Hi Sylwester, My apologies for the delayed answer.
Sylwester Nawrocki wrote: > On 12/16/2012 04:00 PM, Sakari Ailus wrote: >>>>> diff --git a/Documentation/DocBook/media/v4l/controls.xml >>>>> b/Documentation/DocBook/media/v4l/controls.xml >>>>> index 7fe5be1..9d4af8a 100644 >>>>> --- a/Documentation/DocBook/media/v4l/controls.xml >>>>> +++ b/Documentation/DocBook/media/v4l/controls.xml >>>>> @@ -3347,6 +3347,51 @@ use its minimum possible distance for auto >>>>> focus.</entry> >>>>> </row> >>>>> <row><entry></entry></row> >>>>> + <row id="v4l2-auto-focus-area"> >>>>> + <entry spanname="id"> >>>>> + <constant>V4L2_CID_AUTO_FOCUS_AREA</constant> </entry> >>>>> + <entry>enum v4l2_auto_focus_area</entry> >>>>> + </row> >>>>> + <row><entry spanname="descr">Determines the area of the frame >>>>> that >>>>> +the camera uses for automatic focus. The corresponding coordinates >>>>> of the >>>>> +focusing spot or rectangle can be specified and queried using the >>>>> selection API. >>>>> +To change the auto focus region of interest applications first >>>>> select required >>>>> +mode of this control and then set the rectangle or spot >>>>> coordinates by means >>>>> +of the&VIDIOC-SUBDEV-S-SELECTION; or&VIDIOC-S-SELECTION; ioctl. In >>>>> order to >>>>> +trigger again a one shot auto focus with same coordinates >>>>> applications should >>>>> +use the<constant>V4L2_CID_AUTO_FOCUS_START</constant> control. Or >>>>> alternatively >>>> Extra space above. ^ >>>> >>>>> +invoke a&VIDIOC-SUBDEV-S-SELECTION; or a&VIDIOC-S-SELECTION; ioctl >>>>> again. >>>> How about requiring explicit V4L2_CID_AUTO_FOCUS_START? If you need to >>>> specify several AF selection windows, then on which one do you start >>>> the >>>> algorithm? A bitmask control explicitly telling which ones are >>>> active would >>>> also be needed --- but that's for the future. I think now we just >>>> need to >>>> ascertain we don't make that difficult. :-) >>> Do you mean only V4L2_CID_AUTO_FOCUS_START should start AF? >>> What about continuous auto-focus (CAF)? In case of the sensor I am >>> working on, face detection can work in both AF and CAF. >> >> Continuous AF needs to be an exception to that. It's controlled by >> V4L2_CID_FOCUS_AUTO, which interestingly doesn't even mention >> continuous AF. > > I think it does, maybe not exactly in these words, but "continuous > automatic focus > adjustments" doesn't sound like a difference thing to me. Oh. I must have missed that. It's ok then. >>> Should CAF be restarted (ie stopped and started again), to use face >>> detection? >> >> I wonder if V4L2_CID_AUTO_FOCUS_START should be defined to restart CAF >> when >> V4L2_CID_FOCUS_AUTO is enabled. I don't think we currently have a way >> to do >> that; the current definition says that using V4L2_CID_AUTO_FOCUS_START is >> undefined then. What do you think? > > Yes, it might be worth to reconsider this. However, I would like to see > real > use cases first where V4L2_CID_AUTO_FOCUS_START control is needed in > continuous > AF mode. If the CAF focus window is changed, I think it may make sense to tell the CAF algorithm this. If the window moves around based on e.g. output from face detection algorithm it's unlikely there's a need to perform a full search every time this happens. > All in all, we have V4L2_AUTO_FOCUS_STATUS_FAILED AF status control > value and > I can't see anything preventing it to be applicable to CAF. So it might > make > sense to define in the API what needs to be done to bring CAF out of > this state. How would CAF fail? Would this mean that a pre-defined amount of time has been spent on searching focus and none has been found? Shouldn't it be application's decision to tell how long is too long, rather than driver's? >>>>> +In the latter case the new pixel coordinates are applied to >>>>> hardware only when >>>>> +the focus area control was set to >>>>> +<constant>V4L2_AUTO_FOCUS_AREA_RECTANGLE</constant>.</entry> >>>>> + </row> >>>>> + <row> >>>>> + <entrytbl spanname="descr" cols="2"> >>>>> + <tbody valign="top"> >>>>> + <row> >>>>> + >>>>> <entry><constant>V4L2_AUTO_FOCUS_AREA_ALL</constant> </entry> >>>>> + <entry>Normal auto focus, the focusing area extends over the >>>>> +entire frame.</entry> >>>> Does this need to be explicitly specified? Shouldn't the user just >>>> choose >>>> the largest possible AF window instead? I'd even expect that the AF >>>> window >>>> might span the whole frame by default (up to driver, hardware etc.). >>> Yes it could be removed. There are two reasons I have left it: >>> 1. If hardware support only AF on spots, V4L2_AUTO_FOCUS_AREA_ALL >>> seems to be more >>> natural than focusing on the whole image. >> >> If the hardware only supports spots, then wouldn't >> V4L2_AUTO_FOCUS_AREA_ALL >> give false information to the user, suggesting the focus area is actually >> the whole image? > > I think Andrzej meant to say that there can be hardware that supports: > > a. AF where region of interest is whole frame, > b. AF where region of interest is some rectangle of size that may be not > known exactly, and position (center) of that rectangle only is defined > through AF selections. > > So you would be really switching AF algorithms by manipulating AF selection > rectangle only. I would keep the two separate: selecting the algorithm and the area of interest. When the host software runs the algorithm itself the selection is just about the area and nothing else. I think it'd be more flexible not to make other decisions based on it in the driver. Well, an individual driver could still do this if really, really needed but I don't think it should end up to the V4L2 spec. > That said I really think V4L2_AUTO_FOCUS_AREA_ALL is a bad name here. > I originally started with single AF mode control and then after discussions > we came up with V4L2_AUTO_FOCUS_RANGE and V4L2_AUTO_FOCUS_AREA controls. > > My motivation behind V4L2_AUTO_FOCUS_AREA_ALL was to provide a menu > item that would allow to select "normal" AF, with supposedly whole frame > being the AF region of interest. "Normal" AF might mean really any area > of the frame, so I propose to just replace V4L2_AUTO_FOCUS_AREA_ALL with > V4L2_AUTO_FOCUS_AREA_AUTO. This entry would naturally mean that AF area > is automatically selected by an ISP and it might not be known exactly to > user. Like in case of those superb AF algorithms that many companies > value to keep secret... There might be cases where the user doesn't wish to choose the area, and the user shouldn't be forced to do so. In this case the driver either knows the rectangle or it doesn't. For the user this shouldn't matter. If the area isn't known, the driver shouldn't provide access to the whole selection rectangle, or the control. If the area is known to the driver, there likely should be a sane default, at least for the cases where the AF algorithm isn't in the host user space. The sane default most probably would be something else than the full image area. What makes sense likely also depends on the hardware (resolution etc.) and the algorithm used, too. >>> 2. (Hypothetical) Instructing HW to area-focusing on the whole are >>> could have different results than just starting default auto-focus, >>> ie there could be different algorithms involved. It is just a >>> prediction based on my current experience :) >> >> If the algorithm is different in that case, then it should be made a new >> control, not implicitly throught a seemingly unrelated control. >> >> We currently don't have one, and this kind of things could be hardware >> specific, so this could be a private control IMO. > > We have already something like V4L2_CID_AUTO_FOCUS_MODE private control, > common to multiple Samsung camera sensors. And each device has mostly > different set of options in such a control. Not sure if it wouldn't make > more sense to have standard menu control ID with driver specific entries > for all AF modes. It likely makes sense to have common patterns expressed > in standard controls though. It seems current set of AF controls, together > with V4L2_AUTO_FOCUS_AREA covers pretty much of the functionality, > without resorting to the private controls interface, that is so awkward > to use when you have to deal with multiple different devices... How many drivers are there and how many (and which) modes do they provide? This sounds still a little bit specific to Samsung camera modules, but if it's present in many then it could make sense to make it a standard control. I can't say for sure without knowing more, though. -- Cheers, Sakari Ailus sakari.ai...@iki.fi -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
