Real Men Comp With Film

Be careful having dinner with Mike Seymour.

He was sharing with me his nerd-joy over being able to interview Jon Alexander at ILM about the history of optical compositing. I offhandedly mentioned that I had once, out of pure lifelong curiosity, re-created the optical bluescreen extraction workflow using After Effects.

Oops. The next day Mike was in my office with a camera. Watch this whole video. My bit is nerdelicious, Jon’s is wonderflully insightful and grounding, and it all adds up to a great taste of what fxphd members get to enjoy heaping tons of.

Read the companion article here.

Realistic Lens Flares

When technology and art intersect, its often the case that those who know how have no idea why, and those who know why have no idea how.

I can’t stop thinking about this SIGGRAPH video. It shows realistic lens flares being computed in real time using a ray tracing technique. There are some lens artifacts shown here of a complexity and beauty that I’ve never seen faked convincingly before.

Lens flare is caused by light passing through a photographic lens system in an unintended way. Often considered a degrading artifact, it has become a crucial component for realistic imagery and an artistic means that can even lead to an increased perceived brightness.

Jesus nerds. “Increased perceived brightness?” That was the best sales pitch you could give on why being able to synthesise realistic lens flares is worthwhile?

Lens flares are awesome because they are fricking crazy. They are completely unreal. They increase the veil of unreality between the audience and the movie. They are beautiful. They are tiny imperfections magnified by orders of magnitude. They are aliens. And scary buildings. We give them sound effects and music cues. They make movies bigger than life because they have nothing to do with life.

And I want yours.

In the Vimeo comments the poster said:

Anamorphic optics are currently not supported, but this is not a principal limitation of the rendering scheme.

If they had put anamorphic examples in this video I think I’d be standing on their lawn with a boom box right now.

Physically-Based Real-Time Lens Flare Rendering — Hullin, Eisemann, Seidel, Lee

Converting 30p to 24p

As the long-awaited 24p firmware update for the Canon 5D Mark II draws near, I joined Mike Seymour on episode 57 of the Red Centre podcast to talk about how excited I am that it marks the end of painful workarounds for the 5D’s no-man’s-land frame rate of 30.0 frames per second.

For as long as I’ve had my 5D Mark II, I’ve avoided using it for any projects that I could not shoot 30-for-24, i.e. slowing down the footage to 23.976 fps, using every frame. My 5D has been a gentle overcrank-only camera. There are plenty of occasions to shoot 30 frames for 24 frame playback—we do it all the time in commercials to give things a little “float,” or to “take the edge off” some motion. I still do this often with my 7D. Whatever frame rate I shoot—24, 30, 50 or 60, I play it back at 24. Just like film.

Folks ask me about 30p conversions often. Twixtor from RE:Vision Effects is a popular tool for this, as is Apple’s Compressor. Adobe After Effects has The Foundry’s well-regarded Kronos retiming technology built-in. All of these solutions are variations on optical flow algorithms, which track areas within the frame, try to identify segments of the image that are traveling discretely (you and I would call these “objects”), and interpolate new frames based on estimating the motion that happened between the existing ones.

This sounds impressive, and it is. Both The Foundry and RE:Vision Effects deservedly won Technical Achievement Academy Awards for their efforts in this area in 2007. And yet, as Mike and I discuss, this science is imperfect.

In August of 2009 I wrote:

I’m not saying that you won’t occasionally see results from 30-to-24p conversions that look good. The technology is amazing. But while it can work often, it will fail often. And that’s not a workflow. It’s finger-crossing.

On a more subtle note, I don’t think it’s acceptable that every frame of a film should be a computer’s best guess. The magic of filmmaking comes in part from capturing and revealing a narrow, selective slice of something resonant that happened in front of the lens. When you use these motion-interpolated frame rate conversions, you invite a clever computer algorithm to replace your artfully crafted sliver of reality with a best-guess. This artificiality accumulates to create a feeling of unphotographic plasticness.

Of course, it’s often much worse than a subtle sense that something’s not right. Quite often, stuff happens in between frames that no algorithm could ever guess. Here’s a sequence of consecutive 30p frames:

Right-click and select View Image to see full-resNothing fancy, just a guy running up some stairs. But his hand is moving fast enough that it looks quite different from one frame to the next.

Here’s that same motion, converted to 24p using The Foundry’s Kronos:

Right-click and select View Image to see full-resBlech.

Again, don’t get me wrong—these technologies are great, and can be extremely useful (seriously, how amazing is it that the rest of the frame looks as good as it does?). But they work best with a lot of hand-holding and artistry, rather than as unattended conversion processes.

(And they can take their sweet time to render too.)

I’m so glad we’re getting the real thing.

Passing the Linear Torch

I used to show you weird crap like this all the time

Back in the day I blogged a lot about how compositing and rendering computer graphics in “linear light.” a color space in which pixel values equate to light intensities, can produce more realistic results, cure some artifacts, and eliminate the need for clever hacks to emulate natural phenomena. Along with Brendan Bolles, who worked with me at The Orphanage at the time, I created eLin, a system of plug-ins that allowed linear-light compositing in Adobe After Effects 6 (at the mild expense of your sanity). I also created macros for using the eLin color model in Shake and Fusion. Along the way I evangelized an end to the use of the term linear to describe images with a baked-in gamma correction.

Then Adobe released After Effects 7.0, which for the first time featured a 32-bit floating point mode, along with the beginnings of ICC color management, which could be used to semi-automate a linear-light workflow. The process was not exactly self-explanatory though, so I wrote a series of articles (1, 2, 3, 4, 5, 6) on how one might go about it.

Then I rambled endlessly on fxguide about this, and in the processes managed to cast a geek spell on Mike Seymour and John Montgomery, who republished my articles on their fine site with my blessing.

This week Mike interviewed Håkan “MasterZap” Andersson of Mental Images about the state of linear workflows today on that same fxguide podcast.

Which is so very awesome, because I don’t want to talk about it anymore.

It’s just no fun going around telling people “Oh, so you put one layer over another in After Effects? Yeah, you’re doing it wrong.” Or “Oh, you launched your 3D application and rendered a teapot? Yeah, you’re totally doing it wrong.”

You are doing it wrong. And I spent a good few years trying to explain why. But now I don’t have to, because Mike and MasterZap had a great conversation about it, and nailed it, and despite the nice things they said about ProLost you should listen to their chat instead of reading my crusty old posts on the subject.

Because it has gotten much, much simpler since then.

For example, there’s Nuke. Nuke makes it hard to do anything but work in linear color space. Brings a tear to my eye.

And the color management stuff in After Effects has matured to the point that its nearly usable by mortal men.

Since I’ve seen a lot of recent traffic on those crusty old posts, here’s my linear-light swan song: a super brief update on how to do it in AE CS4:

In your Project Settings, select 32 bpc mode, choose sRGB as your color space, and check the Linearize Working Space option:


When importing video footage, use the Color Management tab in Interpret Footage > Main to assign a color profile of sRGB to your footage:


Composite your brains out (not pictured).

When rendering to a video-space file, use the Color Management tab in your Output Module Settings to convert to sRGB on render:

That’s the how. For the why, well, those crusty old articles could possibly help with that, especially this one on color correction in linear float, and this one on when not to use linear color space. Part 6 is still pretty much accurate in describing how to extract a linear HDR image from a single raw file using Adobe Camera Raw importer in After Effects, and this article covers the basics fairly well, although you should ignore all the specifics about the Cineon Emulation mode, which never should have existed. This little bit of evangelism is still a good read.

But the ultimate why answer is, and has been for a while now, within the pages of a book you should have anyway: Adobe After Effects CS4 Visual Effects and Compositing Studio Techniques (deep breath). Brendan Bolles guest-authored a chapter on linear light workflow, and not only does he explain it well, he gives many visual examples. And unlike me, Mark keeps his book up-to-date, so Brendan’s evergreen concepts are linked directly to the recent innovations in After Effects’s color manglement.

OK, that’s it. Let us never speak of this again.

Update on Wednesday, September 30, 2009 at 2:09PM by Stu

I can’t believe I wrote all that without once linking to the official Adobe whitepaper on Color Managed workflows in Adobe After Effects CS4. It’s a great write-up, super detailed, and accurate in every way. Further proof that my work here is done.

The Foundry Un-Rolls Your Shutter

The Foundry have released a $500 plug-in for Nuke and After Effects that attempts to remove rolling shutter artifacting, AKA “Jell-o cam,” from CMOS footage (RED One, Canon HV40, Canon 5D Mark II, etc.). It’s based on a technology demo that they showed at NAB earlier this year.

I’ve tried it, and it works—sometimes. The Foundry are well known for being leaders in the motion estimation field, and they have harnessed their unique experience in this area to attempt the impossible: a per-pixel reconstruction of every part of the frame, where it “would have been” if the shutter had been global open-close instead of read out a line at a time.

When it works, it’s brilliant. But the more motion you have in the frame, the more likely this plug-in, mighty though it may be, will get confused. Unfortunately, when this happens, parts of the image turn to scrambled eggs.

It’s a very similar problem to re-timing 30p footage to 24p actually—in fact, I wish The Foundry had added an option for frame rate conversion to this plug-in. Although, in fairness, I would only rarely use it.

Folks are always asking me about converting 30p to 24. I responded in a thread on the Rebel Café:

…The more motion you have, the more likely it is that any optical flow re-timing system is going to encounter problems.

Not even getting into the combat shots, here’s the Apple Compressor method referenced in Philip’s tutorial failing on one of the more sedate shots in After The Subway:

Now I’m not saying that you won’t occasionally see results from 30-to-24p conversions that look good. The technology is amazing. But while it can work often, it will fail often. And that’s not a workflow. It’s finger-crossing.

On a more subtle note, I don’t think it’s acceptable that every frame of a film should be a computer’s best guess as to what happened between captured frames. The magic of filmmaking comes in part from capturing and revealing a narrow, selective slice of something resonant that happened in front of the lens. When you do these motion-interpolated frame rate conversions, you invite a clever computer algorithm to replace your artfully crafted sliver of reality with a best-guess. I feel (and feel free to disagree, I won’t bother arguing) that this artificiality accumulates to create a feeling of unphotographic plasticness. Screw that. Didn’t you select the 5D because you wanted emotionally resonant imagery? You’d be better off with a true 24p video camera that works with you rather than against you, even if it doesn’t give you the convenient crutch of shallow DOF.

To be crystal clear, that’s Apple Compresser failing to properly estimate the motion in one particular frame when trying to convert from 30p to 24p. Nothing to do with The Foundry or their new plug-in, which actually tackled that same shot quite well.

The Foundry knows that they’ve made a tool to help us limp along while camera manufacturers sort out this CMOS issue. Like any crutch, I wouldn’t plan on leaning too hard on it—but kudos to The Foundry for attacking this problem head on, and making a product out of a technology demo in record time.

Update on Thursday, August 6, 2009 at 2:28PM by Stu

Of course, there will always be some rolling-shutter artifacts that can never be fixed: