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

December 29, 2022

Infrared cameras claim to be so powerful, some netizens asked online, can infrared cameras really see people through clothes? The netizens who asked this question saw that their thoughts are not simple, you know!

So can infrared cameras see through? Does infrared camera have perspective function at night? If there is at night, does the infrared camera also have the perspective function during the day? Below we break down in detail.

First of all, we must make sure that a certain amount of light must be transparent, at least a part can be penetrated, and the part that is not transparent can be refracted or reflected. Our human eyes can only see things because of the stimulation of light, of course, for humans Many lights are invisible.

Among the infrared rays, there is a kind of near infrared rays, which can penetrate people's clothes, reach people's skin, and then reflect them. This gives a theoretical basis for using infrared cameras to see through human clothes and other objects.

Generally, the cameras are optical cameras, which can only catch visible light. There is a thermal imaging camera that can catch light with a lower frequency than visible light-infrared light, and can take a rough outline in the dark.

The reason why the infrared camera can see objects in the dark is because it can use the photosensitive element CCD to sense all the light (visible light \ infrared light and ultraviolet light, etc.), and convert it into an image that we can see with the naked eye. In the daytime, this feature causes the image taken by the camera to be inconsistent with what we see with the naked eye. In order to solve this problem, an ICF infrared filter is added between the camera lens and the CCD. Its function is to block Infrared rays and ultraviolet rays enter the photosensitive element CCD, 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.

In fact, visible light is also transparent. For example, if you wear thin clothes in summer, you can see the underwear underneath through the clothes. Infrared is similar to the reason, the prevention is similar to summer dressing, and the restrictions are also the same. The fabric is thick and cannot be penetrated, and it is difficult to penetrate without being close to the body. If the curtain is basically shading, it can see the silhouette at most, far away. Can't see clearly. The equipment is different from dozens of meters to tens of meters, which is the distance that the general camera can see. The military may be farther away, but can you buy it? No need to worry at all.

Infrared camera principle

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

The infrared lamp emits infrared rays to illuminate the object, and the infrared rays are diffusely reflected and received by the surveillance camera to form a video image. Just like the flashlight illuminates in the dark, the flashlight is equivalent to an infrared lamp, and the camera is equivalent to the human eyeball. The reason is the same. Although the human eye cannot see infrared light, the infrared camera can receive it.

In short, the camera is equipped with an active infrared emitting device, and the receiving system is similar to the principle of a natural light camera. The natural light camera is imaged after receiving the reflection of natural light. Then in a dark environment, without natural light, we will turn on the lights to let the camera get the light source.

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

Passive infrared camera technology uses the principle that any substance emits 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 used The instrument can realize night monitoring. However, this special thermal infrared night vision device is expensive to manufacture and cannot intuitively and clearly reflect the surrounding environment. Therefore, it is rarely used in ordinary night vision systems.

Active infrared camera technology, which uses infrared lamps to generate infrared radiation and emit infrared light that is invisible to the human eye to illuminate the scene and the environment. You can use ordinary low-illumination CCD black and white cameras or "daytime color night automatic black and white" cameras or "infrared" "Low-illumination color camera" to feel the infrared light reflected from the surrounding scenes, so as to achieve the night vision function.

The infrared light-emitting diode of the infrared night camera on the camera is like a lighting lamp. The filter of the camera can only filter infrared light of this special wavelength, not all light can be filtered, and this requires a long exposure time.

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

CCD cameras of different specifications will greatly affect the image effect of infrared cameras. The current CCD camera specifications are 1/2 ", 1/3", 1/4 ". The luminous flux of l / 3" CCD is 44% of 1/2 "CCD, and the luminous flux of 1/4" CCD is 1/3 "CCD 50% of the visible 1/2 ”camera has the best image at night, so you can choose cameras of different specifications according to different environments and monitoring requirements.

Infrared camera parameter analysis

Infrared camera lens is the most critical equipment of the video surveillance system. Its quality (indicator) directly affects the overall index of the infrared camera. Therefore, the appropriate choice of infrared camera lens is not only related to the system quality, but also to the project cost.

The lens is equivalent to the lens of the human eye. If there is no lens, the human eye cannot see any objects; if there is no lens, the image output by the infrared camera is a white piece, and there is no clear image output. This is the same as our home infrared camera and camera. The principle is consistent. When the muscles of the human eye cannot stretch the lens to the normal position, that is, people often say myopia, the scene in front of the eyes becomes blurred; the cooperation between the infrared camera and the lens has a similar phenomenon, when the image becomes unclear At this time, you can adjust the back focus of the camera and change the distance between the CCD chip and the reference plane of the lens (equivalent to adjusting the position of the lens of the human eye), which can make the blurred image clear.

The main parameters we need to pay attention to are:

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

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

1) CCD size, that is, the target surface of the camera. It was originally 1/2 inch, but now 1/3 inch has been popularized, and 1/4 inch and 1/5 inch have also been commercialized.

(2) The CCD pixel is the main performance index of the CCD. It determines the clarity of the displayed image. The higher the resolution, the better the performance of the image details. CCD is composed of area array photosensitive elements. Each element is called a pixel. The more pixels, the clearer the image. At present, most of the market is delimited by 250,000 and 380,000 pixels, and those with more than 380,000 pixels are high-definition cameras.

(3) Horizontal resolution. The typical resolution of a color camera is between 320 and 500 TV lines, mainly including 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. The resolution is expressed by TV lines (referred to as TV LINES), and the resolution of the color camera is 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. Usually, the bandwidth of 1MHz is equivalent to a resolution of 80 lines. The wider the frequency band, the clearer the image, and the larger the line value.

(4) Minimum illumination, also called 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 required and the more sensitive the camera. Moonlight-level and starlight-level high-sensitivity cameras can work in very dark conditions, 2 ~ 3lux is general illumination.

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

(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 without noise.

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

(9) Lens installation method. There are C and CS methods, the difference between the two is that the photosensitive distance is different.

Let's take 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 illuminance: 0LE & TImes; (below 2LE & TImes; night lights automatically start)

Lens specifications: F = 4-16mm optional

White balance: automatic

Signal to noise ratio: greater than 48db

Working power: DC12V

Weight: 1900g