In some cases, like in fish-eye lenses or webcam-style lenses, distortion is intentionally introduced to make the lens work on large angles also providing an even illumination of the detector (in these cases distortion is helpful in reducing cosine-to-the-fourth law effects). Since most machine vision optics have originally been developed for video-surveillance or photography applications, relevant distortion values have usually been considered acceptable, as the human eye can compensate distortion errors up to 1-2%. Distortion can be also viewed as a 2D geometrical transformation of the real world into the virtual space created by the lens as this transformation is not perfectly linear but is approaching 2nd or 3rd degree polynomials, the image becomes slightly stretched and deformed.Ĭommon optics show distortion values ranging from some percent to some tens percent, making precise measurement really difficult things get even worse when non-telecentric lenses are used. Positive radial distortion is also called “pincushion” distortion, negative radial distortion is called “barrel” distortion: note that the distortion depends on the radial position and can also change of sign. Telecentric lenses reduce or even cancel most of these problems, and for this reason have become a key component for all those developing high accuracy gauging applications. object edge position uncertainty, due to lighting geometry.magnification changes, due to object displacement.Successful machine vision integrators are increasingly aware that quality optics produce superior system performances and telecentric lenses are required for any dimensional measurement imaging application: software engineers requiring precise measurement of mechanical parts need high contrast images with the lowest possible geometrical distortion perspective effects, causing change of magnification when the object is not precisely positioned or is highly 3-dimensional, must also be minimized or eliminated.īesides image processing problems, vision system designers must take in account that common, entocentric optics introduce several factors which limit measurement In recent years the use of machine vision technologies in dimensional measurement applications has become very popular: improvements in cameras, software and illumination components have made it possible to reach accuracies sometimes even better than contact and laser-based methods. ![]() Diffusing & polarizing plates for lighting.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |