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Asked by anon-244767 on 30 Apr 2020.
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Malgorzata Drwila answered on 30 Apr 2020:
(somebody correct me if I’m wrong)
The infra-red cameras are measuring the amount of heat the object is emitting and then for each amount of heat different colour is associated. It is not like the spectrum of visible light is being shifted to lower frequencies to ‘see’ the infra red scale. In that case the blueish tones doesn’t mean they are hotter, it means that their frequency is higher.
So to sum up, somebody decided that in infra-red image red is hot and blue is cold, because it was intuitive and now it became a standard. But in reality you can assign any colours you want to ‘hot’ and ‘cold’ if you can hack the instrument/software.
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Sofija Durward answered on 30 Apr 2020:
I think that usually people associate the colour red with hot things (like the red tap at your sink being the hot one) so a lot of people are just more used to it. You’re right though that technically it should be the other way around!
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Roan Haggar answered on 30 Apr 2020:
The colours that we see in infrared images aren’t real, as infrared light can’t be seen by humans. Infrared cameras measure the amount of infrared light produced by different objects in the image, and then calculate the temperature of each object from this.
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However, the colours that are used to represent each temperature are simply chosen by whoever is making the image — they don’t represent real colours or frequencies of light. These are called ‘false-colour images’, and are just a useful way of visualising the information from cameras. Red is usually chosen for the hotter parts, because most people (incorrectly!) associate red with high temperatures, but you could just as easily make the hot parts of the image blue/white. Hope this helps! -
Susan Cartwright answered on 30 Apr 2020: last edited 30 Apr 2020 10:09 am
Infra-red light does not have an intrinsic colour, so thermal camera displays use what astronomers call “false colour”: that is, they assign colours according to some property of the radiation received (wavelength or intensity) in order to make the images easier for the human brain to understand.
Most infra-red cameras are actually measuring the intensity of the light at a particular wavelength, which is greater for hotter objects (this is because they are emitting approximately as “black bodies”, see https://en.wikipedia.org/wiki/Black-body_radiation). Because most people associate red with hot and blue with cold (think of the coloured markings on taps), the cameras are set up to display the most intense radiation as red and the least intense as blue.
In contrast, astronomers are used to thinking of blue as hot and red as cold, so astronomical false colour displays usually show hot regions as blue and cold as red. It’s all done so as to make the pictures as intuitively clear as possible, and different audiences have different expectations.
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anon answered on 30 Apr 2020:
Apart from stars and glowing objects, blue usually is associated with cold and red is associated with warm. These associations come from the world around us – blue water (cool or cold), bluish ice, winter in general is “bluer” – even if the snow is white, other colours are absent and the blue sky reflects in ice and water. Warm colours are the summer colours, and the hottest things on earth – lava, burning wood – are red.
So it’s a more intuitive choice of colour-coding. It can be anything though, there are IR cameras with yellow/purple colourmaps.
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Richard Fielder answered on 30 Apr 2020:
As others have said, it’s not really anything to do with actual temperature, but is just a scale applied to visuallise something that humans can’t normally see. In principle, we could assign any colour to any value we liked, but it’s usual to use a graduated colour scale that appears something like a rainbow. You can see an example of that here – https://en.wikibooks.org/wiki/JPEG_-_Idea_and_Practice/The_colour_components#The_RGB_values
When you want to put colours on a graph, people will usually pick one point on that rainbow for the lowest value, another point for the highest, and then fill in the scale in between. As that page notes, it can also be used as a cyclic scale, meaning that it wraps around and starts from the begining again. That allows you to see the difference between parts of the graph that are close together, then use the same colours again further away where there won’t be any confusion.
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Ashleigh Barron answered on 30 Apr 2020:
As the others have said the colours used in thermal cameras are just to visually show the amount of heat given off a particular scene. The cameras could use any colours but most use red as hot and blue as cold as thats what most people are used to seeing. The company I work for makes IR cameras and not all of them use this colour scheme. Some of them use a grey scale where white is hot and black is cold with a grey gradient of colour for the temperatures between.
Comments
anon-244767 commented on :
Thank you! really helpful 🙂
anon-244767 commented on :
Thank you Roan, Malgorzata and Sofija! 🙂 🙂