By accident, I found out that you can add ICNS icons as Logic Custom Icons.
This would make sense since ICNS supports icon sizes for Regular and Retina displays.

I don't have a Retina display but here's how you can create your ICNS files for Logic icons.

When you add an Logic icon, this is where you can specify an ICNS file.


So what I did was add images for an ICNS file for Regular (using an Apple Application I wrote called ICNSCreator)

and Retina


I found out though, only 3 of the images are being used but I only have a non-Retina display.

Here's some of the places that the icons get displayed.
Arrange Track resized.




Mixer area.


Inspector area.


I've also attached a default Logic Pro ICNS file just so if anyone with a Retina can see if other image sizes are seen in Logic Pro X.

This is kind of cool.
I wound up taking existing ICNS files from AU Instruments that the AU developers already created and added those in Logic Pro X.

Extracted ICNS files from AU Instruments.


Added to Logic Pro X.


Example using the Korg M1 ICNS Icon.

Very cool, added several to my custom icons. Thanks.

You can just drag a grapics file, for example png, jpg, etc., directly onto the image in the Track Header (no need to even open the icon window), and Logic converts it to a tiff file and adds it to its collection stored in the ~/Library/Audio Music Apps/Custom Icons/

So what's the difference with ICON file? Just the embedded multiple resolutions?
.

It's not JUST multiple resolutions.
Depending on the single image you drag and drop, if it's just ONE image Logic will try it's best to display that single image at different sizes.
If not support as in multiple images at different sizes, the image won't display properly.
A 512x512 image auto resized at 64x64 would probably fuse as a single color or a 64x64 image auto resized at 512x512 wouldn't look good.

Also, I don't have a retina display mac, so while I only see 3 of the image sizes being used, on retina displays, I think other sizes might be used.

The shameless plug I'll add as well, with my ICNSCreator application (https://itunes.apple.com/us/app/icns...39006760?mt=12), if you drag and drop an ICNS file on it, I'll extract all the images in that ICNS.

Where did you find all of those icons? Where are they stored?

I did a search on my iMac looking for .icns and none of these turned up despite me owning the Korg and Arturia collections. I’d love to find and use them too exit2studios.

This is about the easiest thing in the world on a Mac and always has been.

CMD+I on whatever app you want the icon for. Click on the icon when the Info window opens up and copy it. Open Preview and paste it into a new file. Bam custom icon you can go drop in Logic in 2 seconds. This even worked all the way back to at least Mac OS 8.

@ boojidad that's because they're all hidden inside the app packages. Spotlight doesn't go through .apps to look at their contents.

Thanks @ Monotremata but I couldn't get that to work- it copied the whole .app. I had to open package contents and drill down to the .icns in resources. Unfortunately, there doesn't seem to be a way to link the plug-in to the icon so that it loads with the plug-in automatically.

A FIND from Terminal would work to find files anywhere on your system.

For the Korg M! do the following.

Show Package Contents


Then look in the Resources folder