Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
Hi, On Wed, Sep 29, 2010 at 16:00, John Hunter jdh2...@gmail.com wrote: On Wed, Sep 29, 2010 at 8:50 AM, Alexander Dietz alexander.diet...@googlemail.com wrote: print ax.transData.transform((10.0, 20.0)) [ 576. 432.] Why do you say it's wrong? Note that in mpl, (0,0) is (bottom left), not (upper,left). So this is saying that the yellow dot at 10,20 (data coords) is 576 pixels up from the bottom and 432 pixels over from the left. This is not correct, either. Since the total width of the image is 800 pixels and the total height is 600 pixels, I get the following coordinates of the yellow dot: x-coord: = 432 y-coord = 600-576 = 24 but in fact, the position of the yellow dot is still at (720, 60)!. (And even if you swapped x and y coordinates it will never be correct.). So anyone another idea how to transform a data-point (10,20) to the image coordinates? Cheers Alex JDH -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
On Thu, Sep 30, 2010 at 3:28 AM, Alexander Dietz alexanderdie...@googlemail.com wrote: Hi, On Wed, Sep 29, 2010 at 16:00, John Hunter jdh2...@gmail.com wrote: On Wed, Sep 29, 2010 at 8:50 AM, Alexander Dietz alexander.diet...@googlemail.com wrote: print ax.transData.transform((10.0, 20.0)) [ 576. 432.] Why do you say it's wrong? Note that in mpl, (0,0) is (bottom left), not (upper,left). So this is saying that the yellow dot at 10,20 (data coords) is 576 pixels up from the bottom and 432 pixels over from the left. This is not correct, either. Since the total width of the image is 800 pixels and the total height is 600 pixels, I get the following coordinates of the yellow dot: x-coord: = 432 y-coord = 600-576 = 24 but in fact, the position of the yellow dot is still at (720, 60)!. (And even if you swapped x and y coordinates it will never be correct.). So anyone another idea how to transform a data-point (10,20) to the image coordinates? Cheers Alex Alex, I don't think it is technically possible. Keep in mind that the coordinate system that is used to display figures is merely a convention used by matplotlib and the GUI system. It is not the same transformation that is used when saving images, and nor should it be because of differences between the resolution of your display and the resolution of your image (typically unknown until save time). In addition to that issue is the figure window itself. In particular, the toolbar is also a part of the same display coordinate system. I would also wonder if there might be some horizontal padding going on that is throwing off the x-coordinates. Ben Root -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
[Matplotlib-users] How to find out the extend of the actual image in pixels
Hi, I would like to know how to find out the extend of the actual image in a plot, in units of pixels. As example I have attached a plot which is essentially empty. The lower left corner is indicated by a red dot - what pixel position does this location have? When opening this image in e.g. kview it is easy to find out that this left corner of the actual plot corresponds to pixel (100,540). And so the upper right corner (the yellow dot) is (720,60). But how do I find out these coordinates when generating such a plot with matplotlib? Are there some variables of the axis or the actual plot that contain these numbers? Thanks Alex attachment: mainplotTEST.png-- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
On Wed, Sep 29, 2010 at 4:44 AM, Alexander Dietz
alexanderdie...@googlemail.com wrote:
I would like to know how to find out the extend of the actual image in a
plot, in units of pixels.
As example I have attached a plot which is essentially empty. The lower left
corner is indicated by a red dot - what pixel position does this location
have? When opening this image in e.g. kview it is easy to find out that this
left corner of the actual plot corresponds to pixel (100,540). And so the
upper right corner (the yellow dot) is (720,60).
But how do I find out these coordinates when generating such a plot with
matplotlib? Are there some variables of the axis or the actual plot that
contain these numbers?
Take a look at the transformations tutorial.
http://matplotlib.sourceforge.net/users/transforms_tutorial.html
To convert from data - pixel coordinates, use the axes transData transformation
In [1]: ax = gca()
In [2]: ax.transData.transform((0.5, 0.5))
Out[2]: array([ 333.125, 245. ])
You can also use mpl events to inspect the coordinates of the point
under the mouse
In [3]: fig = gcf()
In [4]: def on_click(event):
...: print event.x, event.y
...:
...:
In [5]: cid = fig.canvas.mpl_connect('button_press_event', on_click)
In [6]: 188 166.0
300 227.0
384 292.0
In [7]: fig.canvas.mpl_disconnect(cid)
See http://matplotlib.sourceforge.net/users/event_handling.html for more info.
JDH
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Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
Hi John,
thanks for the reply, but I think your method is not working:
On Wed, Sep 29, 2010 at 15:39, John Hunter jdh2...@gmail.com wrote:
On Wed, Sep 29, 2010 at 4:44 AM, Alexander Dietz
alexanderdie...@googlemail.com wrote:
I would like to know how to find out the extend of the actual image in a
plot, in units of pixels.
As example I have attached a plot which is essentially empty. The lower
left
corner is indicated by a red dot - what pixel position does this location
have? When opening this image in e.g. kview it is easy to find out that
this
left corner of the actual plot corresponds to pixel (100,540). And so the
upper right corner (the yellow dot) is (720,60).
But how do I find out these coordinates when generating such a plot with
matplotlib? Are there some variables of the axis or the actual plot that
contain these numbers?
Take a look at the transformations tutorial.
http://matplotlib.sourceforge.net/users/transforms_tutorial.html
To convert from data - pixel coordinates, use the axes transData
transformation
In [1]: ax = gca()
In [2]: ax.transData.transform((0.5, 0.5))
Out[2]: array([ 333.125, 245. ])
I have create a different plot (attached) and the point of the upper right
corner (the yellow dot) is still at (720,60) as before. But with transData I
get a completely wrong result:
print ax.transData.transform((10.0, 20.0))
[ 576. 432.]
Also the lower left points gets wrong coordinates. Maybe I am doing
something stupidly wrong here?
Thanks
Alex
You can also use mpl events to inspect the coordinates of the point
under the mouse
In [3]: fig = gcf()
In [4]: def on_click(event):
...: print event.x, event.y
...:
...:
In [5]: cid = fig.canvas.mpl_connect('button_press_event', on_click)
In [6]: 188 166.0
300 227.0
384 292.0
In [7]: fig.canvas.mpl_disconnect(cid)
See http://matplotlib.sourceforge.net/users/event_handling.html for more
info.
JDH
attachment: mainplotTEST.png--
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Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
On Wed, Sep 29, 2010 at 8:50 AM, Alexander Dietz alexander.diet...@googlemail.com wrote: print ax.transData.transform((10.0, 20.0)) [ 576. 432.] Why do you say it's wrong? Note that in mpl, (0,0) is (bottom left), not (upper,left). So this is saying that the yellow dot at 10,20 (data coords) is 576 pixels up from the bottom and 432 pixels over from the left. JDH -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
This is interesting. It seems that the event.x, event.y values are for the entire figure area rather than limited to the image. Anyone know how to get the image values instead? Also, I wonder how one might get the values of the pixels (i.e. image value) at the pixels that you click on. One more thing -- is there a way to make the cursor be a full plot window cross -- graphically like: -- || | || | || | ||-| || | || | -- It makes it easier to align with the axes sometimes (the IDL astronomy library has a routine called rdplot that does this). Jon -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
Hi, On Wed, Sep 29, 2010 at 16:00, John Hunter jdh2...@gmail.com wrote: On Wed, Sep 29, 2010 at 8:50 AM, Alexander Dietz alexander.diet...@googlemail.com wrote: print ax.transData.transform((10.0, 20.0)) [ 576. 432.] Why do you say it's wrong? Note that in mpl, (0,0) is (bottom left), not (upper,left). So this is saying that the yellow dot at 10,20 (data coords) is 576 pixels up from the bottom and 432 pixels over from the left. ok maybe it is. But then I need the size of the entire figure written to a file. How can I find out the pixel-size of the entire figure, inclusive every title, axis, labels... Thanks Alex JDH -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
If you're just looking for the dimensions of the overall figure in pixels,
you can easily access them through other means. E.g:
import matplotlib.pyplot as plt
fig = plt.figure()
_, _, width, height = fig.bbox.extents # - Extent of the figure in pixels
fig.savefig('temp.png', dpi=fig.dpi) # - Be sure to specify the dpi!!
Note that you'll have to specify that you want to save the figure at the
same DPI it was when you called the extents...
The figure will be saved with whatever default DPI is in your .matplotlibrc,
which is commonly different than the default screen dpi (80).
Hope that helps,
-Joe
On Wed, Sep 29, 2010 at 9:44 AM, Alexander Dietz
alexanderdie...@googlemail.com wrote:
Hi,
On Wed, Sep 29, 2010 at 16:00, John Hunter jdh2...@gmail.com wrote:
On Wed, Sep 29, 2010 at 8:50 AM, Alexander Dietz
alexander.diet...@googlemail.com wrote:
print ax.transData.transform((10.0, 20.0))
[ 576. 432.]
Why do you say it's wrong? Note that in mpl, (0,0) is (bottom left),
not (upper,left). So this is saying that the yellow dot at 10,20
(data coords) is 576 pixels up from the bottom and 432 pixels over
from the left.
ok maybe it is. But then I need the size of the entire figure written to a
file. How can I find out the pixel-size of the entire figure, inclusive
every title, axis, labels...
Thanks
Alex
JDH
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Re: [Matplotlib-users] How to find out the extend of the actual image in pixels
On Wed, Sep 29, 2010 at 11:12 PM, Jonathan Slavin jsla...@cfa.harvard.edu wrote: This is interesting. It seems that the event.x, event.y values are for the entire figure area rather than limited to the image. Anyone know how to get the image values instead? Typically, images in matplotlib are associated with data coordinate. And mouse events have xdata and ydata attributes. However, if you're using imshow with the extent keyword, you need one more step. Below is an example. arr = np.arange(10).reshape((2,5)) x1, x2, y1, y2 = [-1.5, 3.5, 2.5, 4.5] imshow(arr, extent=[x1, x2, y1, y2], origin=lower) from matplotlib.transforms import Bbox, BboxTransform bbox_in = Bbox.from_extents([x1, y1, x2, y2]) bbox_out = Bbox.from_bounds(-0.5, -0.5, arr.shape[1], arr.shape[0]) # transform from data coordinate into image coordinate. tr = BboxTransform(bbox_in, bbox_out) print tr.transform_point((-1, 3)) # pixel (0,0) of arr print tr.transform_point((3, 4)) # pixel (4,1) of arr Also, I wonder how one might get the values of the pixels (i.e. image value) at the pixels that you click on. One more thing -- is there a way to make the cursor be a full plot window cross -- graphically like: -- | | | | | | | | | ||-| | | | | | | -- It makes it easier to align with the axes sometimes (the IDL astronomy library has a routine called rdplot that does this). One option is to use widgets http://matplotlib.sourceforge.net/examples/widgets/cursor.html Regards, -JJ Jon -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users -- Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
