Re: [RFC PATCH 1/4] v4l: Add V4L2_CID_PRESET_WHITE_BALANCE menu control

[Sakari Ailus <sakari.ailus@iki.fi>]

On Wed, Jan 04, 2012 at 11:06:13PM +0100, Sylwester Nawrocki wrote:
> Hi Sakari,
> 
> On 01/04/2012 10:24 PM, Sakari Ailus wrote:
> >>>>> I don't quite understand the purpose of the do_white_balance; the
> >>>>> automatic white balance algorithm is operational until it's disabled,
> >>>>> and after disabling it the white balance shouldn't change. What is the
> >>>>> extra functionality that the do_white_balance control implements?
> >>>>
> >>>> Maybe DO_WHITE_BALANCE was inspired by some hardware's behaviour, I don't
> >>>> know. I have nothing against this control. It allows you to perform
> >>>> one-shot white balance in a given moment in time. Simple and clear.
> >>>
> >>> Well, yes, if you have an automatic white balance algorithm which supports
> >>> "one-shot" mode. Typically it's rather a feedback loop. I guess this means
> >>> "just run one iteration".
> >>>
> >>> Something like this should possibly be used to get the white balance
> >>> correct by pointing the camera to an object of known colour (white
> >>> typically, I think). But this isn't it, at least based on the description
> >>> in the spec.
> >>
> >> Then either the spec is incorrect, or I'm mistaken. My understanding of the
> >> DO_WHITE_BALANCE control is exactly what you described.
> > 
> > This is what the spec says:
> > 
> > "This is an action control. When set (the value is ignored), the device will do
> > a white balance and then hold the current setting. Contrast this with the
> > boolean V4L2_CID_AUTO_WHITE_BALANCE, which, when activated, keeps adjusting the
> > white balance."
> > 
> > I wonder if that should be then changed --- or is it just me who got a different
> > idea from the above description?
> 
> Only you ? :-) Same as Laurent, I understood this control can be used to do white
> balance after pointing camera to a white object. Not sure if the description
> needs to be changed.

Definitely it needs to be changed. Who will submit the patch? :-)

-- 
Sakari Ailus
e-mail: sakari.ailus@iki.fi	jabber/XMPP/Gmail: sailus@retiisi.org.uk