Calibration of Curvature of Field for Depth from Focus

A method for accurate depth measurement in depth from focus is presented. With depth from focus the 3D shape of objects can be measured. To do so, an image series with different distances between camera and object is evaluated to extract focused parts. Combining the results of an edge detection filter with the distance information at which the images have been acquired provides a depth image of the object. The focus information is influenced by optical aberrations. Especially the curvature of field leads to a significant error in the depth image. This error can be seen by measuring the depth information of a planar object with depth from focus. The error in the depth image is approximated by fitting a second order surface to the depth image. To overcome the influence of outliers in the depth image a robust least-squares fitting with suppression of outliers is used. The second order surface is then used to correct depth images, which reduces the influence of the curvature of field on the depth data and leads to more accurate 3D measurements. * Corresponding author.