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"Tek" <tek### [at] evilsuperbrain com> wrote in message
news:4527ad2a@news.povray.org...
> 4/ water material - a physically correct water is simply: pigment{rgbt
> 1}finish{reflection{0,1 fresnel}}interior{ior 1.33 fade_colour ...
> fade_power 2 fade_distance ...}, there's a lot of tweaks you can do but
> that should get you something good. Basically it's transparent,
> refractive, the reflections obey fresnel so there's no need to tweak them,
> and if you want to colour it you should use fade_colour not pigment
> because the colour should be throughout the material not just at the
> surface.
Doh! and of course use conserve_energy in reflections, that's vital!
--
Tek
http://evilsuperbrain.com
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> 1/ a perfect cube always looks very fake, use a slightly irregular shape
> like a superellipsoid or isosurface
Cube is a placeholder, yes. I was attempting to get the stone texture
and the water to look right first. (I intend to replace it with a
rounded cube later.)
> 2/ it's easy to say this after the fact, but the human eye is extremely
> forgiving of reflections in bumpy surfaces, so you really shouldn't worry
> about making a complex sky, just something flat that has the right colours.
> But it sounds like you learnt this the hard way.
I only used the complex volumetric sky because I already had one from
another scene that had the right colours, and I couldn't come up with a
static pigment with anything approaching the right colours.
For my trouble, I ended up with an entire scene that's bright blue. (Why
does the real world not do this BTW? The real sky is blue...)
> 3/ think about the size of the ripples regarding the scale of your scene,
> these ones are huge but smooth (particularly in the last image). Smooth
> usually means very small ripples, which would make the stone block about 1cm
> big! I'd suggest use much much smaller ripples, so the surface is nearly
> flat. if you want a dramatically wavey surface for this scale you need
> something less smooth, the wrinkles pattern is sometimes pretty good for
> this, or granite (inverted to make spikey waves).
OK. I'm currently investigating Christoph's waver macro. Seems to
produce big fractal-like waves. (I'd actually like the ripples to
radiate from the stone block and follow its shape eventually...)
> 4/ water material - a physically correct water is simply: pigment{rgbt
> 1}finish{reflection{0,1 fresnel}}interior{ior 1.33 fade_colour ...
> fade_power 2 fade_distance ...}, there's a lot of tweaks you can do but that
> should get you something good. Basically it's transparent, refractive, the
> reflections obey fresnel so there's no need to tweak them, and if you want
> to colour it you should use fade_colour not pigment because the colour
> should be throughout the material not just at the surface.
The water *itself* is a fairly simple thing, as you say. It's
transparent, refractive and reflective. So basically it doesn't look
like anything by itself... gotta have something nice to reflect.
My main problem seems to be getting a decent sky. :-S
> 5/ stone material - always reference a real material, in your present scene
> I can't tell if it's meant to be a polished stone like marble, or a more
> natural rough finish. A realistic rough finish is easier: just give it a
> noisy normal, like normal { granite -.2 }, and no specular or phong. A
> realistic smooth finish is difficult because smooth things look fake in CG,
> I'd suggest choosing a stone with a very distinctive pattern, like marble or
> something. And on that topic note that pov's granite pattern looks more like
> marble than the marble pattern...
The look I'm eventually going for is water-polished rock. Maybe
limestone or something. So I probably just need to make it look slightly
lumpy... and get better colours...
> 6/ use global_settings { assumed_gamma 1 }, it screws up all the colours in
> the scene so you'll need to adjust them, but it make reflections and
> lighting look more realistic.
I wouldn't have thought assumed_gamma 1 would have *any* effect...
surely that just means that each colour component is raised to the power
of 1 before being output?
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"Orchid XP v3" <voi### [at] devnull> wrote in message
news:4527b397$1@news.povray.org...
>
> Cube is a placeholder, yes.
Spheres usually make better placeholders when tweaking materials IMO, the
hard edges of the cube mean you don't see how it interacts with the light at
all angles, making it very hard to tune effects like specular.
> OK. I'm currently investigating Christoph's waver macro. Seems to
> produce big fractal-like waves. (I'd actually like the ripples to
> radiate from the stone block and follow its shape eventually...)
Well if you want ripples radiating from the block why are you looking at a
macro for fractal like waves?
Radiating from a block is a bit awkward, I suggest basing it on a function,
like:
normal { function { sin(8*pi*sqrt(pow(max(x-1,0),2)+pow(max(z-1,0),2))) } }
that should give nice "distance from a square" based ripples, though if you
plan on changing the shape of your stone it might not look so good.
> The water *itself* is a fairly simple thing, as you say. It's
> transparent, refractive and reflective. So basically it doesn't look
> like anything by itself... gotta have something nice to reflect.
>
> My main problem seems to be getting a decent sky. :-S
Nope I disagree, if you have a realistic water material from this angle it
would be almost completely transparent, the reflection would only show up on
the top edge of the ripples (see attached picture). What's important is the
fall-off of the reflection, which should be either reflection{.01,1 falloff
5} to fake it or reflection{0,1 fresnel} if you have a realistic ior.
> I wouldn't have thought assumed_gamma 1 would have *any* effect...
> surely that just means that each colour component is raised to the power
> of 1 before being output?
Yeah that confused the hell out of me when I first encountered it. The
simple answer is that pov knows what your display gamma is, or rather it has
a default of 2.2. If you don't say "assumed_gamma" it doesn't gamma correct
from the linear colour space of the pov scene to the non-linear gamma of the
monitor. assumed_gamma essentially tells pov what the gamma space of your
scene is, which is a very bizarre thing to do since pov does linear
calculations on light so by definition it has a gamma of 1, it's very
counter intuitive but it works!
Anyway I couldn't resist the urge to have a go at a similar scene myself, so
here's a picture and the source is in p.b.s-f. Most importantly note that
the reflection on the water is very subtle, without the ripples you'd hardly
see the water surface at all.
--
Tek
http://evilsuperbrain.com
Post a reply to this message
Attachments:
Download 'rock mat test.jpg' (62 KB)
Preview of image 'rock mat test.jpg'
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>> Cube is a placeholder, yes.
>
> Spheres usually make better placeholders when tweaking materials IMO, the
> hard edges of the cube mean you don't see how it interacts with the light at
> all angles, making it very hard to tune effects like specular.
I guess so...
>> OK. I'm currently investigating Christoph's waver macro. Seems to
>> produce big fractal-like waves. (I'd actually like the ripples to
>> radiate from the stone block and follow its shape eventually...)
>
> Well if you want ripples radiating from the block why are you looking at a
> macro for fractal like waves?
Because it works by placing multiple concentric rings of ripples
semi-randomly. Now if I place the centers of those ripples to coincide
with the edges of the block, the ripples will follow its outline. (This,
apparently, is how the Real World(tm) works...)
>> My main problem seems to be getting a decent sky. :-S
>
> Nope I disagree, if you have a realistic water material from this angle it
> would be almost completely transparent, the reflection would only show up on
> the top edge of the ripples (see attached picture).
Mmm, OK. In that case, my water is going to be completely black...
> What's important is the
> fall-off of the reflection, which should be either reflection{.01,1 falloff
> 5} to fake it or reflection{0,1 fresnel} if you have a realistic ior.
Is IOR=1.3 "realistic"?
>> I wouldn't have thought assumed_gamma 1 would have *any* effect...
>> surely that just means that each colour component is raised to the power
>> of 1 before being output?
>
> Yeah that confused the hell out of me when I first encountered it.
Here's a random question: does LCD require gamma correction?
> Anyway I couldn't resist the urge to have a go at a similar scene myself, so
> here's a picture and the source is in p.b.s-f. Most importantly note that
> the reflection on the water is very subtle, without the ripples you'd hardly
> see the water surface at all.
0__0
OMG... you created something 17,826% better than what I had in about 20
seconds!
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Orchid XP v3 nous apporta ses lumieres en ce 07/10/2006 11:16:
>>> Cube is a placeholder, yes.
>>
>> Spheres usually make better placeholders when tweaking materials IMO,
>> the hard edges of the cube mean you don't see how it interacts with
>> the light at all angles, making it very hard to tune effects like
>> specular.
>
> I guess so...
>
>>> OK. I'm currently investigating Christoph's waver macro. Seems to
>>> produce big fractal-like waves. (I'd actually like the ripples to
>>> radiate from the stone block and follow its shape eventually...)
>>
>> Well if you want ripples radiating from the block why are you looking
>> at a macro for fractal like waves?
>
> Because it works by placing multiple concentric rings of ripples
> semi-randomly. Now if I place the centers of those ripples to coincide
> with the edges of the block, the ripples will follow its outline. (This,
> apparently, is how the Real World(tm) works...)
>
>>> My main problem seems to be getting a decent sky. :-S
>>
>> Nope I disagree, if you have a realistic water material from this
>> angle it would be almost completely transparent, the reflection would
>> only show up on the top edge of the ripples (see attached picture).
>
> Mmm, OK. In that case, my water is going to be completely black...
>
>> What's important is the fall-off of the reflection, which should be
>> either reflection{.01,1 falloff 5} to fake it or reflection{0,1
>> fresnel} if you have a realistic ior.
>
> Is IOR=1.3 "realistic"?
It is, it's close to the real ior of water. Pure water ior is 4/3. Salt or sea
water's ior is close to 1.4.
>
>>> I wouldn't have thought assumed_gamma 1 would have *any* effect...
>>> surely that just means that each colour component is raised to the power
>>> of 1 before being output?
>>
>> Yeah that confused the hell out of me when I first encountered it.
>
> Here's a random question: does LCD require gamma correction?
>
>> Anyway I couldn't resist the urge to have a go at a similar scene
>> myself, so here's a picture and the source is in p.b.s-f. Most
>> importantly note that the reflection on the water is very subtle,
>> without the ripples you'd hardly see the water surface at all.
>
> 0__0
>
> OMG... you created something 17,826% better than what I had in about 20
> seconds!
Fade_power should be 1 to be physicaly correct. A value of 2 is perfect for a
light source, double the distance and get 1/4 the lighting, not for fading
trough some substance. Light absorbtion trough a substance is linearly
proportional to the thicknessm, double the thickness and the effect double, it
don't quadruple.
Any way, for water, fade_distance is relatively large.
--
Alain
-------------------------------------------------
No matter how good she looks, some other guy is sick and tired of putting up
with her shit.
Men's Room, Linda's Bar and Grill, Chapel Hill , NC
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4527c96f$1@news.povray.org...
> Fade_power should be 1 to be physicaly correct. A value of 2 is perfect
for a
> light source, double the distance and get 1/4 the lighting, not for fading
> trough some substance. Light absorbtion trough a substance is linearly
> proportional to the thicknessm, double the thickness and the effect
double, it
> don't quadruple.
> Any way, for water, fade_distance is relatively large.
>
I don't agree about fade power in water :
daylight rays have to get twice (down and back up) through water before
reaching your eye so double the depth quadruple the thickness
Marc
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>> Fade_power should be 1 to be physicaly correct. A value of 2 is perfect
> for a
>> light source, double the distance and get 1/4 the lighting, not for fading
>> trough some substance. Light absorbtion trough a substance is linearly
>> proportional to the thicknessm, double the thickness and the effect
> double, it
>> don't quadruple.
>> Any way, for water, fade_distance is relatively large.
>>
> I don't agree about fade power in water :
> daylight rays have to get twice (down and back up) through water before
> reaching your eye so double the depth quadruple the thickness
That's still linear.
If it was quadratic, 3x the depth would be 9x the darkening. By your
reasoning, it would be 6x.
Note also that POV-Ray will see that the light passes through the water
twice and darken it twice anyway, so you only need fade_power=1...
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"Marc" <jac### [at] wanadoofr> wrote in message
news:4527d21c@news.povray.org...
> I don't agree about fade power in water :
> daylight rays have to get twice (down and back up) through water before
> reaching your eye so double the depth quadruple the thickness
I think pov will simulate that implicitly anyway, because the shadow cast by
the water onto stuff underneath tints the daylight falling on the underwater
objects, then when we look at them through the water we get more tinting.
But if we're looking at a flat coloured ambient object the amount of tinting
just depends on it's distance from us.
Also I believe the power can be between 1 & 2 for realistic effects, since
the particles of fog can occlude each other... or something. I remember
figuring all this out once but the pov docs say between 1 & 2 so I'll defer
to their judgement :)
Anyway if you want it to look totally right I suggest scattering media...
--
Tek
http://evilsuperbrain.com
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> > > I wouldn't have thought assumed_gamma 1 would have *any* effect...
> > > surely that just means that each colour component is raised to
> > > the power of 1 before being output?
> >
> > Yeah that confused the hell out of me when I first encountered it.
>
> Here's a random question: does LCD require gamma correction?
Yes, PC LCDs are designed specifically to match the response of CRTs.
Post a reply to this message
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> > OMG... you created something 17,826% better than what I had in
> > about 20 seconds!
> Fade_power should be 1 to be physicaly correct. A value of 2 is
> perfect for a light source, double the distance and get 1/4 the
> lighting, not for fading trough some substance. Light absorbtion
> trough a substance is linearly proportional to the thicknessm, double
> the thickness and the effect double, it don't quadruple.
Physically correct is exponential isn't it? ie a certain % of the light
gets attenuated each unit distance. If a certain distance only lets 10% of
the light through, then you'd expect 1% after double the distance, 0.01%
after 4x etc.
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