I just upgraded from my 4870 to a 5770. I was hoping it would fix this odd brightness issue I've had for a long time across different setups and drivers with ATI.
One of my two monitors (both the same model) is noticeably darker than the other. However, putting each into a single monitor config gives the proper brightness/contrast/color they're supposed to have. I haven't been able to figure out why and no amount of adjusting in CCC or Windows fixes it.
My brother told me he encountered the same issue on his ATI card and swapped it out with an Nvidia card and that fixed it but I'm skeptical. Does anyone have any input? I'm stumped and angry (at other 5770 related issues too).
Driving 2 moninitor from 2 outputs of the same video card does not usually mean the images will be identical. This is a common problem when the video card has one DVI and one VGA output, but it will happen to the cards with 2 DVI outputs also.
What I would suggest is that you change the brightness from the display's own settings.
I've tried adjusting the settings on the monitor itself, CCC, and Windows. Nothing gets it working properly. On my 4870, they were hooked up to dual-link DVI ports (card has 2 of them). There should be no forseeable reason for one image to be bright while the other one to be dark. It screams to me that there is something with the architecture of the card(s).