ChromaKey

 

Function
The ChromaKey function examines the HSV values of an image and pulls a matte based upon the parameters. In the interface, you can scrub a color in the Viewer. However, disable the matteMult parameter before you scrub. The hue, saturation, and value of an image each have a set of parameters to describe the exact HSV values you are keying, as a range from that midpoint, a falloff value, and a sharpness value to describe the falloff curve. This is illustrated in the following image.

The ChromaKey function is not Shake’s strongest feature. It is recommended to use Color– ColorReplace; select your blue screen color; choose your destination color (any other color); and then enable affectAlpha.

A typical application is blue screen or green screen removal. You can stack multiple ChromaKey nodes 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