Hi,
On Wednesday 28 December 2011 14:35:00 Sylwester Nawrocki wrote:
> On 12/28/2011 07:23 AM, HeungJun, Kim wrote:
> > It adds the new CID for setting White Balance Preset. This CID is
> > provided as menu type using the following items:
> > 0 - V4L2_WHITE_BALANCE_INCANDESCENT,
> > 1 - V4L2_WHITE_BALANCE_FLUORESCENT,
> > 2 - V4L2_WHITE_BALANCE_DAYLIGHT,
> > 3 - V4L2_WHITE_BALANCE_CLOUDY,
> > 4 - V4L2_WHITE_BALANCE_SHADE,
>
> I have been also investigating those white balance presets recently and
> noticed they're also needed for the pwc driver. Looking at
> drivers/media/video/pwc/pwc-v4l2.c there is something like:
>
> const char * const pwc_auto_whitebal_qmenu[] = {
> "Indoor (Incandescant Lighting) Mode",
> "Outdoor (Sunlight) Mode",
> "Indoor (Fluorescent Lighting) Mode",
> "Manual Mode",
> "Auto Mode",
> NULL
> };
>
> static const struct v4l2_ctrl_config pwc_auto_white_balance_cfg = {
> .ops = &pwc_ctrl_ops,
> .id = V4L2_CID_AUTO_WHITE_BALANCE,
> .type = V4L2_CTRL_TYPE_MENU,
> .max = awb_auto,
> .qmenu = pwc_auto_whitebal_qmenu,
> };
>
> ...
>
> cfg = pwc_auto_white_balance_cfg;
> cfg.name = v4l2_ctrl_get_name(cfg.id);
> cfg.def = def;
> pdev->auto_white_balance = v4l2_ctrl_new_custom(hdl, &cfg, NULL);
>
> So this driver re-defines V4L2_CID_AUTO_WHITE_BALANCE as a menu control
> with custom entries. That's interesting... However it works in practice
> and applications have access to what's provided by hardware.
> Perhaps V4L2_CID_AUTO_WHITE_BALANCE_TEMPERATURE would be a better fit for
> that :)
>
> Nevertheless, redefining standard controls in particular drivers sounds
> a little dubious. I wonder if this is a generally agreed approach ?
No agreed with me at least :-)
> Then, how does your V4L2_CID_PRESET_WHITE_BALANCE control interact with
> V4L2_CID_AUTO_WHITE_BALANCE control ? Does V4L2_CID_AUTO_WHITE_BALANCE need
> to be set to false for V4L2_CID_PRESET_WHITE_BALANCE to be effective ?
Is the preset a fixed white balance setting, or is it an auto white balance
with the algorithm tuned for a particular configuration ? In the first case,
does it correspond to a fixed white balance temperature value ?
[snip]
> > diff --git a/Documentation/DocBook/media/v4l/controls.xml
> > b/Documentation/DocBook/media/v4l/controls.xml index c0422c6..350c138
> > 100644
> > --- a/Documentation/DocBook/media/v4l/controls.xml
> > +++ b/Documentation/DocBook/media/v4l/controls.xml
> > @@ -2841,6 +2841,44 @@ it one step further. This is a write-only
> > control.</entry>
> >
> > </row>
> > <row><entry></entry></row>
> >
> > + <row id="v4l2-preset-white-balance">
> > + <entry
> > spanname="id"><constant>V4L2_CID_PRESET_WHITE_BALANCE</constant> </
> > entry>
>
> Wouldn't V4L2_CID_WHITE_BALANCE_PRESET be better ?
That's what I was about to say.
--
Regards,
Laurent Pinchart
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