[matplotlib-devel] imsave, image size

2010-05-06 Thread Nico Schlömer 
Hi,

today I bumped into a weird issue when including a PNG generated by
imsave into a LaTeX document via \includegraphics. pdftex's very own
Taco Hoekwater then noticed that the image is actually HUGE in what
the specified dimensions concern
, and this
is exactly was causes the error too: The PNG declares an absurd
0.9906x0.9906 pixels per *inch*.

The image was produced by the following code:

== *snip* ==
import matplotlib.pyplot as plt
import numpy as np

from numpy.random import randn

data = np.clip(randn(250, 250), -1, 1)

plt.imsave( fname = 'test.png', arr=data )
== *snap* ==

Cheers,
Nico

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Re: [matplotlib-devel] imsave, image size

2010-05-06 Thread Michael Droettboom 
It looks like the conversion from dots-per-inch (matplotlib's internal 
representation) to dots-per-meter (the unit defined in the PNG standard) 
was bogus.  This should be fixed in SVN r8298.

Mike

Nico Schlömer wrote:
> Hi,
>
> today I bumped into a weird issue when including a PNG generated by
> imsave into a LaTeX document via \includegraphics. pdftex's very own
> Taco Hoekwater then noticed that the image is actually HUGE in what
> the specified dimensions concern
> , and this
> is exactly was causes the error too: The PNG declares an absurd
> 0.9906x0.9906 pixels per *inch*.
>
> The image was produced by the following code:
>
> == *snip* ==
> import matplotlib.pyplot as plt
> import numpy as np
>
> from numpy.random import randn
>
> data = np.clip(randn(250, 250), -1, 1)
>
> plt.imsave( fname = 'test.png', arr=data )
> == *snap* ==
>
> Cheers,
> Nico
>
> --
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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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Re: [matplotlib-devel] imsave, image size

2010-05-06 Thread Ryan May 
On Thu, May 6, 2010 at 1:40 PM, Michael Droettboom  wrote:
> It looks like the conversion from dots-per-inch (matplotlib's internal
> representation) to dots-per-meter (the unit defined in the PNG standard)
> was bogus.  This should be fixed in SVN r8298.

Are you sure that's right? This doesn't look like a conversion to dots
per meter:

size_t dots_per_meter = dpi * 2.54 * 100.0

To my eyes, unit-wise, that looks like dots/inch * cm/inch * cm/m =
dots * m / inch**2. The original looks correct in regard to units to
me:

size_t dots_per_meter = dpi * 100 * (1 / 2.54) -> dots/inch * cm/m *
inch/cm -> dots/m

Am I missing something?

Ryan

-- 
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma

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Re: [matplotlib-devel] imsave, image size

2010-05-06 Thread Michael Droettboom 
You're right.  Thanks for the sanity check.

What's happening is that when using imsave is used, it generates a 
figure image with a dpi of 1 (to force 1 output pixel per input pixel), 
but this is sort of a hack.  Let me see if I can find a way around this 
hack.

Mike

Ryan May wrote:
> On Thu, May 6, 2010 at 1:40 PM, Michael Droettboom  wrote:
>   
>> It looks like the conversion from dots-per-inch (matplotlib's internal
>> representation) to dots-per-meter (the unit defined in the PNG standard)
>> was bogus.  This should be fixed in SVN r8298.
>> 
>
> Are you sure that's right? This doesn't look like a conversion to dots
> per meter:
>
> size_t dots_per_meter = dpi * 2.54 * 100.0
>
> To my eyes, unit-wise, that looks like dots/inch * cm/inch * cm/m =
> dots * m / inch**2. The original looks correct in regard to units to
> me:
>
> size_t dots_per_meter = dpi * 100 * (1 / 2.54) -> dots/inch * cm/m *
> inch/cm -> dots/m
>
> Am I missing something?
>
> Ryan
>
>   

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


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Re: [matplotlib-devel] imsave, image size

2010-05-06 Thread Michael Droettboom 
Ok, I have a better fix in SVN r8300.  imsave now accepts a "dpi" kwarg 
(default of 100) to set the DPI metadata in the file.

Mike

Michael Droettboom wrote:
> You're right.  Thanks for the sanity check.
>
> What's happening is that when using imsave is used, it generates a 
> figure image with a dpi of 1 (to force 1 output pixel per input pixel), 
> but this is sort of a hack.  Let me see if I can find a way around this 
> hack.
>
> Mike
>
> Ryan May wrote:
>   
>> On Thu, May 6, 2010 at 1:40 PM, Michael Droettboom  wrote:
>>   
>> 
>>> It looks like the conversion from dots-per-inch (matplotlib's internal
>>> representation) to dots-per-meter (the unit defined in the PNG standard)
>>> was bogus.  This should be fixed in SVN r8298.
>>> 
>>>   
>> Are you sure that's right? This doesn't look like a conversion to dots
>> per meter:
>>
>> size_t dots_per_meter = dpi * 2.54 * 100.0
>>
>> To my eyes, unit-wise, that looks like dots/inch * cm/inch * cm/m =
>> dots * m / inch**2. The original looks correct in regard to units to
>> me:
>>
>> size_t dots_per_meter = dpi * 100 * (1 / 2.54) -> dots/inch * cm/m *
>> inch/cm -> dots/m
>>
>> Am I missing something?
>>
>> Ryan
>>
>>   
>> 
>
>   

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


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