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Teseo Vectorisation

The digitisation procedure involves usually:

1. extraction of the sample sequence directly from the image, in a manual or automatic way,
2. correct mapping from the image coordinates to amplitude and time of the samples.

The standard seismogram digitisation process is shown in the flow chart of figure 1. The Image process produces a pixel coordinates sequence belonging to the trace (rough digital) and the Correction process transforms it in a time domain seismic signal (final digital). This latter stage needs some instrumental parameters a priori known or obtainable from the seismogram image.

Figure 1. Flow diagram of the standard digitisation process.

Within the Image process we have introduced an intermediate step that produces a vectorial representation of the seismic trace on the image, see figure 2. Vectorial representation is more compact than the pixel coordinates sequence and, in addition, it allows more interactivity with the graphic software.

Figure 2. Flow diagram of the Teseo image process. Note that this approach introduces the vector transformation phase before obtaining the rough digital output.

The seismic trace can be represented by a piecewise cubic Bézier curve, that is, a concatenation of cubic Bézier segments. This vectorial description of the curve needs the definition of 4 points for every Bézier curve (see figure 3). It also allows for an unlimited level of detail in resampling.

Figure 3. Example of a cubic Bézier curve and of its anchor and control points.

Vectorisation methods

1. Manual trace vectorisation. In Teseo manual mode the user can create the curve directly on the image of the seismogram using the mouse pointer to reproduce the shape of the trace by choosing the position of the control and the anchor points.
2. Automatic trace vectorisation colour trace based. The algorithm generates the digital trace applying a weighted mean to pixel colour values of the image.
3. Automatic trace vectorisation neural network based. The algorithm generates the digital trace executing a neural network taking the image as input.