SciPy – 52 – elaborazione di immagini multidimensionali – 4

Continuo da qui, copio qui.

Funzioni filtro generiche
To implement filter functions, generic functions can be used that accept a callable object that implements the filtering operation. The iteration over the input and output arrays is handled by these generic functions, along with such details as the implementation of the boundary conditions. Only a callable object implementing a callback function that does the actual filtering work must be provided. The callback function can also be written in C and passed using a PyCapsule (see Extending scipy.ndimage in C [prossimamente] for more information).

The generic_filter1d function implements a generic one-dimensional filter function, where the actual filtering operation must be supplied as a Python function (or other callable object). The generic_filter1d function iterates over the lines of an array and calls function at each line. The arguments that are passed to function are one-dimensional arrays of the tFloat64 type. The first contains the values of the current line. It is extended at the beginning end the end, according to the filter_size and origin arguments. The second array should be modified in-place to provide the output values of the line. For example consider a correlation along one dimension:

The same operation can be implemented using generic_filter1d as follows:

Here the origin of the kernel was (by default) assumed to be in the middle of the filter of length 3. Therefore, each input line was extended by one value at the beginning and at the end, before the function was called.

Optionally extra arguments can be defined and passed to the filter function. The extra_arguments and extra_keywords arguments can be used to pass a tuple of extra arguments and/or a dictionary of named arguments that are passed to derivative at each call. For example, we can pass the parameters of our filter as an argument

or

The generic_filter function implements a generic filter function, where the actual filtering operation must be supplied as a Python function (or other callable object). The generic_filter function iterates over the array and calls function at each element. The argument of function is a one-dimensional array of the tFloat64 type, that contains the values around the current element that are within the footprint of the filter. The function should return a single value that can be converted to a double precision number. For example consider a correlation:

The same operation can be implemented using generic_filter as follows:

Here a kernel footprint was specified that contains only two elements. Therefore the filter function receives a buffer of length equal to two, which was multiplied with the proper weights and the result summed.

When calling generic_filter, either the sizes of a rectangular kernel or the footprint of the kernel must be provided. The size parameter, if provided, must be a sequence of sizes or a single number in which case the size of the filter is assumed to be equal along each axis. The footprint, if provided, must be an array that defines the shape of the kernel by its non-zero elements.

Optionally extra arguments can be defined and passed to the filter function. The extra_arguments and extra_keywords arguments can be used to pass a tuple of extra arguments and/or a dictionary of named arguments that are passed to derivative at each call. For example, we can pass the parameters of our filter as an argument

or

These functions iterate over the lines or elements starting at the last axis, i.e. the last index changes the fastest. This order of iteration is guaranteed for the case that it is important to adapt the filter depending on spatial location. Here is an example of using a class that implements the filter and keeps track of the current coordinates while iterating. It performs the same filter operation as described above for generic_filter, but additionally prints the current coordinates. Non sono riuscito a riprodurlo, mi da errori per range 😡

:mrgreen:

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