for a 3x3 camera matrix, could skew factor be negative?

Question

for a 3x3 camera matrix, could skew factor be negative? assume the camera matrix is in the form :

[fx s u0]

[0 fy v0]

[0 0 1 ]

could s be negative?

Answer 1

The skew factor you list accounts for the shape of the pixels as explained (somewhat) here. s could be negative if the angle alpha in figure 3.3 becomes negative (i.e. when the pixels "leans" to the left rather than to the right). I'm not sure this occurs in practice though, there are not many cases where the assumption of recangular pixels, even square pixels, is not valid these days.