在 matplotlib 中创建自定义颜色条

Question

如何在 matplotlib 中创建如下所示的颜色条：

这是我尝试过的：

import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
from matplotlib.cm import ScalarMappable
from matplotlib.colors import Normalize

# Define the custom colormap
colors = ['red', 'cyan', 'darkgreen']
cmap = LinearSegmentedColormap.from_list(
    'custom_colormap', 
    [(0.0, colors[0]), (0.5 / 2.0, colors[0]),
     (0.5 / 2.0, colors[1]), (1.5 / 2.0, colors[1]),
     (1.5 / 2.0, colors[2]), (2.0 / 2.0, colors[2])]
)

# Create a scalar mappable object with the colormap
sm = ScalarMappable(norm=Normalize(vmin=3.5, vmax=4.5), cmap=cmap)

# Create the colorbar
plt.figure(figsize=(3, 1))
cb = plt.colorbar(sm, orientation='horizontal', ticks=[3.5, 4.5], extend='neither')
cb.set_label('')

Answer 1

使用 ListedColorMap 会生成一个类似于您在图片中呈现的颜色条：

from matplotlib.cm import ScalarMappable
from matplotlib.colors import ListedColormap, Normalize
import matplotlib.pyplot as plt
import matplotlib as mpl

fig, ax = plt.subplots(figsize=(6, 1), layout='constrained')
cmap = ListedColormap(["red", "cyan", "slategrey"])
norm = mpl.colors.Normalize(vmin=5, vmax=10)
sm = ScalarMappable(norm=Normalize(2.5,5.5), cmap=cmap)
fig.colorbar(sm, cmap=cmap, ticks=[3.5, 4.5], cax=ax, 
orientation='horizontal', label='Colorbar')
plt.show()
cb = plt.colorbar(sm, cmap=cmap, ticks=[3.5, 4.5], cax=ax, 
orientation='horizontal', label='Colorbar')

这是你想要的样子吗？

Answer 2

一种解决方案是在颜色段周围绘制宽的白色边缘（使用下面的

cb.solids.set

），隐藏书脊（

cb.outline.set_visible

）并绘制垂直线作为分隔线（

cb.ax.axvline

）。要匹配所需的颜色条，请确保传递大于 0 的

ymin

。

import matplotlib.pyplot as plt
from matplotlib.colors import ListedColormap, Normalize
from matplotlib.cm import ScalarMappable

fig, ax = plt.subplots(figsize=(3, 0.5))

colors = ['red', 'cyan', 'darkgreen']
cmap = ListedColormap(colors)
norm = Normalize(vmin=2.5, vmax=5.5)
cb = fig.colorbar(
    mappable=ScalarMappable(norm=norm, cmap=cmap),
    cax=ax,
    ticks=[3.5, 4.5],
    ticklocation='top',
    orientation='horizontal',
)
cb.solids.set(edgecolor='white', linewidth=5)
cb.outline.set_visible(False)
cb.ax.tick_params(width=1, length=10, color='k')
for bound in [3.5, 4.5]:
    cb.ax.axvline(bound, c='k', linewidth=1, ymin=0.3, alpha=0.6)
plt.setp(cb.ax.xaxis.get_ticklines(), alpha=0.6)
cb.set_ticklabels([3.5, 4.5], alpha=0.6, color='k', fontsize=15, fontfamily='Arial')

另一种解决方案是不绘制垂直线作为分隔线（通过

drawedges=True

），只需使用颜色条对象本身定义的分隔线。然而，最终结果会与期望的结果略有不同，因为分隔线是从下到上绘制的（无法像上面那样通过

ymin

）。

fig, ax = plt.subplots(figsize=(3, 0.5))

colors = ['red', 'cyan', 'darkgreen']
cmap = ListedColormap(colors)
norm = Normalize(vmin=2.5, vmax=5.5)
cb = fig.colorbar(
    mappable=ScalarMappable(norm=norm, cmap=cmap),
    cax=ax,
    ticks=[3.5, 4.5],
    ticklocation='top',
    orientation='horizontal',
    drawedges=True
)
cb.solids.set(edgecolor='white', linewidth=5)
cb.outline.set_visible(False)
cb.dividers.set(linewidth=1, alpha=0.6)
cb.ax.tick_params(width=1, length=10, color='k')
plt.setp(cb.ax.xaxis.get_ticklines(), alpha=0.6)
cb.set_ticklabels([3.5, 4.5], alpha=0.6, color='k', fontsize=15, fontfamily='Arial')