g>(r+b)/2?(r+b)/2:g
Similarly, you can despill a bluescreen image by setting the expression field for the blue channel to:
b>(r+g)/2?(r+g)/2:b
You can also use the HueCorrect node for despill. For more information, see Suppressing spill .
Ultimatte automatically suppresses spill from the backing onto foreground subject matter. The spill controls are used to suppress excessive spill or to retain color similar to spill that has been over-suppressed. To adjust the spill controls, check the spill suppression box on the Ultimatte tab and click Spill tab:
• cool - Use this control to adjust the amount of spill in cool colored foreground objects. Used to reproduce blue, green or cyan colors that changed through the spill suppression algorithms.
• warm - Use this control to adjust the amount of spill in warm colored foreground objects. Used to reproduce pink, purple and magenta colors for bluescreen, or yellow and orange colors for green screen that changed through the spill suppression algorithms.
• midtones - Use this control to adjust the amount of spill in mid-range foreground objects.
• brights - Use this control to adjust the amount of spill on bright foreground objects.
• darks - Use this control to adjust the amount of spill on dark foreground objects.
• ambience - Use this control to select a color to subtly influence the foreground objects in areas that may have contained spill.
• strength - Use this control to adjust the intensity of the selected ambience color.
• background veiling - This control is used to override the automatic suppression of the backing color. Ultimatte uses the selected backing color to suppress the backing to black. An indication that the automatic settings did not suppress enough backing is "veiling" or a colorized haze in some background areas. An indication that the automatic settings suppressed too much backing is darkened or mis-colored foreground edges and transparencies. In most cases this control should be left at the default setting.
TIP: There are several nodes in Nuke you can use for spill removal. For example, if you are using a greenscreen image, you can add an Expression node after your foreground image and set the expression field for the green channel to:
g>(r+b)/2?(r+b)/2:g
Similarly, you can despill a bluescreen image by setting the expression field for the blue channel to:
b>(r+g)/2?(r+g)/2:b
You can also use the HueCorrect node for despill. For more information, see Suppressing spill .