Uses the brightness and opacity of colors in a mask image to control the opacity in another image.
Where the mask image is black or fully transparent, the corresponding area of the other image is changed to transparent black. Where the mask image is white and fully opaque, the other image is left unchanged. Where the mask image is some color in between, the other image is made partially transparent.
The mask image is stretched to match the width and height of the other image.
Keywords: alpha, brightness, cut, filter, luma, magic, negative, opacity, remove, transparency, wand