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Help!
I'm working with a large height field object, rendered at very very high
resolution and am coming across a strange artifact when I enable smooth.
Basically, I see darkened boxes instead of a smooth shading (I'm also
losing a lot of detail).
I've got enough resolution in my height field source image, as the
terrain is reasonably well contoured and the non smoothed image doesn't
show large jaggies. (although it shows serious stepping, making it
unusable).
Anyone have any suggestions on what might be going on, solutions or
workarounds? Am I hitting some upper limit in significant digits or
precision, or is this related to the normal flipping issue in
heightfields?
I've tried generating a mesh from the source bitmap image using Wilbur,
but that took a LONG time to parse and couldn't ever get the same level
of detail as the heightfield. It also didn't make proper normals, so
it was faceted. I've tried different formats for the source image, with
no change.
here's a jpg of the effect:
http://home.pacbell.net/selmo/smooth.jpg
and the same image without smoothing:
http://home.pacbell.net/selmo/no_smooth.jpg
I'm using POV 3.5 windows beta 11.
It's a 16bit 5000x5000 pixel TIFF source image for the height field,
rendered at 20K x 10K pixels. (yes, I've got good reasons for needing
such high res. :) I've tried disabling the shadow in case it was the
normal-edge issue, but that didn't help either.
height_field
{
tiff "topo.tif"
scale < 1.0 , 0.02 , 1.0 >
smooth
no_shadow
texture
{
finish {specular 0.15 roughness 0.8 crand 0.10 }
pigment
{
White
}
}
}
Help!
Thanks
Lars
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The very first thing you should try is to use double_illuminate to see if
it's the known problem about normal inversion (although it doesn't seem so).
If it's not that, then it *might* be that your color depth is not high
enough with respect to the resolution of the image. Even though you say
that you are generating a 16-bit image, it just might be that the program
you are using to generate the heightfield image just uses 256 different
heights (which can be very insufficient with such high pixel resolution).
If nothing helps, just try making your heightfield image with lower
pixel resolution.
The algorithm POV-Ray uses for calculating the normal vectors (which I
think is just the regular average-the-normals-of-adjacent-triangles) is
not perfect and causes bad shading in some cases.
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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> The very first thing you should try is to use double_illuminate to see if
> it's the known problem about normal inversion (although it doesn't seem so).
I tried that, but it didn't change anything, so I guess it's not the HF
normal flipping problem.
> > If it's not that, then it *might* be that your color depth is not high
> enough with respect to the resolution of the image. Even though you say
> that you are generating a 16-bit image, it just might be that the program
> you are using to generate the heightfield image just uses 256 different
> heights (which can be very insufficient with such high pixel resolution).
I'm guessing that probably wouldn't change the boxing effect I see in
smoothed images, but that might help with trying to get the non smoothed
image looking less stepped. That's what I've been trying to do
recently, but I am having problems finding a good image processing tool
that can handle 16bit grayscale images. I've been taking an 1000 x 1000
8bit image (TGA converted from a DEM) and upscaling it to 5K x 5K,
allowing Photoshop to do bicubic interpolation to create the additional
16bit data between the original 8 bit image source pixels. However,
this obviously wouldn't create a truly smooth gradation since the delta
is only a few pixels, so I'm probably seeing 500-1000 levels of gray
instead of the full 16 bit range. If I could get a smooth or blur
operation on the 16bit data, I might get less stepping and hence get
something usable.
Any recommendations on good tools to smooth and manipulate 16bit
grayscale images under win2000? Photoshop is quite limited in it's
16bit handling, and I'm not having any luck with Wilbur--it seems to
produce a lot of empty images and lose data. HLA didn't run under
windows 2000.
> > If nothing helps, just try making your heightfield image with lower
> pixel resolution.
yah, that makes correspondingly larger squares. :) I'm trying a few
other tricks so see if I can figure out what's going on, including
seeing if I can get a smoother 16bit terrain image souce. Any other
suggestions would be appreciated.
Thanks
Lars
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> I've been taking an 1000 x 1000 8bit image (TGA converted from a DEM)
Have you tried dem2pov? I haven't used it but it might give you better
than 8bit height resolution.
John Haiducek
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Lars wrote:
> Any recommendations on good tools to smooth and manipulate 16bit
> grayscale images under win2000? Photoshop is quite limited in it's
> 16bit handling, and I'm not having any luck with Wilbur--it seems to
> produce a lot of empty images and lose data. HLA didn't run under
> windows 2000.
Have you looked at Leveller? - http://www.daylongraphics.com/
--
Ken Tyler
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Lars wrote:
>
> [...]
> I'm guessing that probably wouldn't change the boxing effect I see in
> smoothed images, but that might help with trying to get the non smoothed
> image looking less stepped. That's what I've been trying to do
> recently, but I am having problems finding a good image processing tool
> that can handle 16bit grayscale images. I've been taking an 1000 x 1000
> 8bit image (TGA converted from a DEM) and upscaling it to 5K x 5K,
> allowing Photoshop to do bicubic interpolation to create the additional
> 16bit data between the original 8 bit image source pixels.
There are various types of so-called 'DEM' data formats which need
different conversion programs. A lot of them are in a quite simple ASCII
form, but some are more complicated. Nearly all are 16 bit data in the
original so the 8 bit you get are probably result of the conversion.
> Any recommendations on good tools to smooth and manipulate 16bit
> grayscale images under win2000? Photoshop is quite limited in it's
> 16bit handling, and I'm not having any luck with Wilbur--it seems to
> produce a lot of empty images and lose data. HLA didn't run under
> windows 2000.
gforge/HF-Lab should compile with Cygwin without problems.
Christoph
--
POV-Ray tutorials, IsoWood include,
TransSkin and more: http://www.tu-bs.de/~y0013390/
Last updated 06 Feb. 2002 _____./\/^>_*_<^\/\.______
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> Have you looked at Leveller? - http://www.daylongraphics.com/
I downloaded the demo and played with it for a bit, and honestly
couldn't figure too much out! :) The cost was an issue for me, so I
didn't look at it too seriously, but I'll look at it a bit further if
you think it will work.
> Have you tried dem2pov?
I haven't--I'll look into it. I used a DEM->TGA converter to begin
with, but I do need to edit the files after they are converted from
DEM--move features around, adjust them, add new features, etc. So I
need some way to edit them once they become 16bit files. (editing them
in 8 bit and then trying to convert them to 16bit after is what I was
doing, but I've been running into the smoothness / stepping issue).
Many of the DEM converters didn't look like an option for me, since I
wouldn't have any way to manipulate the data afterwards.
I saw a couple more programs on the povray.org site, but many were dead
links--earthscape, klevel, smooth, etc. :( If I can't find something
that exists already, I might just write my own 8 to 16 bit converter
with smoothing. Or maybe set up a DOS box to run HLA.
It sounds like the consensus so far is that I should attack this from
the trying to get a smooth 16bit image angle and not use the heightfield
smooth function. None of my experiments to date have suceeded in
getting the smooth function to work without the boxes effect in some
degree.
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> There are various types of so-called 'DEM' data formats which need
> different conversion programs. A lot of them are in a quite simple ASCII
> form, but some are more complicated. Nearly all are 16 bit data in the
> original so the 8 bit you get are probably result of the conversion.
I'm having to deliberately convert them to 8 bit, since that's the only
way I have of editing them after I convert them. If I had image editing
software that could read and manipulate 16bit grayscale images, I'd
start from there and probably not have the problem at all. But so far,
I've been unable to find anything that can manipulate 16bit grayscale
images. I tried UTSCSA's ImageTool 2.0, but it can't handle the large
file sizes needed.
So the lack of a 16bit image editor is the reason why I have to go to 8
bit, edit, then convert to 16, using bicubic interpolation while
increasing the pixel scale to smooth out the results. But it's not
smoothing enough. So I need something that can either edit the 16bit
images, or at least run a good smoothing algorithm on the converted
16bit image.
I'm assuming that if I could get the full dynamic range of 16bit
grayscale, my stepping issue should go away. If not, well, then I'm
back to the drawing board.
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Thanks for the suggestions so far.
I've been able to create a full depth, smoothed 16bit test image for the
heightfield. Unfortunately, even with 16bits, the stepping remains
quite noticable. I've got many many more steps than before, but they
don't blend and remain quite clear. The edges of each change in
elevation are highlighted and it looks like a million slug trails over
the landscape--or maybe those architectural models where they make hills
from layers and layers of flatboard. I think the problem lies in the
terrain is mostly flat, with subtle slow changes in elevation causing
the stepping. Plus it doesn't seem to smooth between to areas, instead
making a dimensional bump between two values. Places with more
pronounced altitude changes don't look as bad. So I think 16bit
elevation data has failed to solve the problem. It appears I need to
find a way to get smooth to behave, or find a different approach.
Using Heightfield "Smooth" tends to produce a more muddied look-- it
appears as if there are only three levels of lighting--dark, med and
light with no gradation between them. It looks very posterized. It's
almost as if the normals are quantized and only allowing for three
levels of specular lighting effect. Plus the boxes problem remains
(which might be related--more gradations might make the boxes harder to
notice). I've tried changing my scale factor, in case it was a
precision issue, but no change.
Anyone have any further ideas on heightfield smooth?
Thanks
Lars
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In povray.general Lars <sel### [at] pacbell net> wrote:
: Anyone have any further ideas on heightfield smooth?
Did you try with a lower resolution? For example divide width and height
by 10. (You don't have to use it; just try it to see what happens).
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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