One easiest way is,

first you have to find the contours,

Then write an if statement, and inside define another if statement in hierarchical form, for finding contour area, once you get the contour append your list and count the number of pixel numbers.

if i in contours:

if cv.contourArea(i)>any pixel number (depends on your application)

polygon1.append(i)

count-number-of pixels.

This is the simplest way. Hope this will help.