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What Do The Colors Mean In Thermal Imaging

Oct 17, 2022 | 03:15 pm 442 0
What Do The Colors Mean In Thermal Imaging

Man can feel heat and cold. As you know, a person has five sense organs—eyes, ears, nose, tongue, and skin. A person can feel the heat and cold through the skin, touching objects, feeling them hot, warm, or cold. To maintain his body in optimal conditions, a person is endowed with the ability to feel heat waves. Heat and thermal radiation play essential roles in life on planet Earth.

Most of the information a person receives through vision – is through the visible spectral range (0.3-0.8 microns). Therefore, it is logical that most of the devices that make it possible to obtain information from other, other than the visible regions of the spectrum are designed and manufactured in such a way as to convert information from the studied range into the visible one. The most characteristic and well-known devices that convert data into the visible spectrum are x-rayed machines, ultrasound, video cameras, night vision devices, and thermal imagers. Each of these devices operates at its wavelengths, but what they have in common is a function that converts the information received into some graphical form that can be seen with normal human vision. In addition, it is a kind of energy transformer, a projection from one area into the area of visible images. In addition, the mechanism of this projection is the mechanism of the function. Thus, what visible image we get depends on the tool (or algorithm) used. Changing the function algorithm makes it possible to obtain completely different visual images of the same observed physical object.

What is the meaning of the Colors?

Let's talk more about thermal imagers. First, let's answer the question of what a thermal imager is. A thermal imager is a measuring device that allows you to see the thermal (infrared) radiation of surrounding objects at any time of the day and measure the temperature at any point on the surface with an accuracy of 0.1°C and higher. The primary purpose of the thermal imager is a non-contact measurement of the temperature of objects of living and inanimate nature, troubleshooting of equipment and electrics, and construction defects. Thermal imaging cameras create sharp thermal images based on temperature differences.

Moreover, complex algorithms of simple-looking cameras read temperature values from these images. The hottest places are colored in red, yellow, and orange, and the coldest in blue and black. Thermal imagers gained popularity due to the possibility of application in all branches of human activity. The most popular applications for thermal imagers are construction, hunting, medicine, and industry. Increasingly, thermal imagers are also used to inspect apartments and private houses, allowing you to find places of heat leaks and electrical problems. Thermal imagers show the thermal distribution of energy on the surfaces of objects, and the function of converting thermal radiation into a visible image can be described as follows. Thermal imaging, observing a particular scene, perceives thermal radiation from all objects located on this scene. Some objects have the most potent radiation, and some – are the least powerful. Some things are closer to thermal imaging; others are further from thermal imaging. The thermal imager has a sensor, and a program works inside it, which converts one type of information received into another. The algorithm that converts thermal radiation energy into a visible image is straightforward. The coldest object is assigned black color. The hottest thing is white.

Further, the entire dynamic range of the received energy from the hardest to the most desirable is divided into 256 gradations. Each value is uniformly assigned its shade of gray. The lower the radiation energy, the closer the hue to black, the greater the power, and the closer the hue to white. Why are 256 gradations used? This number of gradations corresponds to the average value of the ability of the human eye to distinguish between color gradations. The information from the thermal imaging detector to the processor has a 14-bit capacity. Thus, the conversion algorithm could potentially display more than 16 thousand shades of color, from coldest to warmest. Technically, it is possible. However, it is impractical to linearly output all 16K shades of color received from the detector. A person will be unable to distinguish them all, and a vast amount of information will be lost. 14-bit information from the sensor is used for machine vision systems and video processing systems.

Another exciting task in forming a thermal image is the choice of a color palette for displaying 256 color gradations. You can choose any 256 colors and match them with the gradation of the signal from the thermal imager processor. Usually, they do this when forming a thermal imaging palette; they only choose one primary color and make 256 gradations from it—for example, shades of gray, red, green, etc. Some palettes combine several colors or everything from red to purple. As a rule, they use the classic combination of rainbow colors when using such color palettes. Red is the warmest object in the image, and purple is the coldest. Multi-colored palettes on thermal imagers are used primarily in the electric power industry, where it is necessary to find overheated or faulty elements. Then the color image is very informative. However, professionals who have worked with thermal imaging equipment for years use a grayscale palette, even in the electric power industry. The grayscale palette is a classic example of a linear display of information. When using this palette, everything is evident and straightforward. Darker is colder; lighter is warmer. Moreover, a thermal imaging image using a grayscale palette is closest to a traditional black and white photograph from a photo or video camera. Such an image is familiar to the human eye and does not cause discomfort.

An exciting trend now is the beginning of the use of palettes in gradations of red. This palette has two distinct advantages. The first is to attract the operator's attention since red is perceived as the color of danger. And the second - red color is the closest to the invisible IR region of all the rainbow colors. In addition, it affects the eye, least of all, when moving from a lighted place to a dark one. Imagine you went out of a lighted house at night into a dark street. At first, you will not see very well because the eyes need time to adapt to the low light outside, and only after a while does the eyes adjust and see better. Since red is the color closest to infrared, red-based palettes are beginning to be actively used in hand-held thermal imagers, with which the operator works directly on the street or in the field. With this application, it is essential that the eye quickly recovers after working with the device and begins to see in the dark. 

To the greatest extent, the price of a thermal imager depends on the resolution of the IR matrix, temperature range, range, and additional measurement functions. Consider the main characteristics of thermal imagers. The resolution of an infrared detector is the main characteristic that determines the functionality of a particular model and the “efficiency” of thermography. The most affordable are models with a resolution of 60x60; thermal imagers of the upper price range have a resolution of more than 640x480. In most cases, basic models with low resolution are used for operational diagnostics of electromechanical equipment, switching and electric power equipment, searching for leaks, determining sources of heat loss in rooms, etc. 

If you need a thermal imager solely for hunting, you need to consider several important issues before you buy the best device for hunting. Many manufacturers have models with several operation modes for choosing: black and white or color with different shades. It is possible to record an image. Some products are equipped with a GPS positioning function and are equipped with brightness and contrast adjustments. Monoblock body design is preferred. The material of manufacture can be either light aluminum alloy or impact-resistant plastic. Pay special attention to resolution and optical zoom. Today, due to the development of the world of optics, there are quite a few brands on the market, so every hunter will find a device suitable for their needs.

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