Applying Alpha Channel from Images

Hello,

I am an amateur animator (first things first). k. So I have approx. 900 images/frames exported from a 3d modeling software. with these I have a matching 900 images/frames that are in black in white. The black and white images show the alpha channel (black=transparent and white=opaque). I want to apply the alpha channel to the images in blender like a “green screen”. So that I can render the video over top of another video and have the second video show through in accordance with the alpha channel. SO. The end objective here is to import my coloured frames (the sequense of frames go together to make a walkthrough of an animated landscape) then apply my alpha channel (the alpha channel basically makes the sky transparent) then play a video under it (a video of a real landscape). So in the end I have a CGI landscape superimposed over a real landscape. In short I want to apply the alpha layer video to the coloured video. I already know how to make the other video show through once the alpha layer is applied. And I know I could go into photoshop and manually apply the alpha channels to the images and save PNGs and then import them to blend but with 900 frames that would take way too long.

Thanks

You can plug the b/w image into the fac of an alpha over node in the compositor.