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How to get proper temperature values from H20T R-JPEG images?
195 0 9-10 04:57
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Joysn
lvl.1

Austria
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Hello,

how can I extract valid temperature values from the RJPEG files for post  processing? Tried with DJI thermal SDK, does not work reliably. Get  temperatures from range -40 to +120° Celsius. On a day which had around  20°C. Even all DJI Termal Analyzer tools (version 1 to 3) show wrong  temperature values.
When I read exif image meta data, I find K1, K2, K3, K4, KF, B1, B2, D1,  D2, KJ, DB, KK. What do these values mean? Not sure how DJI calls this  meta data, but "exiftool" calls it like this. Seems that somebody did  reverse engineering due to poor documentation from DJI.
Even when I extract the raw data values, they seem to be wrong as well.  At least when I create a histogram for temperature and raw values, they  seem to have the same issues, but as I dont know how to process the  sensor raw values, I cannot tell if the sensors raw values already have issues.

DJI-TAT-image.jpg

I can play with the parameters humidity, emissivity, distance and reflected temp., but I do not get feasable temperatures.
Furthermore, minimum temperature can jump from -2°C (which is already not feasable on a day with min. ~10°C) to around -20°C on two consecutive photos within 3 seconds.

Might there be a sensor issue?

Or am I doing the measurements completely wrong?


DJI-TAT-image.jpg
9-10 04:57
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