DIGITAL FUSION---EXTRACTING ALPHA WITH CHANNEL BOOLEAN

We usually use channel boolean to cut get an alpha channel out of a rgb image. for this we need one alpha channeled image in extra to the rgb image. This tutorial shows you to extract alpha channel from a rgb image. here we have images of a BG and a character without alpha channel and one character image with alpha channel. Now with this image you can cut the charter alpha channel(usually it is available in master beauty pass if you are rendering with multipass render) and apply it on bg in order to composite the bg and character together. we have footage of bg split into AO pass and color pass. character footage in one image without alpha and another with alpha. Now construct the flow. first add bg AO and Color with multiply apply mode. drag a channel boolean node from the tool tab to flow area connect its background connection to the character image without alpha. again connect its foreground connection to character image with alpha. Now merge this connection with bg merge. Now character and bg will be composited. character stays on BG! follow the below images to understand the "channel boolean" tool and the construction of the flow.
channel boolean tool settings.....

channel boolean connections....

the final final should be like this....