Twilight Fisheye

Here's a new angular fisheye render taken at twilight (solar elevation angle −3°) in which you can clearly see the twilight arch, the anti-twilight arch, and the Earth shadow.

To produce the image below, I first took advantage of the symmetry of the render to effectively double the number of samples, using Photoshop to duplicate the high-dynamic range EXR image, flip it horizontally, and composite it onto the original. Then I used Photomatix to tone-map the processed image. The solar (top) side is much brighter than the anti-solar (bottom) side, so without tone-mapping it wouldn't be possible to expose the entire sky nicely at one time—part of the image would be overexposed or part would be underexposed. The tone-mapped image is over-saturated and the relative intensities of different parts of the sky are not accurate, but you can see the entire sky and you can see the colors clearly.

Twilight, tone-mapped.

And below is the PNG that came directly out of my renderer. I applied a mild S-shaped transfer curve before writing to PNG.

Twilight, directly from my renderer.

The sky was clear this evening in Philadelphia and I was able to see the Earth shadow. The colors in the real sky closely resembled those in this render.