the original.
Repeat the above process for all the app icon images.
Now export the image to Xcode and archive your app for submission.
The above process is tedious since you have to repeat all the steps in all the icons and in the cases where we are dealing with editing a lot of images, there is a third party tool that can remove alpha option in images in bulk. Alpha Channel Remover for macOS is a free application by bpolat.
There are two ways to run this application;
Download the application
- Downloading the application from their website. To download, click here then extract the zip file and double click to open.
- In most cases, The installation will be blocked due to verification failure. To disable this click here https://support.apple.com/en-us/HT202491
Running on Xcode
- Go to https://www.cocoacontrols.com/controls/alpha-channel-remover then click on open with Xcode button, This will automatically launch Xcode on your device.
- Select the folder where you would like the cloned source code saved then click on Clone to proceed. When the download the complete, You will need to compile the application to start it.
- Click on the Build icon on Xcode. This will compile the source code and launch the Alpha Channel Remover application on your Mac.
- Drag and drop all the images you would like to edit to Alpha Channel Remover window then click Remove Alpha button
- The app will automatically edit all the images removing the alpha option and saving them to the same folder. The this is completed, the Label on the app will change to Completed
- Now export the image to Xcode and archive your app for submission.