Seeking advice on image analysis process

hello, i'm a complete newbie, however, i somehow got myself faced with an assignment which requires heavy involvement of the jitter software and i'm desperately asking for your help here. i'd appreciate if you will show generosity to provide me some hints. please understand the ironic situation and my lack of eloquence.
basically, the project i've been planning is a simple(?) light-triggered midi controller. jitter will be in charge of the input part which will then be associated with the MIDI controller part consisting of max objects.

i want to have jitter to analyse the light source (ex. laser pointer, flashlight, etc) projected onto a matte wall through a firewire connection to a sony camcoder (with a resolution of 680 x 480px approx).

following things need to be done

1 - detection of specific brightness values(above a certain threshold which will be the brightness value of the matte wall)

if pixel > threshold have it report back grid reference

i'd like to find out which object i should use to solely extract brightness value of an image in greyscale as it won't be necessary to track colour information

with my limited knowledge, i can only assume jit.3m is appropriate for such task though i don't know which outlet does the job i need.

2 - grid-fying the image for multiple analysis

if possible, i want to divide the whole image into grid to utilise each one of them as a shell, to have above process (1) take place in each one of them.

i'm again guessing that jit.findbounds might be able to do it. but would it be possible to apply this in plural manner?

i'd like to know which objects would be most suitable for above explained processes, some specific explanation would be a huge help for me.

i will upload more questions if i manage to simplify the idea..

truthfully,
mr. h