MacOS – Getting Around Alpha Bug for Preview in Sierra 10.12.2

macospreview

I'm running into the problem accurately described here:

https://discussions.apple.com/thread/4229655?start=0&tstart=0

Summary: I take a JPG image, use a selection tool to remove the background so that it will be transparent, and then save the image as a PNG. The image background is represented as black, instead of transparent.

The link there shows that it's a "color profile" bug – is there a correct color profile that supports transparency?

Best Answer

Even though this problem is old, I did figure out a solution that works (on Mojave at least, haven't tried it anywhere else).

  1. Find a PNG image somewhere that already has a transparent background.
  2. In Preview, remove the contents of that image and resize it to match your source image.
  3. Copy the source image and paste it onto this (now blank) PNG image.
  4. Export the image as PNG, making sure Alpha is checked. You now have an image with transparent background and your old image as a second layer.
  5. You can use the Magic Alpha on this new image and it will be saved properly.

Hope this helps anyone out there still struggling with this!

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