Filtering Tool
==============
.. index:: Filtering Tool

* **Tools -> Filtering**

Changes in analytical conditions can cause 'spikes' in data,
regions of extremely low or high signal resulting from instrument noise.
These can be removed by applying a local filter at the position of each spike.
The `Filtering Tool` removes spikes by comparing pixel values to a locally defined threshold,
outlying values are then replaced with the local mean or median.
A visual example is provided in :ref:`filter_image`.

The parameters of the filters in :ref:`Available Filters` are set using the inputs directly below the filter selection box.
To toggle visibility of a filter (for comparison) click the `Filter Visible` button.

.. figure:: ../images/filtering_image.png
   :align: center
   :name: filter_image
   :width: 600 px

   Application of a rolling median filter.


Available Filters
-----------------
.. index:: Filtering Tool Filters

.. table:: Filters implemented in |pewpew|.
    :name: filter_methods
    :align: center

    +----------------+---+--------------------------------------------+
    | Type           | Threshold                                      |
    +================+===+============================================+
    | Rolling Mean   | σ | Distance in stddevs from the local mean.   |
    |                |   | Stddev excludes the tested value.          |
    +----------------+---+--------------------------------------------+
    | Rolling Median | M | Distance in medians from the local median. |
    +----------------+---+--------------------------------------------+

.. seealso::
    :ref:`Example: De-noising an image`.
     Example using the filtering tool.