I have a 720x576 video that was played full screen on a screen with 1280x960 resolution and the relevant eye tracker gaze coordinates data. I have built a gaze tracking visualization code but the only thing I am not sure about is how to convert my input coordinates to match the original video. So, does anybody have an idea on what to do?
The native aspect ratio of the video (720/576 = 1.25) does not match the aspect ratio at which it was displayed (1280/960 = 1.33). i.e. the pixels didn't just get scaled in size, but in shape.
So assuming your gaze coordinates were calibrated to match the physical screen (1280 × 960), then you will need to independently scale the x coordinates by 720/1280 = 0.5625 and the y coordinates by 576/960 = 0.6.
Note that this will distort the actual gaze behaviour (horizontal saccades are being scaled by more than vertical ones). Your safest option would actually be to rescale the video to have the same aspect ratio as the screen, and project the gaze coordinates onto that. That way, they won't be distorted, and the slightly skewed movie will match what was actually shown to the subjects.