Zoom the center of image x by a factor of z+1 while retaining the original image size and proportion.

def zoom_cv(x,z):
    """ Zoom the center of image x by a factor of z+1 while retaining the original image size and proportion. """
    if z==0: return x
    r,c,*_ = x.shape
    M = cv2.getRotationMatrix2D((c/2,r/2),0,z+1.)
    return cv2.warpAffine(x,M,(c,r))