sunkit_image.radial.nrgf(smap, radial_bin_edges, scale=None, intensity_summary=<function nanmean>, intensity_summary_kwargs={}, width_function=<function std>, width_function_kwargs={}, application_radius=<Quantity 1. solRad>)[source]#

Implementation of the normalizing radial gradient filter (NRGF).

The filter works as follows:

Normalizing Radial Gradient Filter a simple filter for removing the radial gradient to reveal coronal structure. Applied to polarized brightness observations of the corona, the NRGF produces images which are striking in their detail. It takes the input map and find the intensity summary and width of intenstiy values in radial bins above the application radius. The intensity summary and the width is then used to normalize the intensity values in a particular radial bin.


After applying the filter, current plot settings such as the image normalization may have to be changed in order to obtain a good-looking plot.

  • smap ( – The sunpy map to enhance.

  • radial_bin_edges (astropy.units.Quantity) – A two-dimensional array of bin edges of size [2, nbins] where nbins is the number of bins.

  • scale (None or astropy.units.Quantity, optional) – The radius of the Sun expressed in map units. For example, in typical Helioprojective Cartesian maps the solar radius is expressed in units of arcseconds. Defaults to None, which means that the map scale is used.

  • intensity_summary (function, optional) – A function that returns a summary statistic of the radial intensity. Defaults to numpy.nanmean.

  • intensity_summary_kwargs (dict, optional) – Keywords applicable to the summary function.

  • width_function (function, optional) – A function that returns a summary statistic of the distribution of intensity, at a given radius. Defaults to numpy.std.

  • width_function_kwargs (function, optional) – Keywords applicable to the width function.

  • application_radius (astropy.units.Quantity, optional) – The NRGF is applied to emission at radii above the application_radius. Defaults to 1 solar radii.

Returns: – A SunPy map that has had the NRGF applied to it.