Some notes on Pre-multiplied Alpha and Nuke so far.
With digital images broken into individual components, RGBA
RGB- specifies how much color contributes to scene Alpha at base generally has no value, but can often be used to represent transparency
Alpha can be calculated in two ways
Conventional- Where RGB Specifies the color and A specifies how solid the color is.
Premultplied calculates the Rgb as how much color the object is adding to the scene. where the A determines how much it obscures whats behind it.
Why multiplied alpha?
in short using pre-multiplied alpha works more effectively for alpha cutouts. It works better as it is a super set of conventional and additive blending.
important for texture filtering, often when we are texture filtering Post multiplied or conventional blending distorts and muddies co lours.
A*rgb apha has been pre-multiplied by color
unpremult> divides rgb by a