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HellRaiZer

Normal Mapping artifacts (wtf is this???)

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Hello all... I've recently started working with normal mapping for my engine, and i have some problems with creating normal maps from detailed objects. The problem(s) are shown in these two shots : Original texcoords Modyfied texcoords First of all, do you recognise anything wrong from these shots? Is this a known problem? The model in the two shots is the same. The head from nVidia's demos. The reason the viewpoint isn't the same, is because in the second shot, the face was fine. No artifacts. The only artifact was this mess behind the ear. In the first shot, texture coordinates for the normalmap is exactly the same as in the original model. In the second shot, texture coordinates were generated using Lightwave's Atlas UVMapper. Normalmaps for these shots were generated from nVidia's Melody and are in object space. But this is not the problem, because i have tried some other normalmappers, like ATI's (as a Lightwave plug-in), and ORB (Open Render Bump), and there are artifacts in all of them. Maybe not the same, but they exist! Low polygon count model was generated from the detailed model, using Lightwave (qemmLOSS3 plug-in) or Melody (Progressive Mesh). I've experimented with some other models too. What i found is : 1) Model size doesn't matter. At least it doesn't solve the problem completely. 2) Texture coordinates have something to do with it (What????) 3) Problem mostly appears on non-convex parts of the model (like the ear, which has some distance from the head). 4) Making the normalmap bigger, doesn't solve the problem. Do you have any idea what's going on? What should i change to solve the problem? Is this model's problem, or it has to do with normalmap creation algorithm? Thanks in advance, and i hope on an answer. HellRaiZer

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This type of thing typically comes from one of two things :

1) The raycasting. Basically, the ear and the head under the ear map to the same part of the texture. This can be fixed by tweaking the minimum distance that you consider a ray must go before it can hit something. I know nvidia's Melody has a setting for this.

2) The texture coordinate unwrapping. Even if #1 is fixed, the triangles in uv space may overlap on the texture. Some tools ( like Melody ) use a spring model to minimize overlap and texture stretching. Sometimes the physics sim may get confused or stuck.

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Thanks for the reply, and sorry for the late posting :)

After some more hours experimenting with texcoords i final concluded to what you said.
For #1 you must mean the "ray bounds" option in Melody. I played with it, but it didn't changed a lot.
But #2 is definetely the problem. I haven't looked at texcoords generated by LW at that moment, and i missed the overlapping triangles.

Using Melody for generating texcoords (one or multiple charts) doesn't fix the problem. Instead the problem gets more noticable.

I'll try to fix the texcoords by hand in one or two models, to see if the problem disappears.

Thanks again

HellRaiZer

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