Thermal Imaging Part 2: Understanding colours

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In the previous post Thermal Imaging Part 1: Tech & Science, we gave a short background and explanation to the technology and science of thermal, or infrared, imaging. Here we turn our attention to thermal colours and their meaning.

thermal image of roof Unity Academy


When you press the button on a thermal camera, an area of thermometers record the temperatures they pick in front of them.

The temperatures are then turned into colours and displayed on the cameras screen, as shown in the picture of a flat roof.

What you then see is technically called a thermogram. Click on the shutter button, and the image is captured.


The deceptive nature of thermal imaging colours

Red is hot and blue is cold . That’s only an example. Let me explain.

Every time you take a picture that temperature data is stored. You can interrogate the image and manipulate it for a variety of reasons.thermal image of house

If you consider  a thermogram of a house for example you often see red or white windows, green walls, blue render, yellow timber cladding etc.

This is where things get scary.

Each image has several parameters you can modify digitally: amongst others, distance to object, humidity, emissivity, level and span – all affect the temperature the camera thinks the object is.

Glass is a nightmare for thermographers. Infrared cannot pass through it and it literally reflects energy from the buildings around it. The image of the mutlicoloured house needs skilled analysis.

You can now imagine how easy it would be to exploit the technical nature of the cameras to mislead vulnerable people to sell insulation for instance.

Also, just to confuse you… red can also be cold if the analysts inverts the pallette. Not that they would of course.

But to continue the house analogy – red on the outside can mean a damp house or missing insulation. That same problem might look blue on the inside.

We have written on this subject many times before and the problem is pervasive.

Cheap cameras often lead to unskilled users with inadequate training and misled unhappy customers.

So red is hot, but sometime not? Yep. Afraid so.  Usually it is though!

Related article:  Infrared thermography highlights Bute House energy loss , Thermal imaging Part 3: How much will a thermal imaging survey cost?

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