中文说明：最直观的印象就是在水平、竖直两个方向上变化均较大的点，即Ix、Iy都较大 边缘：仅在水平、或者仅在竖直方向有较大的变化量，即Ix和Iy只有其一较大 平坦地区：在水平、竖直方向的变化量均较小，即Ix、Iy都较小
English Description：
Most intuitive impression that changes both in horizontal and vertical directions are great, Ix, Iy are large edge: only level, or to have greater variation in the vertical direction only, namely Ix and Iy is only one of the larger flat area: are small changes in horizontal and vertical direction, namely, Ix, Iy are smaller