Function
This is similar to Over, except you have control over curves to help blend the edges together.

Example:

In the following tree, a key is pulled on the foreground with a KeyLight node. The foreground is then attached to the background tree. The first “Closeup” illustration (on the left) shows the default result, a result identical to an Over node. Ringing problems occur along the hair (a bright ring), and along the shoulder (a dark ring). When the curves are adjusted, the ringing is dramatically reduced, resulting in a much cleaner composite.

Tree	Over1
bs	AddMix1
Closeup, default curves	Closeup, modified curves
default curves
modified curves

Given that the curves can dramatically alter opacity of the foreground, you may be obliged (I picked that one up in France...) to make sure the interior of the matte really is 100 percent opaque through the use of additional masking, garbage mattes, etc.

Parameters	Type	Defaults	Function
clipMode	int	1	Toggles between the foreground (0) or the background resolution (1)
preMultiplied	int	1	Tells Shake if the foreground is premultiplied. This is the opposite of the standard Over. If enabled, the foreground curve does nothing.
fgExpr	float	HermiteV(x,0, [1,-50,-50]@0, [0,-50,-50]@1)	The controlling curve of the foreground. To use it, load it into the Curve Editor by hitting the small Load Curve button.
bgExpr	float	HermiteV(x,0, [0,50,50]@0, [1,50,50]@1)	The controlling curve of the foreground. To use it, load it into the Curve Editor by hitting the small Load Curve button.

Synopsis

image AddMix( 
  image Foreground,
  image Background,
  int clipMode,
  int preMultiplied,
  float fgExpr,
  float bgExpr
);

Script

image AddMix( 
   Foreground,
   Background,
   clipMode,
   preMultiplied,
   fgExpr,
   bgExpr
);

See Also
Over