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Hi, all!
I'm trying to use an image_map to color some media in a transparent
box--that is, "extruding" the image_map's colors in the +Z direction,
"filling" the box from front to back with emitting (or scattering) media,
the colors of which correspond to the image_map colors. My image_map has
an alpha channel as well (the idea being that the transparent parts of the
image_map will create NO media density.)
A recent post got me to thinking about this...
http://news.povray.org/povray.general/thread/%3Cweb.44174d8d9ca30044945ca8690%40news.povray.org%3E/
I'm not even sure that what I'm attempting to do is possible; I've tried
various ideas with no luck. Reading the POV docs in sections 3.5.11.15 and
16, I'm thinking that the image_map should first be turned into a pattern
function(?)... Like this:
#declare my_pattern =
function{
pigment{
image_map{png "my_image.png"
map_type 0
interpolate 2
once
}
}
}
and then *trying* to apply it to an interior{media} statement,
like this example (which doesn't work, and generates an error message):
interior{
media{
emission .5
density{
my_pattern
}
}
}
Am I on the wrong track entirely? When I try to use the image_map itself in
the media's density block, I get the error message, "image_map can only be
used in a pigment statement." Perhaps my image_map should instead be
turned into a color_map somehow (?)
I feel like I'm overlooking something obvious. Any help or suggestions would
be most appreciated. This technique would be *very* useful.
BTW, my_pattern works perfectly well when used properly as an isosurface
function, so I'm at a loss as to why it isn't working in media.
Ken
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Wasn't it Kenneth who wrote:
>Hi, all!
>
>I'm trying to use an image_map to color some media in a transparent
>box--that is, "extruding" the image_map's colors in the +Z direction,
>"filling" the box from front to back with emitting (or scattering) media,
>the colors of which correspond to the image_map colors. My image_map has
>an alpha channel as well (the idea being that the transparent parts of the
>image_map will create NO media density.)
If this can be done, then using a single pattern isn't the way to go.
The problem is that you want all four colour channels to affect the
colour and density of the media, but using a pattern reduces the data to
a single channel.
density {image_pattern {png "my_image.png"}}
You can split your image into three: red*alpha, green*alpha, blue*alpha.
Then use an interior that contains three media components. Since you're
using emission media, black is the same as transparent.
interior {
media {
emission .5
density {
image_pattern {png "red.png"}
colour_map {[0 rgb 0][1 rgb x]}
}
}
media {
emission .5
density {
image_pattern {png "green.png"}
colour_map {[0 rgb 0][1 rgb y]}
}
}
media {
emission .5
density {
image_pattern {png "blue.png"}
colour_map {[0 rgb 0][1 rgb z]}
}
}
}
For the other types of media, things get a little more complicated.
--
Mike Williams
Gentleman of Leisure
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"Kenneth" <kdw### [at] earthlink net> wrote:
> Hi, all!
>
> I'm trying to use an image_map to color some media in a transparent
> box--that is, "extruding" the image_map's colors in the +Z direction,
> "filling" the box from front to back with emitting (or scattering) media,
> the colors of which correspond to the image_map colors. My image_map has
> an alpha channel as well (the idea being that the transparent parts of the
> image_map will create NO media density.)
>
> A recent post got me to thinking about this...
>
>
http://news.povray.org/povray.general/thread/%3Cweb.44174d8d9ca30044945ca8690%40news.povray.org%3E/
>
> I'm not even sure that what I'm attempting to do is possible; I've tried
> various ideas with no luck. Reading the POV docs in sections 3.5.11.15 and
> 16, I'm thinking that the image_map should first be turned into a pattern
> function(?)... Like this:
>
> #declare my_pattern =
> function{
> pigment{
> image_map{png "my_image.png"
> map_type 0
> interpolate 2
> once
> }
> }
> }
>
> and then *trying* to apply it to an interior{media} statement,
> like this example (which doesn't work, and generates an error message):
>
> interior{
> media{
> emission .5
> density{
> my_pattern
> }
> }
> }
>
>
> Am I on the wrong track entirely? When I try to use the image_map itself in
> the media's density block, I get the error message, "image_map can only be
> used in a pigment statement." Perhaps my image_map should instead be
> turned into a color_map somehow (?)
>
> I feel like I'm overlooking something obvious. Any help or suggestions would
> be most appreciated. This technique would be *very* useful.
>
> BTW, my_pattern works perfectly well when used properly as an isosurface
> function, so I'm at a loss as to why it isn't working in media.
>
> Ken
Hello!
AFAIK, an image_map is only defined in the x-y plane. So, I guess that using
it as a 3 dimensional pattern will lead to non-zero values only in that
plane, and therefore your density will be non-zero in an infinitely thin
slice of your container, ... which I am afraid will also be valuated to
zero.
Regards.
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"Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> wrote:
> AFAIK, an image_map is only defined in the x-y plane. So, I guess that using
> it as a 3 dimensional pattern will lead to non-zero values only in that
> plane, and therefore your density will be non-zero in an infinitely thin
> slice of your container, ... which I am afraid will also be valuated to
> zero.
>
> Regards.
Ooops! not 100% awake this morning ... My reply was not very smart ...
Forget it. Mike's is much more sensible ...
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"Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> wrote:
> "Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> wrote:
>
> > AFAIK, an image_map is only defined in the x-y plane. So, I guess that using
> > it as a 3 dimensional pattern will lead to non-zero values only in that
> > plane, and therefore your density will be non-zero in an infinitely thin
> > slice of your container, ... which I am afraid will also be valuated to
> > zero.
> >
> > Regards.
>
> Ooops! not 100% awake this morning ... My reply was not very smart ...
> Forget it. Mike's is much more sensible ...
I had a cofee and my brain functions a little now ;)
This piece of code works:
#declare my_pattern = function
{
pigment
{
image_map
{
png "my_image.png"
map_type 0
interpolate 2
once
}
}
}
box
{
0, 1
pigment {rgbt 1}
hollow
interior
{
media
{
emission Red
density {function {my_pattern(x,y,z).red}}
}
media
{
emission Green
density {function {my_pattern(x,y,z).green}}
}
media
{
emission Blue
density {function {my_pattern(x,y,z).blue}}
}
}
}
Regards
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"Bruno Cabasson" <bru### [at] alcatelaleniaspacefr> wrote:
> This piece of code works:
>
> #declare my_pattern = function
> {
> pigment
> {
> image_map
> {
> png "my_image.png"
> map_type 0
> interpolate 2
> once
> }
> }
> }
>
> box
> {
> 0, 1
> pigment {rgbt 1}
> hollow
> interior
> {
> media
> {
> emission Red
> density {function {my_pattern(x,y,z).red}}
> }
> media
> {
> emission Green
> density {function {my_pattern(x,y,z).green}}
> }
> media
> {
> emission Blue
> density {function {my_pattern(x,y,z).blue}}
> }
> }
> }
>
> Regards
Sorry for the delay in replying; I've been experimenting!
Thanks to both you and Mike Williams for posting these techniques; I
wouldn't have thought of either one.
Your code does indeed work. Very neat! The trouble, though, is that the
function seems to be ignoring the alpha channel in the image_map image. Or
rather, it treats the alpha channel as pure white, and fills the box with
full media density there. (I tried *LOTS* of odd tricks to get rid of that,
to no avail.) Any idea why?
I did come up with a workaround--getting rid of the alpha channel altogether
and substituting black for it in the image. That wiped out the offending
surrounding media.
Ultimately, I got your technique to work very well (with a few
modifications) by using THREE versions of my image_map...two as functions,
(no alpha channel)
and one (WITH the alpha channel) simply projected onto the box as a regular
pigment--the give the final object more "definition." Plus, using both
absorbing and emitting media, each with separate functions derived from
different versions of my image_map. The result is a nice solid-looking
object, in the shape of the image, and nicely textured on the outside
"shell"...just what I wanted! Describing this process in detail would be
*most* difficult, so instead, I'll put together a visual description of it,
in steps, and post it soon over at p.b.i., along with the code.
I haven't yet tried Mike Williams' technique; I'll tackle that next.
Just thought I'd add that POV doesn't allow something like emission red as a
color specification (it generates an error). emission <1,0,0> is the
simple workaround, of course.
THANKS AGAIN!
Ken W.
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Kenneth wrote:
> Just thought I'd add that POV doesn't allow something like emission red as a
> color specification (it generates an error). emission <1,0,0> is the
> simple workaround, of course.
>
> THANKS AGAIN!
>
> Ken W.
Quick note: He really specified "emission Red", which is not the same
thing as "emission red". The second requires a float value after the
"red", while the first is #declared in colors.inc as "red 1" (or "rgb
<1,0,0>", I don't know which).
...Chambers
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Chambers <bdc### [at] yahoocom> wrote:
> Kenneth wrote:
> > Just thought I'd add that POV doesn't allow something like emission red as a
> > color specification (it generates an error). emission <1,0,0> is the
> > simple workaround, of course.
> >
> > THANKS AGAIN!
> >
> > Ken W.
>
>
> Quick note: He really specified "emission Red", which is not the same
> thing as "emission red". The second requires a float value after the
> "red", while the first is #declared in colors.inc as "red 1" (or "rgb
> <1,0,0>", I don't know which).
>
> ...Chambers
The identifier "red" followed by a float value is something I didn't know
about. Many thanks. Time for me to re-read 3.2.1.5 Specifying Colors ;-)
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