## Green pixels tracking

Jun 02 2006 | 1:57 pm
Hello, I've been trying out every jitter example but I can't figure out how to solve this. Basically I need to track the number of pixels of a certain RGB value (say green) within a certain treshold (green- and green+) and to see the percentage of this number on the whole matrix to trigger a jit.recordwhen this percentage is above 30%. Would you give me a starting idea on how to track the number of pixels of a certain color? Thank you very much. Ale
P.S. for who is looking for a cheap tv card that works in jitter I just bought a Hauppauge wintv-hdr 1100 and with jit.QT.grab and the abstract plane vdig component works great, while with the jit.DX.grab there is some flickering if I don't leave amcap open in the foreground :s anyway this product works well with jitter :)

• Jun 02 2006 | 2:21 pm
You need to think about the problem a little differently. Instead of thinking about tracking green in an otherwise complex image, you could think about tracking white against a black image (which would be easier, since you could use a histogram or the mean to easily detemine your 30%).
So, then the problem is - how to turn a range of green to white? jit.chromakey in mode 1 is probably the simplest.
Here's a sample patch:
jb
• Jun 02 2006 | 3:00 pm
Thanks a lot! I will use your approach, but before it would be nice to do a shader who just lets pass the pixels of a given value and sets the other to black. I can do that kind of things in a shader with much less effort, right? Then I can count the pixel number with histogram and spill, trigger the jit.record and record the actual output of jit.slab which is already processed. Ciao Ale
• Jun 02 2006 | 3:20 pm
Hi Alessandro, jit.gl.slab is probably not the way to go for analysis procedures. From the sounds of it, what you are looking for is the jit.op object, especially the logical operators (>,p,=). > and < ops will output a binary (black/white) image that can then be sent on to jit.3m.
Cheers, Andrew B.