satpy.enhancements.contrast module

Stretching.

satpy.enhancements.contrast._bt_threshold(band_data, threshold, high_coeffs, low_coeffs)

satpy.enhancements.contrast._cira_stretch(band_data)

satpy.enhancements.contrast._compute_luminance_from_rgb(r, g, b)

Compute the luminance of the image.

satpy.enhancements.contrast._piecewise_linear(band_data, xp, fp)

satpy.enhancements.contrast._srgb_gamma(arr)

Apply the srgb gamma.

satpy.enhancements.contrast.btemp_threshold(img, min_in, max_in, threshold, threshold_out=None, **kwargs)

Scale data linearly in two separate regions.

This enhancement scales the input data linearly by splitting the data into two regions; min_in to threshold and threshold to max_in. These regions are mapped to 1 to threshold_out and threshold_out to 0 respectively, resulting in the data being “flipped” around the threshold. A default threshold_out is set to 176.0 / 255.0 to match the behavior of the US National Weather Service’s forecasting tool called AWIPS.

Parameters:

• img (trollimage.xrimage.XRImage) – Image object to be scaled

• min_in (float) – Minimum input value to scale

• max_in (float) – Maximum input value to scale

• threshold (float) – Input value where to split data in to two regions

• threshold_out (float) – Output value to map the input threshold to. Optional, defaults to 176.0 / 255.0.

satpy.enhancements.contrast.cira_stretch(img, **kwargs)

Logarithmic stretch adapted to human vision.

Applicable only for visible channels.

satpy.enhancements.contrast.gamma(img, **kwargs)

Perform gamma correction.

satpy.enhancements.contrast.invert(img, *args)

Perform inversion.

satpy.enhancements.contrast.piecewise_linear_stretch(img, xp, fp, reference_scale_factor=None, **kwargs)

Apply 1D linear interpolation.

This uses numpy.interp() mapped over the provided dask array chunks.

Parameters:

• img (XRImage) – Image data to be scaled. It is assumed the data is already normalized between 0 and 1.

• xp (numpy.typing.ArrayLike) – Input reference values of the image data points used for interpolation. This is passed directly to numpy.interp().

• fp (numpy.typing.ArrayLike) – Target reference values of the output image data points used for interpolation. This is passed directly to numpy.interp().

• reference_scale_factor (Optional[Number]) – Divide xp and fp by this value before using them for interpolation. This is a convenience to make matching normalized image data to interp coordinates or to avoid floating point precision errors in YAML configuration files. If not provided, xp and fp will not be modified.

Return type:

DataArray

Examples

This example YAML uses a ‘crude’ stretch to pre-scale the RGB data and then uses reference points in a 0-255 range.

true_color_linear_interpolation:
  sensor: abi
  standard_name: true_color
  operations:
  - name: reflectance_range
    method: !!python/name:satpy.enhancements.stretching.stretch
    kwargs: {stretch: 'crude', min_stretch: 0., max_stretch: 100.}
  - name: Linear interpolation
    method: !!python/name:satpy.enhancements.stretching.piecewise_linear_stretch
    kwargs:
     xp: [0., 25., 55., 100., 255.]
     fp: [0., 90., 140., 175., 255.]
     reference_scale_factor: 255

This example YAML does the same as the above on the C02 channel, but the interpolation reference points are already adjusted for the input reflectance (%) data and the output range (0 to 1).

c02_linear_interpolation:
  sensor: abi
  standard_name: C02
  operations:
  - name: Linear interpolation
    method: !!python/name:satpy.enhancements.stretching.piecewise_linear_stretch
    kwargs:
     xp: [0., 9.8039, 21.5686, 39.2157, 100.]
     fp: [0., 0.3529, 0.5490, 0.6863, 1.0]

satpy.enhancements.contrast.reinhard_to_srgb(img, saturation=1.25, white=100, **kwargs)

Stretch method based on the Reinhard algorithm, using luminance.

Parameters:

• saturation – Saturation enhancement factor. Less is grayer. Neutral is 1.

• white – the reflectance luminance to set to white (in %).

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

satpy.enhancements.contrast.stretch(img, **kwargs)

Perform stretch.