Our eyes work by seeing contrast between objects that are illuminated by either the sun or another form of light. How thermal cameras work is by “seeing” heat energy from objects. All objects, both natural and manmade, emit infrared energy as heat. By detecting very subtle temperature differences of everything in view, infrared (or thermal imaging) technology reveals what otherwise would be invisible to the naked eye. Even in complete darkness and challenging weather conditions, thermal imaging gives users the ability to see the unseen.
Because thermal cameras work by “seeing” heat rather than reflected light, thermal images look very different than what’s seen by a visible camera or the eye. In order to present heat in a format appropriate for human vision, thermal cameras convert the temperature of objects into shades of gray which are darker or lighter than the background. On a cold day a person stands out as lighter because they are hotter than the background. On a hot day a person stands out as darker because they are cooler than the background.
Here’s how thermal imaging works:
A special lens focuses the infrared light emitted by all of the objects in view.
The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermogram. It only takes about one-thirtieth of a second for the detector array to obtain the temperature information to make the thermogram. This information is obtained from several thousand points in the field of view of the detector array.
The thermogram created by the detector elements is translated into electric impulses.
The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display.
The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the impulses from all of the elements creates the image.