Mark, These landscape jpgs you're posting are magnificent ... artifacts and all.
Many thanks. Neil Cooke ----- Original Message ----- From: "Mark Heuymans" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, November 01, 2005 6:19 AM Subject: Re: WorldMachine and RS and Displacement and Height maps ... ADDENDUM > At 02:29 PM 10/31/2005 +0000, you wrote: > >Thanks for that. I see your point about the HDR, as 256 discrete steps > >covering a large displacement can't be solved through interpolation. > > > >I'll note an optimisation I don't know if you're aware of or not. In the > >given example the greyscale image ranges from 0 to something like 128. In > >your bump displacement you set bump amount to -0.24. Now because the image > >intensity is only halfway of the maximum range (all BMP's range 0 to 1 for > >0 to 255 scale, the actual range of displament is 0 to -0.12. If you load > >the bmp into PS and histogram it to the full range of 0 to 255, then set the > >RS bump to -0.12, you get the same level of displacement but rendered much > >faster (alternatively you can load the texture and apply a curve in RS but > >the PS method has less overhead). That's because RS has to look for pixel > >displacements up to the maximum, whether you use that peak level or not. > >Setting a lower peak and ensuring your bumpmap covers the full spectrum > >makes a big difference. > > > >David Coombes > >[EMAIL PROTECTED] > > > You are right about all that, it can be optimized but I'm too lazy ;) > One thing to keep in mind when working with HDR is its unclear output > range. Ideally, the middle of the range should be zero displacement. I'm > just substracting a constant now, by trial & error... it can help to reduce > the total required amount of displacement. > > All in all, I don't know if they optimized displacement in SP2 but I have > the impression it's much faster now than it used to be. Yesterday I was > working on a new big scene with 2048*2048 mappings and this rendered quite > easily in <10 minutes even with high quality render settings! :) > It starts to get worse if the resolution of the mesh is increased too much. > But if it's too low there's a bigger chance of artifacts. > > The main problem I had was artifacts, like here: > http://www.xs4all.nl/~ath8n0r/div/big03l_artifacts.jpg > I think they can pop up when you get too close... here's another render > where the camera is higher, that's almost free of artifacts: > http://www.xs4all.nl/~ath8n0r/div/big02.jpg > > If anyone can find a way to get rid of this phenomenon I'd be happy to hear it! > > Another issue: I'm still not sure if a displaced surface has the correct > slope angle in VSL. This could be a problem with slope-sensitive materials. > Something to check out tonight... I'm also curious if 4096*4096 is still > manageable ;) > > happy rendering, > Mark H > >
