Fast correction of lens distortion for image applications

• Main Authors: Fernandes, J.C.A., Ferreira, M.J.O., Neves, J.A.B.C., Couto, C.A.C.
• Format: Conference Proceeding
• Language: English
• Subjects: Cameras; Digital images; Electronics industry; Industrial electronics; Lenses; Manufacturing industries; Manufacturing systems; Optical distortion; Optical sensors; Shape
• DOI: 10.1109/ISIE.1997.649080

The main use of video cameras in industrial applications regards to detection of defects and noncontact measuring. If the first case is usually a problem of mismatching between two images, the absolute position being nonimportant, the second relies on accurate proportional correspondence between image and object dimensions. In the usual set-up, the object is mainly flat and its image is obtained using a video camera whose lens axis is orthogonal and centred relative to the object. The co-ordinate system of the object should be ideally related to that of the image by a simple translation and change of scale, once an initial mechanical rotation adjustment of the set-up is made. The geometric distortions, mainly pincushion and barrel types, must be either avoided, using a well corrected lens in a proper set-up, or corrected through digital image processing techniques. The use of an acceptable lens imposes a higher price or restrictions to the angle of view, as wide angles are harder to correct acceptably. When space limitations are important and a wide angle is sought, an expensive lens and/or time consuming correcting algorithms are mandatory. The proposed algorithm builds a correction table for the set-up in use, which remains fairly constant in industrial applications. This table divides the image in regions. For each region the correction can be put as a single delta-x/delta-y translation of the included pixels. This can be done fairly quickly when compared to the general morphing algorithms.