glHistogram is too slow! Pls help!

Hi ,
I have implemented glHistogram fn to obtain the histogram in a subwindow ,of a paused image in a scrolling display. Once the glHistogram is activated , the scrolling display moves very slow after that.I am enabling the glHistogram only in the keyboard fn and am disabling and resetting the glHistogram once the subwindow is destroyed.I am using glTexImage2D before calling the glHistogram function.
Any suggestions to spped up the display?
pls Help!
Thnx in advance!

Dont use glHistogram or any other ARB_Imaging function they are not well supported. Insead use occlusion queries to generate the histogram as given here

Thanks . I will definitely try this.