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How do you change the opacity of a Photoshop tool (e.g. the brush or the paint bucket) to something other than an integer 1% to 100%, such as 0% or 0.5% or 99.5%?

When I try entering these numbers manually an error window pops up, saying it's invalid:

error

It's my understanding that in many images (8-bit per channel PNGs at least) the alpha channel has a range or 0-255, just like the red, green, and blue channels. So more than half of those alpha values are impossible to reach with an integer from 1-100 (without complicated compositing of multiple transparent layers). After all, Photoshop has 0-255 sliders for RGB, why not for opacity? Or, if so, where can I enable this feature?

I'm using Adobe Photoshop CC 2018 (which has no tag it appears).

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2 Answers 2

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If you want to set the actual value than use a mask and set it to a real 8 bit value. With this method there is no chance of rounding in play.

  1. Select layer you want to control,
  2. select Layer → Layer Mask → Reveal All,
  3. click on the layer mask (in layers palette),
  4. fill layer, Edit → Fill,
  5. choose a ray color of the exact value you want,
  6. OK

You cow have exactly the value you want, no rounding no guessing. Except, if the layer you blend has some alpha values, in which case the result is rounded. Same works for 16-bit of floating point color.

* 1/255 = 0.392156... % so the value of 99.5 would be rounded anyway. And in many practical cases 1% is accurate enough.

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You cannot change it directly because of the software limitations (read integral range of opaqueness). It is analogous to painting with limited colors and brushes and modifying your painting into a directly non-achievable color shade or stroke.

You may also be using some varied opaque sheets (and maybe some design on them) to provide the desired look to your design. It is the concept of photoshop that you have to understand. Below link may help you with what you want to achieve with the photoshop tool.

https://forums.adobe.com/thread/852867

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  • Seems lame that such a popular, long running software has this limitation when free things like GIMP and Paint.NET do not :(
    – Discrete Games
    Sep 9, 2018 at 2:54
  • @Discrete Games Theoretically it appears to be a bane but Adobe is primarily built on the concept of layering which allows flexibility to make graphics. Also, in my personal opinion it provides more creative freedom than the softwares you mentioned.
    – kung_foo
    Sep 9, 2018 at 3:16
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    @DiscreteGames Well if you make a mask then you can use color picker and backspace key to fill the mask and set the true value from 0-255 range in 8bit images, or more for 16bit.
    – joojaa
    Sep 9, 2018 at 5:41
  • @kung_foo - That's not right. GIMP and Paint.NET are also built on the concept of layering, just like Photoshop.
    – Billy Kerr
    Sep 10, 2018 at 11:22
  • @BillyKerr Where did I write that GIMP and Paint.NET are not built on the concept of layering?
    – kung_foo
    Sep 10, 2018 at 15:15

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