Articles by Eran Bluestein
The new buzz in the thermal imaging world goes by many names. In a short time, a small niche in the world of IR, which was previously sidelined to make way for more lucrative markets such as security and defence, has taken the top spot in the attention, production and sales for many manufacturers and integrators. It’s no surprise considering the size of this new market. Suddenly, hotels, cinemas, malls, hospitals, critical services, public transportation, office buildings and more have become consumers of thermal imaging cameras. Along with that, the more traditional markets, such as security, defense and industry are suffering from budget cuts, project cancellations, or postponements. Combine two of these elements, and the new elevated body temperature (EBT) camera market is easily 3-4 times the size of the other markets combined. Thermal imaging cameras and common misconceptions Can thermal cameras detect viruses? The answer is NO. The best the camera can do is tell you if someone has a higher skin temperature than others. There are many reasons for an elevated body temperature which are not all health-related, such as exercise or even sitting in a warm environment without air-conditioning. Are the cameras accurate? The accuracy debate is a significant and controversial discussion with much misinformation running around. When discussing accuracy, there are two considerations: The first consideration is the accuracy of the camera itself versus a blackbody. Blackbodies are devices which can regulate temperature very accurately (although not all are equal) and have a high emissivity level, which means they are almost not affected by surrounding heat or energy. All thermal cameras are calibrated against blackbodies. Still, some manufacturers have been using them in their EBT solutions to give the camera a consistent temperature reference to which it can adjust. The accuracy of the camera in this discussion talks about the camera itself. How sensitive the detector is, internal reflections, lens aperture, noise level and the calibration process itself. Also, if you read the fine print, most manufacturers quote accuracy levels which are valid only in a controlled or laboratory environment. As in, a room with a steady 25°C and a slow shift in temperature (not more than 1°C per hour). Most field conditions don’t allow this – so this low level of accuracy is challenging to replicate in practice.Blackbodies are devices which can regulate temperature very accurately The other focuses on the fact we are not looking for COVID in black bodies. We are looking for it in humans. And, the substance known as human skin acts very differently. To date, there are no medical models which can predict how skin will behave in different scenarios. We don’t know what the external skin temperature of a man weighing X who was exposed for X minutes to direct or indirect sunlight would be. So, while the black body may be spot on – it has no bearing on the temperature reading of humans. So, while we can improve the first issue, the second one is more complicated. One way to circumvent it is by using population statistical analysis and looking for the gradient between the healthy population (which does have existing medical models) to the people with a higher temperature which are statistical anomalies for such a camera. Thermal cameras and their suitability Are all thermal cameras suitable for temperature readings? There is a difference between a thermal camera and a thermometric camera. A thermal camera developed for security and defence are used to detect threats and give situational awareness. We don’t care that two trees with different temperatures will have different colors – we care about the person standing between them. We manipulate the image, so the viewer has a better understanding of what he sees. With thermometric measurement (as in – thermal temperature reading) we do the exact opposite. We want accurate temperatures readings for each pixel in our screen. A thermometric camera will go through a rigorous calibration together with the lens, which often takes longer. We need to offset, in the calibration tables, minute pixel-sized blemishes in the detector and lens. Those blemishes would be invisible in a thermal image – but can skew the temperature reading and produce inaccurate results. We regularly see suppliers who are using regular thermal cameras with blackbodies to auto adjust the temperature reading as described above. But, if you take that same blackbody and move it a meter to one side, you may discover the camera suddenly registers a different temperature – as not all pixels have a uniform calibration. Does it matter where we scan in humans? Yes and no. The inner canthus of the eye (the tear duct) is the most relevant external point with the best correlation to internal temperature. People looking at the inner canthus will manage to avoid a lot of the effects of ambient temperature on the skin. The tradeoff is that the inner canthus is a tiny area, and people would need to remove their glasses. Most of the world’s health organisations consider the difference between a healthy and sick individual to be 1.5° C (or 2.7° F). That change is consistent whether you’re looking at the tear duct, the forehead or a mouth. Thus, the solutions that look at the gradient temperature (population-based solutions) are just as effective when measuring the ambient temperature on the skin of the population tested. Do people need to stop in front of the camera? Not necessarily. It depends on the speed of the camera and the temperature detection algorithm. Some cameras can detect people walking very quickly as they only need a few frames to detect the temperature. Will the camera work outdoors? Most outdoor cameras will suffer from false alarms and misses. Some cameras have very advanced compensation algorithms for this, but they can’t take into account all the dynamic temperature changes, humidity, sporadic energy readings and the “bane of thermal imaging” - turbulence. Therefore, the conditions can strain even the most advanced algorithm. Why invest in this technology? The WHO states, that while asymptomatic transmission exists, it’s much less contagious then symptomatic transmission. Some doctors claim that a person with a fever sheds the virus five times more aggressively than a person with no fever. There are clear regulations for businesses to screen individuals for fever In some countries, there are clear regulations for businesses to screen individuals for fever as they come into the establishment. While you can have a person in the entrance with a contactless thermometer, they must stop people for a 5-second check each time they come in. That would cause long lines in many places with high traffic. And, during testing, standing less than 2 meters from the individual would throw social distancing out the window. If the tester got sick, the next day they would start endangering everyone else they checked. It’s better to screen automatically and only use the IR thermometer in cases where an alert was triggered and needed to be verified. Various forms of technology We’ve also seen much use of the IR tablets recently. While they are low cost, a person usually needs to stand very close (less than 1 meter) from the monitor to be caught by the camera. Thus, spreading his germs on the glass or plastic cover of the tablet while being screened. In conclusion – Thermal EBT cameras are important. They aren’t a miracle cure, and they won’t stop the spread of the virus. And one should be careful of false promises. But along with other solutions (most importantly – masks), they can help protect us during these times and allow the wounded global economy to rejuvenate itself.
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