The Big Top Compositing and Lighting

A big part of the pipeline I designed for The Big Top was using HDRs of the sets for lighting the CG characters. This makes the process of lighting the CG much smoother, and the end result will look better.


We shot 9 exposures from 2 angles using a Canon 5D mkiii, and a 300mm lens.  One of the challenges with shooting HDRs for stop motion sets is the size, so we had to find a camera with a short enough focus distance to capture both angles in the small space, but long enough focal length to fill as much of the frame as possible.



Once we had the images I used Photoshop's HDR Pro function to merge them into one single image which I exported out as an EXR.


I then took this into Nuke, to do the unwrapping process, I did this 
with the spherical transform node, which worked well. Obviously there is massive distortion to the left of the image, and to the right you can see where we were taking the photos, this is where the second image is needed.


I unwrapped the 2nd image and aligned it on top of the 1st image. Because it was shot at a different angle the distortion is in a different area, so I masked out the distortion from the first image and replaced it with data from the 2nd image, which you can see above, although it does need more feathering.


These were the images I was able to render and comp, completed in Arnold and Nuke. I think they are pretty successful. The HDR worked well and I needed to do minimal whitepoint and blackpooint grading. The only additional lighting I had to add was the blinds, which I created with a spot light and a procedural gobo, it's a little to sharp compared to the backplate, but when we get more into production I will paint a more accurate texture map for it, or photograph the physical gobo we are going to use on set, and create an alpha from that.

One thing we will need to get reference for is focus, as for this image I had to guess the amount of blur the character would have. One other thing I am interested in is matching the lens apertures, so the blur from our digital cameras matches as closely as possible to the physical ones.


This comp is from a slightly different angle, you can see the harshness of the gobo texture more here, but the character still sits well within the frame.

I want to create a checklist of things we need to do on set to make the rendering and lighting go as smoothly as possible. One thing I am keen on doing is creating physical props to put in the set as reference for how the lighting affects that model and materials on it, and what the bokeh is like, it will also help us frame up the shots with the backgrounds for the animators in Maya, and final output from Nuke.

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