I made a quick video showing how to change the settings of the game file to allow the brightness slider to work.  But better than that, is to play in a window that is custom set for your monitor size.  In my experience, I have found that windowed-mode works better for brightness but I stretch it out to the full size of the display.  

This video shows how to made those changes in you uoconfig_mp.cfg file.  If you have any questions, let me know.  The link is not live yet but should be very soon!

Also, for Windows 7 users (i'm running 8.1) the maybe another location to save this file  like " C:\Users\"YOUR_NAME"\AppData\Local\VirtualStore\Program Files (x86)\Activision\Call of Duty"

But here is the link ----->>> Click Here

The file is up now but in low quality, will take awhile for Youtube to encode to high res so the text is easier to read!

Thanks for the tutorial I did as you mentioned above........ Got it working but in window mode my maxfps is capped at 60 I can not change this no matter what I do ......Any suggestions?