Hi Sakari, On 12/30/2011 12:34 AM, Sakari Ailus wrote: > On Wed, Dec 28, 2011 at 02:51:38PM +0100, Laurent Pinchart wrote: >> 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 ? > > While I'm waiting for a final answer to this, I guess it's the second. There > are three things involved here: > > - V4L2_CID_WHITE_BALANCE_TEMPERATURE: relatively low level control telling > the colour temperature of the light source. Setting a value for this > essentially means using manual white balance. > > - V4L2_CID_AUTO_WHITE_BALANCE: automatic white balance enabled or disabled. Was the third thing the V4L2_CID_DO_WHITE_BALANCE control that you wanted to say ? It's also quite essential functionality, to be able to fix white balance after pointing camera to a white object. And I would expect V4L2_CID_WHITE_BALANCE_PRESET control's documentation to state how an interaction with V4L2_CID_DO_WHITE_BALANCE looks like. > The new control proposed by HeungJun is input for the automatic white > balance algorithm unless I'm mistaken. Whether or not the value is static, > however, might be considered of secondary importance: it is a name instead > of a number and clearly intended to be used as a high level control. I'd > still expect it to be a hint for the algorithm. > > The value of the new control would have an effect as long as automatic white > balance is enabled. The idea to treat the preset as a hint to the algorithm is interesting, however as it turns out this are just static values (R/B balance) in manual WB mode. I expect some parameters for adjusting auto WB algorithm (WB (R/G/B) gain bias or something similar) to be present in sensor's ISP as well. If I remember well I've seen something like this in one of sensor's documentations. >>>> 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. > > And the menu items would contain the same prefix with CID_ removed. They're > going to be long, but I don't see that as an issue for menu items. Should we call it V4L2_CID_WB_PRESET then ? Anyway V4L2_WHITE_BALANCE_PRESET_INCADESCENT for example is not that long, we have control names that almost reach 80 characters :) -- Regards, Sylwester -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html