Displacement Artifacts

Displacement Artifacts

animate1978 11 Jun 2009 01:41

Well I found some odd artifacts after getting a workable texture build for the latest rigged spider model. I am not sure if this is getting corrected in Mosaic, or if it's a UV mapping error, or if it's an Aqsis bug. If it's a UV error then I am going to give up fixing this, I have spent a month on this spider and I am tired of working on her. If these are Mosaic issues, is this what you were talking about Eric? If it's Aqsis…. I am not sure if you need the complete RIB package.

I think it's pretty obvious what's wrong in this image, however if not - the fangs are now tipped with what resemble cups from the displacements overlapping. Grid cracking that never was there before. Also a strange patch of texture that was never there before. On the base of the arm, it seems detatched. Also the whole displacement map seems a bit too pixelated.

Frustrated now since it appears I need to start all over with this thing again. I will try to cut the displacement amount to minimum (0.005) and see if that helps any.

http://picasaweb.google.com/lh/photo/UTwH3bSw5s37roFsvM1I-g?authkey=Gv1sRgCKqP9vT19rGp0QE&feat=directlink

Re: Displacement Artifacts

animate1978 11 Jun 2009 02:16

Well already I turned down the displacement in Blender to 0.005 and that cut down the issues to nothing, however there is little displacement. Arrgh

At least I know it's not Aqsis.

Re: Displacement Artifacts

c42f 11 Jun 2009 02:43

Does the ring around the arm in the top left represent a seam in the UV mapping? That could be the cause, or it could be something else…

Did you try playing with the displacement bound? The artifacts on the belly remind me of the kind of thing you get when the displacement bound is too small.

As for the funny cone on the end of the fang, I think your displacement texture should be adjusted to give zero displacement there or you should expect to have some artifacts at sharp points in the mesh if you're displacing along the surface normal.

The pixellation on the top left could possibly be an aqsis bug but I would be a bit surprised. I suspect it's more likely just to be a coarse (stretched) texture on that leg of the model.

Anyway, it's looking interesting. How closely are we going to view the spider? maybe some of these artifacts won't be visible anyway?

~Chris.

Re: Displacement Artifacts

animate1978 11 Jun 2009 02:55

Well it won't matter at this point anyway, since Eric is releasing his latest in the next week or so and from our meeting last weekend he did mention that texture mapping will be fixed.

So we will see how things turn out then.

Re: Displacement Artifacts

animate1978 11 Jun 2009 04:16

Considering there is at least 1 shot of a closeup on Gladi's face, I do need to make some modifications to the displacement map anyway since the mouth pieces have quite a bit denser collections of bumps than the rest of the head. I just did a test to see if there were any render artifacts there and no it seems ok.

I wonder if it would be possible to increase the UV map size of just that area, the head part. If that were a bit more uniform to the rest of the area it would look a LOT better so I will be trying to accomplish that. Which would mean a texture map redo is in order if that is the case. One thing I do notice is the displacement is stretched, remembering certain brushes I have made that were 1 pixel in size ended up looking quite large in the render. If I can get away with just adjusting that area I can avoid redoing the ENTIRE map in which case should only take a day or two.

Again I guess it is not so much the rendering causes the artifacts, the maps are. One thing I want to ask is how do I use the included Hair DSO in the latest builds? If I do it right I can mask over the minute artifacts with some hair to distract viewers from them, IF I can't get these to go away under normal means. Of all the models this one gets most screen time so I want to be able to get this one done soon here so I can concentrate efforts on other things like shaders, on the other hand I don't want to leave details out because even the slightest might get seen at HD res.

I guess the ol spider still has some work left in her. At least the rigging is done now, and well done too.

Re: Displacement Artifacts

Eric Back 11 Jun 2009 05:02

Hey guys,

A few months ago I messed around with displacement mapping specifically for baking multires sculptures into displacement maps, but had quite a few problems and decided to wait until after I finished this shader rewrite to continue. Here's a few tricks I picked up that may help (although none of these resolved all the problems).
The "stair stepping" in the displacement is a result of lack of bit depth, you'll need to use a 32bit tif in order to eliminate them. I remember having some difficulty finding a format that both Blender and Aqsis both translated properly but I can't remember what I finally came up with. I also found it helpful to use cinepaint for editing outside of Blender if you don't already have it.

The current displacement shader uses middle gray color(0.5, 0.5, 0.5) as surface level, brighter as raised, darker as lower (pretty much industry standard), however Aqsis is having normal issues so this may appear reversed. Also note that there's a parameter called "Mid" that allows you to tune were middle is, this may help to fine tune the displacement.

Another problem I ran into was the "st" values are mapped from the base mesh to the SDS surface by the renderer during render (this is NOT controlled by MOSAIC), Blender has a button that allows mapping of UV after SDS. The equivalent of this in Aqsis is the "facevertex" option in the "Geometry Setup" tab, I strongly recommend trying this if not already.

The last problem I had was it does appeared that the UV->st conversion would shift off from Blender's, however I've noticed this only happens with SDS so I think it related to differences in how Blender and different renderers map st to SDS surfaces. I'm hoping that adding support for layered UV sets may reveal something but its doubtful :(

Re: Displacement Artifacts

animate1978 14 Jun 2009 01:22

Eric and Chris,

Awesome! While I am away at the coast (I managed to grab a laptop) I'll be doing a lot of research since I can't do so much production other than shader writing.

The displacement map clarification is very much appreciated and as soon as I get back I will go and at least try to fix the map so it's more in tune to the default Blender value. As for using Cinepaint, since I am using Windows I only have an old version of that available but it will work for my needs in this case. Gimp is great for certain things but more and more it seems that it just is not able to handle our needs, so IF I do any texture work in GIMP it will later be fine tuned in Cinepaint. Honestly I was thinking about that myself and wondered why I wasn't using Cinepaint from the start (too used to GIMP and started to use on instinct). I think I should make this noted in the pipeline docs too.

I will look into the UV when I return too, I am not working on a 'production' model of the spider at the moment, just a local copy on my system so once I figure out the hair length method, and the HairDSO, I'll be Appending that to a new file.

So IF the Hair DSO is not fully operational by the time we get into animation, I think it still would be possible to use hair as long as the amount is lower than the default setting. From my own testing with the normal hair export it doesn't take that long, it only starts to choke up when parent and child hairs are set at the normal default values. If those are set below the default it does end up looking fairly decent.

Also I noticed that Aqsis is under feature freeze and that 1.6.0 P1 is being released on Moday? When this does happen is it recommended to take off any 1.5.0 builds and use the new 1.6.0 builds? In regards to that, how much change is there in compiled shaders? It's not THAT big of an issue but if there is no change between 1.5.0 compiled shaders and 1.6.0, it should just save time, if there is a good reason to recompile I will do so, otherwise I will just leave them alone (for now).

Re: Displacement Artifacts

pgregory 14 Jun 2009 08:34

There will be no change in the compiled shader specification betwen 1.5.x and 1.6.0, all shaders should continue to work. I believe there has been a change between 1.4.2 and 1.6.0 but that shouldn't affect you.

Paul

Re: Displacement Artifacts

c42f 11 Jun 2009 05:08

The README.txt in the source directory says a bit about how to use the hair DSO. Note that I haven't tried it for a while and many things have changed in MOSAIC since then.

Also note that it's probably not going to work properly for animations yet (but should be pretty much working for stills). I'll have to revamp some things to fix that.

~Chris.

Re: Displacement Artifacts

animate1978 14 Jun 2009 01:23

I'll look into it. I have sent the README to my email account so I can have immediate access to it while I am gone.

Re: Displacement Artifacts

Eric Back 14 Jun 2009 04:32

Glad to hear you got a laptop, hopefully that means you'll be able to stay in touch a least a little :)

I like Gimp and use it for most graphic work but I mentioned cinepaint because I use it whenever I'm dealing with HDR images. I personally prefer Gimp but of course it can't handle high bit depth formats. I may be mistaken but I thought I read somewhere that their either adding or have already added the infrastructure for Gimp to handle HDR formats?

Also forgot to mention that you can seriously speed up hair export by keeping the "Render" step down around 1 or 2, if your doing straight strands you can even use 0! Unless your dealing with long curly strands its not necessary to use more. Another trick that Chis is using in conjunction with hairgen is to use a displacement shader to ripple or twist the strands, in that case you can export hair with just 2 point (render=0) and still get complex hair ;-)
One final note on a technical side, avoid using RLength as it varies the points in the strands in an uncontrollable way possibly causing big slow downs or export errors!

Eric