When the camera sensor is covered and no light incides, it becomes apparent that weak signals nevertheless appear. This is called dark current and is caused by the formation of spontaneous free charge carriers on the light-sensitive sensor. Like light photons, ambient heat as energy supply can be sufficient in order to generate free electrons, too. This effect is temperature-dependent and can significantly be mitigated by cooling. It is therefore especially important that industrial cameras remain as cool as possible and can dissipate the heating of the electronics. This effect can be mitigated by means of camera calibration (dark image calibration) as the dark current is different for each pixel. Pixels with particularly high dark current are visible as bright dots in the black camera image. They are referred to as "hot pixels". Depending on the sensor quality, a different number of hot / defective pixels are permitted and unfortunately they are almost always observable. Modern cameras can eliminate them by means of vicinity interpolation.