Is it possible to change the opacity/alpha value of a program window such as preview or chrome? I know this was possible in Linux by editing some gnome shell file. Is there anything similar in OS X


You can use afloat. This allows you to set the opacity of a window from the Window menu.


Edit: Dec 2018: It seems that a new replacement for Afloat is out called Deskovery, You should enter your email here to join the beta program: https://www.neomobili.com/products/deskovery/ And browse the blog to figure out which beta version you want: https://www.neomobili.com/blog/ Downloads for all versions of this app are kind of hidden here: https://www.neomobili.com/files/

The previously mentioned Afloat is not working anymore on El Capitan and Sierra since both deprecate applications using code injection techniques.

There seems to be no direct equivalent for this SIMBL using Afloat.

If you now need just a 'mock version', does a mock picture suffice your needs? These needs are a bit underdetermined.

However, you may find a number of possible alternatives available that might offer a somewhat similar functionality:

These are not tested as to whether they may be combinable.

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    For those who are looking to compared image mockups to an app you are buiilding, and thus looking for a transparent image window, LayerX seems useful. – Alan Sep 26 '18 at 20:11
  • Duplicate-any-windows does not seem applicable to this question, though I understand why it was included. – Devin G Rhode Dec 11 '18 at 23:17
  • LayerX is probably better than Deskovery – Devin G Rhode Dec 12 '18 at 0:08
  • LayerX has a big advantage over Deskovery - it does one thing and one thing well. You can only have transparent images, but I think that's the primary use case here. – Devin G Rhode Dec 12 '18 at 0:22

The question is about setting the opacity for a single application, but to globally set transparency off, go to System Preferences -> Accessibility -> Display. Then make sure that "Reduce transparency" is selected. I found this here: https://www.tekrevue.com/tip/reduce-transparency-effects-os-x-yosemite/ for Yosemite, but it works in El Capitan.

  • irrelevant answer! downvote – Shorin Jan 31 at 21:36
  • @Shorin, thanks for not actually downvoting (yet). I don't expect upvotes, but to me, it's a service to the community to include a closely related answer that kind of does the same thing, since people will find this question when they are looking for the answer I give. – Mars Feb 1 at 22:10

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