For scanning animation drawings for import into animation apps such as TVPaint Animation or ToonBoom Animate Pro / Harmony, or Digicel Flipbook you should seriously consider VueScan scanning software. VueScan (for Mac, Windows, and Linux) offers many options for image adjustment/enhancement . Scan your drawings in VueScan, then import to TVPaint (or ToonBoom, or Digicel , though I think of these TVPaint is the best) .
If your are using video capture instead of scanning then get iGlasses for Mac (Mac only, not for PC Windows) . iGlasses gives you many more options for manually adjusting the exposure, focus, and white balance using an HD webcam (such as the Logitech C-920) .