JPEG 2000
And, conveniently, Mac OS X 10.4 (“Tiger”) has a new framework for reading and writing images, and it understands JPEG2000 natively (based on the commercial, C++ Kakadu library). And, in this new Apple framework, there’s a function CGImageSourceCreateThumbnailAtIndex() where you can create a thumbnail of an image you haven’t read in yet, by specifying a maximum side length (kCGImageSourceThumbnailMaxPixelSize). This would be EXACTLY the kind of call in which one would implement the partial-reading of JPEG2000s in order to quickly read in a low-rez versions of high-rez files.
