Thermal Image Vs. Visual Image

Infrared thermal imaging is different from visual image in many ways, mainly in the following aspects:

(1)Wavelength Range

Visible light is an electromagnetic wave that can be seen by humans. Its wavelength range generally falls between 360-400 nm~760-830nm. This electromagnetic spectrum is also called the visible spectrum, and its frequency range is 830-750THz~395-360THz.
Infrared is an electromagnetic wave with a wavelength between microwave and visible light. Its wavelength is between 760 nanometers (nm) and 1 millimeter (mm). It is an invisible light with a wavelength longer than red light. The frequencies are approximately in the range of 430 THz to 300 GHz.

(2) Imaging Principle

Their imaging principles are basically the same. Imaging devices image light waves within a certain wavelength range. In nature, the wavelength range of visible light is from 0.39μm to 0.78μm, while the wavelength range of infrared thermal radiation is from 0.75μm to 1000μm. As long as target temperature is higher than absolute zero -273 ℃, there will be infrared radiation.

(3) Detector

For the core detectors of imaging device, visible light devices use the CCD and CMOS detector, while thermal imaging uses cooled and uncooled detector. The main difference is that visible light CCD/CMOS can perceive light waves in the visible light band, and thermal imaging detectors can sense thermal radiation light waves in the infrared band. Infrared thermal imaging detectors are divided into many types according to different manufacturing processes and packaging materials. The more macroscopic feeling is that infrared thermal imaging detectors are more expensive than visible light CCDs.

(3) Lens

The main difference of the lens is that thermal imaging lens must be made of special materials. The main reason is that infrared heat radiation cannot pass through glass (silicon), so special lenses made of special germanium, chromium and other metal materials are used. This also causes the price of thermal imaging lens to be a bit higher than that of the optical lens, which also increases the price of the whole device.

(4) Image

The difference of the image is that the visible light imaging is colorful with three-channel RGB, but thermal imaging is grayscale, the original thermal image is single-channel. The colorful thermal imaging we see on the market is false color, which is artificially converted. There are many kinds of pseudo-colors which can also be configured. In addition, the image size of thermal imaging is smaller than that of visible light. Now the typical thermal imaging has 384, 640, and the largest 1024 has only been released in recent years. However, visible light is now 1080P or larger 400w, etc.

(5) Application Scenarios

Visible light is generally used during the day or at night when the light conditions are good. Although many star-level devices are released, the imaging effect at night with poor light is not satisfactory. But thermal imaging is effective all-weather. The image can be obtained even there is no light at night.

Of course, thermal image also has disadvantages. Since it relies on temperature difference, when the weather conditions are low temperature, the imaging quality will also decline, or even blur.

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