[Intel-gfx] 3.16, i915: less colors in X?

[Martin Steigerwald]

Am Sonntag, 22. Juni 2014, 00:51:55 schrieb Thomas Richter:
> Hi Martin,

Hi Thomas,

> >> I'm trying to figure out how to ask X what color depth it is using...?
> > 
> > I think:
> > 
> > martin at merkaba:~> xdpyinfo | grep -i "depth of root"
> > 
> >    depth of root window:    24 planes
> > 
> > but am not completely sure.
> > 
> >> This is thinkpad x60 with Debian 6.0.9.
> 
> AFAIK the 830GM chipset does not offer any support for hardware
> dithering. Whether the panel in the x60 does I do not know, though.
> 
> However, what is remarkable is that graphics on a 16 bit(!) screen may
> look more pleasing than graphics on a 24 bit screen, at least for such
> ancient machines. The reason is that the panel cuts the bitdepth down
> from 8 to 6 bits, without any dithering, just by cutting off the LSBs.
> However, if you select a 16bpp mode to begin with, some desktop
> environments (specifically gnome) apply a dithering of their own, even
> though the output is only 5 bit per component.
> 
> This is at least what I see here on the IBM R31 and the Fujitsu S6010:
> Gnome desktop at 16bpp looks better than the desktop at 8bpp, due to the
> lack of hardware dithering.
> 
> The X11 intel driver had an option "Dac6Bit" to signal the 6 bit panel
> resolution to X (even though the display pipeline operates in 8 bit
> mode), but I have never seen this working in the past time. It seems not
> to be supported anymore. Probably that's the culprit.
> 
> Martin, you should probably test Ville's alm_fixes5 kernel branch, its
> support for the 830GM chipset of the X30 is in my experience much better
> than that of the drm-intel-nightly or official kernels.

I didn´t report this. I just mentioned how to find out the screen depth. Pavel 
reported this. On my ThinkPad T42 I do not compile own kernels anymore and on 
this ThinkPad T520 I will wait till 3.16-rc2.

Thanks,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7