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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 of Mac OS X 10.4 and later, Core Image provides a plugin-based architecture for applying filters and effects within the Quartz graphics rendering layer. ^[1] The framework was later added to iOS in iOS 5. ^[2]

Overview

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 single Image 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 an Image 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]}

Like Photoshop, Core Image can apply multiple filters to the same image source. Instead of applying a series of filters individually, Core Image assembles a dynamic instruction 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 a just-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 the Core 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 a CPU fallback mode, generating commands suitable for the current CPU architecture instead. ^[7] CPU fallback uses the vector 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]

History and implementation

Core Image was introduced with Mac OS X 10.4. ^[9] Early examples of its use can be found in the ripple effect in Dashboard, and Apple's professional digital photography application, Aperture. ^[10] Starting with Mac OS X 10.5, any application that implements Image Kit can utilize Core Image. ^[11] Preview and iPhoto are common examples.

In 2011, Apple added Core Image to iOS in iOS 5.0. ^[2]

The Xcode Tools include Core Image Fun House and Quartz Composer; both utilize Core Image.

The Core Image plugin architecture was inspired by that of Core Audio. ^[12]

Pixel accuracy

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 the human 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]}

Supported graphics processors

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]}

• ATI Mobility Radeon 9700 (Mobility Radeon 9600 is also capable)
• ATI Radeon 9550, 9600, 9650, 9600 XT, 9600 Pro, 9700 Pro, 9800 XT, and 9800 Pro
• ATI Radeon X600 XT, X600 Pro, X800 XT, X850 XT, X1600, X1900 XT
• ATI Radeon HD 2400 XT, HD 2600 Pro, and HD 2600 XT
• NVIDIA GeForce FX 5200 Ultra, FX Go 5200
• NVIDIA GeForce 6600, 6600 LE, 6800 Ultra DDL, and 6800 GT DDL
• NVIDIA GeForce 7300 GT, 7600 GT, and 7800 GT
• NVIDIA GeForce 8600M GT & 8800 GT
• NVIDIA GeForce 9400M & 9600M GT
• NVIDIA GeForce GT 120 & GT 130
• NVIDIA GeForce GTX 285
• NVIDIA Quadro FX 4500 & FX 5600
• NVIDIA Quadro FX 4800
• NVIDIA Quadro 4000
• NVIDIA GeForce 320M
• NVIDIA GeForce GT 330M
• NVIDIA GeForce GT 640M
• NVIDIA GeForce GT 650M
• NVIDIA GeForce GTX 660M
• NVIDIA GeForce GTX 675M
• NVIDIA GeForce GTX 680MX
• NVIDIA GeForce GT 750M
• NVIDIA GeForce GT 755M
• NVIDIA GeForce GTX 775M
• NVIDIA GeForce GTX 780M
• Intel GMA 900, GMA 950, or GMA X3100
• Intel HD Graphics 3000(Sandy Bridge)
• Intel HD Graphics 4000(Ivy Bridge)
• Intel HD Graphics 5000(Haswell)
• Intel Iris 5100(Haswell)
• Intel Iris Pro 5200(Haswell)
• Intel HD Graphics 5300(Broadwell)
• Intel HD Graphics 6000(Broadwell)
• Intel Iris 6100(Broadwell)

Note that any GPU capable of handling Core Image instructions is also Quartz Extreme capable. The requirements for Core Image are greater than those of Quartz Extreme. ^[14]

Built-in filters

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 has added to the list. ^{[3] [15]}

• Blurs, like Median, Gaussian, Motion, and Noise
• Color Adjustments & Effects, like Exposure, Gamma Adjust, and Sepia Tone
• Composition Operations, like Addition and Multiply Blends, or Hard Light
• Distortions, like Pinch, Circle Splash, and Vortex
• Generators, like Star Shine and Lenticular Halo
• Geometry Adjustments, such as Crop, Scale, Rotate, and Affine transformation
• Halftone, Tile, and Posterize filters
• Transitions, such as Dissolve and Ripple

An open source documentation website for built-in Core Image filters is maintained at CIFilter.io.

See also

• Aperture
• Core Image Fun House
• Quartz Composer
• LiveQuartz
• Pixelmator
• impromptu
• GEGL, a programming library used by GIMP
• Windows Imaging Component, a Windows component with similar API design but with fewer supported image operations.

References

Bibliography

• Singh, Amit (June 19, 2006). Mac OS X Internals: A Systems Approach. Addison-Wesley Professional. ISBN  978-0-13-270226-3.

External links

• Core Image Programming Guide – Mac OS X Developer Library
• Apple Previews Mac OS X "Tiger" - announcement of Mac OS X 10.4, including Core Image
• Filterpedia - open source Swift app demonstrating almost every available built-in CoreImage filter along with custom GLSL and Metal based filters by Simon Gladman.