Programming iOS 6, 3rd Edition

CIFilter and CIImage

The “CI” in CIFilter and CIImage stands for Core Image, a technology for transforming images through mathematical filters. Core Image started life on the desktop (Mac OS X), and migrated initially to iOS 5, bringing only a limited subset of the desktop filters, as iOS devices are not suitable for certain heavily intensive mathematical operations. In iOS 6, many more filters are provided; of about 140 filters available on the desktop, only about 40 are absent from iOS 6. To use Core Image, you’ll have to link your target to CoreImage.framework.

A filter is a CIFilter. The available filters fall naturally into several categories:

Patterns and gradients

These filters create CIImages that can then be combined with other CIImages, such as a single color, a checkerboard, stripes, or a gradient.

Compositing

These filters combine one image with another, using compositing blend modes familiar from image processing programs such as Photoshop.

Color

These filters adjust or otherwise modify the colors of an image. Thus you can alter an image’s saturation, hue, brightness, contrast, gamma and white point, exposure, shadows and highlights, and so on.

Geometric

These filters perform basic geometric transformations on an image, such as scaling, rotation, and cropping.

Transformation

These filters distort, blur, or stylize an image. They are the most intensive filters, so relatively few of them are available on iOS.

Transition

These filters provide a frame of a transition ...