Can the infrared camera see through? Infrared camera principle and parameter analysis give you the answer

January 08, 2023

The infrared camera is so arrogant that there are netizens asking online, can the infrared camera really see the clothes and see the human body? The netizen who asked this question saw that the mind was not simple, you know!

So in the end, can the infrared camera see through? Does the infrared camera have a perspective function at night? If there is at night, does the infrared camera also have a perspective function during the day? Let's break it down in detail.

First of all, we must make clear that light must be transparent. At least part of it can not be refracted or reflected. Our eyes can see things because of the stimulation of light. Of course, for humans. A lot of light is invisible.

In the infrared, there is a near-infrared light that can penetrate people's clothing, reach the human skin, and then reflect it out. This gives a theoretical basis for the use of infrared cameras to see through other objects such as human clothing.

The general camera is an optical camera that can only capture visible light. There is a thermal imaging camera that can capture light with a lower frequency than visible light - infrared light, which can capture a rough outline in the dark.

The reason why the infrared camera can see the object in the dark is because it can sense all the light (visible light, infrared light, ultraviolet light, etc.) with the photosensitive element CCD and convert it into an image that we can see with the naked eye. In the daytime, this feature causes the image captured by the camera to be inconsistent with the image we see with the naked eye. To solve this problem, an ICF infrared filter is added between the camera lens and the CCD. Light such as infrared rays and ultraviolet rays enter the CCD of the photosensitive element, so that the CCD can only sense visible light, so that the image seen is the same as the image we see with the naked eye.

Visible light is also transparent. For example, if the summer clothes are thin, you can see the underwear underneath through the clothes. Infrared is similar in principle. It is similar to the summer dressing. The restriction is the same. The fabric is thick and can't be penetrated. It is difficult to see through the body. If the curtain is basically transparent, it will see the figure at most. Can't see clearly. The equipment is different from tens of meters and dozens of meters. It is the distance that the general camera can see. The military may be farther away but can you buy it? There is no need to worry at all.

Infrared camera principle

The wavelength range of light is from a few nanometers (1 nm = 10-9 m) to about 1 mm (mm), and only a part of it is visible to the human eye. Light that is longer than the wavelength of red light is called infrared light, and human eyes cannot see infrared rays.

The infrared light emits an infrared ray to illuminate the object, and the infrared ray is diffusely reflected and received by the surveillance camera to form a video image. Just like the flashlight illuminated in the night, the flashlight is equivalent to the infrared light, the camera is equivalent to the human eye, the reason is the same, although the human eye can not see the infrared light, but the infrared camera can receive it.

In fact, it is simply that the camera has an active infrared emission device, and the receiving system is similar to the natural light camera. A natural light camera is a post-reflection image that receives natural light. Then in the dark environment, without natural light, we will turn on the lights to get the light source from the camera.

The current infrared camera technology is divided into passive infrared camera technology and active infrared camera technology.

Passive infrared camera technology is the principle of using any substance to emit infrared light above absolute zero (-273 ° C). The infrared light emitted by the human body and the heat engine is strong, and the infrared light emitted by other objects is relatively weak. The special thermal infrared night vision is utilized. The instrument can be monitored at night. However, this special thermal infrared night vision device is expensive and cannot directly and clearly reflect the surrounding environment, so it is rarely used in the usual night vision system.

Active infrared camera technology, which uses infrared light to generate infrared radiation, emits infrared light that is invisible to the human eye to illuminate the scene and the environment, and can use ordinary low-light CCD black-and-white camera or "daytime color nighttime automatic black-and-white" camera or "infrared" The low-light color camera "feels the infrared light reflected from the surrounding scenes to achieve night vision.

The infrared light-emitting diode of the infrared night camera on the camera is like an illumination lamp. The filter of the camera can only filter the infrared light of this special wavelength. No light can be filtered, and it takes a long time to expose.

The basic configuration of the infrared camera system at this stage is: camera, lens, infrared light, infrared light power supply, etc. The camera requirement here is a low-illumination camera, and the infrared light emitted by the infrared lamp can be received by the camera. The lens is also required to be able to sense infrared light. The smaller the main index F value (light-passing amount), the better the night vision effect. The quality of the camera is directly related to the reasonable selection of cameras and supporting devices.

Cameras with different specifications of CCD will greatly affect the image effect of the infrared camera. At present, the CCD camera specifications have 1/2", 1/3", 1/4". l/3" CCD luminous flux is 1/2" CCD 44%, 1/4" CCD luminous flux is 1/3" CCD 50%, it can be seen that the 1/2" camera night image works best, so you can choose different specifications of the camera according to different environments and monitoring requirements.

Infrared camera parameter analysis

Infrared camera lens is the most critical device of video surveillance system. Its quality (indicator) directly affects the overall camera index of infrared camera. Therefore, whether the selection of infrared camera lens is appropriate is related to system quality and engineering cost.

The lens is equivalent to the lens of the human eye. If there is no lens, the human eye can't see any object. If there is no lens, the image output by the infrared camera is a piece of white, and there is no clear image output. This is related to our home infrared camera and camera. The principle is the same. When the muscles of the human eye are unable to stretch the lens to the normal position, which is often referred to as myopia, the scene in front of the scene becomes blurred; the cooperation between the infrared camera and the lens has a similar phenomenon, when the image becomes unclear When you adjust the back focus of the camera and change the distance between the CCD chip and the lens reference surface (equivalent to adjusting the position of the human eye lens), the blurred image can be made clear.

The main parameters we need to pay attention to are:

Can the infrared camera see through? Infrared camera principle and parameter analysis give you the answer

Since the core component of the camera is a CCD, its main parameters are mostly related to the CCD. The main parameters of the camera are listed below:

1) CCD size, which is the camera target surface. Originally more than 1/2 inch, now 1/3 inch has become popular, 1/4 inch and 1/5 inch have also been commercialized.

(2) CCD pixels, which are the main performance indicators of CCD, determine the clarity of the displayed image. The higher the resolution, the better the image details. The CCD is composed of area array photosensitive elements, each of which is called a pixel. The more pixels, the clearer the image. Most of the market is currently delimited by 250,000 and 380,000 pixels, and more than 380,000 pixels are high-definition cameras.

(3) Horizontal resolution. The typical resolution of color cameras is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. The resolution is represented by a TV line (referred to as the line TV LINES), which has a resolution between 33 and 500 lines. The resolution is related to the CCD and the lens, and is also directly related to the bandwidth of the camera circuit channel. The usual rule is that the bandwidth of 1 MHz corresponds to a resolution of 80 lines. The wider the band, the clearer the image and the larger the line value.

(4) Minimum illumination, also known as sensitivity. It is the sensitivity of the CCD to ambient light, or the darkest light required for normal CCD imaging. The unit of illuminance is lux. The smaller the value, the less light is needed and the more sensitive the camera. Moonlight and star-level high-sensitivity cameras can work in very dark conditions, and 2~3lux is a general illumination.

(5) Scanning system. There are PAL and NTSC systems.

(6) Camera power supply. The AC has 220V, 110V, 24V, and the DC is 12V or 9V.

(7) Signal to noise ratio. The typical value is 46db. If it is 50db, the image has a small amount of noise, but the image quality is good. If it is 60db, the image quality is excellent and no noise occurs.

(8) Video output. Mostly 1Vp-p, 75Ω, all use BNC connectors.

(9) Lens mounting method. There are C and CS modes, the difference between the two is that the sensing distance is different.

Below we use KL–9540DH as an example to illustrate the parameters we need to pay attention to.

Prime number: 795 (H) & TImes; 596 (V), 470K

Synchronization system: internal synchronization

Number of infrared lamps: Ф8mm & TImes; 34

Minimum illumination: 0LE & TImes; (less than 2LE & TImes; night lights automatically start)

Lens specifications: F = 4-16mm optional

White balance: automatic

Signal to noise ratio: greater than 48db

Working power supply: DC12V

Weight: 1900g