I tried a simple array (see the code below) but cannot reproduce the
problem you reported.
import matplotlib.pyplot as plt
import numpy as np
arr = np.zeros((11, 11), dtype="d")
arr[3,3]=1
im = plt.imshow(arr, interpolation="nearest", origin="lower")
cont = plt.contour(arr, levels=[0.5])
plt.savefig("a.eps")
Do you still see the shift with the above example code?
And what version of matplotlib are you using?
If possible, please post a complete script with the data (use a
mock-up data if you want)?
Regards,
-JJ
On Fri, Jul 23, 2010 at 12:16 AM, Jenna Lemonias
<je...@astro.columbia.edu> wrote:
> No, I don't think the issue is a flip in the y-axis. I have a number of
> different examples of this, and many in which the contour is an ellipse so I
> can tell that the overall positioning is correct. It seems like something
> is going wrong only when I save the image... Thanks for the suggestion
> though!
>
> Jenna
>
> On Wed, Jul 21, 2010 at 3:40 PM, Jenna Lemonias
> <je...@astro.columbia.edu>wrote:
>
>> I am trying to save a matplotlib 2d array image with an overlaid contour
>> as
>> an eps file. The contour appears to be shifted with respect to the image
>> underneath in the eps file, particularly when I zoom in on the image.
>> This
>> shift is not noticeable in the plot within matplotlib.
>>
>> I am using imshow to display the image. The contour is created by
>> plotting
>> a list of closely-spaced x,y coordinates. The attached file
>> matplotlib.png
>> is a screenshot of the (zoomed-in) image as displayed by matplotlib. The
>> attached file epsfile.png is a screenshot of the (zoomed-in) eps file.
>> When
>> I save this image as an eps file, it is actually 1 of 20 subplots and the
>> shift is noticeable in each subplot.
>>
>> Thanks in advance for your help!
>>
>> Jenna
>>
>>
> Just as a wild guess, could this actually be an issue with how imshow uses
> the upper-left corner for (0,0)? I have seen 1-pixel shifts before, but
> this shift is a little dramatic and I am left wondering if what we are
> really seeing is that the contour that is desired should actually be fliped
> in the y-axis?
>
> Maybe you could try another example where you try to draw a contour further
> away from the center of the image and see if it still goes in the spot you
> expect it to be?
>
> Ben Root
>
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