# Difference Between Thermal Imaging and Visible Light

2022.01.13

All objects in nature, whether arctic glaciers, flames, human bodies, or even the extremely cold deep space in the universe, emit infrared radiation as long as their temperature is above absolute zero -273°C. Thermal imaging is performed by a non-contact detection device that detects infrared energy (heat) and converts it into an electrical signal, then generates a thermal image and temperature infrared thermal image on a display, and can calculate the temperature value. The above is Baidu Encyclopedia's definition of thermal imaging. Actually, the problem has already been explained. Infrared thermal imager is a device for imaging temperature, and the accurate temperature difference (with ambient temperature, focal plane temperature, etc., not much detail). The thermal imaging in our impression is the following 2 pictures:

Actually, the actual thermographic image is image 1 above, and image 2 is also thermographic, but image 2 is in false color because the actual thermographic image is grayscale, and the image of image 2 in single channel and false color is used for Enhanced visual differences are artificially drawn. So in the real world, what is the difference between thermal imaging and visible light? Infrared thermal imaging differs from visible light in many ways, mainly the following:

(1) Imaging principle

The imaging principle is basically the same. Imaging devices image light waves within a specific wavelength range. The wavelength range of visible light in nature is 0.39 μm to 0.78 μm, and the wavelength range of infrared thermal radiation is 0.75 μm to 1000 μm. Speaking of which, I need to stop. Didn't I say that thermal imaging is not based on temperature (temperature difference) imaging? Why is infrared thermal radiation involved? The fact that must be emphasized is that as long as their temperature is above absolute zero -273°C, infrared radiation is generated, and thermal imaging is achieved by non- The contact detects infrared energy (heat), converts it into an electrical signal, and then generates a thermal image and temperature value on the display. Maybe I'm a bit long, but if you want to learn more about thermal imaging, you must always keep this in mind. Thermal imaging devices also receive light waves (infrared wavelengths) that are invisible to the human eye.

(2) Detector

The core detector of the imaging device is infrared thermal imaging, visible light has CCD, CMOS, thermal imaging has cooled and uncooled types (the difference is whether it has a small cooler, which is mainly used to control the focal length). Plane temperature, remember whether the previous temperature difference is particularly emphasized? The temperature of the focal plane is used as the reference temperature, and its content is not particularly expanded). The main difference is that visible light CCD/CMOS can sense light waves in the visible light band, while thermal imaging detectors can sense thermal radiation light waves in the infrared band. Infrared thermal imaging detectors are divided into various types depending on the manufacturing process and packaging materials. A more macro sense is that infrared thermal imaging detectors are more expensive than visible light CCDs, and visible light CCDs are orders of magnitude or more expensive. This is also the current situation. One of the main reasons for the narrow application of infrared thermal imaging technology. The manufacturing and technology giants of infrared detectors are still stronger in Europe and America, but some very good manufacturers have developed in China in recent years, such as Yantai Airui, AutoNavi, Zhejiang Dali, Guangzhou Sartre, etc., and several other security companies Giants have also actively entered the field of infrared detectors, such as Hikvision Microphotography, Zhejiang Dahua, etc. Whether there will be a massive explosion in thermal imaging in the next few years depends on whether the manufacturers of these detectors can lower their prices and make them widely available in the civilian market.

(3) Lens

The main difference in lenses is that thermal imaging lenses have to be made of special materials. The main reason is that infrared heat radiation cannot penetrate glass (silicon), so special lenses made of metal materials such as germanium and chromium are used. This also results in the thermal imaging lens being a bit more expensive than the optical lens, which also increases the price of the whole machine.

(4) Image

The difference between the images is that visible light imaging is color, RGB three-channel, while thermal imaging is grayscale, and the original thermal imaging image is single-channel. Force conversion. Typically, there are many false colors that can also be configured. In addition, the image size of thermal imaging is smaller than that of visible light. A typical thermal today has 38 4, 640, the largest 1024 has only been released in the last few years, but visible light is now 1080P or larger 400w etc, which are already in practice. China becomes mainstream.

(5) Application scenarios

Visible light is usually used during the day or night in well-lit conditions. Although there are many star-level devices available today, the imaging results are not satisfactory at night when the light is not good, but thermal imaging can work 24/7. At night, it can still image. Of course, thermal imaging also has its drawbacks. After all, imaging is based on temperature differences. Therefore, in rainy weather and severe low temperature conditions, the image quality will also be degraded or even blurred. For example, if blue clothes are dropped into the blue sea, the clothes cannot be seen with visible light equipment. An object with a uniform surface temperature of 30° was placed in a scene with a temperature of 30° and the object could not be seen using thermal imaging equipment. Therefore, in practical applications, appropriate solutions should be formulated according to the site conditions and equipment characteristics.