Hi all, thanks for the replies. Let's stick with reading an image for now. Writing is somewhat similar. Now, reading a large image is typically done in a forward matter. In fact most image formats only support forward. No random access or even backwards is supported naturally. There are exceptions like bmp or other basic formats. Depending on the use case one way to read an image is by reading one or more scanlines. They other way is reading in blocks. Such settings could be setup at construction time but users might want to change them over time. I think I would need some help with constructing an forward iterator adapter. Imagine you have a reader<Device, Format> class and it would be used by the iterator to extract data from the image. Is there any sample code that I could use? Hope this helps, Christian