Inside Macintosh: QuickTime
The Image Compression Manager can compress two kinds of image data: pictures and pixel maps. Pictures may be stored in memory, in a resource, or in a PICT file. Pixel maps are normally stored in a window or offscreen buffer. When compressing an image from a PICT file, the Image Compression Manager provides facilities that allow applications to spool data to and from the disk file, as appropriate to the operation. These application-provided data-loading and data-unloading functions allow arbitrarily large images to be compressed or decompressed without requiring large amounts of memory.
Applications must convert images that are not stored as pictures or pixel maps into one of these formats before compressing them. The Image Compression Manager contains several high-level functions that make it quite easy for applications to work with compressed images that are stored as PICT files. See "Working With Pictures" for more information.