In the last post in this mini-series, Mike gave an overview of the Fourier Transform and then showed you how to use Apple's implementation of the Fast Fourier Transform (FFT).

Last time around I discussed the basics of audio data, how to get it, and how to understand it. Today, I'm going to go into some detail about one of the fundamental tools for more complex audio analysis, the fourier transform, and the FFT algorithm that makes it practical to use on computers.

Continuing the multimedia data processing trend, today I'm switching over to audio. A reader known as Derek suggested a discussion on how to obtain and interpret audio data, which is what I'll cover today.

Last time, I presented the implementation of a basic flood fill. That implementation works fine, but is not terribly fast. Today, I'm going to walk through various optimizations that can be done to make it faster, using techniques which I hope will be useful in many different situations. Ultimately, starting from the original code, I was able to achieve over an order of magnitude speedup while still keeping the code relatively straightforward and clear.

Following up from the previous article about manipulating image data, Marc Palluat de Besset suggested a followup discussing the implementation of a flood fill. Today, I'm going to walk through the theory and practice of implementing flood fill on an NSBitmapImageRep.

Cocoa provides some great abstractions for working with images. NSImage lets you treat an image as an opaque blob that you can just draw where you want it. Core Image wraps a lot of image processing in an easy-to-use API that frees you from worrying about how individual pixels are represented. However, sometimes you really just want to get at the raw pixel data in code. Scott Luther suggested today's topic: fetching and manipulating that raw pixel data.

It's the end of another work week, and time for another Friday Q&A. Reader James Safechuck suggested that I write about encryption, and for today's article I've creatively interpreted the request and will give a tour of the built-in CommonCrypto library.

It's time for another edition of Friday Q&A. In the last Friday Q&A, I discussed how to create classes at runtime in Objective-C. Today, I'm going to discuss how to actually make practical use of this technique.