Simple Detector

I am back to work on the OSX Cocoa multi touch thing after being away doing some paying work for a few weeks. I am pretty happy with the prototype, as far as most of the concepts seemed to work OK. The only thing that was a bit iffy was my recursive blob finding algorithm. It works fairly well and fairly quickly, and it was fun to figure it out, but I am sure that it is very sub-optimal. So, i went to find out how the big boys do it. I grabbed the opentouch libs (thanks Pawel for all the great work!) and read the blob detector code.
Now i am a pretty code-savvy guy, i have been coding in C-like languages for a loong time now, but these pixel-level algorithms make my head spin without some direction as to what is really going on. So i had to look further afield. Somewhere in Pawels documentation I came across a reference to this paper:

A Linear-Time Component-Labeling Algorithm Using Contour Tracing Technique

Which is basically what the opentouch algo is based on. So I started from scratch (so i would know how it all worked in the end) and rewrote the algorithm described in the paper in Cocoa. (well, with a few little C bits, but mostly Cocoa). With a nice working blob finder and a nice working sequence grabber and a stack of other design ideas that are scattered through my prototype, i started a new project form scratch to make a proper application. So far what I have is a very stripped down blob detector.

All it does so far is grab images from any firewire cameras and analyze them for blobs based on a simple threshold and background subtraction. It hasnt really been optimized for speed yet, although it is pretty quick. I think the slowest part is just setting the image into the NSImageView. Those views were never really meant to show video, so if you bump the raw camera size up to 640×480 it can get a bit slow. But I will be doing quite a bit of optimization later on. (and for actual blob detection, you really dont need to see the video, and if you did, it would make more sense to use a different view)

There is a pre-process pipeline (sorta) so if you feel the need to add any filters or anything before it gets to the blob detection portion of the show, you can do that easily. The blob detector is currently written to handle NSImages, but it would be fairly trivial to change that for CIImages or CGImages. (or all three)

In any case, here is the code for anyone who wants it:

bbtouch.tar

[UPDATE:] i managed to more than triple the performance of the blob detector last night. I will post more details and the newer code in a new blog post a bit later this morning once i have had some brekky and caffeine. :-)