All the Cocoa programming that could be crammed into 5 days

I just spent the last week attending the Cocoa bootcamp from Big Nerd Ranch. I have one thing I'd like to clear up before I get started. The hat is just a prop. That's right, when you go to WWDC and you see Aaron Hillegass walking around with his big texas style cowboy hat, he's doing it for marketing purposes. I guess it works, because when I decided to get some Cocoa training, I remembered Aaron and the hat walking around the Moscone center and on the back of his book: Cocoa(R) Programming for Mac(R) OS X (2nd Edition)

Now, I'm not normally a fan of technical training. Give me a book and a web browser and a project and I'm good. Of course this leads to interesting situations like the time I reverse engineered the Windows virtual to physical address mapping structures while not knowing how to refresh an explorer window (It's F5, right?).

I've been poking around in Cocoa for a while now, and though I feel like I made some decent progress, I'm really interested in this technology and wanted to get a comprehensive overview of it from an expert. Sometimes you just want to do things “right.” I figured that in 5 days I'd get a quick but comprehensive overview of most of the technologies in Cocoa from a well known expert in the technology.

The course did not disappoint. We dove right in to code, with Aaron leading us through an example application immediately, before even lecturing. All the lectures were relatively short, and most of the time in the class was spent actually coding. We mostly followed along with the exercises in the book, but we were encouraged to explore and change things as we progressed. In four and one half days we covered nearly the entire book, as well as several additional chapters that were part of the course materials.

In the evenings, most people chose to come back to the classroom and either continue to work on the exercises or to work on a personal project. Aaron typically stayed around until about 10PM answering questions and being generally helpful.

Out on our daily walk (image courtesy of Paul Warren)

The people who took the class came from all over the country and the UK and had varied backgrounds and skill levels, but overall, they were extremely competent and interesting folk. It was enjoyable to meet each of them. I was surprised at how many people were paying their own way to take this class, which was not an insignificant investment in personal time and money. I estimate that about half of the people were there on their own ticket.

The price of the course covers ground transportation to and from the airport, lodging and all meals as well as a copy of Aaron's book and course materials. If you don't want to bring your own computer, a modern iMac will be provided for you to use.

View from my suite

The place we stayed, Serenbe Southern Country Inn, was probably one of the nicest places I've ever stayed. My personal suite had a screened in porch, a kitchen, a large living room with fireplace, a king size bed, whirlpool tub and huge glass shower. They fed us three excellent meals each day, along with snacks and drinks as we wanted them through the day.

I really benefited from this class. Some topics seem complex when you try to explore them on your own, but Aaron was able to make them very accessible. Cocoa Bindings had always seemed somewhat inscrutable to me, but now things are much clearer. The Undo Manager in Cocoa is amazing; it really showcases how a dynamic language can be leveraged to make something that can be hard in other frameworks really easy. And I now feel like I understand how to build custom Views - something that always seemed difficult to me but is actually quite straightforward now.

The idea of a total immersion environment, with all details taken care of and few distractions, along with a very experienced and patient instructor, leads to a learning environment that encourages success. I highly recommend this class to anyone who would like to learn Cocoa.

Cocoa Application with custom Core Image filter 3: Testing the kernel with QuartzComposer

In the last post I wrote a convolution kernel for Core Image. But these kind of things need to be tested. Now, we could package the filter inside an Image Unit (which I'll do in a future post) but that would mean we would have to recompile and install the filter each time we wanted to make a change. It would be much better if there was an interactive environment that could be used to test any changes and to allow us to debug the filter code.

Luckily, Apple has provided just such an environment in QuartzComposer. If you are not familiar, Quartz Composer is an amazing application that provides a visual programming environment that allows the creation of all kinds of visualizations. If you've seen the RSS screensaver. then you've seen a QuartzComposer composition. If you've seen a preview of Time Machine, the swirling galaxy in the background is a QuartzComposer composition. I'm not going to explore this amazing piece of software in depth here, I suggest you look at some of these websites for more information: Quartz Composer Journal or www.quartzcompositions.com or boinx or Quartonian.

As a basic introduction, a composition is defined by dragging patches onto the workspace and connecting them together graphically. Patches contain ports which represent parameters which are passed between the patches. The results are displayed in real time in the viewer window, so you get immediate feedback as you change things. As we'll see later, Quartz composer compositions can be embedded in a QCView in your Cocoa apps, and controlled via Cocoa Bindings.

I've provided a link to my test.qtz composition which consists of four patches. The convolution patch is built by dragging a core image kernel patch onto the editor and then copying the text of the kernel into the patch. You can use the inspector to change the input parameters to adjust the coefficients and test out the composition.


This is the editor window, showing the composition.


Here's the inspector for the Convolution patch showing where you put the kernel code.


This is the viewer, showing the input image filtered by the edge detection filter defined in the Input Parameters to the Convolution filter.


If you have an iSight camera or other video source, replace the Image Importer with a video input, and you will see the convolution filter applied to your video stream in real time. That's just extremely cool.

Here's the editor window with a Video Input instead or the Image Importer.
And here's a view of my living room with edge detection. Notice the frame rate of nearly 60 frames per second on my Mac Book Pro.

Using this basic composition, with some modifications, you should be able to test out any core image kernel you can come up with. Next time, I'll build this filter into an image unit that can be used from any application that uses Core Image filters.

Building a Cocoa application using a custom Core Image filter (introduction)

A couple of months ago, some members of my team were working on a facial recognition project for one of our customers. One thing they were trying to do was to determine if filtering the images in various ways could improve the recognition algorithm.

They were implementing their system in Java, but I immediately thought that Core Image would make their job much faster, since we could offload the image processing to the graphics cards on our Mac Pros rather than writing the algorithms in Java.

If you are not familiar, Core Image is Apple's image processing framework which can provide very high performance image processing by offloading the work of image processing to the graphics card. Core Image includes a huge number of image filters (just check out the list on the Apple web page).

The test system applied a sequence of image convolution filters to images with varying coefficients and then submitted the filtered images to the recognition system where they would be scored. We iterated over different combinations of filters to find a way to improve the scoring of the algorithm in general.

I was surprised to discover that Apple did not include a convolution filter by default. Convolution is the "jack of all trades" of image processing algorithms and can be used for all sorts of things like edge detection, sharpening, blurring, noise reduction, and so on, depending on the coefficients used.

This meant that I would have to develop my own custom image unit that performed convolution. This seemed like it might be a difficult task, but it turned out to be much easier than I expected. Along the way I learned a lot more about Quartz Composer, programming using the Open GL shading language, Cocoa Bindings, and creating custom image units on Mac OS X.

Over the next several posts I'll step through the development process to a working sample Cocoa application that allows you to apply convolution to any image.