[Bug 55121] Limited color range on screen that is connected via HDMI [SandyBridge]

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=55121





--- Comment #7 from Ivan Bulatovic <combuster at archlinux.us>  2013-04-10 21:23:07 ---
(In reply to comment #6)
> As stated in the commit message, the logic selects limited range when a CE
> video mode is used. And your monitor's preferred mode just happens to be one of
> these CE video modes, so there you have it.
> 
> Some monitors/TVs don't even allow you to change the setting from the OSD when
> a CE video mode is used (my TV is like this), so following the spec is pretty
> much the only option we have to guarantee that we see the expected result with
> most displays. In your case your monitor apparently allows you to change the
> setting even when using a CE video mode.

Understood and agreed.

> Unfortunately your monitor doesn't support another feature that would allow it
> to detect which setting is used by the source device, so you must manually
> choose the matching option from the OSD. And for some reason the monitor
> doesn't implement the CEA spec correctly, so it gives you the wrong default
> setting.

OK, let me see if I understood this one.

1. Monitor default mode is CE
2. Monitor OSD default mode is wrong (set for Full range)
3. We automatically search for monitor default mode, CE is the one, set RGB
color range to limited
4. Since OSD mode is Normal (instead of low) I can see white somewhat darker
(it's not 0 now it's 16) and black somewhat lighter (it's 235 instead of 255).
5. Now monitor doesn't pick up that input is set to limited range and stays on
Normal setting

One thing is missing though, what have we done before this commit ? We set the
colorimetry to full range as default and if it isn't supported at all we set it
to 16_235 ? If the data we receive is valid at all ? Looked at intel_sdvo.c and
intel_sdvo_regs.h and still I'm not sure about this one.

But I don't have to be, it would be nice for us to be able to select rgb color
range as a kernel parameter ie (maybe there is already, just not aware of it
yet).

> You said that you get a better picture when you configure your TV for "Low",
> but you said whites are dirty. Does that mean it's still too dark or something?
> I'm not 100% sure we're utilizing the 16-235 range fully, or if we're
> under/overshooting the signal a bit. Unfortunately I'd need a HDMI/DP frame
> grabber or some kind of analyzer to find out for sure, and I don't have such
> devices currently.

Don't worry about this, this isn't about the signal, it's this trash for a
monitor that I shouldn't have bought in the first place. :)

I was just trying to figure out how can we emerge from this, if specs werent
followed strictly - problems are bound to happen either way and the only thing
that can help the end user is to set the parameters himself. Personally I'm
wondering is there a way and how ?

Thanks Ville !

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