How to make a custom value scale?

[Cedric5D51]

I got an idea I want to try on black&white photos. 
Is there a filter or something that would allow me to make a custome scale?
Like say a filter where at a certain value, a colour is shown (e.g at 0, it's black, at 33 is a green, at 67 is a pink, at 100 is a white)

Or a way to apply a gradient, but to the photo's values, not the gradient tool's.

[Barbara Ash · Accepted solution]

What you're asking sounds similar to Gradient Map, which is one of the adjustment layers that you can apply in the Layers panel. 

[Cedric5D51]

Thank you! Gradient map works wonderfully (though I still need to tweak around with colours)

[Barbara Ash]

You can create your own gradient if none of the standard ones work for you.

[Bob_Hallam]

https://www.youtube.com/watch?v=fJU3KOwo0jU

this should get you going in the right direction