I'm building a small Craft site to function as a content backend, exposing all of the content via the ElementAPI.
One field I'm retrieving and displaying in the API is the URL on Amazon S3 for an image asset that's contained in a Matrix field.
What I'd ideally like to do is, when the user uploads this image and it's added to the S3 bucket, to be able to access S3 URLs for the small, medium and large cropped Image Transforms that I've defined. Then, I can make all of these available as an Element API endpoint.
My understanding of Image Transforms and S3 is that Craft usually handles this on-the-fly when an image is referenced in a frontend template. But is there a way to do this when there will be no frontend templates, and the only way that information will be accessed is via the Element API?