[boost] [gil][io_new] Image Reading and Writing Iterator

Hi there, one of the requirements for the acceptance of io_new as the new io extension for gil is the ability to read and write images in more then one step. For that the current state of an operation has to be cached. I have created some meta functions that give access to io_new's reader and writer classes. Right now, it still is very preliminary. I would like to ask the community how I could create an read_iterator and write_iterator classes which users could use to iterate over very large images. I know there are some specific iterator libs in boost but I'm just clueless in how to use let alone be able to come up with an implementation that will be released by boost. Any help would be very welcome! Thanks, Christian