How to convert an Alpha of Texture Sample from SRGB to FLOAT?

Do you mean that I need to check the Scene Settings about Color? Let me explain my problem in Blender, I want a function like in the image below. I don’t want to say “I want a curve”, the real thing I want is a conversion from something between Linear and Non-Linear, I’m sorry I don’t know how to call it, just something like that.