A Detection of hot spots with a thermal (non-radiometric) camera

[pcarvalho]

TL;DR Summary

We need to detect hot spots with a thermal (non-radiometric) camera. The camera retrieves JPEG.
We need to know if it makes sense to do the processing on top of JPEG.

Hello,

We have a thermal camera and its purpose is to detect hot spots at different distances. We made an experiment with a JPEG picture and we noticed the following:

• At the same distance, one object at 600 degrees and an object at 38 degrees (human body) have the same pixel intensity (255 in grayscale).
• The image adjusted when the 600 degrees object exited the scene (parts of the human body and background became brighter).

We will make a detection algorithm and we need to make sure only the 600 degrees object is detected. If we are going to do the algorithm based on the maximum pixel value we belive this will create false positives.
So, I want to understand if it makes sense to use JPEG images to do the processing. If it makes sense, what would be the maximum distance that the algorithm would work fine?
If you have an idea, I would like to ask for references/papers that use jpeg to detect objects that are above a certain threshold in terms of pixel intensity and that make the distinction between high temperature objects and low temperature objects.

Many thanks

 

[sophiecentaur]

TL;DR Summary: We need to detect hot spots with a thermal (non-radiometric) camera. The camera retrieves JPEG.
We need to know if it makes sense to do the processing on top of JPEG.

At the same distance, one object at 600 degrees and an object at 38 degrees (human body) have the same pixel intensity (255 in grayscale).

Hi. Welcome to PF.
A diagram of the system would be useful. Many things spring to mind but, for meaningful results, you need to "control all your variables".

What is the 600c source?
I'm not sure what your experiment is trying to achieve but it seems very likely to me that the images are 'clipping' . Both images have 255. That is surely not a coincidence. If the hot object is causing the measurement of the cool object then, either the gain of the system is being varied (auto exposure) or the 600C object may be larger than its 'obvious' image suggests; is the hot object warming up its surroundings?

You need to calibrate your system. Look at images of the background with and without the hot source in place. Do the pixel values vary? How do the pixel values drop off at the edges of the hot object. Plot a graph using the 'colour dropper' for samples against position.
Also, you should use a mask to isolate the body image.

TL;DR Summary: We need to detect hot spots with a thermal (non-radiometric) camera. The camera retrieves JPEG.
We need to know if it makes sense to do the processing on top of JPEG.

If you have an idea, I would like to ask for references/papers that use jpeg to detect objects that are above a certain threshold in terms of pixel intensity and that make the distinction between high temperature objects and low temperature objects.

I have no idea what specific software is available directly for your purpose but there are many image analysis apps which you could use. Have you done any searching for this? Searching is the way through; it's good for the soul and you can't expect PH to do the legwork for you unless a member happens to have done this sort of thing before! However, without that, you can get the RGB /Y values from the colour dropper and plot your own graph along any line across the screen. Whatever operating system you are using that facility will be available on free photo processing apps. A graph (plot many of them - on paper if necessary) would give you a good idea of what's actually happening.
JPEG is fair enough for that sort of work. The artefacts it generates are not likely to spoil your data.

 

[pcarvalho]

Ok, I'm going to give you more insight. We have an hikvision camera (thermal, not radiometric).
The idea is to spot high temperatures at different distances (10+ kilometers). We know that radiometric cameras can measure temperatures, but these temperatureas are apparent. With a formula we could know more or less the temperature based on the distance. We know that these cameras give raw data. Raw data is data from the ADC of the camera, which means that if the camera is 14 bit we will have a range of 0-16384 values.
But our camera is not radiometric, it is only thermal, which means only the jpeg can be extracted. We want to make our own thermal analysis app. Basically we capture a frame from the camera, do the processing (find hot spots at different distances) for each pixel, and show where it is in the image.
We will have an edge computer that captures the frame from the camera, process it and send to a server. This will be done in a 5-10 seconds time frame.
Besides, we can't find anywhere algorithms that detect high temperatures in jpeg frames. However ChatGPT, says it is possible. I tried one of the algorithms of it and the results are bad (several places of the scene are misindentified as hot source). The hot source we used is a kind of dryer for heat-shrink sleeves. It says it can go to 600º.

Thanks

 

[sophiecentaur]

But our camera is not radiometric, it is only thermal

The only difference (as far as I can tell) is accuracy of the measured temperature. My problem is not knowing how temperature can be measured without at least two filters and two sets of sensors in the array. The ratio of two spectral readings at different wavelengths will tell you where you are on the black body radiation curve and, hence the temperature.

Besides, we can't find anywhere algorithms that detect high temperatures in jpeg frames.

I don't understand that statement. JPEG is only a method of converting a source image to a bit reduced version. Are your images Coloured? (Just to be sure that the output is not monochrome). Plenty of software can change back from JPEG to RGB and to any other coding .

The images from even cheap thermo cameras are all coloured. So (I conclude) White corresponds to high temperatures and red is lower temperatures (or what ever false colours they choose)

I just hope that someone in PF can HELP with how the images give temperatures because I can find nothing that's equivalent to the three colour analysis . It's all 'magic' according to the adverts.

 

[sophiecentaur]

for visible imaging.

 

[pcarvalho]

The only difference (as far as I can tell) is accuracy of the measured temperature. My problem is not knowing how temperature can be measured without at least two filters and two sets of sensors in the array. The ratio of two spectral readings at different wavelengths will tell you where you are on the black body radiation curve and, hence the temperature.

I don't understand that statement. JPEG is only a method of converting a source image to a bit reduced version. Are your images Coloured? (Just to be sure that the output is not monochrome). Plenty of software can change back from JPEG to RGB and to any other coding .

The images from even cheap thermo cameras are all coloured. So (I conclude) White corresponds to high temperatures and red is lower temperatures (or what ever false colours they choose)

I just hope that someone in PF can HELP with how the images give temperatures because I can find nothing that's equivalent to the three colour analysis . It's all 'magic' according to the adverts.

The jpeg image is grayscale. We use the "White hot" pallette.
The ideal solution was to have raw data, but this is not possible with the camera we have. We know that jpeg is a compression algorithm (we are losing information).
Also, we are in this trouble because we need to sell a whole system that includes that camera, but this camera was sent to us wrongly by the seller. Now we don't have time to send it forth and back.
Anyway, I'm more leaned that we can't detect well hot spots with this camera, but I just need someone that confirms that. I was hoping someone from universities that use this kind of equipments could give me a confirmation. Maybe this should be asked directly to a professor?