Texturing hair cards

Hi,

I’m trying to create hair textures for my characters. I want to import them into the Unreal Engine 4 later.
My first question:
Reading this article:

https://docs.unrealengine.com/en-us/Resources/Showcases/PhotorealisticCharacter

They mention different types of hair textures that would be needed in order to make the hair look realistic. I could figure out how to create alpha and diffuse texture with blender. But I’m not sure about the Root, the Depth and the Unique ID texture. How can I create those with blender ?

Next question:

I followed this tutorial:

And everything seems to work fine until I tried to create a diffuse texture with it. When I pressed F12 to make a Render Image the entire screen went black. After 30 seconds or so the screen was normal and the hair texture was finished. But it looks awful:

(I attached the blend file and the images)

So how can I create a good looking realistic hair texture and why went my screen black? Should I be worried?

And by the way: To create the alpha texture I followed this tutorial:

Hair.zip (3.7 MB)