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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Sakari Ailus <sakari.ailus@iki.fi>
Cc: Prabhakar Lad <prabhakar.csengg@gmail.com>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Guennadi Liakhovetski <g.liakhovetski@gmx.de>,
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	Prabhakar Lad <prabhakar.lad@ti.com>,
	Manjunath Hadli <manjunath.hadli@ti.com>
Subject: Re: Gain controls in v4l2-ctrl framework
Date: Mon, 24 Sep 2012 13:05:41 +0200
Message-ID: <2315690.D7OkA08Cfz@avalon>
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On Sunday 23 September 2012 19:27:03 Sakari Ailus wrote:
> Laurent Pinchart wrote:
> > On Sunday 23 September 2012 16:20:06 Sakari Ailus wrote:
> >> Prabhakar Lad wrote:
> >>> Hi All,
> >>> 
> >>> The CCD/Sensors have the capability to adjust the R/ye, Gr/Cy, Gb/G,
> >>> B/Mg gain values.
> >>> Since these control can be re-usable I am planning to add the
> >>> following gain controls as part of the framework:
> >>> 
> >>> 1: V4L2_CID_GAIN_RED
> >>> 2: V4L2_CID_GAIN_GREEN_RED
> >>> 3: V4L2_CID_GAIN_GREEN_BLUE
> >>> 4: V4L2_CID_GAIN_BLUE
> >>> 5: V4L2_CID_GAIN_OFFSET
> >>> 
> >>> I need your opinion's to get moving to add them.
> > 
> > We already have a V4L2_CID_GAIN control and a V4L2_CID_CHROMA_GAIN control
> > in the user controls class. I'd like to document how those controls and
> > the new proposed gain controls interact. At first glance they don't
> > interact at all, devices should not implement both, the user class gain
> > controls are higher- level than the controls you proposed - this should
> > still be documented though, to make sure driver and application authors
> > will not get confused.
> > 
> > A couple of quick questions about the new controls. Do we also need a
> > common gain controls for monochrome sensors ? Is the offset always common
> > for the 4
>
> I think we should have a common gain control for sensors in general,
> whether monochrome or not. Many sensors support global digital gain,
> either only or besides the per-channel gains.

Agreed. The documentation should clearly state that drivers must not implement 
the common gain control as a shortcut to set all color gains to the same 
value.

-- 
Regards,

Laurent Pinchart