Zero-crossing lines of the second derivative Gaussian wavelet. An illustration of zero crossing lines detection. (a) Box signal contaminated with additive Gaussian noise (standard deviation = 0.5). (b) Absolute values of the CWT coefficients. The second derivative of the Gaussian was used as the mother wavelet. (c) All zero-crossing lines are shown. Note how the two longest lines correspond to the two sharp transitions of the box signal.