The sun refracted through millions of ice crystals falling from the upper atmosphere.
The following might be considered slight spoilers for Inception for who don’t want to know anything about the movie before they see it, so avert your eyes quickly.
Practical effects were used skillfully in the making of Inception. One significant example is the use of rotating sets (sometimes 360 degrees). And despite the green-screen background shown in the picture above, director Christopher Nolan strictly favors to create as much as possible on set, before resorting to CGI for the more impossible imagery, which was all handled by VFX studio Double Negative.
So essentially most of what you saw on screen, you may not have realized that the filmmakers pulled it off… for real. Yes, even the train on the streets. A full-scale replica was created and placed on the chassis of a truck, and subsequently barrelled through downtown pavement. Those twisted elevator shots? Real. Realize this: the vertical shaft you see is a horizontally placed set, and the top right wall shown is actually the floor. The camera is upside down and Joseph Gordon Levitt is hung on wires. All very cool and definitely worth the trouble in the end.
And that’s not all to mention that it was shot on 35mm and even higher quality 65mm film. Not digital video. Not 3D. Anyone that’s seen the movie knows how great the cinematography is and how it lends to the visuals. How excellently the shadows, lighting and colors and detail all play with each other. And that’s all very well calculated for the format:
“Film has an enormous amount of exposure latitude and dynamic range, which gives us infinite creative flexibility in creating images,” says Wally Pfister, Nolan’s now go-to director of photography, “I can underexpose it by 3 stops and overexpose it by 5 stops within the same frame and see the entire spectrum on the screen. That’s simply not possible in any digital format I’ve seen. Every digital camera is trying hard to emulate 35mm film, and there’s a reason for that.”