First off, I want to apologize that I'm a bit of a Blender noob. So here is the story. I am making a reskin for a dinosaur in Ark: Survival Evolved. I’m using the Ark Dev Kit which is a custom version of Unreal Engine 4.5 (has not really been updated since 2015 or so). Probably not relevant yet as my issue crops up at Blender in my pipeline. I used ZBrush to model, and UV the character and exported maps. I have a theory that my UV map was exported wrong because the light seems… upside down? So that’s a color I need to switch on export I think? But there’s also something else happening. I’m not sure what steps to take to fix the second issue.

Ark models seem to have a texture for one side, and it’s mirrored on the other, so they can have a more hi-res texture, since one 2k or 4k texture is used twice. Yes, the symmetry is not totally realistic-looking but with scaly dinosaurs, you do want all the pixels you can get.

I wanted to try this in keeping with their style but also, I am prioritizing resolution because of the work I put into the scales.

So, I exported an obj that was half of a dinosaur, with UV’s and textures generated from this half. I imported it all into Blender and all seemed to be well until I brought in the normal map. The light appears to be shining from an inverted direction on the vertical axis… The model looks lit from below when the light is above… So I guess I need to export with vertical axis colors flipped… but the bigger issue seems to be how I duplicated my model and merged it.The normal map is mirrored over to the other side identically lit. I wanted the duplicate side of the model to use the same texture as the original, and I thought the mirror modifier wouldn’t be the way to go about this but maybe it would be smarter somehow. I have only used Blender a few times since I started posting here, so that’s precious little experience so please be patient with my ignorance. I Hope to use ZBrush for as many steps as possible, and hope people will be able to explain any steps I need to take with a bit of description when it comes to navigation. I still get lost in the interface a lot.

I fixed the normals to all be facing out, and there are no un-welded seams that I can find. The texture looks good honestly, I’m just having this problem where the normal map on the far side of the model is lit just like the original side, even if it’s facing away from the light! The light is mirroring basically. I understand what is going on here, but I don’t know the steps to fix it. Should I have used the mirror modifier, and how would that work with my pipeline? Bringing half the model at low poly with UV’s already into Blender?!

Hello Podcreature Since you exported your UV from Zbrush they are upside down that is one issue with Zbrush going back to 3.0 you have to flip your map with in Zbrush before exporting or they will not look right when you import your model into any other modeler whether it be Blender Maya or 3Ds Max especially when using an OBJ file format I think just flipping the direction of the UV's in Zbrush before export might resolve the issue and till then can really trouble shoot the other questions you have till that one thing is resolved

The first issue I see there is that you are using sRGB for your normal map. You need to change that to non-color data. Never use sRGB for normal maps. Once you change the image texture to non-color, it should correct the issue. If not, then it could be the way they were exported, but that's a known issue with sRGB being used for normal maps. In fact, you should ONLY use sRGB for albedo or color maps. Never for any of the other PBR texturing maps.