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"Chris R" <car### [at] comcast net> wrote:
> "Mike Miller" <mil### [at] gmailcom> wrote:
> > "Chris R" <car### [at] comcastnet> wrote:
> > > Maybe this is an obvious trick to some of the veterans here, but I thought it
> > > was an interesting way to get good color maps for wood, so here it goes.
> > >
> > > I was working on some wood flooring for a scene and found a site called
> > > wood-database.com that has images and information on lots of different types of
> > > wood, including images of lumber made from the types of wood.
> > >
> > > I downloaded an image of the wood I wanted to replicate in my scene, (the lower
> > > left inset in the image below), and imported it into GIMP. In the Colors/Info
> > > menu there is a "Smooth Palette" option that creates a palette of the colors in
> > > the image, (seen to the right of the inset). I exported that as a JPEG and then
> > > used some macros I created to pull out the POV-ray colors from the image. I
> > > have used both interpolation and non-interpolation for different effects. I
> > > then use those colors, in the order given, to create the color map for the wood
> > > texture.
> > >
> > > Coming up with the wood pigment and warps is still mostly trial and error, but
> > > the sample is actually pretty close.
> > >
> > > The three boards are rendered using variations on the color map. The center one
> > > is non-translated and unaltered. The right has been lightened, and the grain
> > > was selected randomly from a normal-sized pine tree. The left was grayed by
> > > aging, and also randomly selected.
> > >
> > > In this particular example, I only sampled the colors from a single ring of the
> > > wood pattern. For others, the colors vary across rings, so it works better to
> > > use all of the colors in the color map, but scale the pigment so the ring sizes
> > > stay the same.
> > >
> > > Anyway, I'm finding this is a lot easier than my usual hit or miss method of
> > > creating a wood colormap, and allows for greater variation in the colors, which
> > > enhances realism.
> > >
> > >
> > > -- Chris R.
> >
> >
> > That's excellent Chris. Nice work. I came close to writing a macro to do the
> > same - generate a pov color_map from a given image. Mind sharing the macro? :)
> > Mike.
>
> I am doing some more experiments and cleaning up the code. I'll get around to
> posting it eventually after I look at some of the suggestions from below as
> well. The version I have right now just creates a pigment function using an
> image_map from the palette jpeg, and then scans it from <0,0,0> to <1,0,0> in
> steps based on the size of the color map I want to generate. It then just dumps
> the colors it found using #debug as a color_map {} and I copy and paste from the
> message window into my code.
>
> There's a bunch of things to clean up based on failed experiments.
>
> -- Chris R.
For what it's worth, here's the new macro I defined. It now actually generates
a color_map so you can include it as part of modeling, but gives the option of
dumping it to #debug so you can copy and paste it and modify it for artistic
purposes.
I updated it to take any pigment as input to represent the color palette, as
well as allowing you to specify a range other than 0.0 to 1.0 for the range to
sample colors from. This makes it easier to select a subset of the palette.
I'm sure there's a better way to ignore the alpha channel, but this was quick
and dirty so I didn't hunt for one.
#macro Wood_colormap(PalettePigment,MaxEntries,Start,End)
#ifdef (Wood_colormap_debug) #debug "color_map {\n" #end
#local _cm = color_map {
#local _cur_pt = Start;
#local _cur_offset = 0.0;
#local _step = (End-Start)/MaxEntries;
#local _step_offset = 1/MaxEntries;
#while (_cur_pt <= End)
#local _cur_color = eval_pigment(PalettePigment,<_cur_pt, 0, 0>);
#local _scolor = <_cur_color.red, _cur_color.green,
_cur_color.blue>;
#ifdef (Wood_colormap_debug) #debug concat(" [", str(_cur_offset,
0, 3), ", rgb <", vstr(3, _scolor, ",", 0, 4), ">]\n") #end
[_cur_offset, rgb _scolor]
#local _cur_pt = _cur_pt + _step;
#local _cur_offset = _cur_offset + _step_offset;
#end
#ifdef (Wood_colormap_debug) #debug "}\n" #end
}
_cm
#end
The image uses this color_map directly:
#local _board_cm = color_map { Wood_colormap(_colors_pigment, 24, 0.0, 0.9) }
#local _board_pigment = pigment {
wood
warp { ... }
color_map { _board_cm }
}
Here's the #debug output:
color_map {
[0.000, rgb <0.9473,0.7682,0.5972>]
[0.042, rgb <0.8815,0.6459,0.4811>]
[0.083, rgb <0.8542,0.5965,0.4078>]
[0.125, rgb <0.8364,0.6356,0.4650>]
[0.167, rgb <0.8929,0.7560,0.5718>]
[0.208, rgb <0.9048,0.7418,0.5618>]
[0.250, rgb <0.8388,0.6732,0.4993>]
[0.292, rgb <0.8236,0.6438,0.4899>]
[0.333, rgb <0.7335,0.5126,0.3459>]
[0.375, rgb <0.8308,0.6514,0.4851>]
[0.417, rgb <0.8309,0.6514,0.5029>]
[0.458, rgb <0.8574,0.6605,0.4905>]
[0.500, rgb <0.8372,0.6424,0.4701>]
[0.542, rgb <0.8276,0.5571,0.3510>]
[0.583, rgb <0.8125,0.6235,0.4699>]
[0.625, rgb <0.7305,0.5059,0.3492>]
[0.667, rgb <0.8252,0.6073,0.4353>]
[0.708, rgb <0.8156,0.6383,0.4741>]
[0.750, rgb <0.8228,0.6445,0.4793>]
[0.792, rgb <0.8308,0.6119,0.4425>]
[0.833, rgb <0.9098,0.7310,0.5561>]
[0.875, rgb <0.9140,0.7396,0.5553>]
[0.917, rgb <0.7859,0.5887,0.4250>]
[0.958, rgb <0.8085,0.5634,0.3648>]
[1.000, rgb <0.8583,0.6620,0.5145>]
}
-- Chris R.
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Attachments:
Download 'woodgrains.png' (234 KB)
Preview of image 'woodgrains.png'
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