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.