It is a bit like demand paging, yes. There are formats for which rectangular regions map to contiguous block of memory.<p>TIFF has specs for tiles, strips, subfiles, layers, etc. AFIAK, hardly anyone uses those, but they certainly exist.<p>JPEG is also composed of 8x8 squares and is easy to stream. The API has per-scanline read &amp; write callbacks IIRC. But you&#x27;re right; a very very wide one might be a case it can&#x27;t deal with.