Hello,
there is a known problem with newer generations of graphic-cards (or drivers) concerning their obvious inability to generate 16-bit dithering. It affects a large amount of older games (pre-2004), which are based on 16 bit - including the Thief-Games (Thief 1 + 2 and System Shock 2), Outcast, Wing Commander Prophecy, Panzer Elite, Interstate 76, Undying, Might and Magic 8, Alone in the Dark: The new nightmare, Gothic 2, Myth TFL etc. ...
The result is an inferior graphic quality, especially in transitions between darker textures. As I see, these problems are also in the gog-releases. Is there a possibility to solve this problem, perhaps by forcing the games using 32-bit-rendering?

For the Dark engine games (Thief I, II and System Shock II) they only way I know of is to use DDFix. Thief II looks pretty amazing in it, for a 10 year old game.
http://www.ttlg.com/forums/showthread.php?t=121449
It was originally written to fix the DDraw problems with DX6 calls not being supported, but Jermi has added lots of things recently to it such as 32-bit graphics.

Thank you for your reply,
I use ddfix myself, but for all the other games, there seems to be no solution - and that's a shame, because these games actually looked much better back in those days than they do on our hightech-graphic-cards...

If you have an nVidia card, maybe nVidia Inspector can help?

EDIT: clarification

Hello,
The mentioned problem affects all modern graphic-cards. I - for example - experience the same problems on GeForce- and ATI-Cards and even on the onboard-solution of my laptop. It's a general issue of modern hardware, not limited on a certain card. If a (older) game is built on 16-bit-dithering, a newer graphic-card simply isn't able to display the same quality of filtering. You can see it clearly on colour-transitions on textures, for example in Panzer Elite: The grass underground shows a very ugly banding. Or in Might and Magic VIII: The sky shows the same banding-problem. The same for Alone in the Dark (sky-textures in the beginning of the game) and many, many others. I still know the look of these games back in the nineties and I know for sure they looked much better on my old GeForce 6800 or ATI 1950. I just can't enjoy these titles in their current state.