Ben's Comp Newsletter: Issue 039


The first group of 86 students have just finished up my Python for Nuke 101 course, and are getting into creating their own projects. If you missed out on the first round, it's not too late to sign up and level up your Compositing skillset!

This issue of Ben's Comp Newsletter includes a couple of neat tutorials about keying & image convolution, and sheds some light on a fascinating Physicist who has solved an age-old optics problem.


STMap Keyer Tutorial

Not long after I interviewed him, Erwan Leroy released this cool tutorial on how to create a custom keyer using STMap. Erwan's tutorial gives a brief but insightful look into how keyers work, and how we can create our own!
Click here to read the tutorial.

Convolution Matrix Tutorial

Andrea Geremia has a neat resource on his website covering the basics of image processing. He dives into the theory behind what the computer is doing, and also provides some simpler practical examples of how you can blur, sharpen, anti-alias or edge-detect your images in different ways with a matrix node!

I really appreciate that Andrea includes "Useful Links" at the top of this, and every one of his blog posts or tutorials, so you're able to further explore the topic should you want to learn more.
Click here to read the tutorial.
P.S. I wrote a simple article last year about Understanding the ColorMatrix node, which is different to the standard Matrix node. Worth a read to understand both!


I often look towards past show-based problems when thinking of what to share in this newsletter, in the hopes that a learning experience for me will pay off in a learning experience for you too! Something I've had to deal with in the past couple of shows is strange non-uniform bokeh shapes in plates coming from anamorphic lenses.

For the first show, my team got away with munging up an already-defocused image and it worked well enough for what we were doing. The next show, however, had a lot of bright defocused lights on dark backgrounds, causing defined, distorted bokeh very clearly in the plates. We had to match this in a procedural way, which proved to be a challenge...

This phenomenon of distorted bokeh with "cats eye" shapes (as shown in the image above) becomes obvious when a wide lens' aperture is wide open. The distortion, or curved nature of the image, comes from light entering the lens at different points across the curved surface before hitting the camera's sensor -- this is an extreme example of lens distortion that we're all accustomed to in a VFX pipeline.

For the "cats eye" squeezing of the bokeh shapes, what we're seeing is essentially the same as what happens when we create custom bokeh shapes with custom-shaped apertures. More clearly, light enters the lens through the curved glass, travels through the aperture blades which are wide open, and most of that light makes it to the camera's sensor. However, a small portion of that light gets blocked by the barrel of the lens, therefore causing the "cats eye" shape vs. a perfectly spherical/anamorphic oval bokeh shape.

While pgbokeh is great for defocusing images with nice, custom bokeh kernels, it can't emulate the "cats eye" phenomenon. Upon testing a few gizmos online, W_CatsEye by Wes Heo seemed to be the best solution! Out of the box, it can't take an input zDepth pass, but cracking open the gizmo and making some minor adjustments will allow you to do this.
Click here to download W_CatsEye from Nukepedia.

Goodbye Aberration

If you follow the incredible compbanter instagram account, you may have already seen a silly meme about a Physicist that has solved the problem of aberration in lens optics.

Sillyness aside, what Rafael G. González-Acuña (and by extention, Héctor A. Chaparro-Romo) have discovered is nothing short of incredible, and is sure to make waves in the film industry in the coming years.

If you're interested, you can read the paper here, but it's far from a relaxing bed-time read...

Click here to read a more-digestible article about the discovery.

Did you find this newsletter informative?

Have you created, or do you know of any outstanding Gizmos, Python Scripts or Tutorials that you would like to share with the global Compositing community? Please send me an email, and I will do my best to include it in a future issue of this newsletter.

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