xlandsat.equalize_histogram

xlandsat.equalize_histogram(composite, kernel_size=None, clip_limit=0.01)

Adaptive histogram equalization for a composite

Use this function to enhance the contrast of a composite when there are a few very dark or very light patches that dominate the color range. Use this instead of rescaling intensity (contrast stretching) to try to preserve some detail in the light/dark patches.

If the composite has an alpha channel (transparency), it will be copied to the output intact.

Warning

Results can be very bad if there are missing values (NaNs) in the composite. Use xlandsat.interpolate_missing on the scene first (before creating the composite) if that is the case.

Parameters:

• composite (xarray.DataArray) – A composite, as generated by xlandsat.composite.

• kernel_size (int or None) – The size of region used in the algorithm. See skimage.exposure.equalize_adapthist for details and defaults.

• clip_limit (float) – Clipping limit, normalized between 0 and 1 (higher values give more contrast).

Returns:

equalized_composite (xarray.DataArray) – The composite after equalization, scaled back to the range of the original composite.

Notes

This function first converts the composite from the RGB color space to the HSV color space. Then, it applies skimage.exposure.equalize_adapthist to the values (intensity) channel. Finally, the composite is converted back into the RGB color space.