cv2.CAP_PROP_EXPOSURE is different in ubuntu and windows, and what is the meaning of each the value of cv2.CAP_PROP_EXPOSURE ?

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Hello

I was working my project with one webcam in both windows10 and ubuntu 16.04, and I find when I get this webcam's exposure bycap.get(cv2.CAP_PROP_EXPOSURE), I will get a negative integer (around -5 to -7) in windows10, and a positive integer (around 70) in ubuntu 16.04, I want to know why there is difference? and what is the meaning of value of cv2.CAP_PROP_EXPOSURE in windows10 and ubuntu 16.04 is respectively?

In both operating system, I have my python environment as follow:

python=3.5.4

opencv-python=4.1.0.25

Thanks a lot!