Develop example Swift application for OS X reading and manipulating images

Develop small example application that can read an image from a file (NSImage?). The image is displayed onscreen. A method is called to obtain the underlying pixels in an efficient manner so that they can be iterated. A calculation is done on each pixel with the result becoming a pixel in another separate image which is returned by the method and displayed next to the original image. For example, the calculation might involve comparing a given pixel to its immediate neighbors, perhaps figuring out a "difference": for each neighboring pixel, calculate the total difference of the Red, Green, and Blue values. Resulting pixel might be a grey scale value where black is no difference, white is maximum difference. The key to the value of this project is understanding how to _efficiently_ access image pixels, and how to create a new image to display on the screen. Prelude to larger project.