Grayscale images strange behavior on shaders

When using Grayscale images (just 1 channel) it’s not the same as using the same image on rgb. It’s like if the white took strength and all gray parts are whiter.

However, it isn’t only a shader thing, it also happens if it is opened in some programs (like intellij or netbeans, for example) that the difference is visually appreciable.

Example images:



The difference between seems minimal but they have a huge visual difference. If they are open with intellij/netbeans it can be easily seen.

So I was wondering if there is any spacific way to work with grayscales on the engine and how?