From what I learned, viola jones needs images with faces upfront. Tilting the head a few degrees to each side can botch the algorithm. Is it possible to take an image, take a several rotated copies of it and run the algorithm on each one?

This limitation sounds like only a minor neusense to me. Is there a stronger reason for the limitation?

  • $\begingroup$ What exactly do you mean by tilted? Where did you read that? A few degrees? Are you sure? $\endgroup$ – D.W. Mar 12 '18 at 19:31
  • $\begingroup$ Tilted - move the head to the sides. To make the task more manageable, Viola–Jones requires full view frontal upright faces - Wikipedia on Viola-Jones. Not sure how many degrees would qualify as not "frontal upright", but I ask why any rotation of the head should have an affect? $\endgroup$ – CIsForCookies Mar 12 '18 at 19:50
  • $\begingroup$ I couldn't find any place in the Wikipedia article that says that tilting the head a few degrees to each side causes errors. Where are you getting that from? Are you sure? That is not my understanding. I suspect you are starting from a faulty premise. $\endgroup$ – D.W. Mar 12 '18 at 21:21
  • $\begingroup$ The requirement of an upright frontal face does not disqualify tilted head? I thought that was the exact meaning of this $\endgroup$ – CIsForCookies Mar 13 '18 at 5:03
  • $\begingroup$ That's not what you wrote. Again, you wrote "Tilting the head a few degrees to each side can botch the algorithm". I'm adding some highlighting there to focus your attention to a specific part that I've tried to draw attention to twice. I don't see any support for that statement in Wikipedia. $\endgroup$ – D.W. Mar 13 '18 at 5:18

Tilting your head a few degrees to the side doesn't cause Viola-Jones face detectors to fail. They are more robust than that. I suggest trying some experiments to see for yourself.

As an aside: It's not always possible to rotate an image to the extent one might like. You have a 2D representation of a 3D object. As an extreme case, imagine trying to take a photograph and simulate rotating the face by 180 degrees around the vertical axis. You can't, because that would require knowing what the back of their head looks like. Even tilting around a horizontal axis has limits; imagine trying to tilt by 180 degrees -- which would require simulating the effect of your hair pointing in a different direction. So while it may be possible to simulate rotation to a limited extent, but there are limits to what kind of synthetic rotation is possible.

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