matplotlib-users

[Matplotlib-users] imshow axis directions

[Stephen W. <ste...@cs...>]

Hi,

I was just comparing images displayed with imshow() with what I get from 
IRAF's display command and ds9.  The latter puts the first axis 
increasing horizontally and the second axis increasing vertically, as if 
the image array were addressed as img[ix,iy], where ix and iy are 
integer x and y coordinates.  The axes imshow() produces are labeled as 
if this is true for it as well, but in fact the image is upside down 
with respect to what I see with IRAF.  Even odder, to see the same 
display I see in IRAF I have to do imshow(img[::-1,:]), as if I'm 
reversing the direction of the first axis.

I've tried to look at the source, really, but I feel like I'm *years* 
away from being enough of a Python hacker to understand matplotlib.

Steve

Re: [Matplotlib-users] imshow axis directions

[Perry G. <pe...@st...>]

check out the .matplotlibrc image.origin configuration parameter. The 
default is to have pixel 0,0 on the upper left which is opposite of 
what us weird astronomers think is the natural locationl

Perry

On Apr 7, 2005, at 2:08 PM, Stephen Walton wrote:

> Hi,
>
> I was just comparing images displayed with imshow() with what I get 
> from IRAF's display command and ds9.  The latter puts the first axis 
> increasing horizontally and the second axis increasing vertically, as 
> if the image array were addressed as img[ix,iy], where ix and iy are 
> integer x and y coordinates.  The axes imshow() produces are labeled 
> as if this is true for it as well, but in fact the image is upside 
> down with respect to what I see with IRAF.  Even odder, to see the 
> same display I see in IRAF I have to do imshow(img[::-1,:]), as if I'm 
> reversing the direction of the first axis.
>
> I've tried to look at the source, really, but I feel like I'm *years* 
> away from being enough of a Python hacker to understand matplotlib.
>
> Steve
>
>
>
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Re: [Matplotlib-users] imshow axis directions

[John H. <jdh...@ac...>]

>>>>> "Stephen" == Stephen Walton <ste...@cs...> writes:

    Stephen> Hi, I was just comparing images displayed with imshow()
    Stephen> with what I get from IRAF's display command and ds9.  The
    Stephen> latter puts the first axis increasing horizontally and
    Stephen> the second axis increasing vertically, as if the image
    Stephen> array were addressed as img[ix,iy], where ix and iy are
    Stephen> integer x and y coordinates.  The axes imshow() produces
    Stephen> are labeled as if this is true for it as well, but in
    Stephen> fact the image is upside down with respect to what I see
    Stephen> with IRAF.  Even odder, to see the same display I see in
    Stephen> IRAF I have to do imshow(img[::-1,:]), as if I'm
    Stephen> reversing the direction of the first axis.


Does changing the rc param

  image.origin : upper             # lower | upper

to lower help?


    Stephen> I've tried to look at the source, really, but I feel like
    Stephen> I'm *years* away from being enough of a Python hacker to
    Stephen> understand matplotlib.

Hmm, the code's not that bad is it :-)

JDH

Re: [Matplotlib-users] imshow axis directions

[Stephen W. <ste...@cs...>]

John Hunter wrote:

>>>>>>"Stephen" == Stephen Walton <ste...@cs...> writes:
>>>>>>            
>>>>>>
>Does changing the rc param
>
>  image.origin : upper             # lower | upper
>
>to lower help?
>  
>
Yes, it makes the image the right way around.  I was simply confused 
because I expected the pixel at (x,y) in the imshow display to be the 
value of img[x,y].  It appears not to be.  I hasten to add MATLAB's 
worse, as the pixel at (x,y) is actually the value of img[y,x];  MATLAB 
displays with the first array coordinate increasing downward and the 
second from left to right.

>    Stephen> I've tried to look at the source, really, but I feel like
>    Stephen> I'm *years* away from being enough of a Python hacker to
>    Stephen> understand matplotlib.
>
>Hmm, the code's not that bad is it :-)
>  
>
I'm sure the code is fine, John, and it's just me.  Specifically, if I 
want to see how matplotlib is doing something, I can't just trace 
function calls like I'm used to doing with Fortran and C, because there 
are methods too and I have to find the class which defines those methods 
to see what's happening.  Is there anything like ctags for Python?

Steve

Re: [Matplotlib-users] imshow axis directions

[Robert K. <rk...@uc...>]

Stephen Walton wrote:

> I'm sure the code is fine, John, and it's just me.  Specifically, if I 
> want to see how matplotlib is doing something, I can't just trace 
> function calls like I'm used to doing with Fortran and C, because there 
> are methods too and I have to find the class which defines those methods 
> to see what's happening.  Is there anything like ctags for Python?

Exuberant ctags

http://ctags.sourceforge.net/

-- 
Robert Kern
rk...@uc...

"In the fields of hell where the grass grows high
  Are the graves of dreams allowed to die."
   -- Richard Harter

Re: [Matplotlib-users] imshow axis directions

[Stephen W. <ste...@cs...>]

Robert Kern wrote:

> Exuberant ctags
>
> http://ctags.sourceforge.net/
>
Which, as it turns out, is the version of ctags on Fedora Core 3.  I did 
a 'ctags -R' in the matplotlib root directory and am now happily 
browsing the source using nedit.

Thanks, Robert!

Steve