python - How to make pylab.savefig() save image for 'maximized' window instead of default size

Question

I am using pylab in matplotlib to create a plot and save the plot to an image file. However, when I save the image using pylab.savefig( image_name ), I find that the SIZE image saved is the same as the image that is shown when I use pylab.show().

As it happens, I have a lot of data in the plot and when I am using pylab.show(), I have to maximize the window before I can see all of the plot correctly, and the xlabel tickers don't superimpose on each other.

Is there anyway that I can programmatically 'maximize' the window before saving the image to file? - at the moment, I am only getting the 'default' window size image, which results in the x axis labels being superimposed on one another.

Answer 1

There are two major options in matplotlib (pylab) to control the image size:

1. You can set the size of the resulting image in inches
2. You can define the DPI (dots per inch) for output file (basically, it is a resolution)

Normally, you would like to do both, because this way you will have full control over the resulting image size in pixels. For example, if you want to render exactly 800x600 image, you can use DPI=100, and set the size as 8 x 6 in inches:

import matplotlib.pyplot as plt
# plot whatever you need...
# now, before saving to file:
figure = plt.gcf() # get current figure
figure.set_size_inches(8, 6)
# when saving, specify the DPI
plt.savefig("myplot.png", dpi = 100)

One can use any DPI. In fact, you might want to play with various DPI and size values to get the result you like the most. Beware, however, that using very small DPI is not a good idea, because matplotlib may not find a good font to render legend and other text. For example, you cannot set the DPI=1, because there are no fonts with characters rendered with 1 pixel :)

From other comments I understood that other issue you have is proper text rendering. For this, you can also change the font size. For example, you may use 6 pixels per character, instead of 12 pixels per character used by default (effectively, making all text twice smaller).

import matplotlib
#...
matplotlib.rc('font', size=6)

Finally, some references to the original documentation: http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.savefig, http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.gcf, http://matplotlib.sourceforge.net/api/figure_api.html#matplotlib.figure.Figure.set_size_inches, http://matplotlib.sourceforge.net/users/customizing.html#dynamic-rc-settings

P.S. Sorry, I didn't use pylab, but as far as I'm aware, all the code above will work same way in pylab - just replace plt in my code with the pylab (or whatever name you assigned when importing pylab). Same for matplotlib - use pylab instead.