What is a NUC (Non-Uniformity Correction) for Thermal Cameras?

Glossary Definition

Thermal image sensors are very precise pieces of technology that require very precise readings, however the heat that they are imaging is only accurate if all of the pixels on the sensor are calibrated to read the same temperatures at the same value. Due to minor fluctuations in heat on the internal components as well as lens temperature and lens characteristics, this calibration often needs adjustment. A non-uniformity correction (NUC) adjusts for those fluctuations by reading a flat, even scene and using that to calibrate all of the pixel readings for the same output.

NUC operations can be performed either internally or externally. For an internal NUC, the camera will cover the sensor with a shutter and use that shutter as a flat temperature reading. When performing an external NUC, the camera’s field of view must be filled with an object that has a flat, even temperature, which will then be used to calibrate the pixels. Note that any slight temperature fluctuations on an object, like a handprint on a board or wall, will create an inaccurate calibration resulting in a ghost-like image in the video feed. This can be fixed by performing another NUC on something with an even, flat temperature. If no objects can be found, a cloudless portion of the sky can sometimes work to even out the image.

More advanced camera systems have the ability to store multiple NUC calibrations for different lens positions, temperatures or other variable aspects of the camera system.