Oblique scaling: an algorithm to correct for a non-perpendicular camera view in tendon strain measurements

Image distortion due to a non-perpendicular camera view introduces serious errors in tendon and ligament strain measurements when data are recorded using a single camera. These errors can be corrected with the oblique scaling algorithm using two pairs of scaling markers attached to the tendon surface. Computer simulations show that application of this algorithm reduces errors over 100 times to less than 0.06%. The method is relatively insensitive to measurement errors in the scaling marker distance but sensitive to the accuracy of alignment of the scaling markers. It can be concluded that the oblique scaling algorithm eliminates the influences of a non-perpendicular camera view in single-camera tendon and ligament strain measurements.