Hi, I use some mask to export mask pixels ,open in the excel,Why the number is so little? look forward to your answer.
I am doing classification，I have some square training samples,I want to get the spectral mean of the training sample on different bands.
This are the value extracted directly from a unprocessed S2A Level 2 product or from your processed product?
Extract from my processed product,but,I just performed simple processing, atmospheric correction, resampling, mosaic and subset,then use Export mask Pixels to extract.
In this case it seems quite normal to me, the pixel values for the bands are small (as you can see in the histogram by clicking on the bottom left panel “Colour Manipulation”), for example for B3 typical values are around 1e-3 for black and around 0.14 for white. 
yes，Just like you, Thank you for your help. I have understand it.