How can I unroll a 3D sphere image into a 2D image. Please note that I don't want to flatten the image as this makes the flattened image a circle of the viewed side of the sphere. What I want is to take the entire surface of the sphere and unroll it as if I was reversing the original create 3D sphere process.
The reason I want to do this is that I want to make hand drawn planets. I do the initial work in 2D and then wrap the drawing to a 3D sphere which creates a seam. I then work on the image more in 3D mode to eliminate the seam. When completed I want to now unroll the 3D back to 2D so I can use this flat image to wrap in software like After Effects.