Orchid XP v3 <voi### [at] devnull> wrote:
>
> 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...)

Tek wrote:
> > 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.

Actually, water really *is* blue.  Sky reflection contributes little to the
color of the sea.  As someone else mentioned, water reflects the sky color
significantly only at shallow angles, due to the Fresnel effect.  It's only
a coincidence that the sky and water are similar colors.

The sky looks blue due to Reyleigh scattering; whatever light is *not*
scattered into the is still present in the direct sunlight.  By contrast,
water absorbs (removes) light preferentially from the red end of the
spectrum, leaving blue and green to illuminate the scene.  That's why
underwater scenes (without camera lights) look blue, whereas objects on
land do not.  Also, shallow water looks greener than deep water because
water absorbs green faster than blue.

The reason a glass or a bathtub full of water looks completely clear is that
water absorbs very little light.  If your bathtub were as big as a pond, the
water would be bluish.

In Real Life, bodies of water contain particulates, which often dominate the
color of the water.  The slow-moving water at the lower ends of rivers looks
brown because of the silt mixed in.  The water of cold ocean currents
contains a lot of plankton, giving it somewhat of a dark greenish cast.
Some rivers contain tannin, which literally dyes the water a reddish-brown
color.

BTW, from what little i know of these things, fade_power 1 seems to make
sense for absorption.  (Point light sources, of course, are subject to the
inverse square law, i.e., fade_power 2.  The formula POV uses isn't quite
inverse square, but i have a feeling that the Team did it that way to
compensate for the limited dynamic range of the output.)

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