If you’ve ever wondered what goes into converting a 2D-shot film into 3D, and what changes have to be made to the film to make it work in 3D, then you must read this recent Twitter thread from filmmaker David F. Sandberg. The director behind Lights Out and Annabelle: Creation took the helm of the DC movie Shazam! most recently, and in tackling a major blockbuster Sandberg was also presented with the need to convert his movie into 3D. As it turns out, the process requires more changes than you might think.

3D was all the rage after the successful box office debuts of Avatar at the tail end of 2009 and Alice in Wonderland at the beginning of 2010, and that led to a boon in studios thinking 3D was what was going to save the film industry. Almost every major blockbuster was post-converted, sometimes incredibly poorly (see: Clash of the Titans) and sometimes adequately (see: every Marvel movie). A few were actually shot in 3D as filmmakers ranging from Martin Scorsese to Ang Lee toyed with the new technology, but Hollywood soon discovered that Avatar and Alice in Wonderland were outliers and audiences would no longer be fooled by crappy, rushed 3D post-conversions with upcharged tickets.

And yet, studios still create 3D versions of most blockbusters, as was the case with Shazam!. Sandberg took to Twitter to visualize the difficulty in converting an image shot in 2D into 3D, especially with elements like snow and Christmas lights. Ultimately Sandberg comes to the same conclusion most filmmakers have: 3D is really only worth doing if the film is shot with a 3D presentation in mind. And beyond the upcoming Avatar sequels, not many films are created specifically for 3D anymore.

Regardless, this is a fascinating and insightful thread, especially for those interested in the filmmaking process. Check it out below.

I used to think that for 3D conversions they use the 2D footage as one eye and then just create a second eye but they actually create two new eyes. The original footage is sort of a center view. pic.twitter.com/smsn06nvlU — David F. Sandberg (@ponysmasher) February 25, 2020

If you switch from left to center to right in quick succession you might think that you'd get a mini version of The Matrix's bullet time. But no, you often get this weirdness. pic.twitter.com/bOqcfkhZuc — David F. Sandberg (@ponysmasher) February 25, 2020

Suddenly you see all the warping and trickery used. Things are enlarged to cover up more background rather than re-creating the background, things are erased to solve problems, etc.

Look at these guys raving! *unts unts unts* pic.twitter.com/Rso0I3UWjs — David F. Sandberg (@ponysmasher) February 25, 2020

Using the left-center-right works as you'd expect in simpler shots though. pic.twitter.com/bSw7Ss6FfV — David F. Sandberg (@ponysmasher) February 25, 2020

Sometimes you get a background object covered up in one eye but visible in the other eye which gets uncomfortable. That was the case with the fire behind Sivana in this shot, so for 3D that fire was painted out to spare you the headache. pic.twitter.com/J2gz0eyYyT — David F. Sandberg (@ponysmasher) February 25, 2020

To get depth from things like falling snow it's easier to just paint out the snow and replace with CG snow (or just leave it out). Here's flipping between original 2D and one of the 3D eyes. You can see some of the snow disappearing. pic.twitter.com/H5jWkYUFRp — David F. Sandberg (@ponysmasher) February 25, 2020

Normally I prefer my 3D to go deep into the screen rather than pop out. But a problem with 3D is "ghosting". When you have a bright object against a dark background, the two angles of the bright object can end up visible in both eyes. — David F. Sandberg (@ponysmasher) February 25, 2020

Having a movie set at a Christmas carnival at night will present a lot of ghosting challenges from all the lights. One way to fix this is to make sure that the two images converge where the lights are. — David F. Sandberg (@ponysmasher) February 25, 2020

This is what it WOULD look like if the convergence was at the girl in the foreground. In a theater this would look like the screen is a window and everything is behind it. pic.twitter.com/DLLJEaw72f — David F. Sandberg (@ponysmasher) February 25, 2020

But because of the bright lights in the BG the convergence had to be set much further back which means that the movie "comes out of" the screen instead. pic.twitter.com/nItJMvnP6Y — David F. Sandberg (@ponysmasher) February 25, 2020

I used to be a much bigger 3D fan. Loved my ViewMaster as a kid, loved my Nintendo 3DS as well as my old timey 3D viewer bought in an antique store. The concept of 3D is awesome. pic.twitter.com/4ATg43CpZu — David F. Sandberg (@ponysmasher) February 25, 2020

For film though I think it's not really worth it unless you not only shoot 3D but also change your whole film language to adapt to 3D and take full advantage. And we really need a way of viewing it without glasses. It's all too much of a hassle currently. — David F. Sandberg (@ponysmasher) February 25, 2020

I've seen a ton of movies in 3D but when I think back on them my memories are in 2D. I don't remember the 3D. Maybe that's just me though. — David F. Sandberg (@ponysmasher) February 25, 2020

As a director I know it's expected for bigger movies to be in 3D and I don't have a problem with that. There's some really cool 3D stuff in Shazam. The priority for me will always be the 2D version though. — David F. Sandberg (@ponysmasher) February 25, 2020