When most people hear the words "alpha channels", they think "transparency", but that's not exactly accurate. The truth is more complex, and a quite bit more interesting! Join longtime VFX artist, editor, software developer, and business owner Simon Ubsdell for Part 3 of the best look behind the technology of compositing that you've ever seen, packed with practical advice for applying the secrets of alpha channels that's simply not possible before understanding these underlying principles. No matter which applications you're using for editing, compositing, or visual effects, this one is a must-see!
Welcome the third tutorial in this series on the basics of compositing theory in which we're going to be focusing on one thing: the alpha channel, and it's a subject where understanding the underlying maths is really of huge benefit. Getting to grips with the numbers opens up a perspective on this problem that you simply can't arrive at any other way.
So far in this series we've looked at ways of blending two images together but this time we're looking at putting one image on top of another. This operation is what's commonly known as either Normal or Over.
One major topic that I want to flag up that we'll be covering is premultiplication, because I know it's something that a lot of people find tricky to understand. And the most intriguing discovery we're going to make is that although alpha is usually talked about as defining transparency, that's not an accurate description of what's actually happening -- and the reality is quite a bit more interesting.
There's s certain kind of magic to compositing in general, and alpha channels in particular, going back to the video hardware keys of early broadcast switchers, but even before that, to the whole business of how you do it on film, which of course provides the original model for suppressing the background, isolating the foreground, and adding them together.
Computers have somehow made it all a little bit less sexy at least in terms of the user experience, because they introduce levels of abstraction that obscure the interesting stuff happening below the surface.
Perhaps we all used to understand this kind of compositing a bit more clearly in a bygone time, because we were closer to physical processes. I suppose that's part of why I am interested in unpacking the maths, to show a bit more of the underlying principles that then make those principles easier to apply.
Hi, I'm Simon Ubsdell, Creative Director of TOKYO PRODUCTIONS
, a UK-based boutique creative shop specializing in movie trailers, sales promos and TV Spots for the independent film sector both in the UK and across Europe.
I've been a film and video editor for over 30 years as well as being involved in motion graphics, sound design and mixing, music composition, visual effects and compositing, 3D modelling and animation, and colour grading, not to mention writing, directing and producing, and most recently, software development.
I am also a developer of plug-ins for the video post-production market having released a range of successful and acclaimed products both under the Tokyo brand
and as Hawaiki
with Robert Mackintosh.
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