Re: Sending VCGT data to wide gamut monitors using i2c?

[Richard Hughes <hughsient gmail com>]

On 29 June 2010 13:32, Graeme Gill <graeme2 argyllcms com> wrote:
> Naturally I've considered this.

I had hoped so :-)

>        There is no standard X mechanisms for doing this. X accesses
> the monitors i2c to load the EDID, but doesn't provide a general purpose
> communication channel. The logical place for it is in XRandR, since it
> knows about outputs (monitors). Although the i2c might be accessed elsewhere
> in Linux, there is the problem of figuring out the association between
> the i2c and the outputs.

Right, I've looked at doing this in X (or the kernel, via KMS) and it
basically comes down to ic2 being so slow. X can't run threaded, and
using i2c means we have to block for huge amounts of time. Doing it in
the kernel makes threads possible, although it makes things much
harder in other ways.

> The above wouldn't have stopped me doing this for MSWin and OS X,
> but there is the second problem: there is no standard i2c video monitor
> protocol for this. Each manufacturer can do it their own way, and
> doesn't publish how they do it. You have to reverse engineer it
> for each monitor. Without access to a representative set of
> monitors, the coverage of monitors is likely to be spotty.

Right, agreed. I've been looking at the database table in ddcontrol
and it only supports a few monitors out of the thousands of different
kinds ever made. With no agreed standard, I agree this is a classic
chicken and egg thing. I've been trying to use the standard (no
quirks) mode of ddcontrol and it seems to work kinda-okay, although
that could be me getting lucky.

> (I don't have a single monitor with this feature.)

I've got an LG monitor with this functionality, although I'm only
basing all my assumptions of "it'll work fine" on a sample size of 1.

Whether it's worth doing, I'm not sure. Maybe effort is better put
into putting the color conversion into a GLSL shader rather than
poking about with VCGT-type data.

Richard.