Applying Compositing to Real Renders

I applied the logic I discussed in my last post to some real renders today! I’ll speak a bit more about my simulation and lighting setup in another post, but I’d like to mention a few additions to the expression and a couple of gotchas that I found.

The simulation that I’d created was far too small at the beginning for me to want in my sheet – I was trying to create something that was fairly generic and didn’t have too much movement inside of the flipbook as this would be done in the particle system in engine.

Because of this, I wanted to start my render partway in, and of course, I didn’t want 240 images in my sheet, so I only used every third image.


To load in the rendered images for the composite, I took my previous file loading logic, but added the start frame – 1 to it. This allowed me to offset the number that the node stepped though.

N = frame increment , S = start frame

padzero(4, (($F-1)*N+1)+(S-1))


This didn’t work for me originally, until I found a wee gotcha. As I’d rendered the image from frame 49, the file node was defaulting to a frame range between 49 and 240. To correct this, I overrode the frame range to do 1 – 64, one frame for each of my flipbook frames.


This worked brilliantly, but the final images came out very dark. I’m not sure if this was due to my light setup or something common to Houdini (I have heard others mention using gamma adjustment before rendering out) but I’d like to find out!


To correct this I upped the gamma and the levels slightly.


This is my final result! A 2k 64 frame flipbook, created from a 240 frame simulation.



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