I believe the description for imagick::COMPOSITE_MINUS is incorrect. It states:
"Subtracts the source from the target"
But according to ImageMagick's documentation:
"The original method name 'Minus' is a synonym for 'Minus_Dst' meaning 'minus the destination'"
And defines "Minus_Dst" as:
"Src - Dest"
So the description of "imagick::COMPOSITE_MINUS" should be "Subtracts the target from the source"