Via the Video Sequence Editor
Import your Image Sequence into the VSE and in the Properties Modifiers Panel with your Strip selected you can add a Strip Modifier for your whole Image Sequence like a Color Balance or a White Balance Modifier.
You could copy them to other Strips if needed selecting Replace or Append now since 2.77.
In the White Balance Modifier you can pick a Color from your Sequencer Preview to set a White Level:
All pixels will then mathematically be divided by this choosen color.
Apart from that, the Bright/Contrast Modifier might help you with the blacks. Or when you use a Curves Modifier, you can easily boost your black level when you lift the bottom left part of the curve:
Unfortunately, the Curves Modifier for Strips doesn't have the White and Black Level Color Choosers as the RGB Curves Node does - where you can set exactly what you want.
But this RGB Curves Node is only available in Compositing via Nodes. So You might consider using one of the VSE to Compositing Add-ons for this:
Alternatively via Compositing
To use only nodes you might set your frame range to the length of your Image sequence, make sure, in the Post Processing Panel in your Properties' Render Tab you have only Compositing selected, check Use Nodes in the Compositing Node tree, remove the Render Layers Node and add an Input > Image Node instead. Set it to Image Sequence and set its frame range accordingly. Put the Color > RGB Curves Node between it and the Composite Node and hit Animation (F12).
(You might have to delete your default camera to prevent Blender rendering your Default Scene again and again, but I think it shouldn't do that when you delete that Render Output Node)