Open the Original BMP and Mask render. Select the white area in the Mask render, save selection. Switch to Original & load the selection. Copy and paste to a new layer. Handy Tip: You can select each layer object as if you were using the magic wand tool by Holding the CRTL/key Windows - CMD/key MAC, Left click on the layer in the layer menu.

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Ockham's razor- It's that simple