Re: [Matplotlib-users] Plot aliasing

This is now fixed in SVN HEAD.

Two changes were made:

a) Be more conservative about when segments are simplified based on 
their length

b) Honor the (already existing) path.simplify rcParam in the *Agg backends.

John's suggested patch is also a valid workaround, if you don't want to 
track SVN.  path.py lives in

/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/matplotlib 


on a Mac.  Simply replace the line where should_simplify is set to 
"self.should_simplify = False"

Mike

Michael Droettboom wrote:
> You can hold off on updating.  I am actually able to see it now, even on 
> SVN HEAD.  I'll look further and see if I can find a workaround.
>
> Cheers,
> Mike
>
> Kaushik Ghose wrote:
>   
>> Hi Mike,
>>
>> I'm using 0.98.3 with the TkAgg backend on Mac OS X.
>>
>> I will update matplotlib from the site and try again. My attempt to 
>> use GtkAgg failed presumably because I don't have things set up with 
>> GTk on my Mac.
>>
>> best
>> -Kaushik
>>
>> Michael Droettboom wrote:
>>     
>>> I'm not able to reproduce this on matplotlib SVN head with the GtkAgg
>>> backend.  Which version and backend are you using?
>>>
>>> Mike
>>>
>>> Kaushik Ghose wrote:
>>>       
>>>> PS. In the code just disregard the line N = 1000 - it does nothing.
>>>>
>>>> Ghose, Kaushik wrote:
>>>>
>>>>         
>>>>> Hi John,
>>>>>
>>>>> OK. I've managed to pare it down to the following pattern:
>>>>>
>>>>> import pylab
>>>>>
>>>>> N = 1000
>>>>> x = pylab.zeros(200)
>>>>> x[1] = .5
>>>>> x[2:24] = 1.0
>>>>> x[24] = .5
>>>>> x[26] = -.5
>>>>> x[27:49] = -1.0
>>>>> x[49] = -.5
>>>>> x = pylab.tile(x, 100)
>>>>> pylab.plot(x)
>>>>>
>>>>>
>>>>> The above code is sufficient to repeat the glitch (just resize the 
>>>>> window to
>>>>> check this). The half-way values (0.5) are important - if we have a 
>>>>> straight
>>>>> jump   the glitch isn't visible.
>>>>>
>>>>> I'm sorry but I couldn't find path.py under
>>>>>
>>>>> /Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/ 
>>>>>
>>>>>
>>>>> so I couldn't try it out. (Is it under a different place in mac?)
>>>>>
>>>>> thanks
>>>>> -Kaushik
>>>>>
>>>>>
>>>>>
>>>>> John Hunter wrote:
>>>>>
>>>>>           
>>>>>> On Sat, Dec 27, 2008 at 10:29 AM, Kaushik Ghose
>>>>>> <Kau...@hm...> wrote:
>>>>>>
>>>>>>             
>>>>>>> Hi Gang,
>>>>>>>
>>>>>>> I was plotting some data collected from an ADC and noticed an odd 
>>>>>>> aliasing
>>>>>>> issue. Please see the images on the following site.
>>>>>>>
>>>>>>> http://assorted-experience.blogspot.com/2008/12/odd-aliasing-issue-with-matplotlib.html 
>>>>>>>
>>>>>>>
>>>>>>> I wonder if there is any way to avoid this kind of aliasing. I 
>>>>>>> vaguely remember
>>>>>>> our old arch-foe (MATLAB) handles this gracefully. I have found 
>>>>>>> matplotlib's
>>>>>>> plotting to be superior to MATLAB's in every way (except for 3D) 
>>>>>>> and it would be
>>>>>>> nice if aliasing could be handled gracefully.
>>>>>>>
>>>>>>>               
>>>>>> I'm almost certain this is a result of the path simplification logic.
>>>>>> Could you upload some sample data and a self contained script so we
>>>>>> can test?
>>>>>> You can test this by editing site-packages/path.py and replacing::
>>>>>>
>>>>>>   self.should_simplify = (len(vertices) >= 128 and
>>>>>>                                 (codes is None or np.all(codes <= 
>>>>>> Path.LINETO)))
>>>>>>
>>>>>> with::
>>>>>>
>>>>>>   self.should_simplify = False
>>>>>>
>>>>>> Michael, perhaps we could override path.should_simplify with an rc or
>>>>>> line property?
>>>>>>
>>>>>>
>>>>>>             
>>>>>>> Also, thanks for the excellent binary packages for Mac!
>>>>>>>
>>>>>>>               
>>>>>> Thanks for testing them!
>>>>>>
>>>>>>             
>>>>> ------------------------------------------------------------------------------ 
>>>>>
>>>>> _______________________________________________
>>>>> Matplotlib-users mailing list
>>>>> Mat...@li...
>>>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>>>>>
>>>>>           
>>>> ------------------------------------------------------------------------------ 
>>>>
>>>> _______________________________________________
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>>>>
>>>>         
>>> -- 
>>> Michael Droettboom
>>> Science Software Branch
>>> Operations and Engineering Division
>>> Space Telescope Science Institute
>>> Operated by AURA for NASA
>>>
>>>       
>
>   

-- 
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA