Re: [Matplotlib-users] Saving figure with an image and a time axis as an EPS shifts image relative to other plot features

[Benjamin R. <ben...@ou...>]

On Thu, Aug 2, 2012 at 7:21 PM, Chad Parker <par...@gm...>wrote:

> Hello everyone-
>
> I'm a new Python/Matplotlib user, but I have quite a bit of plotting
> experience with octave/matlab and gnuplot. So, I apologize in advance if my
> python style is terrible and if I give you all the wrong information!
>
> I'm having a problem saving figures that contain images as eps files when
> my x-axis is a date/time axis. The trouble is that in the resulting eps
> file, the image data is shifted relative to the axis. I've attached two
> images as an example. In the .png file the alignment is correct and in the
> eps file it's not. The png is also nearly identical to what I get when I
> plot to the screen. The script I wrote to generate these plots is at the
> end of this message.
>
> It's worth noting that the two output images are identical if the x-axis
> is simply numerical and not a time series.
>
> I'm using python 2.7.3 and Matplotlib 1.1.0
>
> Some Google searches dug up this old thread, however, the shift that I'm
> experiencing seems to be much greater, so I don't know if it's related:
> http://old.nabble.com/Saving-as-eps-file-shifts-image--td29232680.html
>
> Can anyone help me solve this?
> Thanks in advance,
> --Chad
>
>
> Here is a minimal script that I used to generate these plots:
>
> import matplotlib.pyplot as plt
> import matplotlib.dates as dts
> from matplotlib.colors import LogNorm
>
> imgData = [[1.0/x + 1.0/y for x in range(1,100)] for y in range(1,100)]
>
> tMin=dts.epoch2num(1343947266)
> tMax=dts.epoch2num(1343947266+100)
>
> axImg=plt.subplot(111)
> axImg.imshow(imgData, norm=LogNorm(),extent=(tMin,tMax,1,100),\
>                 interpolation='none', origin="upper")
> axImg.xaxis_date()
> axImg.set_aspect('auto')
>
> plt.savefig("imageshift.png")
> plt.savefig("imageshift.eps")
>
>
Confirmed.  This is a fairly nasty-looking result.  And I am not exactly
sure what is happening here.  Note that it does not matter if the png or
the eps images were saved first.  It looks like an auto-scaling bug, but
given that it doesn't impact the png image, I am not so sure.

Could you file a bug report on this at the github tracker?  I would like to
see this fixed before the 1.2.0 release.

Thanks!
Ben Root