# About the camera principal axis skew factor 's'

When I calibrate the camera using ‘calibrateCamera’ function in Opencv,or using Matlab Camera Calibrator App,I can’t get the skew factor 's ’ of camera intrinsic matric, I don’t know if it’s precise enough without ‘s’.

Should you care about axis skew?

Whew, that was a lot of work! You might be relieved to know that you don’t have to consider the axis skew for most modern cameras because the axes of modern CCD cameras are usually at 90∘90∘ with respect to each other.

Here’s an excerpt from the section “ Camera Intrinsics ” on page 46 of the book Computer Vision Algorithms and Applications by Richard Szeliski.

Note that we ignore here the possibility of skew between the two axes on the image plane, since solid-state manufacturing techniques render this negligible.

And here are excerpts from the sections “ Finite projective camera ” and “ When is s ≠≠ 0 ” on pages 143 and 151 respectively of the book Multiple View Geometry in Computer Vision by Richard Hartley and Andrew Zisserman.

The skew parameter will be zero for most normal cameras. However, in certain unusual instances it can take non-zero values.

A true CCD camera has only four internal camera parameters, since generally s = 0. If s ≠≠ 0 then this can be interpreted as a skewing of the pixel elements in the CCD array so that the x- and y- axes are not perpendicular. This is admittedly very unlikely to happen.

In realistic circumstances a non-zero skew might arise as a result of taking an image of an image, for example if a photograph is re-photographed, or a negative is enlarged. Consider enlarging an image taken by a pinhole camera (such as an ordinary film camera) where the axis of the magnifying lens is not perpendicular to the film plane or the enlarged image plane.

In fact, OpenCV8 does away with the skew parameter altogether…

Thanks for your explanation,I get it