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I want to make everything that is 50% Gray in Photoshop trasnaprent. Black and White should be 100%, but all in the middle transparent.

Let's compare these to images to demonstrate:

Start:

enter image description here

Goal:

enter image description here

Yes the checkerboard is part of the image in order to illustrate which effect I want to accomplish

I would like to do it mathematically exact, rather than faking it.

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    What have you attempted, yourself? Is this being applied to an existing image, or will it always be as linear as you have above? Also, I suspect you have your wording slightly wrong and mean everything that is 50% grey should be transparent. – Paul Aug 22 '16 at 11:25
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    The problem is that in your goal you didn't remove only 50% gray. That would leave a stripe in the middle transparent as next to it you would have 49% and 51%. What I think you want is to select > color range and blend form the colour you want to mask/delete. – SZCZERZO KŁY Aug 22 '16 at 11:48
  • It is good to remember that monitor color is not linear! – joojaa Aug 22 '16 at 12:06
  • I just want to know how I can make gray opaque. @SZCZERZOKŁY. Thanks, u r correct it is more of an masking than removing. – Type-Style Aug 22 '16 at 14:01
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I've made a video showing this very thing for another question, here it is at the relevant starting point: https://youtu.be/F6IhXVxBSQM?t=5m36s

Going off your image:

  • Middle Gray is 128, 128, 128
  • 1 stop Lighter is 191, 191, 191
  • 1 stop Darker is 64, 64, 64

So adjust the Blend If slider accordingly:

enter image description here

enter image description here

If you want it to look more like your "Goal" though it's not actually only removing 50% than adjust the sliders to your liking.

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  • 128 to 255 white 0 to 127 black would be correct I guess. But it does not leave the black and whites untouched. And in your example, the dark gray is still 100%. – Type-Style Aug 24 '16 at 9:52
  • @Type-Style huh? You only wanted the 50% gray removed according to your question so I don't understand your comment. What are you wanting? – Ryan Aug 24 '16 at 11:07
  • I am sorry, 0/127 for white and 12/255 for black in the sliders works fine. I wanted only the #000 and #fff to be untouched. Everything in between gets more and more transparent, the closer it gets to gray. – Type-Style Aug 24 '16 at 12:02

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