Introduction to the Image Compression Manager
The Image Compression Manager provides your application with an interface for compressing and decompressing images and sequences of images that is independent of devices and algorithms.Uncompressed image data requires a large amount of storage space. Storing a single 640-by-480 pixel image in 32-bit color can require as much as 1.2 MB. Sequences of images, like those that might be contained in a QuickTime movie, demand substantially more storage than single images. This is true even for sequences that consist of fairly small images, because the movie consists of such a large number of those images. Consequently, minimizing the storage requirements for image data is an important consideration for any application that works with images or sequences of images.
The Image Compression Manager allows your application to
The Image Compression Manager compresses images by invoking image compressor components and decompresses images using image decompressor components. Compressor and decompressor components are code resources that present a standard interface to the Image Compression Manager and provide image-compression and image-decompression services, respectively. The Image Compression Manager receives application requests and coordinates the actions of the appropriate components. The components perform the actual compression and decompression. Compressor and decompressor components are standard components and are managed by the Component Manager. For detailed information about creating compressor and decompressor components, see Inside Macintosh: QuickTime Components.
- use a common interface for all image-compression and image-decompression operations
- take advantage of any compression software or hardware that may be present in a given Macintosh configuration
- store compressed image data in pictures
- temporally compress sequences of images, further reducing the storage requirements of movies
- display compressed PICT files without the need to modify your application
- use an interface that is appropriate for your application--a high-level interface if you do not need to manipulate many compression parameters or a low-level interface that provides you greater control over the compression operation
Because the Image Compression Manager is independent of specific compression algorithms and drivers, it provides a number of advantages to developers of image- compression algorithms. Specifically, compressor and decompressor components can
- present a common application interface for software-based compressors and hardware-based compressors
- provide several different compressors and compression options, allowing the Image Compression Manager or the application to choose the appropriate tool for a particular situation
Subtopics
- Data That Is Suitable for Compression
- Storing Images