Histogram Values Before and After Mask

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#1

Hello everyone,

I tried masking out land pixels from a subset of a B11 image, and wanted to compare the histograms before and after. For the masking, I added the following on the “Valid Pixel Expression” : &&(B11<0.0375). The result was the following

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On the left is the original subset, and its histogram right underneath. The number of pixels that have values roughly 0.0125 reaches about 800. However, after the masking, it drops to about 110 (histogram on the right). Why is that ? Am I missing some basic principle of masking ? I figured since 0.0125 < 0.0375 the number of pixels having that value shouldn’t have been affected, or at least not by that much.

Thank you for your time !

#2

Histrograms divide the X-axis into intervals or bins, typically a configurable number. For data with a reduced range of values, the intervals will be shorter, so you should expect fewer values in each range.

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#3

Thank you very very much ! It makes so much sense, yet it had not crossed my mind !