Enhancements
Built-in enhancement methods
stretch
The most basic operation is to stretch the image so that the data fits to the output format. There are many different ways to stretch the data, which are configured by giving them in kwargs dictionary, like in the example above. The default, if nothing else is defined, is to apply a linear stretch. For more details, see enhancing the images.
linear
As the name suggests, linear stretch converts the input values to
output values in a linear fashion. By default, 5% of the data is cut
on both ends of the scale, but these can be overridden with
cutoffs=(0.005, 0.005) argument:
- name: stretch
method: !!python/name:satpy.enhancements.stretch
kwargs:
stretch: linear
cutoffs: [0.003, 0.005]
Note
This enhancement is currently not optimized for dask because it requires getting minimum/maximum information for the entire data array.
crude
The crude stretching is used to limit the input values to a certain range by clipping the data. This is followed by a linear stretch with no cutoffs specified (see above). Example:
- name: stretch
method: !!python/name:satpy.enhancements.stretch
kwargs:
stretch: crude
min_stretch: [0, 0, 0]
max_stretch: [100, 100, 100]
It is worth noting that this stretch can also be used to _invert_ the data by giving larger values to the min_stretch than to max_stretch.
histogram
gamma
invert
crefl_scaling
Deprecated. Use ‘piecewise_linear_stretch’ instead.
piecewise_linear_stretch
Use numpy.interp() to linearly interpolate data to a new range. See
satpy.enhancements.piecewise_linear_stretch() for more information and examples.
cira_stretch
Logarithmic stretch based on a cira recipe.
reinhard_to_srgb
Stretch method based on the Reinhard algorithm, using luminance.
The function includes conversion to sRGB colorspace.
Reinhard, Erik & Stark, Michael & Shirley, Peter & Ferwerda, James. (2002). Photographic Tone Reproduction For Digital Images. ACM Transactions on Graphics. :doi: 21. 10.1145/566654.566575
lookup
colorize
The colorize enhancement can be used to map scaled/calibrated physical values to colors. One or several standard Trollimage color maps may be used as in the example here:
- name: colorize
method: !!python/name:satpy.enhancements.colorize
kwargs:
palettes:
- {colors: spectral, min_value: 193.15, max_value: 253.149999}
- {colors: greys, min_value: 253.15, max_value: 303.15}
It is also possible to provide your own custom defined color mapping by specifying a list of RGB values and the corresponding min and max values between which to apply the colors. This is for instance a common use case for Sea Surface Temperature (SST) imagery, as in this example with the EUMETSAT Ocean and Sea Ice SAF (OSISAF) GHRSST product:
- name: osisaf_sst
method: !!python/name:satpy.enhancements.colorize
kwargs:
palettes:
- colors: [
[255, 0, 255],
[195, 0, 129],
[129, 0, 47],
[195, 0, 0],
[255, 0, 0],
[236, 43, 0],
[217, 86, 0],
[200, 128, 0],
[211, 154, 13],
[222, 180, 26],
[233, 206, 39],
[244, 232, 52],
[255.99609375, 255.99609375, 63.22265625],
[203.125, 255.99609375, 52.734375],
[136.71875, 255.99609375, 27.34375],
[0, 255.99609375, 0],
[0, 207.47265625, 0],
[0, 158.94921875, 0],
[0, 110.42578125, 0],
[0, 82.8203125, 63.99609375],
[0, 55.21484375, 127.9921875],
[0, 27.609375, 191.98828125],
[0, 0, 255.99609375],
[100.390625, 100.390625, 255.99609375],
[150.5859375, 150.5859375, 255.99609375]]
min_value: 296.55
max_value: 273.55
The RGB color values will be interpolated to give a smooth result. This is contrary to using the palettize enhancement.
The above examples are just two different ways to apply colors to images with
Satpy. There is a wealth of other options for how to declare a colormap, please
see create_colormap() for more inspiration.
palettize
three_d_effect
The three_d_effect enhancement adds an 3D look to an image by convolving with a 3x3 kernel. User can adjust the strength of the effect by determining the weight (default: 1.0). Example:
- name: 3d_effect
method: !!python/name:satpy.enhancements.three_d_effect
kwargs:
weight: 1.0