matplotlib savefig plots different from show

Question

When I use show   to plot the graphs in X  the graphs looks very good  However when I start to use savefig   to generate large amount of graphs  the savefig   generated graphs   font  lines  polygons all look smaller than the show   generated graph  My environment is Ubuntu and the backend for show   is Qt4Agg  How can I make the show   plot and the savefig   plot looks consistent

User · Answer

I have fixed this in my matplotlib source, but it's not a pretty fix. However, if you, like me, are very particular about how the graph looks, it's worth it.

The issue seems to be in the rendering backends; they each get the correct values for linewidth, font size, etc., but that comes out slightly larger when rendered as a PDF or PNG than when rendered with show().

I added a few lines to the source for PNG generation, in the file matplotlib/backends/backend_agg.py. You could make similar changes for each backend you use, or find a way to make a more clever change in a single location ;)

Added to my matplotlib/backends/backend_agg.py file:

    # The top of the file, added lines 42 - 44
42  # @warning: CHANGED FROM SOURCE to draw thinner lines
43  PATH_SCALAR = .8
44  FONT_SCALAR = .95

    # In the draw_markers method, added lines 90 - 91
89  def draw_markers(self, *kl, **kw):
90      # @warning: CHANGED FROM SOURCE to draw thinner lines
91      kl[0].set_linewidth(kl[0].get_linewidth()*PATH_SCALAR)
92      return self._renderer.draw_markers(*kl, **kw)

    # At the bottom of the draw_path method, added lines 131 - 132:
130 else:
131     # @warning: CHANGED FROM SOURCE to draw thinner lines
132     gc.set_linewidth(gc.get_linewidth()*PATH_SCALAR)
133     self._renderer.draw_path(gc, path, transform, rgbFace)

    # At the bottom of the _get_agg_font method, added line 242 and the *FONT_SCALAR
241     font.clear()
242     # @warning: CHANGED FROM SOURCE to draw thinner lines
243     size = prop.get_size_in_points()*FONT_SCALAR
244     font.set_size(size, self.dpi)

So that suits my needs for now, but, depending on what you're doing, you may want to implement similar changes in other methods. Or find a better way to do the same without so many line changes!

Update: After posting an issue to the matplotlib project at Github, I was able to track down the source of my problem: I had changed the figure.dpi setting in the matplotlibrc file. If that value is different than the default, my savefig() images come out different, even if I set the savefig dpi to be the same as the figure dpi. So, instead of changing the source as above, I just kept the figure.dpi setting as the default 80, and was able to generate images with savefig() that looked like images from show().

Leon, had you also changed that setting?

User · Answer

Old question  but apparently Google likes it so I thought I put an answer down here after some research about this problem   If you create a figure from scratch you can give it a size option while creation   import matplotlib pyplot as plt  fig   plt figure figsize  3  6    plt plot range 10    plot example plt show    for control  fig savefig  temp png   dpi fig dpi    figsize width height  adjusts the absolute dimension of your plot and helps to make sure both plots look the same   As stated in another answer the dpi option affects the relative size of the text and width of the stroke on lines  etc  Using the option dpi fig dpi makes sure the relative size of those are the same both for show   and savefig     Alternatively the figure size can be changed after creation with   fig set size inches 3  6  forward True    forward allows to change the size on the fly   If you have trouble with too large borders in the created image you can adjust those either with   plt tight layout    or  plt tight layout pad 2    or   fig savefig  temp png   dpi fig dpi  bbox inches  tight    or  fig savefig  temp png   dpi fig dpi  bbox inches  tight   pad inches 0 5    The first option just minimizes the layout and borders and the second option allows to manually adjust the borders a bit  These tips helped at least me to solve my problem of different savefig   and show   images

User · Answer

You render your matplotlib plots to different devices  e g   on-screen via Quartz versus to to-file via pdf using different functions  plot versus savefig  whose parameters are nearly the same  yet the default values for those parameters are not the same for both functions   Put another way  the savefig default parameters are different from the default display parameters    Aligning them is simple if you do it in the matplotlib config file  The template file is included with the source package  and named matplotlibrc template  If you did not create one when you installed matplotlib  you can get this template from the matplotlib source  or from the matplotlib website   Once you have customized this file the way you want  rename it to matplotlibrc  no extension  and save it to the directory  matplotlib  note the leading      which should be  in your home directory   The config parameters for saving figures begins at about line 314 in the supplied matplotlibrc template  first line before this section is      SAVING FIGURES    In particular  you will want to look at these   savefig dpi         100           figure dots per inch savefig facecolor   white         figure facecolor when saving savefig edgecolor   white         figure edgecolor when saving savefig extension   auto          what extension to use for savefig  foo    or  auto    Below these lines are the settings for font type and various image format-specific parameters    These same parameters for display  i e   PLT show    begin at about line 277 a in the matplotlibrc template  this section preceded with the line      FIGURE    figure figsize     8  6           figure dpi         80             figure facecolor   0 75        figure edgecolor   white        As you can see by comparing the values of these two blocks of parameters  the default settings for the same figure attribute are different for savefig versus display  show

User · Answer

savefig specifies the DPI for the saved figure  The default is 100 if it s not specified in your  matplotlibrc  have a look at the dpi kwarg to savefig    It doesn t inheret it from the DPI of the original figure   The DPI affects the relative size of the text and width of the stroke on lines  etc   If you want things to look identical  then pass fig dpi to fig savefig   E g   import matplotlib pyplot as plt  fig   plt figure   plt plot range 10   fig savefig  temp png   dpi fig dpi

[python] matplotlib savefig() plots different from show()

Examples related to python

Examples related to graph

Examples related to plot

Examples related to matplotlib