I decided to try my hand at capturing textures with a cross polarizing light setup and this was the result of todays test.
The relevant equipment I used is as listed:
I generated albedo, normal and specular/roughness maps.
I am left with 10 images, first I bring them into photoshop, label and stack all into a single file (I should have brought into lightroom and done lens corrections etc).
Then I extract the specular of each direction by overlaying the image with highlights over the one without highlights (cross polarized) and setting the layer to difference.
As you can see, it isn't perfect at A I get weird hue shifts where the leaf colour varies and overall I go not much value at B due to angle of the lights/curl in the leaf, the room was also pretty dark, so there wasn't much other light contaminating the scene.
I do this for all 5 directions, and then I desaturate and blend all the channels together using a lighten. to get my specular and invert for roughness.
I generate my normal maps using the maps except for the frontal using the method shown here http://www.zarria.net/nrmphoto/nrmphoto.html
Because I split out the specular fairly cleanly, this method actually works decently for objects with different colours along a contiguous surface.
For the Albedo, I blend all the 5 cross polarized images using lighten.
I brought my albedo, roughness and normal into substance designer so I could tweak things. I did have to brighten the albedo a bit I'll get a colour chart to do this more accurately in the future. It is important to not blow out the highlights on the specular images, so I rather under expose the albedo, than screw up the normal and roughness.
My take aways are to get a colour chart, experiment with the light angles/softboxes, get some strong double sided tape to flatten those fucking leaves out. Ideally I would get a few more lights and stands so I could just turn the lights on and off as I need rather than re-positioning each shot.
Where I currently live there are a wide variety of interesting plants and as I refine my process I'd love to share them, maybe throw them up on gumroad or something like that.