Fig. 4

Depth results estimated by the NDC of largest eigenvalue of structure tensor with different normalization functions and different standard deviations \(\delta x\) and \(\delta {\text{y}}\) in the Gaussian envelop. a By arithmetic mean (\(\delta x = \delta {\text{y } = \text{ }}0.1\)); b by median (\(\delta x = \delta {\text{y } = \text{ }}0.1\)); c by geometric mean (\(\delta x = \delta {\text{y } = \text{ }}0.1\)); d by arithmetic mean (\(\delta x = \delta {\text{y } = \text{ 1}}\)); e by median (\(\delta x = \delta {\text{y } = \text{ 1}}\)); f by geometric mean (\(\delta x = \delta {\text{y } = \text{ 1}}\)); g by arithmetic mean (\(\delta x = \delta {\text{y } = \text{ 10}}\)); h by median (\(\delta x = \delta {\text{y } = \text{ 10}}\)); i by geometric mean (\(\delta x = \delta {\text{y } = \text{ 10}}\))