Rotate an image ...

[Alex Tweedly]

I have a PNG file which I want to rotate 90 degrees.

My script does
    import paint from file "d:/icons/myfile.png"
    rotate image "myfile.png" by 90
    export image "myfile.png" to file "d:/icons/myfilerotated.png"
which ALMOST works.

It gives me an image with, at first glance, the correct appearance - but 
the size is 100x100 so there is spurious white border. I had expected to 
get a new image that was 100x60.

Is there a way to rotate an image to get just the original image, but rotated ?
Or some other way to trim it back to original size (except rotated) ?

Thanks,
-- Alex.