The histogram does not need to be "live"... that is, it should be part of the passive thumb bitmap.
Here is an example:
User should have Options to...
1. Display/hide the histogram
2. Set background color and transparency
Also, since an histogram may not be useful for all thumbs, perhaps it would be appropriate to display an option dialog (to enable/disable the histogram) when the user selects View->Rebuild thumbs.
As always, thanks for listening!
