how to average image pixels without taking black color pixels (pixel=0)

i'm using m= mean2 (current_image);

mean2 takes all pixels ,the balckpixel=0 do not have value but they are counted in total number of pixels ( n )

 mean2= h1+h2+....+h10+....+hn / n

if h1 = 0 ,so it is not counted in numerator but it is counted in the denominator

i wantn't count them in denominator

thanks in advance