When most people think of visual effects, they may think of actors standing in front of a green screen or staring at a tennis ball. Or perhaps they imagine editors sitting in rooms for long hours, creating worlds out of nothing. They might even think of editors spending hours trying to figure out how to get that mustache off Henry Cavill. And while all of that is certainly true, one crucial method tends to go unnoticed. That process involves High Dynamic Range Image (HDRI).
Many times, films or shows will choose to shoot on location, but VFX artists will still have to add in objects to the location to make it fit the fictional world of the film. The difference between a CG object blending in perfectly or standing out like a sore thumb comes down to one thing: lighting. To get accurate lighting, VFX artists will be running on set in between takes to try to capture an HDRI.
One of the main methods to capture HDRI’s is the mirror ball, which is exactly what it sounds like. A shiny ball that reflects from all sides. By shooting bracketed images of the mirror ball in the location the object is supposed to be, it functions as a sort of 360 image that VFX artists can download data from. They see how the lighting interacts and can apply it to their CG object.
There are other methods to capture this image as well, and many artists will choose these to save time. To learn more, and to see an example in action, check out this Vox video. And next time you watch a film, give a little more credit to the hard working shiny balls.