Issues with Normal Map in Iray

Toyen

Hey guys!

I´ve come across a strange issue when creating a normal map for a shirt. (Normal map was baked in Blender for the purpose of adding detail of sculpted folds on the shirt).

The normal map is making the polygon structure visible in the render and I have no idea why.

I checked this in 3Delight too and the issue only seems to appear in Iray.

Has this happened to anybody?

Let me know! I´d love to hear your thoughts.

 

mjc1016

Try adding one level of SubD to the mesh...

Toyen

Hey there!

Just tried it, didn´t help unfortunately.

mjc1016

The differences between the way Iray and 3DL do subdivision are the root cause...if you have too big a difference between the baked resolution and the one the map is applied to you can get artifacts.  Also texture compression can mess with normal maps.   Or mismatched sizes...try baking it at a different rsolution...if the diffuse is 4096 x 4096 make sure the bake is also that size.   There's probably a dozen other things that can contribute/cause problems, too...but I can't think of them right now...like whether smoothing is is on/off when doing the bake in Blender (off and you can bake the 'faceted'/not smoothed surface into the normal map, too, but that one will usually show in 3DL, also...and with a good look at the map itself).

Toyen

No idea really, the item is smooth, the map was baked from multiresolution where the baked version was subdivided to 4 times and the base version of the object I´m applying the map to is subdivided only once.

So yes, there is a big difference between polygon count on the base item and on the most detailed version I baked the normal map from.

But thats the point of the normal map, it should add the detail to a low poly object. No idea why is it acting up like that.

I appreciate your help though : )

 

mjc1016

Yeah, but with some of them, I've found that 4 levels in multires is too much...of a difference.

Toyen

Just tried to put the normal map on a level 2 subdivided mesh (this is as high as I can go, more would be too much) and the issue persists though the sharp polygons that are visible are now smaller.

Very strange.

mjc1016

Some have reported duplicating the mesh and applying the multires to one of them and removing it from the other gives better results.  That way you can use the Selected to Active option and play around with the Bias and Distance settings.

Also make sure that 'Subdivide UVs' is ON, in the Multires modifier.

Toyen

I do think this is Iray issue.

The normal map renders perfectly fine in 3Delight.

mjc1016

Like I said earlier...Iray and 3DL have very different approaches to subdivision.  Reading a bunch of stuff in various places about making normal maps for Iray is where I've come across the not have too great a difference between the hi/lo versions.  Generally, from my reading 4 levels difference is too much.

Some of the others are from various Blender tuts/forum posts. 

And 3DL is much more forgiving, when it comes to things like this.  Iray is very, very picky and not too 'fault tolerant' (my own observations).  As a result, little things that aren't problems in 3DL tend to show up/be amplified in Iray.

Toyen

Well 2 levels of difference should be just fine I guess but still it doesnt work.

I´ve tried converting the image to .tif as I have noticed V7s normal maps were .tifs, I also tried blurring the map a bit but nothing worked so far.

I must get to the bottom of this! : D

Toyen

Update: Something must be wrong with my normal map after all. I just tried to bake a quick normal map in gimp with a pattern and it renders properly.

Hmm, wonder what could it be.

mjc1016

Try the duplicate/apply trick, in Blender...for that one, it's supposed to not matter how many levels difference there is.

Toyen

Could you elaborate please? Not sure which trick is that : D : )

Also I did a quick test to find out whether there was something wrong with my topology by baking a normal map for a simple sphere but the problem persists so I guess my topology is fine but there must be something else wrong with maps baked in Blender that is making them appear this way.

I´ve tried cycles baking as well but still the same problem.

 

mjc1016

You duplicate the mesh, apply the Multires modifier to the duplicate so it actually fixes the hi-res geometry (make sure you have the update UVs checked before you apply it) and then remove the Multi-res modifier from the other copy (orginal) then use the bake Selected to Active option, instead the bake from multi-res.  Doing this would give you the hi-res (with the modifier applied) and lo-res (one with the modifier removed) meshes.   This enables the distance and bias variables.  Supposedly this will allow a larger bake range...and by using the bias adjustments can compensate for 'base geometry' showing.

Toyen

Ah you mean that!

Tried it with both cycles and blender render on a simple sphere, not working : (

mjc1016

What version of Blender?

I was using 2.73 for quite a while and baked a bunch of normal maps...not sure if I've used any in Iray or not, but I didn't have any obvious problems (3DL and Luxrender...I know that I used them in those two).  I haven't baked any with any later versions of Blender.  And I was doing both ways.

Toyen

Oh figured it out! At last!

When creating a base image you wish to bake on, it is important to leave "Alpha" checked, otherwise a black canvas will be created and the normal map baked on that black background will be a much lighter shade of blue than it is supposed to be and thus will cause trouble in Iray.

Silly me! 

Thank you for your assistance mjc! : )

mjc1016

Dang...that's too easy!