重力异常四次导数和重力异常二次导数一样，具有突出局部异常，压制区域异常的作用。

As the second derivative does, the forth, derivative of gravity anomaly projects local anomaly but suppresses regional anomaly.

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而且为了保持图像特征，利用图像的方向导数局部地调整非线性扩散系数。

To preserve image features, the nonlinear diffusion coefficients are locally adjusted according to the directional derivatives of the image.

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为了保持图像的特征和细节，文章利用图像的方向导数局部地调整正则系数。

To preserve image features and fine part, the regular coefficient is locally adjusted according to the directional derivatives of the image.

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