What is contrast?
Contrast inspection is performed by so-called "energetic" optoelectronic sensors. The object (passive object) is illuminated by the sensor. The light that is reflected back to the sensor (diffusely or directly) from the surface of the object provides information about the brightness of the object.
High-speed contrast detection
For measuring the speed of turbo-chargers, for example, contrast color (black, white, or fluorescent) is applied to one of the blades. The turbo-chargers may reach rotation speeds of up to 100000 rpm, which requires correspondingly fast evaluation for frequency measurement. The SPECTRO-1 sensor here benefits from its high scan frequency of up to 180 kHz. Contrast mark detection in the printing industry also requires fast scanning of the print marks.
Contrast measurements of passive and active objects can be performed with the SPECTRO-3-28-45°/0°-MSM-ANA-VIS and SPECTRO-3-12-DIF-MSM-ANA-VIS true-color sensors. In addition to the color values a* and b* these color sensors also provide the brightness value L*, which for this purpose can be used as a measure for the contrast value. The color sensors are calibrated to reference surfaces, the contrast value thus can be used as a measurand.