Intel - Dithering on a 6 bit panel

Stephane Marchesin marchesin at
Wed Mar 11 00:52:50 PDT 2009

On Tue, Mar 10, 2009 at 23:34, Adam Jackson <ajax at> wrote:
> On Fri, 2009-03-06 at 18:28 -0500, Benjamin M. Schwartz wrote:
>> Hash: SHA1
>> Eric Anholt wrote:
>> > On Tue, 2009-03-03 at 23:57 +0000, James Legg wrote:
>> >> Hello,
>> >>
>> >> I have an Asus X58L laptop, which has Intel GM965 graphics. The
>> >> framebuffer configurations reported by glxinfo all have 8 bits for each
>> >> of the colour channels. However, the output looks like 6 bits with
>> >> static 2 by 2 spatial dithering. Assuming the display is actually 6
>> >> bits, is there any way I can get temporal dithering?
>> >
>> > Yeah, your panel is likely only 6 bits.  I've never seen any knobs for
>> > better dithering.
>> If you're looking for a project, you could add a setting to the driver to
>> do the temporal dithering in software, on the GPU.
>> That would be a terrific hack.
> I have difficulty imagining any implementation of this that wouldn't
> absolutely murder your battery life.

Well, right now the video quality on intel is quite horrible because
of that regular 2x2 dithering pattern, even on a laptop it would be
nice to have the option. And if your machine is not a laptop it
doesn't matter anyway how long your battery lasts. FWIW I gave it a go
and tried to change PFIT_CONTROL bits but none seems to affect the
dithering more than just on/off.

An alternate solution I experimented with is to use the overlay, and
add/remove 1 to the brightness 60 times a second (or whatever your
vrefresh is). That results in temporal dithering and makes the ugly
regular dithering pattern mostly invisible. However properly
implementing this in the driver is another matter...


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