Colormaps are palettes constructed by sampling some continuous function between two end colors. Colormaps are generally used to encode data values on a pseudo-third dimension. They are are implemented with the LinearSegmentedColormap and PerceptuallyUniformColormap classes, which are subclassed from LinearSegmentedColormap in matplotlib (see Making new colormaps).

ProPlot adds several features to help you use colormaps effectively in your figures. This section documents the new registered colormaps, explains how to make and modify colormaps, and shows how to apply them to your plots.

Included colormaps

On import, ProPlot registers a few sample PerceptuallyUniformColormap colormaps (see Perceptually uniform colormaps) plus a ton of other colormaps from other online data viz projects. Use show_cmaps to generate a table of registered maps. The figure is broken down into the following sections:

  • “User” colormaps, i.e. colormaps saved to your ~/.proplot/cmaps folder. A great way to save colormaps to this folder is using the Colormap function. See Making new colormaps for details.

  • Matplotlib and seaborn original colormaps.

  • ProPlot original Perceptually uniform colormaps.

  • Miscellaneous diverging colormaps.

  • cmOcean colormaps designed for oceanographic data but useful for all scientific fields.

  • ColorBrewer colormaps included with matplotlib by default.

  • Colormaps from the SciVisColor online interactive tool. There are so many of these maps because they are intended to be merged with one another.

ProPlot removes some default matplotlib colormaps with erratic color transitions. Note that colormap and color cycle identification is now flexible: Colormap names are case-insensitive (e.g. 'Viridis', 'viridis', and 'ViRiDiS' are equivalent), diverging colormap names can be specified in their “reversed” form (e.g. 'BuRd' is equivalent to 'RdBu_r'), and appending '_r' or '_shifted' to any colormap name will return the result of cmap.reversed() or cmap.shifted(180). See CmapDict for more info.

import proplot as plot
f = plot.show_cmaps()
/home/docs/checkouts/ ProPlotWarning: Rebuilding font cache.

Perceptually uniform colormaps

ProPlot’s custom colormaps are instances of the PerceptuallyUniformColormap class. These colormaps generate colors by interpolating between coordinates in any of the following three colorspaces:

  • HCL (a.k.a. CIELUV LCh): A purely perceptually uniform colorspace, where colors are broken down into “hue” (color, range 0-360), “chroma” (saturation, range 0-100), and “luminance” (brightness, range 0-100). This space is difficult to work with due to impossible colors – colors that, when translated back from HCL to RGB, result in RGB channels greater than 1.

  • HPL (a.k.a. HPLuv): Hue and luminance are identical to HCL, but 100 saturation is set to the minimum maximum saturation across all hues for a given luminance. HPL restricts you to soft pastel colors, but is closer to HCL in terms of uniformity.

  • HSL (a.k.a. HSLuv): Hue and luminance are identical to HCL, but 100 saturation is set to the maximum saturation for a given hue and luminance. HSL gives you access to the entire RGB colorspace, but often results in sharp jumps in chroma.

The colorspace used by each PerceptuallyUniformColormap is set with the space keyword arg. To plot arbitrary cross-sections of these colorspaces, use show_colorspaces (the black regions represent impossible colors). To see how colormaps vary with respect to each channel, use show_channels. Some examples are shown below.

In theory, “uniform” colormaps should have straight lines in hue, chroma, and luminance (bottom figure; top row) – but in practice, this is difficult to accomplish due to impossible colors. Matplotlib and seaborn’s 'magma' and 'Rocket' colormaps are fairly linear with respect to hue and luminance, but not chroma. ProPlot’s 'Fire' is linear in hue, luminance, and HSL saturation (bottom left), while 'Dusk' is linear in hue, luminance, and HPL saturation (bottom left).

import proplot as plot
f = plot.show_colorspaces(axwidth=1.6, luminance=50)
f = plot.show_colorspaces(axwidth=1.6, saturation=60)
f = plot.show_colorspaces(axwidth=1.6, hue=0)
f = plot.show_channels(
    'magma', 'rocket', 'fire', 'dusk',
    axwidth=1.4, minhue=-180, maxsat=300, rgb=False

Making new colormaps

ProPlot doesn’t just include new colormaps – it provides tools for merging colormaps, modifying colormaps, making Perceptually uniform colormaps from scratch, and saving the results for future use. For your convenience, most of these features can be accessed via the Colormap constructor function. Note that every plotting command that accepts a cmap keyword passes it through this function (see cmap_changer).

To make PerceptuallyUniformColormaps from scratch, you have the following three options:

  • Pass a color name, hex string, or RGB tuple to Colormap. This builds a monochromatic (single hue) colormap by calling the from_color static method. The colormap colors will vary from the specified color to pure white or some shade near white (see the fade keyword arg).

  • Pass a list of colors to Colormap. This calls the from_list static method, which linearly interpolates between each color in hue, saturation, and luminance.

  • Pass a dictionary to Colormap. This calls the from_hsl static method, which draws lines between channel values specified by the keyword args hue, saturation, and luminance. The values can be numbers, color strings, or lists thereof. Numbers indicate the channel value. For color strings, the channel value is inferred from the specified color. You can end any color string with '+N' or '-N' to offset the channel value by the number N.

Below, we use all of these methods to make brand new PerceptuallyUniformColormaps in the 'hsl' and 'hpl' colorspaces.

import proplot as plot
import numpy as np
state = np.random.RandomState(51423)
f, axs = plot.subplots(
    [[0, 1, 1, 2, 2, 0], [3, 3, 4, 4, 5, 5]],
    ncols=2, axwidth=2, aspect=1

# Monochromatic colormaps
    xlabel='x axis', ylabel='y axis', span=False,
    suptitle='Building your own PerceptuallyUniformColormaps'
data = state.rand(30, 30).cumsum(axis=1)
axs[0].format(title='From single color')
m = axs[0].contourf(data, cmap='ocean blue', cmap_kw={'name': 'water'})
cmap1 = m.cmap
axs[1].format(title='From three colors')
cmap2 = plot.Colormap(
    'brick red_r', 'denim_r', 'warm gray_r',
    fade=90, name='tricolor'
axs[1].contourf(data, cmap=cmap2, levels=12)

# Colormaps from channel value dictionaries
axs[2:4].format(title='From channel values')
cmap3 = plot.Colormap({
    'hue': ['red-90', 'red+90'],
    'saturation': [50, 70, 30],
    'luminance': [20, 100]
}, name='Matter', space='hcl')
axs[2].pcolormesh(data, cmap=cmap3)
cmap4 = plot.Colormap({
    'hue': ['red', 'red-720'],
    'saturation': [80, 20],
    'luminance': [20, 100]
}, name='cubehelix', space='hpl')
axs[3].pcolormesh(data, cmap=cmap4)

# Colormap from lists
m = axs[4].pcolormesh(
    data, cmap=('maroon', 'desert sand'),
    cmap_kw={'name': 'reddish'}
cmap5 = m.cmap
axs[4].format(title='From list of colors')

# Test the channels
f = plot.show_channels(cmap1, cmap2, axwidth=1.4, rgb=False)
f = plot.show_channels(
    cmap3, cmap4, cmap5, minhue=-180,
    axwidth=1.4, rgb=False

Merging colormaps

To merge colormaps, simply pass multiple positional arguments to the Colormap constructor. Each positional argument can be a colormap name, a colormap instance, or one of the argument types described in Making new colormaps. This lets you create new diverging colormaps and segmented SciVisColor-style colormaps right inside ProPlot. Segmented colormaps are often desirable for complex datasets with complex statistical distributions.

In the below example, we create a new divering colormap and reconstruct the colormap from this SciVisColor example. We also save the results for future use by passing save=True to Colormap.

import proplot as plot
import numpy as np
f, axs = plot.subplots([[0, 1, 1, 0], [2, 2, 3, 3]], axwidth=2, span=False)
state = np.random.RandomState(51423)
data = state.rand(30, 30).cumsum(axis=1)

# Diverging colormap example
title1 = 'Custom diverging map'
cmap1 = plot.Colormap('Blue4_r', 'RedPurple3', name='Diverging', save=True)

# SciVisColor examples
title2 = 'Custom complex map'
cmap2 = plot.Colormap(
    'Green1_r', 'Orange5', 'Blue1_r', 'Blue6',
    name='Complex', save=True
title3 = 'SciVisColor example reproduction'
cmap3 = plot.Colormap(
    'Green1_r', 'Orange5', 'Blue1_r', 'Blue6',
    ratios=(1, 3, 5, 10), name='SciVisColor', save=True

# Plot examples
for ax, cmap, title in zip(axs, (cmap1, cmap2, cmap3), (title1, title2, title3)):
    func = (ax.pcolormesh if cmap is cmap1 else ax.contourf)
    m = func(data, cmap=cmap, levels=256)
    ax.colorbar(m, loc='b', locator='null',
    xlabel='xlabel', ylabel='ylabel',
    suptitle='Merging existing colormaps'
Saved colormap to '/home/docs/.proplot/cmaps/Diverging.json'.
Saved colormap to '/home/docs/.proplot/cmaps/Complex.json'.
Saved colormap to '/home/docs/.proplot/cmaps/SciVisColor.json'.

Modifying colormaps

ProPlot allows you to create modified versions of existing colormaps using the Colormap constructor and the new LinearSegmentedColormap and ListedColormap classes, which are used to replace the native matplotlib colormap classes. They can be modified in the following ways:

  • To remove colors from the left or right ends of a colormap, pass left or right to Colormap. This calls the truncated method, and can be useful when you want to use colormaps as Color cycles and need to remove the “white” part so that your lines stand out against the background.

  • To remove central colors from a diverging colormap, pass cut to Colormap. This calls the punched method, and can be used to create a sharper cutoff between negative and positive values. This should generally be used without a central level.

  • To rotate a cyclic colormap, pass shift to Colormap. This calls the shifted method. ProPlot ensures the colors at the ends of “shifted” colormaps are distinct so that levels never blur together.

  • To change the transparency of an entire colormap, pass alpha to Colormap. This calls the set_alpha method, and can be useful when layering filled contour or mesh elements.

  • To change the “gamma” of a PerceptuallyUniformColormap, pass gamma to Colormap. This calls the set_gamma method, and controls how the luminance and saturation channels vary between colormap segments. gamma > 1 emphasizes high luminance, low saturation colors, while gamma < 1 emphasizes low luminance, high saturation colors.

import proplot as plot
import numpy as np
f, axs = plot.subplots(
    [[1, 1, 2, 2, 3, 3], [0, 4, 4, 5, 5, 0], [0, 6, 6, 7, 7, 0]],
    axwidth=1.7, span=False
state = np.random.RandomState(51423)
data = state.rand(40, 40).cumsum(axis=0) - 12

# Cutting left and right
for ax, coord in zip(axs[:3], (None, 0.3, 0.7)):
    cmap = 'grays'
    if coord is None:
        title, cmap_kw = 'Original', {}
    elif coord < 0.5:
        title, cmap_kw = f'left={coord}', {'left': coord}
        title, cmap_kw = f'right={coord}', {'right': coord}
        data, cmap=cmap, cmap_kw=cmap_kw,
        colorbar='b', colorbar_kw={'locator': 'null'}
    ax.format(xlabel='x axis', ylabel='y axis', title=title)

# Cutting central colors
levels = plot.arange(-10, 10, 2)
for i, (ax, cut) in enumerate(zip(axs[3:], (None, None, 0.1, 0.2))):
    if i == 0:
        title = 'With central level'
        levels = plot.edges(plot.arange(-10, 10, 2))
        title = 'Without central level'
        levels = plot.arange(-10, 10, 2)
    if cut is not None:
        title = f'cut = {cut}'
    m = ax.contourf(
        data, cmap='Div', cmap_kw={'cut': cut},
         extend='both', levels=levels
        xlabel='x axis', ylabel='y axis', title=title,
        suptitle='Truncating sequential and diverging colormaps'
    ax.colorbar(m, loc='b', locator='null')

# Rotating cyclic
f, axs = plot.subplots(ncols=3, axwidth=1.7)
data = (state.rand(50, 50) - 0.48).cumsum(axis=1).cumsum(axis=0) - 50
for ax, shift in zip(axs, (0, 90, 180)):
    m = ax.contourf(data, cmap='twilight', cmap_kw={'shift': shift}, levels=12)
        xlabel='x axis', ylabel='y axis', title=f'shift = {shift}',
        suptitle='Rotating cyclic colormaps'
    ax.colorbar(m, loc='b', locator='null')

# Changing gamma
f, axs = plot.subplots(ncols=3, axwidth=1.7, aspect=1)
data = state.rand(10, 10).cumsum(axis=1)
for ax, gamma in zip(axs, (0.7, 1.0, 1.4)):
    cmap = plot.Colormap('boreal', name=str(gamma), gamma=gamma)
    m = ax.pcolormesh(data, cmap=cmap, levels=10, extend='both')
    ax.colorbar(m, loc='b', locator='none')
        title=f'gamma = {gamma}', xlabel='x axis', ylabel='y axis',
        suptitle='Changing the colormap gamma'

Downloading colormaps

There are plenty of online interactive tools for generating perceptually uniform colormaps, including HCLWizard, Chroma.js, SciVisColor, and HCL picker.

To add colormaps downloaded from any of these sources, save the colormap data to a file in your ~/.proplot/cmaps folder, then call register_cmaps. The file should be named name.ext, where name will be the registered colormap name. See register_cmaps for valid file extensions.