Source code for photutils.utils.colormaps

# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""
This module provides tools for generating matplotlib colormaps.
"""

import numpy as np

__all__ = ['make_random_cmap']




def make_random_cmap(ncolors=256, seed=None):
    """
    Make a matplotlib colormap consisting of (random) muted colors.

    A random colormap is very useful for plotting segmentation images.

    Parameters
    ----------
    ncolors : int, optional
        The number of colors in the colormap.  The default is 256.

    seed : int, optional
        A seed to initialize the `numpy.random.BitGenerator`. If `None`,
        then fresh, unpredictable entropy will be pulled from the OS.
        Separate function calls with the same ``seed`` will generate the
        same colormap.

    Returns
    -------
    cmap : `matplotlib.colors.ListedColormap`
        The matplotlib colormap with random colors in RGBA format.
    """
    from matplotlib import colors

    rng = np.random.default_rng(seed)
    hue = rng.uniform(low=0.0, high=1.0, size=ncolors)
    sat = rng.uniform(low=0.2, high=0.7, size=ncolors)
    val = rng.uniform(low=0.5, high=1.0, size=ncolors)
    hsv = np.dstack((hue, sat, val))
    rgb = np.squeeze(colors.hsv_to_rgb(hsv))

    return colors.ListedColormap(colors.to_rgba_array(rgb))