How can I use scipy.ndimage.interpolation.affine_transform to rotate an image about its centre?

I am perplexed by the API to `scipy.ndimage.interpolation.affine_transform`. And judging by this issue I'm not the only one. I'm actually wanting to do more interesting things with `affine_transform` than just rotating an image, but a rotation would do for starters. (And yes I'm well aware of `scipy.ndimage.interpolation.rotate`, but figuring out how to drive `affine_transform` is what interests me here). When I want to do this sort of thing in systems like OpenGL, I'm think in terms of computing the transform which applies a 2x2 rotation matrix `R` about a centre `c`, and therefore thinking of points `p` being transformed `(p-c)R+c` = `pR+c-cR`, which gives a `c-cR` term to be used as the translation component of a transform. However, according to the issue above, scipy's `affine_transform` does "offset first" so we actually need to compute an offset `s` such that `(p-c)R+c=(p+s)R` which with a bit of rearrangement gives `s=(c-cR)R'` where `R'` is the inverse of `R`. If I plug this into an ipython notebook (pylab mode; code below maybe needs some additional imports): ``` img=scipy.misc.lena() #imshow(img,cmap=cm.gray);show() centre=0.5*array(img.shape) a=15.0*pi/180.0 rot=array([[cos(a),sin(a)],[-sin(a),cos(a)]]) offset=(centre-centre.dot(rot)).dot(linalg.inv(rot)) rotimg=scipy.ndimage.interpolation.affine_transform( img,rot,order=2,offset=offset,cval=0.0,output=float32 ) imshow(rotimg,cmap=cm.gray);show() ``` I get which unfortunately isn't rotated about the centre. So what's the trick I'm missing here?