This is a list of iOS image filtering, processing, OCR, utilities and helper libraries and frameworks that I have come across for iPhone and iPad development and thought that they may be useful in one places:
1. GPU Image
By Brad Larson, GPUImage is a fantastic fast processing library to apply gpu accelerated filters to both live camera feed, movies or stills. It works on iOS 4 and above. It includes a range of filters such as Sepia, Grayscale, Blur but you can write your own easily.
2. Core Image
This is an apple framework available from iOS 5. It leverages the GPU and you don’t need to know details of OpenGL, OpenGL ES.
Documentation: Apple Core Image Docs
One of the biggest computer vision libraries this has a broad range of inbuilt filter, algorithms, processes and more for image.
CKImageAdditions is a collection of additional functions and methods for working with Core Graphics and UIImages on iOS 3.0+. It features blending images, adjusting hue, saturation and lightness, trimming images and more.
5. iOS Image Filters
Image processing functions that give your iPhone or iPad application the instagram style filters. It was built on the idea of building photoshop filters in objective c. A useful library to apply filters to UIImage.
6. Simple Image Processing
Handling the UIImage it can perform: Canny edge detection, Gaussian Blur, Histogram equalisation, Skeletonisation, Thresholding (adaptive and global), Brightness normalisation, Blob extraction, Connected region extraction and interpolated resizing.
This is quite an old library as it has not been changed for 2 years. It was originally designed to perform a large image composite in the background so not blocking the main thread. FRImageOperation is an abstract class for creating NSOperations that allow for drawing in a background thread. FRBlockOperation does the same as the above, however instead of subclassing you can just a block.
This library shows enhanced speed of image processing by using Apple’s vDSP API. The library provides UIImage categories and provides allows you to easily apply sharpen, blur (box, gaussian and motion), and emboss filters.
9. UIImage ResizeMagick
Resize a UIImage ImageMagick style
Image filter library based on filtrr.js
11. XBImage Filters
XBImageFilters allows you to obtain filtered versions of any image or from the camera in realtime. It uses OpenGL ES 2 to filter the images through fragment shaders you write yourself so you can filter your images in whatever way you want and it is super fast.
12. iOS Image Filters
High-level CIImage-based image filtering on iOS 6+ using CoreImage & raster graphic overlays.
13. UIImageView Face Aware Fill
This category applies Aspect Fill content mode to an image and if faces are detected it centres them instead of centring the image just by its geometrical centre.
14. Tesseract OCR library
It helps you to use OCR in iOS projects, writing Objective-C. Easy and fast.
This provides the popular imagemagick library as a static library for iOS, which means you can resize, flip, mirror, rotate, distorat and sheer images, adjust iamge colours, apply sfx and draw lines, ellipses, polygons and Bezier curves.