How is the image formed in our eyes? When light hits an object or surface it reflects or bounces back this reflected light falls on the retina on inside of our eyeball thus this light is converted to image by the sensors. This same principle is used for all cameras here reflected light falls to the camera sensor (CCD or CMOS) these sensors converted light to images.
For getting clear image the detectors or sensors must get sufficient light. But in night time there is no such light like sunlight there is only moonlight and some artificial lights. This will not help to get clear images in cameras.
What is Thermal Imaging?
Thermal imaging is a technique used to improve the vision in the night or dark environment by detecting the infrared radiation emitted by objects and creating the image based on that information. Thermal imaging is otherwise called ‘Thermography’. This is how thermal imaging works; all objects emit infrared in the form of heat or temperature. This emitted infrared energy is called ‘Heat Signature’. If the object is hotter it emits a large heat signature. The thermal sensor capable of collecting the small difference in the temperature. The thermal sensor collects the IR radiation from the objects in the surrounding and creates an electronic image based on information about temperature differences. Thermal images are in grayscale: Black objects are cold, white objects are hot depth of gray scale shows variation or difference between two. Some thermal cameras give different colors to images to help people to identify objects at different temperatures.
For the use of thermal imaging in surveillance, we use special thermal imaging cameras. First of all they are not cameras they are really sensors. Thermal imaging is a type of IR imaging, which provides IR as visible light for making images. Every object emits a certain Electromagnetic radiation this is called black body radiation with temperature. The camera sensor detects the electromagnetic radiation and creates a detailed temperature pattern. This temperature pattern is called ‘Thermogram’. Main components used in the camera are an optic system, detector, amplifier, signal processing unit and display, Modern thermal cameras are easy to use. The image it produces is easy to understand it requires no training.