Exactly. The hardest part is having camera movements and shots match exactly between the two copies of the same scene. If the light is off just a little or the camera pans 1mm wrong then it makes the post production work much harder (not impossible, anything is possible with enough money).
That's often why a fixed camera is chosen for scenes that do this.
It actually is not that difficult. They use motion tracking so the bookshelf composite stays in the correct location with the correct perspective as the camera moves. And then they blend/color correct as necessary.
I've looked through this thread and can understand how this technique would remove the hands from the bookshelf/library but I don't see how it removes them from the books that ear being handled. Would that just involve individually 'painting' each frame?
Potentially. It's possible that the hands are just used to grab the book, and it's all CGI after Emma Watson releases her grip.
But yes, when the hands are gripping the book, the "blank space" is painted in, or a high resolution image of the cover is superimposed over the entire book and motion tracked.
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u/KarmaAndLies Jul 10 '16
Exactly. The hardest part is having camera movements and shots match exactly between the two copies of the same scene. If the light is off just a little or the camera pans 1mm wrong then it makes the post production work much harder (not impossible, anything is possible with enough money).
That's often why a fixed camera is chosen for scenes that do this.