User Manual

Alpha Threshold
The Alpha Threshold is used for limiting particle generation so that pixels with semitransparent
Alpha values will not produce particles. This can be used to harden the edges of an otherwise
soft Alpha channel. The higher the threshold value, the more opaque a pixel must be before it
will generate a particle. Note that the default threshold of 0.0 will create particles for every
pixel, regardless of Alpha, although many may be transparent and invisible.
Lock Particle Color to Initial Frame
Select this checkbox to force the particles to keep the color with which they were born
throughout the life of the particle. If this is off, and the input image changes on successive
frames, the particles will also change color to match the image. This allows video playback on a
grid of particles.
Create Particles Every Frame
Enabling this creates a whole new set of particles every frame, instead of just one set on the
frame. This can lead to very large particle systems but allows some interesting effects—for
example, if the particles are given some initial velocity or if emitting from an animated source.
Try a small velocity, an Angle Z of -90, and a seething Fast Noise as a source to get smoothly
varying clouds of particles that you could fly through. Note that if this checkbox is left off, only
one set of particles is ever created, and thus animating any of the emitter’s other controls will
have no effect.
X/Y/Z Pivot
These controls allow you to position the grid of emitted particles.
Use Z Channel for Particle Z
If the input image used to generate the particles has a Z depth channel, that channel can be
used to determine the initial position of the particle in Z space. This can have an interesting
hollow shell effect when used in conjunction with camera rotation in the pRender node.
Common Controls
Conditions, Style, Region, and Settings Tabs
The Conditions, Style, Region, and Settings tabs are common to all Particle nodes, so their
descriptions can be found in “The Common Controls” section at the end of this chapter.
Sets Tab
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