I'm very glad you reply me quickly. But this maybe a very complex method in my animation (the level of grayscale in many areas will be changing during animation) , because there would be lots of areas that I had to keyframe. If my customer want to change the map(the global grayscale map), the quantity of work will be a nightmare.
My original idea is I hope I can control the dencity of the trees on the whole surface just by animating one grayscale bitmap (Such as one sequence of files exported by After effects. )
AND I came up with a idea. It might be a good workaround. But I do not know if this can be done in 3DSMAX.
1. In photoshop, if I turn my grayscale map into "dot chart" bitmap I would use this "dot chart" picture as distribution map in forest pro.(Please see my attachments.)
2. But how can I turn my grayscale map into "dot chart" bitmap in material editor dynamiclly during animation in 3DSMAX 2012 ?
Can you give me some suggestion ?