Using the calibration plate, which is placed in the field of view of the vision sensor, image distortions can be automatically corrected and world coordinates can be set up in Application Suite. © Baumer

The optimum solution is therefore to completely rectify the entire image using calibration, mathematical processes and high computing power. How is this possible? If the ideal image is known, the deviation can be derived from the image captured by the vision sensor and a known template. This means that even a laterally distorted view, which can occur when the camera is mounted at an angle, can be mathematically corrected, as can distortion caused by the lens. Selected 700/800 series VeriSens models from the XF and XC series already support image rectification in real time or can be retrofitted with a simple software update. After image calibration using a calibration plate, the vision sensor knows the image conditions from the installation position, viewing angle and lens and corrects the entire image automatically. It thus resembles a top view. The inspection task is therefore carried out on an "ideal" image without distortions. Objects thus correspond to the appearance perceived by humans. This is easy for the user and supports a correct and quickly set up application.

Calibration is a simple and structured process that does not require reading any documentation. Intelligent algorithms in the background constantly check the calibration conditions and provide information on when teaching is advisable. The user is only required where the VeriSens vision sensors need further information.

Integrated shading correction

Angled mounting also changes the lighting conditions, as part of the light source is further away from the object. For this reason, an optional shading correction was implemented at the same time. A white sheet of paper is sufficient as a template to teach the algorithm the ideal situation with a click of the mouse. As a result, this is then included in the image correction and regulates the image brightness for each pixel to match the installation situation.

After image calibration, a completely rectified image is available for the subsequent inspection task (left without distortion correction, right after distortion correction). © Baumer

Comparison with world coordinates is an established function of VeriSens vision sensors. This allows any unit of measurement to be processed instead of pixels. This supports applications such as dimensional inspection and pick-and-place, where thinking in pixels is often not enough. Teaching the world coordinates benefits from the image structure of the calibration plate for image distortion and uses its square structure for automatic setup.

Precise image analysis

A rectified image is an optimal prerequisite for demanding dimensional inspections. The effects of the perspective position of the object can be reduced in addition to lens distortion. Presence and completeness checks, where the vision sensor often has to be mounted at an angle to avoid reflections or to facilitate access, are also made easier. Due to the image rectification, this no longer has any influence on the recording and inspection of objects and imprints.

If robots use image processing for orientation, the image processing coordinate system is added to the robot coordinate system, which is naturally undistorted. If this is rectified, appropriately scaled and adapted to the origin and orientation, the direct positions of the objects can be transmitted to the robot. Visually, there are no deviations between the image and the robot orientation. If the vision sensor is permanently installed above the robot, the image processing may get in the way of the robot in pick-and-place applications. An angled installation solves the problem with the aid of rectification. VeriSens vision sensors are able to detect several objects simultaneously and provide the robot with intelligent input. Both the optimum arrangement of the objects and the consideration of unwanted part overlaps are possible.

It is now possible to rectify the image capture without time delay, even with vision sensors, and thus gain new degrees of freedom for applications. Numerous applications can benefit from this. The decisive factor is the applicability for "everyone", as image processing experts are few and far between. VeriSens offers these possibilities by utilizing innovative algorithms. These functions can also be retrofitted to the monochrome 700/800 models in the XF and XC series via a software update.

Michael Steinicke, Product Manager in the Vision Competence Center at Baumer / am