Support Website Contact Support Blog

Processing temperature deviation of FLIR Vue Pro r thermal image

We use the rjpeg format. We find that the value of the reflectance map generated after splicing is inconsistent with the value read in FLIR tools by the original rjpeg format, and there is a deviation of 2-3 ℃. After extraction, the value read from TIF file in converted folder is consistent with that in FLIR tools. What is the reason for this? Is there any change in the value during splicing? Is there any solution? Please Help!

Did you mean “inconsistent” After extraction, the value read from TIF file in the converted folder is consistent with that in FLIR tools.? Can you give me a screenshot showing the difference? Pix4DMapper uses a FLIR SDK that converts the rjpeg images (using the radiometric information from the rjpeg) into tif and uses them for further processing. When the final reflectance map is generated, each pixel is a weighted average of all the overlapping images containing the same pixel.

As shown in the figure

The original image was read at a temperature of 9.0

The pixel value of the extracted image is also 9.0

The pixel value of the corresponding position after splicing is 7.9

The final map Pix4dmapper generates will have a different value. This is because the value of each pixel is obtained as a weighted average of the pixels in the original images that correspond to this particular pixel. There might be some images containing that pixel which has a different temperature value.

What method is used for this weighted average? How to calculate the weight, or directly use the average value

I found that there was a significant difference in temperature between one band and the next.
For example, in the following two pictures, the first one was taken at 10:13:09 and the other was taken at 10:13:51. However, the temperature of the latter one is much lower than that of the previous one. In principle, it should be higher than the previous one, and it won’t be so different. Is it my improper use of the camera?
20201201_101309 20201201_101351

It might happen if the camera has not been calibrated in a long time. I think this part from our thermal article might give you an answer:

How to fix the discontinuities of thermal intensity between consecutive images?

If the temperature seems to drift with time, this is due to the characteristics of the camera (usually uncooled cameras exhibit this behavior) and this cannot be corrected by software. The camera provides an automated way to recalibrate the intensity, usually by taking a picture with the shutter closed. What happens is that the thermal image of a surface having uniform temperature is not itself uniform: it might rather show patterns, peculiar of a specific camera, and highly variable in time.

Check with the camera manufacturer for more details.

For weighted average, one of the parameters for the weight is the distance of the center of the camera from the pixel/object.