Case study

2D

http://www.youtube.com/watch?v=ME0UF7U7rZs

Evian advert, the water drip character is the top layer with plain blue background. It only consists of X and Y, since the image is flat.This animation is completely made up of solids. If there was real life footage behind the animation that would be a plate. This animation mainly used its X axis (the objects moving sideways). But also frequently uses the Y axis when solids fall into the image (up and down movement).

3D

http://www.youtube.com/watch?v=-ybk7Vub2U0

The advert begins as 2D, utilising only the X and Y axis, the image is completely made up of solids. it then transforms when the 'drop' character lands on a cloud expands into a 3D character. The difference between the both is it changes from a flat looking images to looking rounded and more like an animation than a drawing. It creates the illusion that there is depth in the image, like something you could touch, this is because of the it having X, Y and Z. You can create 3d channels by selecting the 'cube' in after effects. 

Matte and Alpha Channels

http://www.youtube.com/watch?v=hQw3mVWXncg

To achieve this look the girl would be placed in front of a green screen which would then be removed from the image, leaving only the matte of the girl. You are simply using a mask to blank out a part of the image, then replacing it with something else (the girl).The background is the alpha channel, and the character (the foreground) is the matte. The alpha channel is a mask which can be edited without changing the foreground layer.

Key Frames-

All the ads above are examples of key frames, since every moving advert animation or not has them. When using animation you need to edit frame by frame, each frame is every part of motion. For example someone jumping, every time they jump it would require multiple key frames in order to show the motion.