Is there any way to implement materials that blur the image behind them?

Making it less transparent doesn't distort the image, just lets less of it
through.  Same thing happens with media.. just changes intensity/color of
light, but not its path.

The degree of blur should be related to the path length of light passing
through a material so surface distortions won't work right.

Please email replies to kev### [at] dukeedu

Thanks,
Kevin

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IOR + surface normal will simulate, say, frosted glass. (For a real frosted
look, use scattering media inside it. But that's not necessary for the
distortion.)

 - Slime
 [ http://www.slimeland.com/ ]

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In article <web.3f6a075848b4e2fa6099662b0@news.povray.org>, 
kev### [at] dukeedu says...
> Is there any way to implement materials that blur the image behind them?
> 
> Making it less transparent doesn't distort the image, just lets less of it
> through.  Same thing happens with media.. just changes intensity/color of
> light, but not its path.
> 
> The degree of blur should be related to the path length of light passing
> through a material so surface distortions won't work right.
> 
Hmm. There is an idea.. How about extending IOR, which is basically a 
function of the surface itself, so that you can use patterns to create 
permutations and noise in the value? Could be an interesting effect and 
placed on a small enough scale it would possibly create such a blur 
effect. Of course I have no clue how to code such a thing myself. :( 
Sigh...

-- 
void main () {

    call functional_code()
  else
    call crash_windows();
}

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Kevin <kev### [at] dukeedu> wrote:
> Is there any way to implement materials that blur the image behind them?

  Yes:

http://tag.povray.org/povQandT/languageQandT.html#blurredreflection

  (Even though it talks about blurred reflection, it can be used for
blurred refraction as well, as the text mentions at the end.)

> Please email replies to kev### [at] dukeedu

  If you post a question to a newsgroup you should check the newsgroup
for answers and not expect people to deliver the answers to you personally.

-- 
#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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Warp wrote:
>Kevin <kev### [at] dukeedu> wrote:
>> Is there any way to implement materials that blur the image behind them?
>
>  Yes:
>
>http://tag.povray.org/povQandT/languageQandT.html#blurredreflection
>
>  (Even though it talks about blurred reflection, it can be used for
>blurred refraction as well, as the text mentions at the end.)
>

Thanks Warp,
That seems to do the trick.  I was concerned that a surface texture might
not meet the criteria of blurring more as the path length in the material
increases.  I've run a few tests and at least for some simple test cases it
seems to do a pretty good job.

-Kevin

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Kevin wrote:

Well Ok, doesn't quite meet the specifications.
The amount of blur doesn't increase with path length, rather it increases
with the difference in the normals of the front and back surfaces.
Makes for a pretty nice blur tho... one observation is that if you put the
blur texture on the interior then you can get unblurred reflections and
blurred refractions.

What we need to modify this code with is a function that sets the blur
amount that is related to the optical path length of the ray through that
object at whatever point it is rendering.  That way the blur amount can
vary.

I haven't a clue how to implement this.. it might require a patch.

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Kevin <kev### [at] dukeedu> wrote:
> Well Ok, doesn't quite meet the specifications.
> The amount of blur doesn't increase with path length

  What do you mean by "path length"?

  The blurred refraction trick blurs the background more if it's farther
away than if it's closer. I don't understand what else you are after.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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In article <3f6f56f8@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   The blurred refraction trick blurs the background more if it's farther
> away than if it's closer. I don't understand what else you are after.

I think he's trying to simulate scattering throught a material. The 
probability of a photon getting scattered in a random direction 
increases with the length of its path through the material, and can 
occur at any point inside the material. Blur textures only simulate 
surface scattering, like ground glass.

This type of scattering would be quite expensive to compute, since it 
would involve tracing many rays for each transmitted ray. You could 
simulate it by using several surfaces with the blurry texture in the 
interior of the object, but POV has no built-in facility for doing this.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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Chris has the right idea... what I'm looking for is a material that blurs
the image more if the ray has to pass through a lot of the material rather
than just a tiny bit.

I agree that to do this the right way would be really expensive, but a quick
way around it might be to determine the length of the ray that passes
through the material and then set the local blur size (for that ray) to
some function of the path length.

Hmmm.... maybe if you could define a gradient of the normal bump sizes you
could simulate this effect.. or by playing with normal maps... I'll have to
fiddle with that.


Christopher James Huff wrote:
>In article <3f6f56f8[at]news.povray.org>, Warp <war### [at] tagpovrayorg>
>wrote:
>
>>   The blurred refraction trick blurs the background more if it's farther
>> away than if it's closer. I don't understand what else you are after.
>
>I think he's trying to simulate scattering throught a material. The
>probability of a photon getting scattered in a random direction
>increases with the length of its path through the material, and can
>occur at any point inside the material. Blur textures only simulate
>surface scattering, like ground glass.
>
>This type of scattering would be quite expensive to compute, since it
>would involve tracing many rays for each transmitted ray. You could
>simulate it by using several surfaces with the blurry texture in the
>interior of the object, but POV has no built-in facility for doing this.
>
>Christopher James Huff <cja### [at] earthlinknet>
>http://home.earthlink.net/~cjameshuff/
>POV-Ray TAG: chr### [at] tagpovrayorg
>http://tag.povray.org/
>

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Kevin <kev### [at] dukeedu> wrote:

> Chris has the right idea... what I'm looking for is a material that blurs
> the image more if the ray has to pass through a lot of the material rather
> than just a tiny bit.

What real-life material does this?
IMHO blurring normally only occurs on surfaces.

Lutz-Peter

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