I'm only starting out with Registax myself. I have similar issues. You have obviously tinkered, with the brightness/contrast etc? Is it stacking correctly or blurring? I have found a secondary program such as Photoshop, or Gimp (Free download) can be helpful to finish an image.
Could you post what you have so far? I'm sure someone more knowledgable than myself, maybe able to fix it / tell you how to.
