SickleYield writes wonderful little journals where she explains things to the 3D world and tells stuff she has just learned to the people who watch her. I love that she does that, so why shouldn´t I try to do the same... because this is how we all grow, yes? Learning from each other is very important and I myself had wonderful teachers. So...
Here is a little crash course about displacement mapping or better - how those are made and set up in Photoshop / Gimp and DAZ.
In Daz Studio, displacement maps work pretty much like bump maps. Light areas render as positive while dark areas render as negative. To make a map for veins on arms, for example, I load the limbs texture into Photoshop as a guide layer, create a transparent layer above it, and simply airbrush the veins (white) using the texture as a guide. Some textures have veins that are visible and very easy to follow, while others do not and you just have to kinda wing it. It always helps to look at photos of very defined bodies where the veins show a lot, so you can look how the veins on arms look like.
I add in a black background behind the vein layer. Generally, so they have a nice soft appearance, I duplicate the vein layer, and run the bottom copy through a gaussian blur filter. This gives an more gradual fading of the edges of the veins, while the top original layer will leave the centers raised nicely. You really need to find out how you set the Gaussian blur yourself, play with it and try different settings.
When satisfied with what I've got, I delete the bottom texture guide layer, merge the remaining layers, flatten the image, and reduce it to greyscale, then you can save it as a .jpg or as a .tif file.
THE REDUCING TO GRAYSCALE IS VERY IMPORTANT! I tend to forget this and then wonder, why my characters look odd because if you keep the map RGB, it will add a weird thickness to the mesh, distorting your character by making the skin look thicker. I have no idea why it is like that but actually it is enough for me to know, that is does this. Always discard the color information by making the map a grayscale picture and there will not be any surprises.
The best way to figure out displacement maps is simply with textures on a 2D panel in Daz Studio. Test out the displacement settings to see how everything looks at different levels. For just veins on skin using a white on black map, I use 100% strength, 0% negative, and depending on how bright the white is and how strong you want the veins, between 0.10 & 0.60% positive. The strengths really depend on the map you use.
If you have a texture that uses displacement maps, open them up and take a look at them, and take a look at the settings they use. This will give you an understanding of what the settings do. There is also displacem,ent maps that do not have black as a base color but a tone of gray, such as the "M4 Displacement Maps" from DAZ3D.com. Those have muscular definition as well as vein displacement, and they have to be applied with negative strength and positive strengths as exact opposites (like -0.50% & +0.50%). To be honest, I use them for my own displacement maps as a base quite often because I love the muscle definition that they have. I can highly reccommend buying those and as long as you keep them for yourselves and don´t include them in stuff that you plan to give away, you may of course edit them to your own liking, even though they already looks fantastic without any additional work. I just sometimes add my own scar displacement that a specific character of mine has, for example.
Thank you very much for reading! I hope, this could be of any help! Of course, for working with Lux, the maps need to be set differently and as soon as I found the best settings for myself, I will share those!