Man said:
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headaches from 3d comes from being stereoblind. Can't see the picture in the 3d-dot stereograms? You have stereoblindness and will get a headache from 3d movies.
Basically, the premise is that if you are stereoblind, you cannot determine depth based on disparity ie, the distance something moves when you switch eyes. If you look at a corner of your wall with one eye closed and then switch eyes quickly, the corner will not appear to move to much as opposed to say, looking at a finger a couple inches away from your face.
However, when you watch a 3d movie, your eyes do not determine what is close and what is far. The movie does that for you. Things up close are rendered with greater disparity, and therefore pop out. Things in the background are rendered with less disparity and don't shift from eye to eye.
My ability to render depth tells me what is foreground and what is background. The difference, is that people who are stereoblind are not getting this information as well as I am, and so background and foreground appear to be on the same plane. Basically, they are watching a movie in which the out of focus background scenery is the same distance as the in focus scenery. Because stereoblind people rely heavily on other cues such as shadowing, relative distance, and focus, when their eyes cannot bring an out of focus picture into focus, it presents a problem. This happens primarily because they are looking at the out of focus background elements in order to perceive depth which results in looking at a blurry picture for 2 hours. That would give anyone headaches.
