Chest Dino

Here is the basic workflow that I used

I started by shooting the video background plate. This just means that I set up a video camera and videotaped myself acting out the scene.

Next, I converted the video frame size from 720 x 480 to 648 x 480. I did this because digital video has a pixel aspect ratio of .9 which means that the pixels are 1 unit tall but only .9 units wide. This is a problem because computer graphic use a pixel aspect ratio of 1 which means that they use square pixels. If I didn't convert the video frame size, the background plate would look strangely wide. For a lot of people this is a strange and hard to understand idea but once you work with it a while, it makes sense.. Another way to handle the difference in the pixel aspect ratio would have been to set up the rendering camera in Maya to deal with the digital video but, I chose to do it by converting it instead.

In Maya, I set up a camera that used the video as an image plane. Since the video I shot did not make use of a moving camera, I don't have to worry about animating it. Instead, I locked the translate and rotate attributes so that the camera could not be accidentally moved.

Now that everything is set up, I had to model a front torso that would be used as a model of my torso. The model didn't have to match my body exactly for this particular shot. It only had to be close enough so that any shadow I would create later would look like they were actually on my skin and not just on a flat plane. I also made a copy of the torso model and used it to make a model of the chest that would have a large hole in it. I turned that model into a blend shape so that I could animate the torso model opening.

Click image for a larger view...

Now for the hardest part of this shot; motion tracking. I had to animate the torso model so that it would move the same as my torso in the video. If you look at the picture of me, you will notice some freckles on my skin. Actually, those aren't freckles. I drew those on using a brown eyebrow pencil to act as tracking points. They helped me to keep the torso model lined up with my torso. I also used my tattoos to help me line things up too. This took a long time and required me to make a lot of PlayBlast animations to check my work.

After the torso model was animated well enough, I modeled the inside of the chest using a NURBS sphere. Nothing fancy..

Click image for a larger view

Since the torso model is already animated, all I had to do was parent the inside of the chest (guts) to the torso model. Then I positioned the fully rigged T-rex model inside the guts. The model was much larger than I needed it to be so I had to scale it down to fit. Since the root joint of the T-rex model controls the entire model and it is a child of the "IKROOT" control object, all I had do do was scale down the IKRoot object to scale down the entire model, including skeleton, eyes, teeth, everything! What this means is that if you choose the object or joint (root joint) at the top of the hierarchy and scale it up or down, everything below it in the chain will scale also...

Click image for.... well, you get the idea by now...

I wanted the T-rex to follow along with the torso model so that it looked like it was inside the body. I could have simply parented the root control of the T-rex rig to the torso model but, after he jumps out of the chest I didn't want him following the chest any longer so instead of parenting, I used a "Parent" constraint. By using a constraint instead of simply parenting the T-rex to the torso, I could turn the constraint off any time I wanted to. I keyframed the constraint on while he was in the chest then I keyframed it off after he jumped out..

To make it easier to animate the T-rex while he was in the chest, I turned off (muted) the chest translate and rotation so that it wouldn't move. By doing this I didn't have to deal with the side to side movement and rotation of the chest and could concentrate on the rex animation. I made notes for myself so that I knew at what frame the chest was turning left or right or facing straight ahead so that I could have the rex "act" accordingly.

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Here is a PlayBlast animation of the T-rex inside the Torso model. Blast44.avi (5.2meg avi file)

I rendered the scene using Mental Ray.

For lighting, I tried to mimic the lighting on the video. When I shot the video, I was facing a large sliding glass window and indirect sunlight was coming in. In Maya I set up an area light to simulate the window. I also put an area light above the animation to simulate bounce light off the ceiling. Since the entire video scene was shot with nothing but indirect lighting and their aren't any deep shadows, I had to illuminate the animation in a similar way so what I did was set up a large sphere around the entire scene and used it as a light source for a lighting technique called FINAL GATHER. With final gather, each area of the scene is analyzed to determine how its brightness will affect other areas in the scene. The large sphere that I made was colored white and it had a fair amount of incandescence to it. In other words, it was giving off light for the final gather process to read. This approach gave me some pretty good and pretty even lighting. Oh yeah, I used almost no ambient light at all.

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The scene was rendered in several layers:

You may have noticed that the T-rex is much larger than I am and that when he was in the animation, his legs and tail and most of his body were sticking out of the guts chamber.

To deal with this problem, I modeled a curtain that would block his legs and also the outside of the guts model so that it wouldn't render.

The way this works is that you apply a material to the object that you want to act like a mask. then, under the material attributes, you go down to the "Matte opacity" tab and set it to BLACK HOLE. This will make it so that whatever object has that material applied to it will not render but it will block anything that it gets in front of. Kind of like that blanket that Harry Potter had; you couldn't see the blanket but you also couldn't see anything that it was wrapped around either. I never say Harry Potter but I think that's the way it worked. Anyway, that's how I blocked out the legs and outside of the guts model.

I almost forgot; since the large T-rex had to fit through the opening of the chest, I used a wire deformer that caused his body to "squeeze" through the opening then go back to its original size and shape.

I used the same technique to allow the rex to be inside of the chest while having his head outside of the chest. When I rendered the chest model, I left the rex model in the shot but I turned his skin (material) into a black hole so that it would not render but would block out any part of the chest that it was in front of. I did the same thing with the guts model so that it would block out any part of the rex that would look funny if you saw it in the hole such as his tail. It would have looked funny if you saw his tail within my chest since the tail was about 6 feet from the rex's head. The illusion of space would have been shattered.

For the shadows on the chest I applied a lambert shader to the torso model then ran the animation with the chest and the rex but not the guts. Instead of doing a beauty pass for this rendering, I did a shadow pass. Now, I only wanted shadows that were on the chest so I went to the rex model and turned off Primary Visibility under Render Stats for the rex model. I also made sure that Cast Shadows was on. By doing this, the rex was still in the scene to cast shadows but it was not there to be rendered. The only thing that rendered with this set up was the shadows that were cast onto the torso model...

I composited the layers in After Effects. Some of the things I had to adjust are; contrast, color saturation, and color balance.

Here is a PHOTOSHOP file that will show the layer breakdown. Layer photo (1 meg. You need Photoshop to open this file)

I hope you enjoyed this explanation of the workflow I used to create the Chest Monster clip. Here are a couple more pictures for you to see.(click on them)