jit.matrix single cell data

Hi everyone. I'm fairly new with Max. I have a question concerning how to extract single cell data in jit.matrix.

What I'm trying to do is: I have a black and white jpeg image of just lines read from jit.movie attached to a pannr that cycles the x offset with the twiddlr. The image just moves linearly and repeats. Essentially what I'm trying to do is just to send a bang when the white line reaches the end of the screen. I want the white lines to act as triggers for different samples whenever they reach the end. Ideally maybe like 10 different sounds controlled by dividing up the y axis. I would only really need to read the last few cells on the x axis. When it reaches a certain point it would (to start simply for now) just trigger a bang if white, or close to white.

Can anyone point me in the right direction? Thanks