ImageIO

ImageIO is a software framework developed by Apple that provides interfaces for loading, decoding, encoding, and metadata handling of image data. It is designed to support a wide range of image formats and to integrate with other graphics tools on macOS and iOS.

The framework allows reading image data from various sources, including files, data objects, or URLs, through the CGImageSource API, and writing image data to destinations via CGImageDestination. ImageIO supports numerous formats such as JPEG, PNG, TIFF, GIF, and HEIC/HEIF, as well as many RAW formats supported by the platform. It also manages image metadata, including EXIF, IPTC, GPS, and XMP, and preserves color profiles during encoding.

Key features include on-demand or progressive decoding to optimize memory usage, thumbnail generation, and support for platform-specific metadata handling. ImageIO is designed to work in concert with Core Graphics and Core Image, enabling efficient integration into image workflows while maintaining metadata integrity and color management.

Usage typically involves Objective-C or Swift APIs. Developers create image sources with functions like CGImageSourceCreateWithData or CGImageSourceCreateWithURL, and create destinations with CGImageDestinationCreateWithData or CGImageDestinationCreateWithURL. Thumbnail extraction can be performed with CGImageSourceCreateThumbnailAtIndex, among other utilities. The framework is available on macOS, iOS, tvOS, and watchOS, and is intended for efficient image I/O and metadata operations rather than general image processing.

Limitations include its focus on input/output and metadata rather than advanced editing; for processing tasks, ImageIO is commonly used alongside Core Image or Core Graphics.