Roto Toon plug-in, Shadow Outlines group
Shadow Outlines fills in the dark areas of the image with the Outline Color, which is typically black. This can quickly create a dramatic effect.
Shadow checkbox
Turned off by default. Turning this option on will activate the Shadow controls. The Shadow effect finds the shadows of the image and fills them in with the Outline Color. Keeping this checkbox off will give you standard Roto Toon color fields.
Threshold
Sets the relative overall size of light and dark regions. Threshold determines how dark the color has to be for that color to be replaced by the Shadow. Default value is 50%. Value range is 0 to 100.
By default, only the darkest color areas will be filled by shadow. As you increase the Threshold, lighter areas start getting filled with the shadow. For images with dark backgrounds, you can easily create a dramatic effect by turning the entire background black. It's also interesting to experiment with Shadow's Threshold in conjunction with other line and contrast effects, like the Comic group and Soft group.
Antialias
Antialias is a percentage slider for the final output that helps to tone down any jagged edges. Default value is 100%. Value range is 0 to 100.
An Antialias of 0% is very slightly faster, but otherwise the render speed is the same as at higher values. Sometimes Antialias of 100% can look a bit blurry. If this is the case, just lower the setting a bit.
Tint Foreground checkbox
Turned off by default. Tint Foreground acts as an extreme Lightness control. Tint leaves the footage colors but wipes out darks. It was built to fill in the missing darks within Shadow outlines.
If Threshold is set to 0, the Tint effect will be applied to the whole image. If Threshold is at any other value, then the Shadows will show but its darkness will be affected by the Tint overlay.
Transparency
This sets the opacity level of the Shadow effect. The default is 0%, which is fully transparent. Value range is from 0 to 100. The higher the value, the more transparent the Shadow darkness is. The lower the value, the more opaque it is.