Minor ticks in matplotlib's colorbar

matplotlib, python

Solution

You're on the right track, you just need `cb.ax.minorticks_on()`.

For example:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LogNorm

# fill grid
x = np.linspace(1,10,10)
y = np.linspace(1,10,10)

X, Y = np.meshgrid(x,y)
Z = np.abs(np.cos(X**2 - Y**2) * X**2 * Y)

# plot
f, ax = plt.subplots()
p = plt.pcolormesh(X, Y, Z, norm=LogNorm(), vmin=1e-2, vmax=1e2)
cb = plt.colorbar(p, ax=ax, orientation='horizontal', aspect=10)

cb.ax.minorticks_on()

plt.show()

If you want just the ticks that you specify, you still set them in the "normal" way, but be aware that the colorbar axes coordinate system ranges from 0-1 regardless of the range of your data.

For that reason, to set the specific values that you want, we need to call the normalize the tick locations using the same `norm` instance that the image is using.

For example:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LogNorm

# fill grid
x = np.linspace(1,10,10)
y = np.linspace(1,10,10)

X, Y = np.meshgrid(x,y)
Z = np.abs(np.cos(X**2 - Y**2) * X**2 * Y)

# plot
f, ax = plt.subplots()
p = plt.pcolormesh(X, Y, Z, norm=LogNorm(), vmin=1e-2, vmax=1e2)
cb = plt.colorbar(p, ax=ax, orientation='horizontal', aspect=10)

# We need to nomalize the tick locations so that they're in the range from 0-1...
minorticks = p.norm(np.arange(1, 10, 2))
cb.ax.xaxis.set_ticks(minorticks, minor=True)

plt.show()

Problem

I'm currently trying to set minor ticks in the colorbar but simply can't make it work. There are 3 approaches which I've tried (see code below), but all of them didn't appear to be working. Is it actually possible to have minor ticks in the colorbar? ``` import numpy as np import matplotlib.pyplot as plt from matplotlib.colors import LogNorm from matplotlib.ticker import FixedLocator, FormatStrFormatter # fill grid x = np.linspace(1,10,10) y = np.linspace(1,10,10) X, Y = np.meshgrid(x,y) Z = np.abs(np.cos(X**2 - Y**2) * X**2 * Y) # plot f, ax = subplots(1) p = plt.pcolormesh(X, Y, Z, norm=LogNorm(), vmin=1e-2, vmax=1e2) cb = plt.colorbar(p, ax=ax, orientation='horizontal', aspect=10) minor_ticks = np.arange(1,10,2) #cb.set_ticks(minor_ticks, minor=True) # error: doesn't support keyword argument 'minor' #cb.ax.xaxis.set_ticks(minor_ticks, minor=True) # plots an extremely small colorbar, with wrong ticks #cb.ax.xaxis.set_minor_locator(FixedLocator(minor_ticks)) # nothing happens plt.show() ```

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