Since I suspect this change will be a little bit of work, I just wanted
to put my hand up and say I'm looking into it so we don't duplicate
effort here.
I think it's a worthwhile experiment, in any case.
Mike
Andrew Hawryluk wrote:
>
> I’m really excited about the new path simplification option for vector
> output formats. I tried it the first time yesterday and reduced a PDF
> from 231 kB to 47 kB. Thanks very much for providing this feature!
>
> However, I have noticed that the simplified paths often look more
> jagged than the original, at least for my data. I can recreate the
> effect with the following:
>
> [start]
>
> import numpy as np
>
> import matplotlib.pyplot as plt
>
> x = np.arange(-3,3,0.001)
>
> y = np.exp(-x**2) + np.random.normal(scale=0.001,size=x.size)
>
> plt.plot(x,y)
>
> plt.savefig('test.png')
>
> plt.savefig('test.pdf')
>
> [end]
>
> A sample output is attached, and close inspection shows that the PNG
> is a smooth curve with a small amount of noise while the PDF version
> has very noticeable changes in direction from one line segment to the
> next.
>
> <<test.png>> <<test.pdf>>
>
> The simplification algorithm (agg_py_path_iterator.h) does the following:
>
> If line2 is nearly parallel to line1, add the parallel component to
> the length of line1, leaving it direction unchanged
>
> which results in a new data point, not contained in the original data.
> Line1 will continue to be lengthened until it has deviated from the
> data curve enough that the next true data point is considered
> non-parallel. The cycle then continues. The result is a line that
> wanders around the data curve, and only the first point is guaranteed
> to have existed in the original data set.
>
> Instead, could the simplification algorithm do:
>
> If line2 is nearly parallel to line1, combine them by removing the
> common point, leaving a single line where both end points existed in
> the original data
>
> Thanks again,
>
> Andrew Hawryluk
>
>
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--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA
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