i'm new here because this is my last hope

I have to reproduce "screen", "darken" and "soft light" from photoshop. I could only find "multiply" which I was using before.
In fact i have the original picture and a second picture which is basically only a layer of one simple color. What i have to do is use this layer with one of the three photoshop filters and combine them with the original picture in php. I just don't know what to do, because i don't exactly understand how they work.
Does anyone of you have an idea how to start this?
I rely on your help
Ganon