User Guide#

Accessing the colormaps#

After importing colorcet as cc, all the colormaps shown in this notebook will be available for use in different forms. It’s a bit difficult to describe, but the idea is that colorcet should have at least one such form convenient for any particular application. There are three distinct versions for each colormap, each of which consists of 256 distinct colors:

  1. An ordered list of normalized RGB triples of numerical magnitudes. I.e., each color is represented as a tuple of three numbers, each between 0 and 1.0, such as [1, 0.54028, 0.0002582]

  2. A Bokeh-style palette, i.e., a Python list of RGB colors as hex strings, like ['#000000', ..., '#ffffff']

  3. If matplotlib is installed and importable, a Matplotlib LinearSegmentedColormap (for continuous maps) or ListedColormap (for categorical maps), using normalized magnitudes, like LinearSegmentedColormap.from_list("fire",[ [0.0,0.0,0.0], ..., [1.0,1.0,1.0] ], 256)

The numerical lists are the original format, useful if you want to access the underlying numerical values. These are available as attributes in the colorcet namespace as full names with no prefix, e.g. cc.linear_kryw_0_100_c71 or cc.glasbey_bw.

The Bokeh-compatible hex-string palettes are provided as attributes in the colorcet namespace as long names prefixed with b_. E.g. linear_kryw_0_100_c71 can be accessed as cc.b_linear_kryw_0_100_c71. The same Bokeh palette is also sometimes available with a shorter name like cc.fire, which is the same object as cc.b_linear_kryw_0_100_c71. These names should tab complete once cc has been imported. Because Bokeh palettes are just Python lists, you can always reverse them using normal Python syntax, e.g. list(reversed(cc.fire)), or use subsets of them with slice notation, e.g. cc.fire[25:]. If you want to access the Bokeh palettes by string name, they are also collected into a dictionary named palette, so you can use cc.palette["linear_kryw_0_100_c71"] or cc.palette["fire"] or cc.palette.fire; whichever is more convenient. Finally, the subset of colormaps that have short, readable names are available separately, accessible as cc.palette_n.fire or cc.palette_n["fire"], e.g. for use in GUI widgets selecting a colormap by readable name.

The Matplotlib colormaps are also provided as tab-completable attributes, but consistently with a prefix m_, e.g. cc.m_linear_kryw_0_100_c71 or cc.m_fire. Already reversed versions are also available, as cc.m_linear_kryw_0_100_c71_r or cc.m_fire_r. The same colormaps are also registered with matplotlib’s string-based dictionary with the prefix cet_, making them available by name within various matplotlib functions (e.g. cet_linear_kryw_0_100_c71, cet_linear_kryw_0_100_c71_r, cet_fire, or cet_fire_r). Finally, if you want to access the Matplotlib colormaps by string name without using Matplotlib’s registry, they are also stored in the cc.cm dictionary, e.g. cc.cm["linear_kryw_0_100_c71"], cc.cm["linear_kryw_0_100_c71_r"], cc.cm["fire"], cc.cm.fire, cc.cm["fire_r"], or cc.cm.fire_r.

In each case, the colormap names used are the shortest ones that are expected to be unique in that context, and in practice you are only likely to need one of these forms for any particular application.

Example#

Here we show importing fire and printing the first 5 colors in the set.

import colorcet as cc

cc.fire[:5]

['#000000', '#060000', '#0d0000', '#120000', '#160000']

Plotting#

For ease of use, we also provide minimal plotting commands for use with colorcet. These depend on holoviews, which needs to be installed before they can be used. Once set up, these commands provide easy viewing capability of the colormaps.

Example#

Import swatch or swatches from colorcet.plotting and load your desired backend into holoviews. Then call swatch with the name of a colormap.

from colorcet.plotting import swatch, swatches
import holoviews as hv
hv.extension('matplotlib')

swatch('fire')

Using colorcet via matplotlib.cm.get_cmap#

The colorcet colormaps are all available through matplotlip.cm.get_cmap by prepending cet_to the colormap name.

from matplotlib.cm import get_cmap

get_cmap("cet_fire")

/tmp/ipykernel_2445/1693774644.py:3: MatplotlibDeprecationWarning: The get_cmap function was deprecated in Matplotlib 3.7 and will be removed two minor releases later. Use ``matplotlib.colormaps[name]`` or ``matplotlib.colormaps.get_cmap(obj)`` instead.
  get_cmap("cet_fire")
cet_fire
cet_fire colormap
under
bad
over

Using colorcet to visualize custom colormaps using swatch#

color_list = ['#000000', '#380000', '#560000', '#760100', '#980300', '#bb0600', '#df0d00', '#f93500', '#fe6800', '#ff9100', '#ffb402', '#ffd407', '#fff324']

swatch(name='custom', cmap=color_list)

Complete list#

The swatches command accepts the optional key word argument group to show just the colormaps whose names match the given string - try ‘glasbey’, ‘cyclic’, or ‘diverging’. When no arguments are provided, swatches returns all of the colorcet colormaps.

swatches()

For more explanation of the various options see categorical and continuous.