Learning About Calibration

Many users want to calibrate their systems from pixels to real world units, such as inches, mils, or millimeters. For many applications, this can be as simple as calculating the size of each pixel and multiplying. Other more stringent applications require frequent recalibration or calibration of the squareness of the pixels, perspective distortion calculation, or even calibration to compensate for the effects of lens distortion. There are a number of calibration plates that can be purchased from companies like Melles Griot and Edmund Optics. For Cognex In-Sight™ users, we have developed a template called AutoCal that includes a rectangular calibration plate designed specifically for Machine Vision cameras. If you begin with this when developing your applications, you can very quickly, easily, and automatically calculate the conversions to real world units. You do need to be aware that these calculations are only as accurate as the laser printer that you print the calibration target on. In other words, this target is suitable for most general calibration applications, but may not be appropriate for ultra high precision applications. AutoCal currently supports a few systems currently, but that list is expanding. Users of other systems can feel free to use our calibration target by itself as a starting point for the development of your own calibration routines.