Get legend as a separate picture in Matplotlib

Question

I\'m developing a Web application and want to display a figure and its legend in different locations on the page. Which means I need to save the legend as a separate png fil

Answer 1

This calculates the size of the legend automatically. If mode == 1, the code is similar to Steve Tjoa's answer, while mode == 2 is similar Andre Holzner's answer.

The loc parameter must be set to 'center' to make it work (but I do not know why this is necessary).

mode = 1
#mode = 2

import pylab
fig = pylab.figure()
if mode == 1:
    lines = fig.gca().plot(range(10), pylab.randn(10), range(10), pylab.randn(10))
    legend_fig = pylab.figure(figsize=(3,2))
    legend = legend_fig.legend(lines, ('one', 'two'), 'center')
if mode == 2:
    fig.gca().plot(range(10), pylab.randn(10), range(10), pylab.randn(10), label='asd')
    legend_fig = pylab.figure()
    legend = pylab.figlegend(*fig.gca().get_legend_handles_labels(), loc = 'center')
legend.get_frame().set_color('0.70')
legend_fig.canvas.draw()
legend_fig.savefig('legend_cropped.png',
    bbox_inches=legend.get_window_extent().transformed(legend_fig.dpi_scale_trans.inverted()))
legend_fig.savefig('legend_original.png')

Original (uncropped) legend:

Cropped legend:

Answer 2

use pylab.figlegend(..) and get_legend_handles_labels(..):

import pylab, numpy 
x = numpy.arange(10)

# create a figure for the data
figData = pylab.figure()
ax = pylab.gca()

for i in xrange(3):
    pylab.plot(x, x * (i+1), label='line %d' % i)

# create a second figure for the legend
figLegend = pylab.figure(figsize = (1.5,1.3))

# produce a legend for the objects in the other figure
pylab.figlegend(*ax.get_legend_handles_labels(), loc = 'upper left')

# save the two figures to files
figData.savefig("plot.png")
figLegend.savefig("legend.png")

It can be tricky though to get the size of the legend figure right in an automated manner.

Answer 3

It is possible to use axes.get_legend_handles_labels to get the legend handles and labels from one axes object and to use them to add them to an axes in a different figure.

# create a figure with one subplot
fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot([1,2,3,4,5], [1,2,3,4,5], 'r', label='test')
# save it *without* adding a legend
fig.savefig('image.png')

# then create a new image
# adjust the figure size as necessary
figsize = (3, 3)
fig_leg = plt.figure(figsize=figsize)
ax_leg = fig_leg.add_subplot(111)
# add the legend from the previous axes
ax_leg.legend(*ax.get_legend_handles_labels(), loc='center')
# hide the axes frame and the x/y labels
ax_leg.axis('off')
fig_leg.savefig('legend.png')

If for some reason you want to hide only the axes label, you can use:

ax.xaxis.set_visible(False)
ax.yaxis.set_visible(False)

or if, for some weirder reason, you want to hide the axes frame but not the axes labels you can use:

ax.set_frame_on(False)

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ps: this answer has been adapted from my answer to a duplicate question