Rails - How would I get the URL of a single image asset in the controller?

I've tried including ActionView::Helpers::AssetTagHelper and then using the image_path() method however it gives me grief:

undefined local variable or method `config' for ActionView::Helpers::AssetTagHelper:Module

There's probably something simple I'm missing. Any ideas?

I found the solution in Barlow's answer here: How can I use image_path inside Rails 3 Controller

view_context.image_path('/path/to/image')

seems to work for me, no need to include helpers in the Controller