Mailinglist Archive: radeonhd (699 mails)

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Re: [radeonhd] Dithering, how to disable
  • From: Luc Verhaegen <libv@xxxxxxxxx>
  • Date: Fri, 2 Nov 2007 10:56:19 +0100
  • Message-id: <20071102095619.GA27832@xxxxxxxxx>
On Thu, Nov 01, 2007 at 09:22:22AM +0100, Pierre Ossman wrote:

It seems that Lenovo doesn't really believe in the concept of truth in
marketing. The panel advertised as 24-bit is actually 18-bit (they
claim 16.7 M colors, not 16.2 M or the actual 262 k). To compensate,
there is some dithering involved, and seems to give an effect most
people describe as "sparkling".

Could it be that it really is a 24bit panel and that, since we do not
know any better, we set it up as an 18bit panel and it still works?
When i'm back in the office; i should probably try to set up the hp
laptop as 24bits. This laptop is a mobility r5xx, 1680x1050, so i was
initially quite surprised to see that it was only an 18bit panel. Iirc,
i attempted to drive it differently, without success, but this was in
the hectic days right before XDS.

This grainy, or sparkly, appearance is a bit annoying and might be the
reason why I perceive this display as straining. So I'd like to
disable it and see if that makes me a happy camper.

I've been fiddling with the register LVTMA_BIT_DEPTH_CONTROL,
disabling the relevant dither bits there. That does indeed remove so
much of the dithering that you can start seeing the banding caused by
the 18-bit truncation. Unfortunately, the display is still grainy, so
something is still active.

Please describe what you mean by grainy? Could there be something else
going on besides dithering? I hope it is not something as
straightforward as adjusting gamma.

So my question is if there are more things I can tweak or if the
remaining issue is just a property of the matrix.
TMDSA_BIT_DEPTH_CONTROL seems to be just for TMDS (which is just for
DVI?), but there's also a DVOA_BIT_DEPTH_CONTROL which I'm unsure
where it fits in.

These are both for seperate outputs and will not influence your panel.

Luc Verhaegen.
SUSE/Novell X Driver Developer.
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