Sentinel 1 radiometric resolution in SNAP

Hi everybody,
I downloaded a Sentinel-1B image (GRDH, IW) and then calculated the statistics of amplitude VH band. I have 2 questions :

  • what do represent the x and y axes of the histogram displayed on the left ?
  • the value displayed at the top of the table is : #pixels total: 420113269. What does it represent? it can not be the radiometric resolution since the image is normally encoded on 16 bits !!

Thank you in advance.