What you describe sounds a bit like demand paging of a memory-mapped file. The problem with implementing it for a 2d image is that a given rectangular region doesn&#x27;t map to a contiguous area in memory. It&#x27;s easy to construct a long thin image that would cause problems for a line-based demand paging strategy. For example, ten pixels high by a billion pixels wide.<p>Edit: skipping sections of the line to get to the region of interest is fine, I suppose, but what&#x27;s really needed is a hierarchical quadtree-like organization of the storage, surely...