No fillalpha after eps export?

eps
opacity

asked 2013-02-06 13:51:53 +0100

pinwheel
51 ●3 ●3 ●7

updated 2015-01-14 10:36:53 +0100

FrédéricC

5251 ●3 ●44 ●116

Hey guys,

this is a slightly modified example from the sage help pages:

(plot(1+e^(-x^2), xmin=-2, xmax=2, ymin=0, ymax=2.5, fill=0.5, fillcolor='green', fillalpha=0.5)).save('t.eps')

It shows an exponential function which is filled from below by green color. The option fillalpha=0.5 should make this filling slightly transparent, which works perfectly when exporting to pdf, but repdroducably fails when exporting to eps. Is there any workaround?

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answered 2013-02-06 17:30:33 +0100

fidbc

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Hi,

Not really a sage solution and far from optimal. You can try

sage: P=plot(1+e^(-x^2), xmin=-2, xmax=2, ymin=0, ymax=2.5, fill=0.5, fillcolor='green', fillalpha=0.5)
sage: P.save( 't.pdf')

And then

$ pdftops t.pdf
$ ps2eps t.ps

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Long story short, (e)ps does not properly support alpha. So, this is probably the best solution at present. There is no automatic way to make figures with alpha in (e)ps.

ppurka ( 2013-02-09 10:02:14 +0100 )edit

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answered 2013-02-06 20:54:45 +0100

kcrisman
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The problem is in our Polygon class - somehow it's not saving correctly. Compare these.

sage: polygon([(0,0), (1,1), (0,1)],alpha=.1).save('test.pdf')
sage: polygon([(0,0), (1,1), (0,1)],alpha=.1).save('test.eps')

If I can narrow it down a little more, I'll open a ticket. It's conceivable that it's a matplotlib issue, but I'd guess it's ours first.

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See http://trac.sagemath.org/sage_trac/ticket/14074 - my guess is still that we are doing something wrong, but it could be an mpl bug, in principle.

kcrisman ( 2013-02-06 21:11:59 +0100 )edit

I have updated the ticket after opening an upstream mpl bug https://github.com/matplotlib/matplotlib/issues/1740

ppurka ( 2013-02-08 04:11:36 +0100 )edit

And now matplotlib says this is actually not supported by ps.

kcrisman ( 2013-02-08 10:02:17 +0100 )edit

That is not correct. eps supports alpha channels. Here's proof: http://ompldr.org/vaGViZg/drawing.eps Ok. It is not so clear whether ps really really supports alpha. Some libraries use some tricks to get in some alpha support.

ppurka ( 2013-02-08 10:34:04 +0100 )edit

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