Babysitting the previz render farm

Yes. I know, it is way, way too long since my last post. A new round with the flu and a death in the family slowed things down considerably for a while. I’m back now though and we have charged into the previz. A little late maybe as the deadline is on monday, but we’ve gotten a lot done the last couple of days and I believe we’ll be all right.

While Aleksander, Andreas and Jamie are all working hard, squeezing out shots, it is my job to render them, do some polishing in Nuke and have them ready for the edit on Friday (hoping we’ll be ready by Friday).

So in between receiving scenes and rendering them, I run the ones I have rendered through my Nuke pipeline. The process goes like this:

The 3D render is imported into Nuke.

As the render does not come with skies, I add those first. I found a nice image for this over at CGTextures. I add the sky separately, so that I can easily animate clouds, change sky colour etc.

To add the sky, I use a matte that comes with the 3D render. White determines what is visible, while black determines that which is invisible. By applying the matte to the render and positioning the sky image behind it, the sky gets added to the shot.

Next up is to add some depth to the scene using a depth map that also comes from the 3D render. A depth map determines the relative distance between different objects based on brightness values. Dark colours are far away while lighter colours are closer to the camera.

Based on the depth map, I am able to focus on one particular part of the scene. I then tell Nuke to keep this part in focus while gradually blurring the parts of the image that is further away. The result is depth of field, or DoF, that can be applied much faster than in 3D and can be adjusted after the 3D render. Definitely handy!

Finally, I add a sense of atmosphere by inverting the depth map so it looks like the one above, change the colour to light blue and add it to the render to wash out background colours. This is importaint to make the mountains look like they are further away. This is actually done before applying DoF, but needed to explain what a depth map is first.

When I’ve done everything above, I colour-correct the footage, blur it slightly, add some grain and render the result to Apple ProRes format, which we’ll use during the edit. The final Nuke script looks like this:

I repeat this process for each shot. For the most part I only need to replace the files from the 3D render and reposition the sky.