Re: Gain controls in v4l2-ctrl framework

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi,

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 
channels, or could devices implement a per-channel offset ? Is the offset 
applied before or after the gains ? How does it relate to black level 
compensation ?

> I think these controls can fit under the image processing controls class
> --- image processing and not image source since these can also have a
> digital implementation e.g. in an ISP.

Sounds good to me.

-- 
Regards,

Laurent Pinchart