Colored Shadow Penumbra

kqp•23 minutes ago

This page helped me understand what they’re going for: https://patapom.com/blog/Lighting/Colored%20Penumbra/Colored....

The way I’m intuiting it: some things will “glow” when strongly illuminated, and the glow is more colored than the reflected light, so if the illumination has a hard edge then the penumbra can end up saturated by the more strongly illuminated part’s glow.

OP’s rendition isn’t quite landing for me, though, and I’m not enough of an artist to be sure why. Maybe it’s just that saturation is cranked way up for the demo, but it might also be that it shouldn’t occur on rock, or that color seems sometimes to not react to a change in which material is glowing.

hughes•about 2 hours ago

What's the physical basis for this effect? Does it happen in reality or is it a style choice?

Dave_Rosenthal•39 minutes ago

Simple answer: There is no physical basis, it's style

Pedantic answer: Unless the light source has different colors on different sides

Complex answer: Kind of. Even a linear color fade (from reality) can turn non-linear (and therefore induce color effects) when pushed through a color grading pipeline. So if you count e.g. film emulation as a "physical effect", then yes.

soraki_soladead•39 minutes ago

The post links another that goes into the theory a little: https://shahriyarshahrabi.medium.com/in-the-valley-of-gods-s...

Apparently a combination of Mie and Rayleigh scattering.

- https://en.wikipedia.org/wiki/Mie_scattering

- https://en.wikipedia.org/wiki/Rayleigh_scattering

AlotOfReading•33 minutes ago

It happens in reality, though I've only noticed it with desert sunlight. It's caused by light cast into the penumbra from scattering and diffuse reflection. You can't see this in the lit area because your photoreceptors saturate, which looks white.

alnwlsn•41 minutes ago

Not sure it happens with the sun, but if you have differently located light sources of different colors you can get shadows of different colors (because the shadow area is one source being blocked but it is still illuminated by the other sources)

adamjs•about 1 hour ago

This seems more like a chromatic aberration "hack" for HDR landscapes (intensely-lit portions of the scene would have color fringing apparent at the boundaries of light/dark due to dispersion in the observer's lens).

(And it's def a style choice, looks cool when done right! :))

https://en.wikipedia.org/wiki/Chromatic_aberration

tobr•about 1 hour ago

Came to ask this. I suppose if the edge of the sun glows in a different color than the rest, it would tint the edge of the shadow too? So maybe appropriate for sunsets, where the sky near the sun is red but the sun itself still glows bright white. Honestly just guessing.

sambaumann•29 minutes ago

Cool!

FYI the arrows on both photos only actually control the top photo.

Colored Shadow Penumbra

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