Thermal Imaging Glossary

Thermal Imaging Glossary and terms

While almost all of us have heard about night vision or seen it in the movies, thermal imaging is something that many of us may not be familiar with the terms associated with it or how it differs from night vision. While similar to night vision in the fact that it helps you see and detect objects in the dark thermal imaging is very different than night vision and there are pro's and con's to each technology.

Thermal imaging uses the difference in temperatures from the infrared radiation emitted by objects to generate a thermogram (image) allowing users to detect animals while hunting, leaks in pipes behind walls and HVAC issues among many other things.

Night vision works in a very simple way in that is magnifies the available light 1,000's of times which in turn generates an image that we can see. Thermal imaging can work in complete darkness and can detect heat differences (generating an image) behind walls and through smoke and fog.

Because a thermal image is not simply generated by magnifying the available light there are many terms and comments that you might not have heard about before.

Let’s look at some of the terminology used when we talk about thermal imaging so you can learn about this technology and be better informed when you are looking for the thermal imaging device that is right for you.

Accuracy:

The thermal measuring accuracy of the thermal imager you’re using will differ from one device to the next. The accuracy will be influenced by the quality and price of the device you’re using. But even when you’re using top of the range thermal imagers you might still not end up with a 100% accurate measurement.

Most thermal imaging cameras are accurate to within 2-5 degrees when measuring temperatures.

The accuracy of the imager is influenced by several factors including:

  • Expertise: If you’re not experienced in the thermal reading field you might end up translating the images incorrectly.
  • Block outs: Yes, it’s true these devices are made to look through dense objects & they mostly succeed. But it’s still possible for some objects such as windows to block out heat. Any object that blocks heat or reflects it will result in a less accurate image.
  • Sensitivity: A slight change in temperature can change the reading as these devices are extremely sensitive.

Color Palettes:

thermal imaging Color Palettes

Take a look at the last pictures you’ve taken on your SmartPhone or camera. Do you see all the colors clearly as you would if you were looking at the same scene with your eyes? Unless you used some sort of filter, the colors on the picture will be the same as when you took the picture & the same as we see it in real life. This is called true color.

False color is used in thermal devices to outline or highlight a specific area. For instance a color imager will show a white, red, orange or yellow color on the screen to accentuate a warm object.

Cold & cool objects will be seen as the color blue or violet on the screen. The colors are not directly transferred to the screen but rather have assigned colors according to temperature changes. If a device makes use of monochrome picture visually black will be a warm area whereas white or grey will show a cool colder object or surface.

The reason thermal images differ in this way is because they are not detecting an "image" but rather detecting the temperature differences between objects and using this data to generate an image.

Cooled Infrared Image Detector:

Cooled image detectors have been used in the military for many years as well as industrial applications. Although it has evolved it still doesn’t have your average price tag. Be prepared to pay much more for a cooled infrared thermal detector/camera.

Bigger is better? Well not always. Cooled detectors are large and used on aircraft or military vehicles to scan an area. Not much has changed size wise throughout the years.

Cooled infrared detectors as the name indicates, cool down the temperature of the thermal sensor using a cryocoller which has many moving parts and has to be built to very tight specifications to function correctly. They also have to be periodically rebuilt because of wear and tear and the helium gas that leaks out of the system. Because the thermal sensor is cooled to subzero temperatures you are able to get much clearer images with many more details.

Due to the large size and very high cost cooled thermal cameras are only used by large companies and the military.

Image Frequency or Refresh Rate:

The image frequency or refresh rate of a thermal camera is measured in Hz. The detector needs to capture images quickly. The Hz refers to the number of images the device is able to create in a second. An 8Hz camera will be able to create eight images in one second. 30Hz thus refers to a thermal imager that can create 30 images in a second. Your TV typically has a 60Hz refresh rate.

Cameras with a faster frequency rate are the better option but will also be pricier. 

Infrared Vision:

Have you ever accidentally touched a hot pan on the stove or taken hot meat right off the barbeque grill? All of us have encountered & touched something hot at some point or another. It’s safe to say you can feel the heat being radiated from a stove or a fire.

The same goes for ice cold objects. Think about those warm summer days where you’ve opened up the freezer to get a frozen yogurt to cool down. You can feel the coldness of the ice even before you touch the yogurt.

Infrared radiation can be seen on and around warm objects as well as some cold items. If you’re standing two feet away from your closed freezer or oven you won’t be able to feel the cold (or the heat it still radiates) right?

This is where infrared vision comes in. If you had to use infrared vision while boiling eggs on the stove, you’ll be able to see the heat radiating from the pot even when standing four feet away & not being able to feel the heat at all.

If you’re wondering who the genius is behind the discovery of infrared detection, you can thank Sir William Herschel. This British astronomer discovered infrared in the 1800’s.

Focus:

When you’re using a thermal imager you want to make sure it gives you precise, clear images. Blurry images can cause you to get an incorrect position of a person or object and can change the actual readings by more than 25°.

There are many different focus systems available. Let’s have a look at some of them:

  • Manual focus devices: Manual focus systems are the most popular type of system used by professional thermographers. The reason is that it is the most reliable to give exact, blur free images. Manually changing the settings are  time consuming & you need to be precise to get the perfect results.
  • Multifocal capture apparatus: Images taken from different ranges can be taken and stored with the multi-focal image capture device. Multiple images can be combined into a single image.
  • Auto focus imagers: If you’re looking for a faster option than the manual focus imager, you’ll probably select the auto focus. It’s fast & can be clear and precise.

The auto focus imager works best in an open area where the object can easily be seen or identified as this type of imager tends to identify different objects at once. 

FOV:

Also known as field of view, this refers to the biggest area the device can view and is measured in angular degrees. You can look into a smaller FOV if you’re mainly working on big areas and you need to identify small objects within those areas.

Microbolometer:

The microbolometer is what allows a thermal camera or scope to function and is the sensor that detects the changes in heat. A microbolometer has thousands of very small sensors that can detect infrared radiation typically in the 7 to 14µm wavelength. When the sensors detects infrared radiation their electrical resistance changes. The changes are then measured and converted into the thermal image that you see on your screen. 

MSX:

Do you often work with thermal imagers? Do you mostly need a digital camera & a thermal imager to get different pictures from a scene? It can be very frustrating & time consuming having to use two different cameras for the same purpose. If only there was a way to use one camera & get both types of images at the same time.

Let me introduce you to the FLIR's MSX technology. The MSX or Multi-Spectral Dynamic Imaging allows you to take thermal videos as well as capture images. The quality of this camera is outstanding & the images accurate.

Both there thermal image and visual image are taken at the same time. The thermal image is overlaid on the visual image. This allows you to see details taken in the visual image as well as the temperature differences in the thermal image.


Night Vision:

Night vision is often confused with infrared/thermal vision. Night vision helps you see objects in the dark that you wouldn’t otherwise be able to see.

Did you know that you still need light to see when using night vision? Light, whether it be moonlight or a streetlight in the far distance is filtered by the lens of the device. The filtered light is then amplified to be able to see the object in the dark. Night vision devices mostly portray images through a green screen or lens.

Night vision devices can also not but used during the daytime as thermal can be. Bright light will damage the photo intensifier tube.  This means that night vision devices have to be kept in a dark place and typically come with a storage case to prevent damage from light when being transported.

Night vision and thermal vision are two different types of devices each built for different purposes. Night vision devices tend to be cheaper than thermal devices.

Resolution:

Have you ever heard photographers talking about their newest cameras? The first and most important thing they’d compare and talk about is the resolution of their latest investment.

Cameras aren’t the only devices where pixels matter. The pixels in thermal imagers affect the quality of the image and the amount of detail you are able to capture. Higher resolution will make diagnosing issues much easier especially if you are scanning smaller objects.

Common thermal resolutions include:

  • 160x120
  • 320x240
  • 640x480

You can determine the number of pixels that your thermal cameras image will have by multiplying the resolution. Example 160 X 120 = 19,200 pixels per image. To you give an idea of the amount of pixels in 3 mega pixel camera are 2048 x 1536 = 3,145,728.

It should be noted though that thermal cameras are designed to show  temperature changes and not to capture high resolution images showing all the details in the image as visual cameras do.

High resolution devices used to come with a hefty price tags leaving consumers with low resolution detectors that weren’t as accurate. This luckily changed over the years and you can easily get a 320 x 240 pixel detector for under $5,000 these days.

Seek Fusion:

Seek is a thermal imaging compay that makes a variety of different thermal devices.

It’s compact, it’s smart, it’s effective & it’s easy to use. We’re talking about the new Seek fusion thermal image camera.

Measurement tools can easily be added to make your experience time effective & simple. You can easily send data via Wi-Fi if you’d like the images on your other smart devices such as your tablet.

This smart innovation allows you to do it all on one device. You can edit the images after capturing it on your Seek device.

The Seek range is affordable & you’ll be able to get a device for under $800. The Seek range offers eight color palette technology & more than 10 times the pixels than most devices in its category.

This range is made to be lightweight and they succeeded in making an intelligent, handy gadget. 

Thermal Sensitivity :

Thermal sensitivity, which is overlooked sometimes refers to how sensitive the microbolometer is to different temperatures. Most normal (uncooled) thermal cameras will have a thermal sensitivity of 0.1°C. Where as a very cheap one may have a 0.2°C sensitivity. For reference cooled thermal cameras can have a sensitivity of 0.08°C or less. This is why images from a cooled thermal camera are so clear and crisp.

While this does not seem like a lot it can drastically affect the image quality because the camera will be unable to detect differences between temperatures. This results in grainy or blurry images that may cause you to miss out on important details.

Thermography:

Thermography is when we use heat wave lengths also known as infrared radiation. This allows you to see objects & movement in areas with poor lighting or that’s unclear to the human eye.

Thermography can be used in videos or images & it’s also being used in the medical industry. Medical professionals are using thermography to identify areas in the body with potential cancer or tumor growth as it radiates more heat than the rest of the organs. 

Uncooled Image Detector:

If you’re looking for an affordable, smaller sized detector the uncooled detector’s your go to. You can get one of these gadgets for less than $2000. They’re also a lot lighter, most of them not weighing more than a tablet or camera.

So what’s the catch? Why can you get an uncooled detector for a fraction of the cost of a cooled detector?

As noted above a cooled thermal camera uses a cryocooler to bring the temperature of the micorobolometer down to subzero levels this allows for much more clear pictures because the sensor can very easily detect temperatures that are much higher than its own in its cooled state.

Because of the cryocooler cooled thermal cameras are very expensive.

Wavelength:

When we measure the distance from one consecutive point in a wave to the next we get the frequency or wavelength of the specific area. Wavelengths can be short or long. Short wavelengths are called gamma rays. Radio waves on the other hand are longer wavelengths.

Infrared wavelengths (image below) can be found in between gamma & radio waves. These wave lengths are detected and are what allow the image to be generated.

Infrared spectrum

Final Thoughts:

Thermal imaging devices are very useful in so many different applications some of which include commercial, home use, hunting, building maintenance, law enforcement and military applications.

If you want to invest in a thermal imager we’d recommend doing proper research about the features and specs of the device. Get an imager that’ll last you a lifetime, give you more precise readings & higher definition. You can check out our comparison chart as well as our list of the best cheap thermal cameras.

If you looking for a thermal scope or monocular for hunting we have also reviewed several of our top picks.

Lives are being saved, changed and made easier with these nifty gadgets that are becoming smarter & more accurate day by day.

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