Is there a simple way to plot an image in a notebook? I.e. the output of the imshow function in matplotlib...

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Anonymous

I have been wondering how to do something seemingly really simple, but seem to be missing something - sage allows users to do all kinds of fancy plotting in the notebook but I can't get it to display a 2d matrix as an image (matplotlib's imshow function).

I see that it is possible to call imshow and save the result to file, but I want to display the result in the notebook instead - did I miss something?

Cheers

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answered 13 years ago

kcrisman
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I've modified the examples you're alluding to in the Sage plotting reference, under "NUMERICAL PLOTTING" (caps in original).

from pylab import * 
imshow([[(0,0,0)]])
savefig('')

This works. Because I don't know much about how matplotlib works, unfortunately when I do another figure it just adds to this one (or if I do another one first, this adds to it). Hopefully someone else - or you - can answer that for me!

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And once that's resolved, we should probably add this to the doc, right?

kcrisman ( 13 years ago )

1

use clf() to "clear" the figure and stop adding to it.

Jason Grout ( 13 years ago )

Jason (G.), let's add that to the documentation, shall we? This is now http://trac.sagemath.org/sage_trac/ticket/12114. More and more SD 35.5 fodder...

kcrisman ( 13 years ago )

I'm doing imshow(img) and I get this AxesImage(60,48;372x384) AxesImage(60,48;372x384) What does it mean?

roi.holtzman ( 7 years ago )

It means it generates an image. Sage doesn't actually show the image onscreen without further commands, such as savefig; see @benjaminfjones answer below.

kcrisman ( 7 years ago )

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answered 13 years ago

Jason Grout
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matrix_plotuses matplotlib's imshow to plot a matrix. matrix_plot should be called automatically if you try to plot a matrix. See, for example, http://sagenb.org/home/pub/1685/

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Oh, I thought he was asking about wanting to do it in the context of some other mpl stuff in the notebook, not just to plot a matrix.

kcrisman ( 13 years ago )

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answered 13 years ago

benjaminfjones
2775 ●8 ●44 ●76 http://bfj7.com/

(referencing @kcrisman 's answer) I think it is maybe better not to import pylab into the global namespace, so just import pylab. To reset the plot, so to speak, you should call pylab.close() (or just close() if you import *) like this:

import pylab
pylab.imshow([[1,0],[0,1]])
pylab.savefig('plot1.png')
pylab.close()
pylab.imshow([[1,2],[0,1]])
pylab.savefig('plot2.png')

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Do these saved files ever get deleted once they are created?

Jason ( 13 years ago )

Only if you do it yourself. If you're working in the Sage notebook, they exist in the DATA directory associated to the worksheet. For example when I ran the above in the Sage notebook I get files created called $HOME/.sage/sage_notebook.sagenb/home/admin/0/cells/1/plot1.png

benjaminfjones ( 13 years ago )

1

They aren't stored in the DATA directory, but in a cell-specific output directory. They are supposed to be deleted when the cell is deleted, or even when the output of the cell is deleted (but apparently this didn't actually happen, but a patch was recently merged that actually does delete such files).

Jason Grout ( 13 years ago )

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Is there a simple way to plot an image in a notebook? I.e. the output of the imshow function in matplotlib...

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