Question for expression killers ( particles )

[cynamonster]

My mind is in particles again. Heres what I want to achieve.
Ive got greyscale bitmap mapped on simple plane. The task is to  place particles over the plane basing on greyscale levels of texture : If black - particles are lower, if white - they are higher. 
So lets say I emit particles to goal, and add offset attribute to them ... but the trick is what attribute of the texture am i to attach my particles, to place them like I wrote above ( black :lower, white: higher ???How am i to get values of greyscale to tranlsate them to scale from 0 to 1 ?
Any masters out there to help? Or you may know of some workaroud for this?
Thanks for help a lot !

[ldunham1]

im not sure if this is the way you'll want to go about this but you can plug any one of the rgb color attrs and as white is regestered as 1 1 1 and black 0 0 0, therefore for any one of the rgb attrs, white is 1 and black is 0.

Hope that helps.