Reducing the size of pdf figure file in matplotlib

Question

In matplotlib, I am using LineCollection to draw and color the countries, where the boundaries of the counties are given. When I am saving the figure as a pdf file:

fig.savefig('filename.pdf',dpi=300)

the figure size are quite big. However, on saving them as png file:

fig.savefig('filename.png',dpi=300)

and then converting them to pdf using linux convert command the files are small. I tried reducing the dpi, however that do not change the pdf file size. Is there a way the figures can be saved directly as smaller-pdf files from matplotlib?

Answer 1

The PDF is larger, since it contains all the vector information. By saving a PNG, you produce a rasterized image. It seems that in your case, you can produce a smaller PDF by rasterizing the plot directly:

plt.plot(x, y, 'r-', rasterized=True)

Here, x, y are some plot coordinates. You basically have to use the additionally keyword argument raterized to achieve the effect.

Answer 2

I think using "rasterized = True" effectively saves the image similarly to png format. When you zoom in, you will see blurring pixels.

If you want the figures to be high quality, my suggestion is to sample from the data and make a plot. The pdf file size is roughly the amount of data points it need to remember.