QuickTime 4 Reference

How Graphics Exporters Work

QuickTime provides a base graphics export component which provides abstractions that greatly simplify the work of format-specific graphics exporter components, while offering applications a rich interface.

Format-specific graphics exporters, such as the exporters for JPEG, PNG and TIFF, are relatively simple components. When a format-specific exporter is opened, it opens and targets an instance of the base graphics exporter. Subsequently, it delegates most of its calls to the base exporter instance, as shown in Figure 17-1 .

Figure 1 Delegating calls to the base graphics exporter

The base exporter communicates with data handler components to write image file data. If necessary, it calls the Image Compression Manager to perform compression operations.

There are three modes that format-specific exporters can operate in:

Transcode. Data is transferred from one image file to another without decompressing and recompressing. (The data may be modified along the way, if appropriate.)
Using a Compressor. The graphics exporter provides an atom container identifying which compressor to use, and any settings to be passed to that compressor.
Standalone Export. The graphics exporter component does all the work itself, without using an image compressor.