JeffBTX nous illumina en ce 2009-05-29 21:55 -->
> I am using POVRay version 3.6.1.msvc8.win64, OS is WinVista Home Premium 64 bit.
> 
> I am getting back into POVRay after a LONG hiatus. Its been maybe ... 4 or 5
> years at least since I last touched POVRay.
> 
> Yesterday I started experimenting with .DF3 files. I've had SOME experience with
> them under POVRay 3.5 (but I think I fully understand them). I've used Pod's
> tga2df3 utility, and also experimented with using a program that I wrote to
> *create* blank DF3s (just the header, plus filled with zeros). I've
> experimented and figured out how to calculate the offset into a DF3 given x,y,z
> coords. My results arwe what I expect, IE I'm not doing anything wrong, voxels
> are where they are supposed to be.
> 
> I've noticed something odd. I THINK I know what is happening, but could use
> input from a "Guru".
> 
> Assume you have a "blank" DF3 (just the header, plus filled with zeros). Assume
> an 8 bit DF3, of say, dimensions 10x10x10 or 100x100x100 (because that is what
> I've been experimenting with so far). Now... "activate" a *corner* of the DF3
> by filling it (with, say, a density value of 255). The offset (for a 10x10x10)
> (assuming zero-base coords of 0-9) would be x + (y*10) + (z*10*10) + 6. Or
> substitute 100 for 10, for a 100x100x100 DF3. Okay... if you fill x,y,z = 0
> with 255, you have filled the lower left forward corner of the cube.
> 
> If you use interpolate 0 with the DF3, the result is exactly as expected,
> nothing strange... just a blocky "pixellated" voxel.
> 
> If you use interpolate 1 with the DF3, there are "artifacts" at other corners
> and occasionally in other unexpected places (even in the center (?) of the cube
> sometimes? huh?).
> 
> If you use interpolate 2 with the DF3, the artifacting becomes stranger and
> extremely "wacky".
> 
> Okay, I guess the interpolation is ... "averaging" (kind of like antialiasing)
> the region around that corner, and is unexpectedly "wrapping around" to the
> other corners? And why are artifacts showing uop in odd places, like the middle
> of the cube?
> 
> Okay ... so I say to myself, no problem, just make sure that you stay at least
> one voxel away from all corners, edges and faces to avoid this "wrap-around" /
> "bleeding" effect.
> 
> No good - if you are one voxel away from the corner, using interpolate 2, there
> is still some "bleeding". Probably there is a "magic number" (number of voxels)
> as a "safety zone"... before I try to find it by experimenting, I thought I
> would ask for input, and maybe an explanation of what is happening.
> 
> -Thanks
> -jeff
> 

Interpolate 2 have problems when the density reatch zero, it seems that it tries 
  to create some negative values that wrap around to be large positive values.

The common solution is to not reatch zero. For your "empty" DF3, it can mean 
filling it with 1's instead of 0's.

Alain

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