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Tools and Technologies for Working with 3D on the Set
The nature of how we shoot 3D and monitor it on set has changed as we have learned from our mistakes. Today, I would say 75% of stereographers out there prefer DPs to shoot in parallel. Not necessarily parallel rigs, with cameras side-by-side, since beam-splitter rigs are more flexible and therefore much more common -- but instead, pointing both cameras straight ahead, literally shooting parallel to each other.
Of course, there are two schools of thoughts about this. There's one that says, "Let's get it in the camera and be finished." I can see certain advantages to just shooting, then handing it off to post. But then I see a lot of stereographers who abuse convergence. They have toed in to set the convergence at the center of their scene, giving no consideration to the threedimensional depth, or the distribution of objects, in the scene.
What happens in post production at that point? Well now, I want to shift the convergence. But in the simple act of toeing the cameras in towards the center, you create a keystone effect. Now each camera has an opposing keystone that we have to correct. Any time that we saved on set by shooting converged might be gone, because now we're doing more correction in post production.
The software tools that we have developed can handle that, though. Many other tools in the market can also handle keystone correction, but it's one of the tougher disparities to actually fix up by eye. You're basically introducing a third dimension of geometric correction at that point, which takes a lot more time to fix.
This is one of the major advantages to shooting parallel: convergence can be added in post with more control, with fewer errors to fix. There is still the challenge of finding out what potential errors might be developing in a shoot, and this is what we are beginning to address.
Connecting Production and Post
We are typically using beam-splitter rigs. One camera will have a flip or flop in it, because it is shooting through the mirror. That is going to have to be rectified at some point. Even before that, we have to deal with the fact that these are two, separate, parallel streams. We haven't done a horizontal shift to choose a convergence point, so when the two streams are muxed, everything in the scene is going to be in negative parallax, coming out of the screen.
Of course, we don't want to show the client that. We want to show the client or the director exactly what the final product is going to look like. So in our software, we can do a convergence shift. We can also line up any disparities between the cameras that for whatever reasons we haven't either had time to tune out, or maybe we're using a particular rig that day has an inability to tune out a certain disparity. So we can actually show the clients a sense of the finish product, while having some sense of what we need to do to complete it.
Until now, we have been using Blackmagic's own capture software. But we have developed our own software to support ingest of 3D material, and output to monitors or for recording, called Stereo3D CAT. It takes the two inputs, and analyzes the images coming in. We can check color calibration and geometric calibration. We can calculate the depth of the scene, and actually see representation of the depth in the scene. We can see where the convergence point is, and make adjustments.
This works in conjunction with a chart we have developed with DSC Labs, called the Dashwood 3D Chart. It has visual code trackers that automatically track to 1/1000th of a pixel for ideal stereo alignment. The chart also offers an interface for live feedback to assist in automating camera alignment, sync testing and slating, and color and gamma calibration. All of these tools link back to the Stereo3D Toolbox software suite that we have already been shipping for Final Cut Pro, Motion and After Effects. Any information that the on-set stereographer has gathered using Stereo3D CAT can be passed through to editorial, where they will use Stereo3D Toolbox to address it. This direct communication from the on-set stereographer to the editor in post is one of the ways that we hope to bridge the gap between production and post production.
All of this begins with on-set monitoring of the 3D signals. The big tool that we use for this is the Blackmagic HD Link DisplayPort 3D box to mux our 3D streams. Anyone doing 3D needs to plan to have a few of them in their inventory --for instant dailies, for preview, and so many purposes, it's just a wonderful little box. No matter what we're shooting, we have some of those around.
The left and right signals we send through it are of course already genlocked together. We can capture that output if we want, put it on tape, we can down convert it --there are a lot of things we can do with that signal, but in our case, mostly we just view it on a monitor.
For ingest on set, we use the DeckLink HD Extreme 3D card inside a Mac Pro, recording a separate left file and a separate right file, full raster 1920 by 1080. That's going to an internal RAID in ProRes HQ.
The great thing about the HD Extreme 3D is that it has HD-SDI inputs and outputs with loop through. We can go into the Mac Pro first, so it's recording the separate left and right eyes, and then we can loop into the DisplayPort 3D muxed. We can then also record that output on a different computer, so that we can get our side by side dailies immediately.
We've actually been using Blackmagic cards for 3D for years. Before the DeckLink card even existed, we were using two Intensity cards with HDMI, and Blackmagic HD-SDI to HDMI converters to get our HD-SDI signal in. We even put two Intensity cards into a Mac Pro and they showed up as two separate inputs. Then Blackmagic came out with the Duo card, which is basically the same thing, but on a single slot. But today, having the DisplayPort 3D box, and the Extreme 3D card in our Mac Pros, has made a big difference. I'm really glad they came out with these.
Founder of Stereo3D Unlimited
Related Keywords:Tim Dashwood, Stereo3D Unlimited, Stereo 3D, Blackmagic Design, stereographer, Stereo3D CAT, Blackmagic HD Link DisplayPort 3D, DeckLink HD Extreme 3D
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