Cousin Ricky <ric### [at] yahoocom> wrote:
> I was curious about how Norbert Kern's light & shadows lighting
> environment compares to my 4th prefab render rig's outdoor setting, so I
> wrote a couple of scenes to illustrate them.
>
> Image nkern-light+shadows2.jpg uses Norbert's lighting setup, including
> his sky, his radiosity setting, and the finish he posted.  The colors
> used were:
>
>    Gray sphere:          srgb 0.5
>    Green sphere:         CHSV2RGB (<115, 0.65, 0.08>) / 0.6
>    Post:                 CHSV2RGB (<23, 0.75, 0.12>) / 0.6
>    Yellow-green sphere:  CHSV2RGB (<92, 0.8, 0.12>) / 0.6
>    White sphere:         srgb 1
>    Brown square:         CHSV2RGB (<23, 0.75, 0.12>) / 0.6
>    Green square:         CHSV2RGB (<91, 0.80, 0.18>) / 0.6
>
> I had previously derived the greens and the brown from photographs I
> took of grass, leaves, and soil.  I calibrated the colors against 96%
> white paper, decreasing the assumed paper luminance very slightly due to
> its age.
>
> The rc3-nkern-ltshad-e*-2.jpg images used my 4th prefab render rig.  The
> following colors were used, with the diffuse finish values applied
> directly to the objects:
>
>    Gray sphere:          srgb 0.5                      diffuse 0.6
>    Green sphere:         CHSV2RGB (<115, 0.65, 0.08>)  diffuse 1
>    Post:                 CHSV2RGB (<23, 0.75, 0.12>)   diffuse 1
>    Yellow-green sphere:  CHSV2RGB (<92, 0.8, 0.12>)    diffuse 1
>    White sphere:         srgb 1                        diffuse 0.6
>
> I used these radiosity settings:
>
>    radiosity
>    { count 200
>      error_bound 0.5
>      normal on
>      Radiosity_Pretrace (0.8, 2) // posted in p.b.s-f
>      recursion_limit 2
>    }
>
> In addition, the render rig automatically supplies radiosity { media on
> }, because the sky is fog based.
>
> The lighting is not so straightforward, since the render rig creates its
> own black box environment, but since I wrote it, I can give some
> specifics.  The dirt and grass have these colors with diffuse 1:
>
>    Dirt:   CHSV2RGB (<23, 0.75, 0.12>)
>    Grass:  CHSV2RGB (<91, 0.80, 0.18>)
>
> The rig uses rgb <1.038, 0.989, 0.956> for the direct sunlight.  The
> sky, disregarding the clouds, contributes about 1/8 the luminance of the
> direct sun; this is the best amount I could determine for a Sun at 45°.
> (I positioned the Sun at Norbert's 47°, but I haven't gone through the
> trouble of programming dynamic sky colors into my render rig, and the 2°
> shouldn't make that much difference.)  I did not take aerosols into
> account, and I presumed that my sources were measured at low turbidity.
> And if you know me, you don't need to ask about the assumed_gamma.
>
> The exposure figure is a multiplier for the sunlight and sky colors.
>
> Since all renders used radiosity with POV-Ray 3.7, any ambient settings
> were moot.
>
> As you can see, my sky is considerably lighter than Norbert's, resulting
> in lower contrast.  However, Norbert's scene is in a heavily forested
> area, which naturally lends itself to dark shadows.  When I look
> outside, my instinct tells me that the sky should be lighter than I have
> made it, but for the time being, I am trusting scientifically measured
> numbers over my non-linear vision.  It should be noted that since blue
> is a low luminosity color, that 1/8 figure is lower than the flux ratio.


Hi,
I like your fourth image with exposure 4.0. It looks like a good summer sky
setting.

My settings for L&S aren't suitable for naturalistic images.
If I would start from scratch, there would be much more shadows and stronger
lights. Of course then I would increase the sky brightness values too - a bit.
Most textures were tweaked to increase the hue values. So the image is green in
general with blueish shadows. Flowers and animals introduce some colorful spots.

The impression I wanted to generate is something like a glade, with much
stronger contrasts than in reality - like in the part render from a different
perspective.

My personal standard set for sky and light is rather simple -

#declare lights = <-80000,50000,-50000>;
light_source {
        lights,
        color srgb <2.42,2.23,1.87>
}

sky_sphere {
        pigment {
                function {max (min (y, 1), 0)}
                color_map {
                        [0        srgb <212,221,239>/255]
                        [0.1029   srgb <219,229,244>/255]
                        [0.1512   srgb <233,241,250>/255]
                        [0.1949   srgb <223,239,252>/255]
                        [0.2444   srgb <201,227,252>/255]
                        [0.2921   srgb <180,213,250>/255]
                        [0.3732   srgb <144,180,239>/255]
                        [0.4255   srgb <137,172,235>/255]
                        [0.7067   srgb <97,126,198>/255]
                        [0.774    srgb <92,119,190>/255]
                        [0.8275   srgb <88,114,185>/255]
                        [0.885    srgb <85,111,180>/255]
                        [0.9425   srgb <82,107,175>/255]
                        [1        srgb <79,103,170>/255]
                }
        }
}

I got the sky values from a photograph and the light values are very old - in
fact I derived them from radiosity newsgroups discussions back in 2000 or 2001
(rgb <1,0.87,0.57>*7 IIRC).

This differs very much from your value - I should take a look in your render
rig...


Regards,
Norbert

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