Before we dive in to what the background controls do, let’s do a recap on how Z Vector works. The depth map inputs are basically grids of a certain resolution, with the size of the grid depending on the resolution of the depth sensor in use (for example in the case of a Kinect for XBOX 360, 640x480 pixels). In case you ever played with one, you could think of the resulting grid as a kind of a dynamic, constantly updated pin toy (you know, the kind you can push your hand of face through). Indeed the background controls are in fact a toolkit for manipulating how the individual 3D pixels (or geometrical forms, depending on your geometry settings) that make up the grid act in various situations.
Your main tool in the Background controls is Bleed. This controller directs the amount of time each individual 3D pixel takes to transition from a foreground pixel to a background pixel. In order to understand what this means, try setting your geometry count to a relatively high value, move bleed all the way to maximum and wave your hand in front of your live sensor input. When bleed is set to zero, the Z position of any 3D pixels that crossed the of your hand get instantly updated from foreground to background, while when bleed is set to maximum, this update takes much longer, creating a sort of slowly disappearing trail of pixels appears where ever your hand used to be.
Bleed, especially when combined with other controllers in the Background section, namely Spread, Gravity, Wind and Colorize gives you a number of interesting looks depending on your geometry settings.
Spread controls the scale of your background plane (to which your individual 3D pixels will try to return to). Gravity moves the background plane on the Y axis, while adding some gravity like acceleration effects to the 3D pixels. Wind moves the background plane on the X axis. Colorize affects the color of the 3D pixels as they move towards the background.
Pro tip: For achieving longer/smoother fade out times for your bleed, try different values on the Input -> Depth -> Fade/Front controllers. These two controllers (some of the few ones not covered in detail in the basics tutorial series), affect at which depth the 3D pixels start and end their fade to black cycle.
Continue to the final part in the tutorial series: