Does picture control refresh time depend on the content of the picture?

[Rolfe]

I'm trying to create a program which includes some custom displays built using picture controls, each of which updates very rapidly (about 10 updates/sec). The images are mostly contructed using Draw Point. When I construct the desired image and output it to the screen on each iteration, my front-panel update VI takes 10-20 ms per iteration. If I construct the correct display but instead output an empty picture, the front-panel update VI takes only 1-2 ms per iteration (in this case the correct image is not wired to anything, so I imagine it is possible that the compiler simply doesn't construct the image at all, but I don't know how to check if this is the case). What influences the speed with w
hich a picture control can be refreshed? Is there any way I can speed up the writing of the new image to the screen?

Thanks,
Jason

[Rolfe]

Well, some more probing reveals that pictures are in fact long strings which explicitly contain every point/line in the picture, rather than bitmaps (which is what I assumed the picture used for its underlying representation). I guess I need to use bitmaps (or something like them) explicitly.