Underwater Light Effects

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Nathanomir
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Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 7:30 pm

I'm working on a scene of a woman swimming underwater in a shallow river. Now, those of you who have seen photographs of similar subjects instantly know what the lighting ought to look like. The colors are muted. The surface has a mirror-like quality, unless the camera is almost perpendicular (between 70 and 110 degrees). Even the slightest motion on the surface turns the water into a series of prisms that shatter the light into dozens of refracted directions, resulting in a dappled effect. That same multiple prism quality warps the mirror effect, as well as anything visible on the shore.

After testing different water surfaces, it turned out the best underwater lighting effects are achieved with the good old Reality water plane by its little lonesome.

I performed a series of tests on the different wave options to see which one worked the best for the scene. I thought I'd recreate them and share them with you.
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Nathanomir
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 7:33 pm

The Test

All tests were performed with the exact same settings, listed below.

System: DAZ Studio 4.8 Pro, Reality 4.3, Luxrender 1.6.

Configuration: CPU-Accelerated, Type = Bidirectional, Sampler = Metropolis, Light Passes = Auto

Set: The set is identical to the one used in the final art scene, except that Jenny consented to don a bikini. This way, you can see how the light affects different objects of different sizes and shapes in different locations.

Of importance is the "ceiling," a plane set with a sky map and parallel about fifty feet above the water surface, but also set so as not to block the sun light. The water plane works from underneath as it does from above. From above, the water plane needs a floor, otherwise the Clarity of Depth aims for the Mariana's Trench. From below, it needs a ceiling, otherwise the Clarity of Depth aims for the Moon. Using a ceiling permits some sky or whatever scenery you wish to show through those sections of the water directly perpendicular to the camera. Ergo, the blue streaks of the sky.

Lights: Lights used are the Sun-Sky, and One Mesh Light for fill. Sun-Sky Y axis is set perpendicular to Jenny, with a X axis of -45. The Mesh is perpendicular to Jenny and even with her Y height.

Sun = Gain of 2.5, Sky = Gain of 1.5, Mesh = Gain of 750, Temp of 7000.

Camera: ISO = 100, F = 8, Shutter = 1/125, Film Response = NONE

The film response was an accidental discovery. Film response of none yielded the muted colors expected of underwater scenes. All the film responses, including our favorite Advantix, made the colors too bold for the diffusive quality of water. Of course, you want bold colors if you're up close and personal with a clown fish and a sea anemone.

Render Time: 500 s/P. That was good enough for a test. The light patterns are obvious at a mere 50 s/P, but the subtleties of highlights and shadows take time. Obviously, for a fully developed artistic render, it will take much longer.

Scale of Water Plane: 50%. More on that later.

Waves: I tested all six of the available wave options (Classic, Classic 2, Bubbly, Frosty, Light, and Frothy).

Ripple Amount = Each tested at .35 and .65.
Displacement = Automatic. I didn't mess with this.
Clarity of Depth = 100.
Color tint = 255, 255, 255.
Volume = Default for Reality water plane.
IOR = Default of 1.33.
Last edited by Nathanomir on Sun Jun 12, 2016 8:50 pm, edited 2 times in total.
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Nathanomir
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 7:42 pm

Bubbly Wave Pattern.

At Ripple .35

Image

At Ripple .65

Image
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 7:51 pm

Classic Wave Pattern.

At Ripple .35

Image

At Ripple .65

Image
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Nathanomir
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 7:55 pm

Classic 2 Wave Pattern.

At Ripple .35

Image

At Ripple .65

Image
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 7:57 pm

Frosty Wave Pattern.

At Ripple .35

Image

At Ripple .65

Image
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 8:00 pm

Frothy Wave Pattern.

At Ripple .35

Image

At Ripple .65

Image
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 8:03 pm

Light Wave Pattern.

At Ripple .35

Image

At Ripple .65

Image
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Nathanomir
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 8:05 pm

Scale

Scaling the water plane does affect the wave pattern, and therefore the refractions and the dappled light effect. Below is a test of Bubbly at .65, but with the water plane is scaled to 35%. Compare it to the above test of Bubbly at .65 at 50%. Scaling the water plane gives you another good option for achieving the different looks of pool, river, lake, and ocean.

Image
Last edited by Nathanomir on Sun Jun 12, 2016 8:08 pm, edited 1 time in total.
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Re: Underwater Light Effects

Postby Nathanomir » Sun Jun 12, 2016 8:07 pm

Final Thoughts regarding earlier tests and combinations.

I tried using a cookie to achieve the dappled light effect. It yielded spectacular results! By itself. When used in conjunction with a surface of either glass or water, it gave me bizarre results.

The cookie and glass cancelled each other out. By itself, the cookie worked. By itself, a surface of glass reflected the objects under it. Together, it was as if neither was present.

The cookie and water was equally useless. The cookie prevented the light from ever reaching the water. Even at 1,000 s/P, the scene was dark, with no sunlight present (even with Sun gain increased to 25). Sky worked just fine.

For comparison, here is the cookie in place, without any water surface. The texture used is the Wave Pattern map from the UltruMarine set, used as a transmap on a plane.

Image

A gobo would be a good option for a mesh light or spotlight, but for this scene, the light source was just too far away from the subject to produce any sort of dramatic lighting effect.

You can play around with those options. Just because they didn't work for me, doesn't mean they won't work for you.

Note on Physical Clarity: Having grown up around (and often in) the spring-fed runs of central Florida, I can attest that it is possible for water to be this clear. In a larger river or lake, you'll want silt and a background that fades into nothing. An earlier test gave good silt effects using a cube, set to null, and filled with the water volume. I decided it wasn't necessary for this particular scene. Play around with that. That may be a good place for some fog. At a greater depth, light in silty water can create godrays.

For the blue or green color of deeper water, simply tint the water plane. Be subtle. 235, 235, 255 was BLUE!

AND FINALLY ... I have to decide which pattern I want to use. Decisions, decisions ...
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