Measure the light intensity of a fish eye image

Hi everyone, I’m a biology student. For my essai, I want to measure light intensity incoming in dry stone walls with a Fish Eye photo. I would like to know the light intensity that reaches my walls, taking into account obstacles such as trees or surrounding houses. I’m a newbie on ImageJ. I would like to know if its possible to have this kind of measurement.
I am attaching a Fish Eye image.

Thanks for your answers.

Corentin De Keyser

How do you define light intensity exactly ?
What about just taking the mean pixel intensity of the image ?
If the black background at the periphery of the images is the same for all images then it should correlate well.

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Hello, forgive me, I was not specific enough. I want to study the percentage of canopy cover. So from the Fish Eye image, I would like to know the percentage of light present in the photo. So if we assume that there is 100% light, we would have to subtract obstacles such as trees.
With all this data, I could hypothesize that the flora present on the dry stone walls depends on the light received by the wall.

So you want the proportion of sky in the image or inversely the proportion of tree ?

I think you could try thresholding to isolate the canopy (or the sky), probably you should convert the RGB-image to grayscale first

Yes, this is exactly what I want ! Thank you for your answers, I will read tutorials to see how to do that, thanks !!

You will also find some suggestions here form older threads, see:

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Thank you for your help ! This is what I need !