Alpha Multiply Node

Alpha Multiply is the exact inverse of Alpha Divide. It takes a straight alpha image (RGB independent of the alpha) and multiplies the RGB by the alpha. Result: a premultiplied image ready for the final merge.

No parameters: a pure math operation. Always used as the second step of the sandwich Alpha Divide → grading → Alpha Multiply.

• Effects Library: Tools > Matte > Alpha Multiply
• Quick add: right-click in the Node Editor → Add Tool > Matte > Alpha Multiply

• Input (orange) - required. The straight alpha 2D image to premultiply again.
• Effect Mask (blue) - optional. Limits the multiplication to a masked area.

MediaIn (premultiplied CGI)
   ↓
Alpha Divide ← 1. into the sandwich
   ↓
Color Corrector / Curves / Brightness Contrast / etc.
   (clean grading in a straight alpha context)
   ↓
Alpha Multiply ← 2. out of the sandwich
   ↓
Merge 2D → Saver

Alpha Multiply must sit after the grading and before any Merge 2D that expects premultiplied input.

The two nodes are inseparable. Using one without the other always breaks something:

• Alpha Divide alone (no Multiply after) → the image stays in straight alpha, and the Merge 2D downstream handles it incorrectly.
• Alpha Multiply alone (no Divide before) → you multiply RGB values that were already premultiplied → double premultiplication, an image that gets darker in transparent areas.

Rule: always as a pair, and always in this order: Divide before grading, Multiply after.

• End of a grading chain on CGI - after an Alpha Divide + several color correction nodes, Alpha Multiply puts the image back in premultiplied form for the merge.
• After custom compositing - if you did manual operations on the RGB/A channels of a straight alpha image, Alpha Multiply brings it back to the standard format.
• Quick sandwich check - if you see halos on the edges of a keyed element after grading, check that Alpha Multiply is in the right place.

• Double premultiplication = danger - do not add an Alpha Multiply if the image is already premultiplied. Symptom: semi-transparent edges become unusually dark.
• Pre-Divide/Post-Multiply - reminder: for a grading chain with a single node, ticking Pre-Divide on that node replaces Alpha Divide + Alpha Multiply. Lighter in the graph.
• No parameters - a simple node, nothing to adjust. Just put it in the right place in the flow.
• Like Alpha Divide, it is invisible on a frame viewed on its own - the final render stays correct, the effect of the multiply shows up in the context of the composite.