Images are represented as instances of the class
UIImage. Although this class contains several useful methods
(e.g. to draw images, to create images from different
sources) we will often need to process the images’ pixels.
To do this we recommend the use of the helper class
ImageHelper (see [2]) that contains several macros and
class methods, including:
Methods to convert between instances of UIImage and
arrays of characters for direct pixel access;
Macros to get and set pixels in these arrays of characters;
Methods to get images from views;
Methods to scale an image and to center it around a
view;
Using methods in this class makes manipulation of the
pixels easy, as seen in the code snippet shown in listing 5,
which gets an image from a view, processes it (converts it
to grayscale) and display it.