The layers are built by creating a basic model in blender, rendering it out and then painting each layer by hand before combining them into a result.
I start with the diffuse, then ambient occlusion, then each of the contributing lights, and then anything else like monitors and switches and gleams and glare etc.
With this technique you can easily adjust the hue/intensity of lights or the base diffuse colours of objects. It works surprisingly well. I stopped short of painting a GI pass as the elements I had seemed to combine okay without it.
Completed in Photoshop with the line-work done in Illustrator though Inkscape and Krita would have been more than fine for the job.
It can be quite tricky. I don’t know if I will continue painting this way as, looking back on it, it does look like a LOT of work
I have some higher rez versions of each step on my Artstation page if it’s any help to you…
I had a look at your ArtStation and Website, wow! You do some awesome stuff! I particularly liked the Large Insect since I am going to do an insect drawing myself in a few weeks.
Yeah now you mention it, that workflow does seem like a lot of work, some people just start with very simple 3D models and digitally paint over the top. I dunno, maybe the 3D scene could be used as a basis for general lighting and then the digital paints could flow from that? Sorry just thinking out loud - ignore me!