Pixelated fonts when plot saved as jpeg #5302

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1. tacaswell commented on Oct 24, 2015

   

   tacaswell

   on Oct 24, 2015

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   Odd that it only hits the tick labels, but not the other text.

   Can you please move the images and example code over here? I do not trust SO long-term.
2. cbreeden commented on Oct 25, 2015

   

   cbreeden

   on Oct 25, 2015

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   Here is code to reproduce the pixelated fonts when saving a figure as a jpeg (when using jupyter):

   %matplotlib nbagg
   
   import matplotlib.pyplot as plt
   import numpy as np
   
   x    = np.linspace(-1.2,1.2,1000,endpoint=True)
   y    = np.copy(x)
   x,y  = np.meshgrid(x,y)
   z    = -x**2 + y**2 - y**3
   
   fig = plt.figure()
   ax  = fig.add_subplot(111)
   
   CS = plt.contour(x,y,z, [0,-0.1,0.1], colors=['black','blue', 'gray'])
   plt.clabel(CS, fontsize=14, inline=1, fmt='%1.1f', manual=[(-0.15,0), (-0.4,0), (0.25,0.5)])
   
   plt.title('Contour Sets')
   
   plt.savefig('plot.png', format='png')
   plt.savefig('plot.jpg', format='jpg')
   

   This produces a plot.png shown here:

   

   and plot.jpg shown here:

   

   Adding the following code will "fix" this issue and produce jpegs that look nearly identical to the png files (with the undesirable side-effect of have non-transparent figures rendered in your jupyter notebooks):

   import matplotlib
   matplotlib.rcParams['nbagg.transparent'] = False
   

   Another example for how PIL handles these transparent regions while trying to encode the raw data into jpeg is given by taking the first example and adding the code:

   import matplotlib
   matplotlib.rcParams['savefig.transparent'] = True
   

   plot.jpg in this case looks like this:

   

   I'm not exactly sure if this problem should be handled by the PIL team of the matplotlib team, but it might be worth looking into adding code to remove transparent regions when trying to save figures to file formats that can't handle transparency. I don't think it would be a difficult issue to fix, and might be able to write up a pull request for a suggested solution at some point in time.

   This issue also seems to surface when trying to create animations.
3. mdboom

   self-assigned this

   on Oct 26, 2015
4. mdboom

   added a commit that references this issue on Oct 26, 2015

   Fix matplotlib#5302: Proper alpha-blending for jpeg

   This issue will close once commit bdea63d is merged into the 'master' branch.

   bdea63d
5. mdboom

   added

   status: needs review

   on Oct 26, 2015
6. mdboom

   closed this as completedin bdea63don Oct 28, 2015
7. tacaswell

   added a commit that references this issue on Oct 28, 2015

   Merge pull request #5324 from mdboom/transparent-jpg

   ...

   This issue will close once commit b9957b1 is merged into the 'main' branch.

   b9957b1
8. mdboom

   removed

   status: needs review

   on Oct 28, 2015
9. QuLogic

   added a commit that references this issue on Oct 16, 2016

   Merge pull request matplotlib#5324 from mdboom/transparent-jpg

   ...

   This issue will close once commit 1e437d3 is merged into the 'main' branch.

   1e437d3