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Welcome to the Smoke Learning Channel, I am your host, Grant Kay.
Though out this video series, we will be dealing with the technical challenge of alpha channels.
For those of you who do not know about alpha, this is a great primer to get you started.
And for more experienced users, this series will show you all the workflows
involving alpha channels and how to use them correctly within Autodesk Smoke.
Let’s get started.
A typical video image normally consists of colour channels.
The RED, GREEN and BLUE channels are added together to form the final colours in our image.
This is expected of all image formats and movie formats.
So what has all of this got to do with the alpha channel?
In one simple word, “Transparency”.
Unlike the RED, GREEN, and BLUE channels that are designed to store colour,
certain image and movie formats can also store another channel that is dedicated to transparency.
The alpha channel controls the transparency or opacity of the RED, GREEN and BLUE colour channels.
By defining black, grey and white values in the Alpha channel,
you can cutout certain portions of your image.
This is the mechanism behind compositing images together.
For example, if you had to composite a CGI character over a live action background,
the CGI image files would be rendered with an alpha channel to very easily cut them out
and composite them over the background.
Image files such as Targas, Tiffs, PNG and OpenEXR as well as movie files
such as Animation QuickTime and Apple ProRes are a few of the formats
that can support the alpha channel alongside the RGB colour channel.
The final important part of alpha channels is to be aware that there are two types.
The Straight Alpha and the Pre-Multiplied Alpha.
Further on in the series, there will be a video dedicated to the differences
and how they affect your compositing in Autodesk Smoke.
You might also hear me refer to alpha as a matte or a cut-out.
This is because over time, the alpha channel has been known by these names
because of how they were created for traditional film and video formats.
That’s just a bit of extra knowledge for you to digest.
So why do a series on alpha channels in Autodesk Smoke
if alpha channels are common practice these days?
Well, unlike most applications, Smoke breaks the alpha channel out
into a separate clip to make it more versatile.
That does affect the way you approach tasks through out all areas of Smoke.
So to ensure that you don’t miss a thing, we are starting at the very beginning dealing with importing
going all the way through editing, timeline compositing, node-based compositing
and ultimately exporting out with an alpha channel.
Please continue to the next video on how to import files with an alpha channel.
Thank you for watching and please subscribe to the Smoke Learning Channel for future videos.