>         crand .001      //does anyone even use this?

Not much these days.
And looking at it, using crand AND aa seems rather futile. Crand darken 
a random pixel, this causes aa to kick in and mostly kill the crand 
effect: Most of the subsampling won't be affected by the crand.

A use I can find, in an animation:
Simulate the grain of the film.


Akain

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> clipka wrote:
>> (This difficulty to find realistic settings also appears to be the 
>> reason why highlights are not taken into account for radiosity sample 
>> rays; theoretically they should be, while a comment claims that this 
>> "causes problems with colors being far too bright" - which is actually 
>> an indication that energy conservation is violated somewhere.)
> 
> Why not extend "conserve_energy" to affect highlights?
> 
> ...Chambers

I had the same though. I was about to post that same comment.


Alain

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Zeger Knaepen schrieb:
>> But modulating the highlight intensity (or even colour) according to the 
>> highlight falloff - that's something new indeed.
> 
> you think it's feasible?

Why not? Should be some work, but not much of a problem.

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
> Zeger Knaepen schrieb:
> >> But modulating the highlight intensity (or even colour) according to the
> >> highlight falloff - that's something new indeed.
> >
> > you think it's feasible?
>
> Why not? Should be some work, but not much of a problem.


Hooray!  I was thinking of how it could be used to make those fancy metallic car
paint jobs.  The aoi pattern is also handy for that, but some color effects are
more around the specular highlights than anything else.

If you ever need any other suggestions on where a color_map can be added to make
things more complicated, let me know.  I have quite a few in mind.


-Reactor

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"Reactor" <rea### [at] hotmailcom> wrote:

> If you ever need any other suggestions on where a color_map can be added to make
> things more complicated, let me know.  I have quite a few in mind.
>
>
> -Reactor

Yes, They are handy in any software and would be intuitive IMNO (In My Noobish
Opinion) to use the same way in pov. Set color maps free! :)

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clipka <ano### [at] anonymousorg> wrote:
> Zeger Knaepen schrieb:
> > I'm not sure about the highlights-block.. If that gets through, I believe
> > there should also be a diffuse-block.
>
> Might become worth it - it has already ceased to be a strictly
> single-value statement.
>
> > And to be honest, I actually like Reactor's idea of allowing a color_map.
> >
> > Something like this:
> > ...
>
> Hm... that's actually a neat idea! So far I had understood the idea to
> be about getting a different brightness or roughness for different
> points on the object - which I wouldn't have considered too
> entertaining, given that this can be achieved with texture maps already.
>
> But modulating the highlight intensity (or even colour) according to the
> highlight falloff - that's something new indeed.
>
> > color_maps would allow for a whole range of special effects, including
> > simulating the effects of combined highlights.
>
> Yup.

I've been playing with the SSLT stuff the last 2 days and I noticed that in the
Jensen SSLT SIGGRAPH paper there's a third RGB Diffuse Reflectance parameter
(like a color_map for highlights, yes?) used to fine tune the material. So that
would just mean extending the existing diffuse component of a finish to use a
full RGB color vector instead of an assumed grayscale color vector
as it is currently, which makes a lot of sense to me (and a second vector for
the backlit stuff that Clipka did).

Well, I've been thinking about this for a while, and wondering... Xander
Enzmann's (a former POV-Ray contributor) Polyray was doing something like that
15 years ago (among other things, like using various microfacet highlight
distribution models). Take a read through the old Polyray docs at Paul Bourke's
website: http://local.wasp.uwa.edu.au/~pbourke/dataformats/polyray/
It's like listening to an old Led Zeppelin album; you sometimes forget how good
they were back in those days.

Regardless, accurate simulation of different physical materials requires
different mathematical models to handle the various cases. I know what (and
who) Phong is, but I'm not really sure what model POV-Ray's "specular"
represents (just a guess - Cook-Torrence?). So, why limit POV-Ray to "phong"
and "specular?" Why not just take into account several shading models for
various materials, just like the high-dollar Hollywood boys do? (and they're
pretty damned convincing most of the time)

That simply means making available various *combinable* shading models for
various materials. Blinn/Phong for plastics, Lambert for simple
non-reflective surfaces, Cook-Torrance for metals, Oren Nayar for rough
surfaces, and Ward-anisotropic for objects with anisotropic reflections like
brushed metal, fur, hair, etc. That's the utmost in flexibility as far as I can
see.

Just my 2 cents.

-Rob

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Robert McGregor schrieb:
> I've been playing with the SSLT stuff the last 2 days and I noticed that in the
> Jensen SSLT SIGGRAPH paper there's a third RGB Diffuse Reflectance parameter
> (like a color_map for highlights, yes?) used to fine tune the material.

Which of the two papers are you referring to here? The 2001 
Jensen/Marschner/Levoy/Hanrahan paper ("A Practical Model for Subsurface 
Light Transport"), or the 2002(?) Jensen/Buhler follow-up ("A Rapid 
Hierarchical Rendering Technique for Translucent Materials")?

The 2001 paper had no such parameter: The scattering and absorption 
coefficients and the refractive index are essentially the only 
parameters in the model presented there. (I'm deliberately ignoring the 
phase function, as Jensen et al. themselves presumed isotropic 
scattering when they went on to measure the parameters of real-world 
materials.)

The 2002 paper does indeed mention a "diffuse reflection coefficient" 
with reference to the 2001 paper, Rd, but in the 2001 paper that was 
actually the /result/ of the SSLT computations (or, rather, with the 
formula referred to in the 2002 paper, even just an approximation).

The 2002 paper does indeed take this diffuse reflection coefficient as a 
parameter, but not in addition to the scattering and absorption 
coefficients appearing in the BSSRDF formula, but to reparameterize the 
whole smash, in order to compute the scattering and absorption 
coefficients from parameters that are more intuitive (said diffuse 
reflection coefficient, as well as the "mean free path" per color 
component).

The diffuse reflection coefficient, in that reparameterization, would be 
equivalent to the product of the pigment color and POV-Ray's the 
"diffuse" parameter.


 > So that
> would just mean extending the existing diffuse component of a finish to use a
> full RGB color vector instead of an assumed grayscale color vector
> as it is currently, which makes a lot of sense to me (and a second vector for
> the backlit stuff that Clipka did).

The diffuse colorization is what is currently in the pigment (which, as 
you will certainly agree, is much more flexible than just a color 
vector). Note that the pigment does not affect highlights or reflections 
unless used with the "metallic" keyword. Even then, they can be 
"decoupled" by using multi-layered textures.


> Regardless, accurate simulation of different physical materials requires
> different mathematical models to handle the various cases. I know what (and
> who) Phong is, but I'm not really sure what model POV-Ray's "specular"
> represents (just a guess - Cook-Torrence?).

No, it's actually just the Blinn-Phong model.

 > So, why limit POV-Ray to "phong"
> and "specular?" Why not just take into account several shading models for
> various materials, just like the high-dollar Hollywood boys do? (and they're
> pretty damned convincing most of the time)

Maybe because someone needs to implement the whole stuff? And maybe the 
people using it are not high-dollar Hollywood boys who know exactly when 
to employ what model?

And last not least, maybe it's also because the syntax to this day is 
not particularly inviting to add more alternative highlight models.

> That simply means making available various *combinable* shading models for
> various materials. Blinn/Phong for plastics, Lambert for simple
> non-reflective surfaces, Cook-Torrance for metals, Oren Nayar for rough
> surfaces, and Ward-anisotropic for objects with anisotropic reflections like
> brushed metal, fur, hair, etc. That's the utmost in flexibility as far as I can
> see.

I guess I do agree that it would be nice to have additional highlighting 
models, and maybe even be able to combine them.

However, given that the average user will use just /one/ of these many 
models, I would consider it a waste of memory (and a bit of computing 
time, too) to combine all of these side by side in each and every single 
texture finish.

I would therefore rather suggest to have a texture finish support 
exactly /one/ highlight model (let the user pick which one), which 
experienced users can then combine by using multi-layered textures.

Post a reply to this message

clipka <ano### [at] anonymousorg> wrote:
>
> The 2002 paper does indeed mention a "diffuse reflection coefficient"
> with reference to the 2001 paper, Rd, but in the 2001 paper that was
> actually the /result/ of the SSLT computations (or, rather, with the
> formula referred to in the 2002 paper, even just an approximation).
>
> The diffuse reflection coefficient, in that reparameterization, would be
> equivalent to the product of the pigment color and POV-Ray's the
> "diffuse" parameter.

Okay, I misunderstood completely then (which isn't terribly unusual). Thanks for
clarifying that.

> > So, why limit POV-Ray to "phong"
> > and "specular?" Why not just take into account several shading models for
> > various materials, just like the high-dollar Hollywood boys do? (and they're
> > pretty damned convincing most of the time)
>
> Maybe because someone needs to implement the whole stuff? And maybe the
> people using it are not high-dollar Hollywood boys who know exactly when
> to employ what model?

You are *so* warm and fuzzy sometimes :)

> And last not least, maybe it's also because the syntax to this day is
> not particularly inviting to add more alternative highlight models.
>
> > That simply means making available various *combinable* shading models for
> > various materials. Blinn/Phong for plastics, Lambert for simple
> > non-reflective surfaces, Cook-Torrance for metals, Oren Nayar for rough
> > surfaces, and Ward-anisotropic for objects with anisotropic reflections like
> > brushed metal, fur, hair, etc. That's the utmost in flexibility as far as I can
> > see.
>
> I guess I do agree that it would be nice to have additional highlighting
> models, and maybe even be able to combine them.
>
> However, given that the average user will use just /one/ of these many
> models, I would consider it a waste of memory (and a bit of computing
> time, too) to combine all of these side by side in each and every single
> texture finish.

As computing power continues to increase I don't think this is really an issue.
Besides, we're *ray-tracing*, which typically uses "a bit of computing time"
anyway, so let's make the most of it.

> I would therefore rather suggest to have a texture finish support
> exactly /one/ highlight model (let the user pick which one), which
> experienced users can then combine by using multi-layered textures.

Okay, I understand that. Although I often combine phong and specular in the same
finish block to get a wide, soft, general hightlight and a sharp specular
highlight it's no big deal to layer them instead.

I just wanted to prompt some thinking about adding some additional models (maybe
for POV-Ray 4). As far as syntax, I wouldn't suggest to change it, just add a
few keywords and maybe change some things under the hood. For example:

// use default Blinn-Phong
finish {specular 0.5}

// switch to Cook-Torrance
finish {specular 0.5 metallic}

// switch to Ward-anisotropic (for say, brushed metals)
finish {specular 0.5 anisotropic{gradient radial ramp {rgb 0, rgb 1}}}

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Robert McGregor wrote:

> Okay, I understand that. Although I often combine phong and specular in the same
> finish block to get a wide, soft, general hightlight and a sharp specular
> highlight it's no big deal to layer them instead.

But still sounds like we have a valid use case for using two highlight
models simultaneously, namely to approximate a third unsupported one. Of
course, that would no longer be necessary if the new syntax would some
day allow to specify a custom highlight model (as a function?), after
which the old keywords could be phased out.

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Zeger Knaepen wrote:

> I was thinking about that too, but it's inconsistent with current behaviour: 
> normally, specifying a value overwrites the previous value, which is a good 
> thing and imho must be kept.

arguably, adding highlights in a finish block could be seen
similarly to adding media to an interior or densities to media,
both cases where the effects are combined.

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