Rolling Shutter Artifacts on a Moving Inspection Line
Rolling shutter inspection lines require pulsed strobe lighting within global overlap windows or native global shutter sensors to eliminate motion shear errors.
Spatial Aspect Distortion
Geometric Error
Geometric error in an imaging system where the scale of an object in the horizontal axis does not match the scale in the vertical axis. Optical sensors suffer from spatial aspect distortion when the lens magnification is non-uniform or when the motion of the object is not synchronized with the camera trigger. It affects the accuracy of dimensional measurements and the reliability of pattern recognition algorithms.
Perspective Alignment
Mounting the camera at an angle to the target surface creates a trapezoidal effect where one side of the image appears larger than the other. This manifestation of spatial aspect distortion is common in conveyor belt applications where space constraints prevent a perpendicular view. Software correction uses homography matrices to remap the pixels back into a square coordinate system.
Motion Error
Discrepancies between the sensor acquisition rate and the material velocity lead to objects appearing stretched or squashed. In a system experiencing spatial aspect distortion, a circular feature might be measured as an ellipse by the vision software. Precise timing signals from an encoder ensure that the horizontal and vertical resolutions remain identical.
Verification involves measuring a calibrated target with known dimensions to calculate the scaling factor for each axis.
Lens Aberration
Imperfections in the optical elements can cause the magnification to vary from the center to the edges of the field of view. This type of spatial aspect distortion requires a polynomial correction model to flatten the image. High quality telecentric lenses are used to minimize these effects in precision metrology applications.