Encoding video for 262k color screen

[swiftygem]

Hi, I recently got the Sony Ericsson W900i and I'm trying to encode videos for it, but there is a little problem. On color gradients like skin tones or light-dark transitions, I can see rings of the same color, not a smooth transition. I guess that's because video on computer is 24/32 bit and the screen on the W900 is only 18 bit. So, is there some way to perform this color depth conversion better during encoding?
BTW the format of video is MP4, XViD Simple @ L3 + AAC sound.

[scharfis_brain]

add some noise.
at least 2 bits of luma and chroma noise variation each.

18bit RGB = 6 bit per channel = roughly 6 bits for luma and 6 bits for chroma
24bit RGB = 8 bit per channel = roughly 8 bits for luma and 8 bits for chroma

so you have a difference of two bits to smooth over.

of course, adding noise WILL hurt compression.
also you need fairly high bitrates to preserve this grain (dither!).
becouse if you compress too much you'll loose that noise and thus it becomes useless.

[swiftygem]

The highest usable video bitrate for W900 is around 350-370 kbps with the Simple L3 profile, will that work?