ChromaKey

Function
I'll be honest, this isn't our strongest feature. I would instead try Color - ColorReplace, selecting your bluescreen color, and then choosing any other color as your destination color, and then turning on affectAlpha. If you insist on using ChromaKey:

This function examines the HSV values of an image and pulls a matte based upon the parameters. In the gui, you can scrub a color on the Viewer, but we recommend turning off the matteMult parameter before you scrub. The hue, saturation and value all of values, followed by a range, a falloff, and a sharpness for each set:

A typical application is blue- or greenscreen removal. You can stack multiple ChromaKey operators to extract different ranges. With the arithmetic parameter, you can choose to add to, subtract from, or replace the current mask.

Parameters
Type
Defaults
Function
hue, sat, val
float
.666, 1, 1 Picks the center value to be pulled on hue, saturation, and value.
Range
float
.2, .4, .8 Plus and minus from the initial hue, sat, or value that is picked
Falloff
float
.1,.8,.1

Describes the falloff range from hueRange that is picked, with the values ramping down

Sharpness
float
.5, .5, .5

Describes the falloff curve from hueRange to hueFalloff.

0 = linear dropoff
1 = smooth dropoff

matteMult
int
1

toggle to pre-multiply the RGB channels by the pulled mask

0 = no pre-multiply
1 = pre-multiply

arithemetic
int
0 0 = replace existing mask
1 = add to existing mask
2 = subtract from existing mask

Synopsis

image ChromaKey( 
  image, 
  float hue, 
  float hueRange, 
  float hueFalloff, 
  float hueSharpness,
  float sat, 
  float satRange, 
  float satFalloff, 
  float satSharpness,
  float val, 
  float valRange, 
  float valFalloff, 
  float valSharpness,
  int matteMult,
  int arithmetic
);

Script

image = ChromaKey( 
   image, 
   hue, hueRange, hueFalloff, hueSharpness,
   sat, satRange, satFalloff, satSharpness,
   val, valRange, valFalloff, valSharpness,
   matteMult,
   arithmetic
);

Command Line

-chromakey hue hueRange etc...

Example

shake parrot.jpg -chromakey .66 .2 .1 .5 1 .4 .8 .5 1 .8 .1 .5

See Also
LumaKey