The pictures in the dark areas get blocky.
"Grainy", "blocky"... are you refering to
pixelation?
Otherwise, if you are refering to
banding in the dark & grey shades, it may be that you have your gamma / contrast settings too high.
If you are referring more to a
cloudy look in the blacks, then this is a trait of the panel (vs. CRT, anyways) and again, may be less noticable if your adjust your contrast / gamma.
Rough rule of thumb:
1. Go into your Display settings -> graphics card drivers and set the colors / gamma settings to their defaults.
2. Then find a greyscale map (Each review at www.dpreview.com has one)
3. Adjust your room lighting like it will be 85% of the time.
4. Turn the monitor's contrast all the way up.
5. Adjust the monitor's brightness settings until black is really black, without loosing sight of the first dark-grey bar.
6. Now adjust the contrast so that the first grey bar next to the white is not pure white (so that you are not loosing highlight detail).
The above should at least roughly adjust your monitor to display the greyscale as best as possible. If you are still not happy with your blacks, then look for a "movie" or "games" setting in the OSD. This will hike up the contrst levels - something you don''t want for text work, but will love for gaming, movies, etc.
Let us know how it goes
P.S. (aka edit...)
From
Trusted Reviews:
"In our DisplayMate test, the 226BW put in a very good performance; so long as the extreme Dynamic Contrast mode wasn’t used. Colours were vivid without being overdone and colour fading was excellent. There was a hint of banding in the 256 Intensity Level Colour Ramp test but it was only really evident with the Dynamic Contrast mode."