CGImage

CGImage is a Core Graphics image object that represents an immutable bitmap image within Apple's Quartz 2D framework. In C it is known as CGImageRef, and in Swift it is exposed as CGImage. A CGImage provides access to the image’s pixel data as well as the metadata that describes how that data should be interpreted by a graphics context.

A CGImage encapsulates key properties of the image, including width, height, bits per component, bits per pixel, and bytes per row. It also stores a color space and bitmap information that define how pixels are stored (such as alpha handling and byte order), along with a rendering intent used for color management when converting between color spaces. Because CGImage is a bitmap representation, it does not encode drawing commands; it simply provides the pixel data for rendering.

Creation and sources: CGImage objects can be constructed directly via creation functions (for example, using a data provider that supplies pixel data) or generated from image data using Image I/O, such as through CGImageSource. CGImageSource can read common formats from files or data and produce CGImage instances. CGImage is immutable, so modifications require creating a new image—typically by drawing into a bitmap context to produce a new CGImage.

Usage and rendering: CGImage itself does not render; it must be drawn into a graphics context with functions like CGContextDrawImage. In practice, CGImage is often wrapped by higher‑level objects for display, such as UIImage on iOS or NSImage on macOS, while still enabling low‑level image processing and efficient rendering.

Memory management: CGImage is a Core Foundation type and uses reference counting. In C you release it when finished; in Swift, bridging and ARC manage lifetime automatically.