The original was shrunken to the posting size, but it was easy enough to again grab your posted picture and plug the numbers into a paint program's histogram function (which I use for quick tests):
You may have some other program or plug-in to apply this to your video, but I've used the VirtualDub plug-in Gradation Curves and it's just as interactive as a paint program, with improved features. It's supposed to be Avisynth compatible but I couldn't get that to work (Avisynth is not interactive anyway and interactivity may not show there). See my post in the THX 1138 preservations thread http://originaltrilogy.com/forum/topic.cfm/THX-1138-preservations-Italian-Cut-available-see-1st-post/post/589761/#TopicPost589761 for more information and examples.