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After Effects: August 2008 Archives

Application: Fonts and Vector Images
Antialiasing also has something to do with why fonts and vector images always look good, even if they're really big or really small.  Actually, fonts are vector images, so that's a bit of a strange thing to say - but at any rate, vector images are simply a set of mathematical equations that describe the curves that make up a shape.  So, like the real world, the computer can "look at" these images with infinite precision.  Therefore, it knows enough about the shapes to behave like our eyes do, and approximate the way we would see the fonts and such if they didn't have to be on a quilt of pixels.

Application: Photoshop
One place where this knowledge might help you think is in Photoshop, especially if you're designing for compositing software or DVD production.  Say you're doing a glass bug for your video: did you notice the anti-alias checkbox when you used the Magic Wand tool?  That checkbox means that the computer will actually select fractions of pixels on the edge of the selection it shows - "blurring" the selection boundary in the same way that it did to the red channel in the example reproduced below.
B2B-AA-CirclesBoth.png

We know antialiasing best as "smoothing" the jagged edges that any digital editor will eventually happen across.  Why do we need to antialias, and where do aliasing artifacts come from in the first place?  The answer is a little mathy, but we'll bring it down to size.

B2B-AA-Teaser.png

Masks vs. Alphas

Alpha channels are our most sophisticated way to handle transparency, but they're by no means the only way.  We commonly use the term "Mask" to refer to something similar to the alpha channel above - that is to say, a full range of "see-through-ness" for each point.  Photoshop, for example, uses the term "Mask" to mean just that.  But more primitive incarnations of "image masks" in applications like DVDs and some still image files like GIFs use a different approach.


Alpha Channels

As we first start thinking about transparency in a computer sense, let's go back to the beginning of how computers think about our NTSC broadcast images.  You might remember that, for our purposes, a computer thinks about videos as a sequence of many individual images (frames).  It thinks about each frame as a big rectangular "quilt" of pixels, or individual dots of color - for our purposes, 720 dots wide and 480 dots tall.  And it thinks of each of those dots of color as the amount of red, green, and blue in the color.


B2B-Alpha3.png
Whether you're using titles, creating supers, or doing any other sort of compositing, you're trying to tell the computer to show some parts of an image but to hide other parts.  

I've been surprised by the number of folks who were never really taught how that process works from the computer's point of view.  After the jump, an easy little primer that may help you understand --

B2B-Alpha1.png

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This page is a archive of entries in the After Effects category from August 2008.

After Effects: September 2008 is the next archive.

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