[Matplotlib-users] Rotating in imshow

[Thomas R. <tho...@gm...>]

Hello,

I was wondering whether there is a way to rotate a grayscale/ 
colorscale when using imshow.

I have been using PGPLOT (a fortran/c plotting library) for many years  
now, and the equivalent to imshow is called PGGRAY (or PGIMAG). One of  
the arguments this function takes is a 6-element array TR which is a  
transformation matrix. From the PGPLOT documentation:

"The transformation matrix TR is used to calculate the world  
coordinates of the center of the "cell" that represents each array  
element. The world coordinates of the center of the cell corresponding  
to array element A(I,J) are given by:
X = TR(1) + TR(2)*I + TR(3)*J
Y = TR(4) + TR(5)*I + TR(6)*J"

This is actually the same as the ImageMatrix element in the Postscript  
language:

"ImageMatrix array (Required) An array of six numbers defining a  
transformation from user
space to image space." (http://www.adobe.com/devnet/postscript/pdfs/PLRM.pdf 
, page 298)

This allows arbitrary rotation/translation of the image to plotting  
without any loss in quality for vector graphics formats (EPS, PDF, SVG).

So far, I have found that imshow has an 'extend' keyword, which is the  
equivalent of four of the matrix elements, but there is no way to  
specify the rotation. Is there such a feature in matplotlib already?  
If not, would it be possible to implement it?

Just to be clear, I am not talking about rotating with some kind of  
interpolation, which would degrade the image (this can be done with  
PIL). What I want is to be able to specify a transformation matrix  
which includes rotation, which means that there is no resampling done  
if I save my plot in a vector graphics format.

Thanks in advance for any help!

Thomas