Ben's Comp Newsletter: Issue 006


This issue is all about colour transformation & image filtering. The latter is something that confused me in the past, so I thought I'd share the resources I found to help me better-understand what they do...

There are 3 types of matrix operations available in Nuke: the Matrix node, a Transform Matrix, and a Colour Matrix. We'll be focusing on the first one here.

The Matrix node is essentially an image convolution filter, and is great for blurring, sharpening, edge-detecting, etc. your image. This article is an insightful read to understand the math behind how the Matrix node works, and different uses for it. Additionally you can download a gizmo on Nukepedia with a bunch of pre-defined values to help you learn more about it!

A transformation matrix defines a set of raw transformation coordinates of a 3D object in local or world space. In other words, it is how Nuke determines your 3D object's position, rotation and scale. I set out to understand more about this, and came across this article on Nukepedia that does a pretty good job of explaining what's what!

Each row of knobs represents a colour channel. For example, the output of the red channel is the result of knobs 1 (input red), 2 (input green) and 3 (input blue), being added together.

In English, the above image reads:
For the red channel, output the result of ((R * 1) + (G * 0) + (B * 0))
For the green channel, output the result of ((R * 0) + (G * 1) + (B * 0))
For the blue channel, output the result of ((R * 0) + (G * 0) + (B * 1))

Because we're using only 100% of the red channel for output red, 100% of green for output green and 100% of blue for output blue, the image will look identical to the input image.

If we were to change knob 2 from the image above to a value of 0.5, a pixel in our image with a sampled value of 0.00000, 1.00000, 0.00000, would turn into 0.50000, 1.00000, 0.00000. We're essentially taking 50% of the green channel, converting it to the red channel, then adding it back to itself, which causes the greens to be more-yellow. The image below is a more-visual representation of what's going on.

So, when should you use a ColorMatrix node? It is most useful for transforming colourspaces, although in certain cases, I've found it incredibly useful to grade fire elements & FX renders into a more natural range of colours. Let me know what uses you've found for the ColorMatrix node by replying to this email!

One for the more-junior compositors subscribed to this list -- this article lays out the concepts of what a colourspace is, why they are necessary, and explains how the math works when converting between two colourspaces in the simplest manner I've seen. It also outlines how Nuke natively deals with colourspaces.

Read more here

Confusing name, but it's a fun little physics sandbox that can simulate solids, liquids & gasses at the same time, in real-time!

Download it here!


Don't let the sharing stop here!

If you've recently come across some interesting or unique knowledge, please reply to this email and let me know about it's existence! I'd love to help spread the word, to help us all be better compositors together.

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