calculate the centre of mass of an image

Function/c centreofMass2D(w,xx,yy)
wave w,xx,yy
//w is a 2D image wave.
//xx and yy are abscissa and ordinates of image wave
//xx and yy should be 1 point larger than w, as we are considering an image wave
//return C-O-M via a complex value
 
variable ii,jj,totalmass=0,sumrmx=0,sumrmy=0
 
for(ii=0;ii<dimsize(w,0);ii+=1)
    for(jj=0;jj<dimsize(w,1);jj+=1)
        totalmass+=w[ii][jj]
        sumrmx += w[ii][jj]*(xx[ii]+xx[ii+1])/2
        sumrmy+=w[ii][jj]*(yy[jj]+yy[jj+1])/2
    endfor
endfor
return cmplx(sumrmx/totalmass,sumrmy/totalmass)
 
End