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Core Image is a pixel-accurate, near-realtime, non-destructive image processing technology in Mac OS X. Implemented as part of the QuartzCore framework ofMac OS X 10.4 and later, Core Image provides a plugin-based architecture for applying filters and effects within theQuartz graphics rendering layer.[1] The framework was later added to iOS iniOS 5.[2]
Core Image abstracts the pixel-level manipulation process required when applying a filter to an image, making it simple for applications to implement image transformation capabilities without extensive coding. In a simple implementation, Core Image applies a singleImage Filter to the pixel data of a given source to produce the transformed image. Each Image Filter specifies a single transform or effect, either built into Core Image or loaded from a plugin called anImage Unit. Combined with preset or user-defined input parameters, the filter can be applied to the original pixel data without modifying it, thereby providing non-destructive image editing.[3][4]
LikePhotoshop, Core Image can apply multiple filters to the same image source. Instead of applying a series of filters individually, Core Image assembles a dynamicinstruction pipeline so that only one calculation needs to be applied to the pixel data to achieve a cumulative effect. Applying the pixel operations associated with multiple filters can be achieved simultaneously and without a significant increase in processing time. Regardless of the number of filters, Core Image assembles the code for this instruction pipeline with ajust-in-time compiler, which is executed by either the CPU or graphics card's GPU, whichever can perform the calculation faster.[5]
Filters are written in theCore Image Kernel Language, which shares a subset of commands with OpenGL Shading Language (GLSL).[6] When a compatible GPU is available, the Core Image compiler writes the instruction pipeline using GLSL, handling buffers and states transparently. Although GPU rendering is preferred[citation needed], the compiler can operate in aCPU fallback mode, generating commands suitable for the current CPU architecture instead.[7] CPU fallback uses thevector processing capabilities of the current CPU or CPUs, and it is multi-processor aware. Thus, Core Image performance depends on the GLSL capabilities of the GPU or the processing power of the CPU. With a supported GPU, most effects can be rendered in realtime or near-realtime.[8]
Core Image was introduced withMac OS X 10.4.[9]Early examples of its use can be found in theripple effect inDashboard, and Apple's professional digital photography application,Aperture.[10] Starting withMac OS X 10.5, any application that implements Image Kit can utilize Core Image.[11]Preview andiPhoto are common examples.
In 2011, Apple added Core Image to iOS in iOS 5.0.[2]
TheXcode Tools includeCore Image Fun House andQuartz Composer; both utilize Core Image.
The Core Image plugin architecture was inspired by that of Core Audio.[12]
All pixel processing provided by an Image Unit is performed in a pre-multiplied alpha (RGBA) color space, storing four color channels: red, green, blue, and transparency (alpha). Each color channel is represented by a 32-bit,floating point number. This provides exceptional color depth, far greater than can be perceived by thehuman eye, as each pixel is represented by a 128-bit vector (four 32-bit color channels). For color spaces of lower bit-depth, the floating-point calculation model employed by Core Image provides exceptional performance, which is useful when processing multiple images or video frames.[3][13]
Any programmable GPU that supports the required OpenGL Shader (GLSL) commands is Core Image capable. Apple has used the following graphics cards to support Core Image GPU processing in Mac OS X 10.4 and Aperture, so the following list could be considered an example of minimum requirements:[10][14]
Note that any GPU capable of handling Core Image instructions is alsoQuartz Extreme capable. The requirements for Core Image are greater than those of Quartz Extreme.[14]
macOS includes many built-in filters, including the following ones. Mac OS X 10.4 introduced over 100 of them, and Mac OS X 10.5 added to the list.[3][15]
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