[plt-scheme] programmatically saving 2htdp/image images? (quasi-patch included)

The 2htdp/image library is awesome. I'd like to use it to generate web page images for test case success/failure, e.g.: 

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However, I couldn't figure out how to save these things as files without using a right-click.

I wrote this function:

(define (image->file/png image filename)
  (let* ([bitmap (make-object bitmap% (image-width image) (image-height image))]
         [dc (new bitmap-dc% [bitmap bitmap])])
    (render-image image dc 0 0)
    (send bitmap save-file filename 'png)))

...and it appears to work. It appears to me that this might be useful to add something like this to mrlib/image-core, if it's not already there.  Perhaps I just overlooked it?

John

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