EddieOffermann dot com

Read this question on cgtalk tonight and thought I'd kick the question and my response out here since I've repeated much this same advice many, many times.

I use Boujou for matchmoving but am tracking 640x480 camera resolution all of the time... I often have shots with handheld very shaky camera and motion blur. Boujou has trouble tracking it. Is it just that there's to much blur/shakiness or would a higher camera resolution help?

and my response:

Well, it looks like there are a number of issues to overcome:

First, the quality of the footage: handheld/shaky/moblurred footage is just awful to work with. If you're just the artist, ie, you get what's handed to you: you work with what you have. There's no telling Mann, Fincher or Stone they have to reshoot because your job is hard. Their job is harder and it's them the client paid for, not you. If it's for your own projects, ie, you're the director or at least the vfx supervisor on a smaller project: you have to take this into your hands (so to speak) and fix it before it gets past the camera! Since you're working with 640x480 footage, I have to assume you can address it at this stage: these are obviously personal projects, not features or broadcast. Fix the source first! Don't shoot/allow to be shot footage that's going to suck to do post on!

Second, the resolution of the footage: Until you've worked in HD or film res, it's hard to appreciate just how much easier it is to work with on a tracking level. A dot that is so small it'll disappear into noise at NTSC is an obvious crosshair at 2k. Smudges on the wall and skin blemishes become usable tracking points. If you have the option to work with higher resolution footage, insist on it!

Third: Lighting. Again, this is only something you can influence if you're shooting your own projects, but remember to light for contrast not final levels. More light means faster shutter speeds means less motion blur. Light for the type of shadows you want, not how dark you want the scene when you're shooting for visual effects. If your key and fills are set properly, you can always make the shot darker when grading. This isn't as much of an issue when shooting film or deep color digital like the Arri Digital cameras since their shadow detail is good enough to boost for tracking detail. But if you're shooting with consumer or prosumer cameras, you've got jack but noise in the shadows and the low light levels will mean excessive blur and bad noise overall.

Fourth: Manual vs Auto. Boujou has a reputation as being the fire-and-forget solution for people that don't understand tracking. The really hard shots are going to need manual solutions. I don't mean hand-keyed (necessarily) but we're talking careful selection of usable tracking detail and improved setting of constraints. Personally, I recommend SynthEyes - unbelievably good price point and an unbeaten feature set. I know there are shots that people say they can click a button and get a solve on in Boujou that they can't get in SynthEyes, but the reverse is true far more often than it's not. When the footage is hard to work with, throw away the automatic solutions. Give them one run at it if you've got the time and processor power to spare, then move to something where you have some control.

Fifth: Tracking techniques. Track the center, not the edges. When doing a supervised track of moblurred features, follow the center of those blurs.

Sixth: Rendering techniques. Moblurred footage is hard to render to match because what you have to match is a particular slice of time. Think of it this way: you're placing tracking points on each frame, generally spaced apart at the rate of 24, 25 or 30 frames per second. Between frame 1 and frame 2, there's a fraction of a second where anything could happen. The camera could jump up a couple centimeters and back down for instance, before hitting frame 2. This will show in the motion blur but not in the keyframes. You can't easily fix for this! (See tip 1). More often, though, the problem is the phase of the render. How to address this will depend on your renderer. You may be able to adjust this in the renderer, you may have to adjust it in the actual animation keyframes depending on what 3d software you're working from. Basically, you need control of the shutter timing and shutter offset: when in that frame it opens and how long it stays open.

For high end vs. low end facilities, #6 can often be the difference between them. For all the skill you can buy from freelancers in tracking, modeling, animation, textures, etc: having the resources to do test renders and tweak that setting (and having someone on staff who can make sure you're addressing this) makes all the difference.

A few weeks ago, I posted a video covering the process of relighting rendered CG elements in a compositing tool like Shake using a surface normals pass.

Since that covered normals-based relighting of rendered cg elements, I thought I'd write an article that takes the concept a little farther and should stretch the reader's mind on what's possible with this sort of approach.

The earlier tutorial covered something that naturally can be accomplished by going back to the original scene in your 3d application, adjusting lighting and re-rendering: but I think there are times when we want to adjust the lighting primarily in the compositing application but want more than some masked-off gamma correction, lifts and crushes. So it's handy, then, to be able to apply an effect more similar to real-world lighting and that's what a rendered surface normals pass will enable us to do.

But what about real world imagery? Can this same technique be applied to live action footage just as it can be on a CG element?

Absolutely!

You'll want to start with a few elements like the following:

A full-color image like the above picture of a farmhouse. Under ideal conditions, you'd have an image with very diffuse lighting: something with a lot of bounce light or an exterior on an overcast day. The idea here is that there are relatively few real shadows in the image. The reality is that you won't have that very often and you'll have to use what you've got. You may decide that the shadows that do exist need to be painted out before you continue. I haven't done that for this example, but you'd be hard pressed to find a high end effects project that relit a real world environment and didn't remove the existing shadows at some point in the pipeline.

The above image is a matte of the farmhouse pictured above. You'll probably need to generate something like this for your scene if you haven't already.

A surface normals pass of a polysphere with its shading set to be as unsmooth as possible. I prefer this because I have a better feeling of where these surfaces are facing than I do straight from a sphere. It makes it like a special kind of color palette so I can perform the next step:

Next, I roto out a super-simple normal map of the surface in the image. This can be more or less complicated, depending on how much detail you want in the relight. If the surfaces are softer, you may want to blur the resulting image some: this will soften the transitions. Pick colors for each of your surfaces from the faces of the polysphere normal pass, making sure to keep parallel faces the same color as you interactively create a normal pass for your real-world element.

Then, I set up the OpaqueWhite OneLight Plus node as described in the normals relighting video here. Shake users can download the tool for free here.

It'll look similar to this:

Over on the right, you see where I've created the interactive surface normals pass. Those are groups with a few quickshapes and Mult nodes layered to create the interactive normals. In this case, since I didn't build out the ground and the barn next to the farmhouse, I chose to use the alpha from the interactive normals as the matte for the OW_OneLight+ node instead of the matte extraction I showed above. A smoothly blended surface for the ground, and a couple blurred normal shapes for the trees could make this quite convincing.

On the left, the fade leading into the over and the mix node to mix the whole thing back together is just one way of tweaking the levels of relighting that you're doing.

I posted a really short render of the light source moving across so that you can get an idea of what can be done. I kept it fairly subtle, and keep in mind that a little more work to create normals data for the ground, barn and trees would be required for a real project.

Moving footage naturally requires animated roto work to generate the interactive surface normals pass (keep the colors the same unless the element itself is moving!), and more complex objects with broader camera moves can be relit if you:

1. Build 3d geometry to match the visible elements
2. matchmove that geometry to match the footage
3. render a surface normals pass of those elements
4. use that rendered surface normals pass to relight the live footage.

In a future installment, I'll describe a method to generate surface-normals data by painting a bump map onto an image. In the meantime, I'll leave it as an exercise to the curious reader: how could you convert a simple greyscale height map into surface normals data in Shake?