media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline)

[Mauro Carvalho Chehab]

Em Wed, 15 Mar 2017 19:04:21 +0100
Pavel Machek <pavel at ucw.cz> escreveu:

> Hi!
> 
> > > Well, I believe first question is: what applications would we want to
> > > run on complex devices? Will sending control from video to subdevs
> > > actually help?  
> > 
> > I would say: camorama, xawtv3, zbar, google talk, skype. If it runs
> > with those, it will likely run with any other application.  
> 
> I'll take a look when I'm at better internet access.

Ok.

> > > mplayer is useful for testing... but that one already works (after you
> > > setup the pipeline, and configure exposure/gain).
> > > 
> > > But thats useful for testing, not really for production. Image will be
> > > out of focus and with wrong white balance.
> > > 
> > > What I would really like is an application to get still photos. For
> > > taking pictures with manual settings we need
> > > 
> > > a) units for controls: user wants to focus on 1m, and take picture
> > > with ISO200, 1/125 sec. We should also tell him that lens is f/5.6 and
> > > focal length is 20mm with 5mm chip.
> > > 
> > > But... autofocus/autogain would really be good to have. Thus we need:
> > > 
> > > b) for each frame, we need exposure settings and focus position at
> > > time frame was taken. Otherwise autofocus/autogain will be too
> > > slow. At least focus position is going to be tricky -- either kernel
> > > would have to compute focus position for us (not trivial) or we'd need
> > > enough information to compute it in userspace.
> > > 
> > > There are more problems: hardware-accelerated preview is not trivial
> > > to set up (and I'm unsure if it can be done in generic way). Still
> > > photos application needs to switch resolutions between preview and
> > > photo capture. Probably hardware-accelerated histograms are needed for
> > > white balance, auto gain and auto focus, ....
> > > 
> > > It seems like there's a _lot_ of stuff to be done before we have
> > > useful support for complex cameras...  
> > 
> > Taking still pictures using a hardware-accelerated preview is
> > a sophisticated use case. I don't know any userspace application
> > that does that. Ok, several allow taking snapshots, by simply
> > storing the image of the current frame.  
> 
> Well, there are applications that take still pictures. Android has
> one. Maemo has another. Then there's fcam-dev. Its open source; with
> modified kernel it is fully usable. I have version that runs on recent
> nearly-mainline on N900. 

Hmm... it seems that FCam is specific for N900:
	http://fcam.garage.maemo.org/

If so, then we have here just the opposite problem, if want it to be
used as a generic application, as very likely it requires OMAP3-specific
graph/subdevs.

> So yes, I'd like solution for problems a) and b).
> 
> > > (And I'm not sure... when application such as skype is running, is
> > > there some way to run autogain/autofocus/autowhitebalance? Is that
> > > something we want to support?)  
> > 
> > Autofocus no. Autogain/Autowhite can be done via libv4l, provided that
> > it can access the device's controls via /dev/video devnode. Other
> > applications may be using some other similar algorithms.
> > 
> > Ok, they don't use histograms provided by the SoC. So, they do it in
> > software, with is slower. Still, it works fine when the light
> > conditions don't change too fast.  
> 
> I guess it is going to work well enough with higher CPU
> usage.

Yes.

> Question is if camera without autofocus is usable. I'd say "not
> really".qv4l2

That actually depends on the sensor and how focus is adjusted.

I'm testing right now this camera module for RPi:
   https://www.raspberrypi.org/products/camera-module-v2/

I might be wrong, but this sensor doesn't seem to have auto-focus.
Instead, it seems to use a wide-angle lens. So, except when the
object is too close, the focus look OK.

> > > I believe other question is: will not having same control on main
> > > video device and subdevs be confusing? Does it actually help userspace
> > > in any way? Yes, we can make controls accessible to old application,
> > > but does it make them more useful?   
> > 
> > Yes. As I said, libv4l (and some apps) have logic inside to adjust
> > the image via bright, contrast and white balance controls, using the
> > video devnode. They don't talk subdev API. So, if those controls
> > aren't exported, they won't be able to provide a good quality image.  
> 
> Next question is if the libv4l will do the right thing if we just put
> all controls to one node. For example on N900 you have exposure/gain
> and brightness. But the brightness is applied at preview phase, so it
> is "basically useless". You really need to adjust the image using the
> exposure/gain.

I've no idea, but I suspect it shouldn't be hard to teach libv4l to
prefer use an exposure/gain instead of brightness when available.

> > > > > In addition, I suspect end-users of these complex devices don't really care
> > > > > about a plugin: they want full control and won't typically use generic
> > > > > applications. If they would need support for that, we'd have seen much more
> > > > > interest. The main reason for having a plugin is to simplify testing and
> > > > > if this is going to be used on cheap hobbyist devkits.    
> > > > 
> > > > What are the needs for a cheap hobbyist devkit owner? Do we currently
> > > > satisfy those needs? I'd say that having a functional driver when
> > > > compiled without the subdev API, that implements the ioctl's/controls    
> > > 
> > > Having different interface based on config options... is just
> > > weird. What about poor people (like me) trying to develop complex
> > > applications?  
> > 
> > Well, that could be done using other mechanisms, like a modprobe
> > parameter or by switching the behaviour if a subdev interface is
> > opened. I don't see much trouble on allowing accessing a control via
> > both interfaces.  
> 
> If we really want to go that way (is not modifying library to access
> the right files quite easy?), I believe non-confusing option would be
> to have '/dev/video0 -- omap3 camera for legacy applications' which
> would include all the controls.

Yeah, keeping /dev/video0 reserved for generic applications is something
that could work. Not sure how easy would be to implement it.

> 
> > > You can get Nokia N900 on aliexpress. If not, they are still available
> > > between people :-)  
> > 
> > I have one. Unfortunately, I never had a chance to use it, as the display
> > stopped working one week after I get it.  
> 
> Well, I guess the easiest option is to just get another one :-).

:-)  Well, I guess very few units of N900 was sold in Brazil. Importing
one is too expensive, due to taxes.

> But otoh -- N900 is quite usable without the screen. 0xffff tool can
> be used to boot the kernel, then you can use nfsroot and usb
> networking. It also has serial port (over strange
> connector). Connected over ssh over usb network is actually how I do
> most of the v4l work.

If you pass me the pointers, I can try it when I have some time.

Anyway, I got myself an ISEE IGEPv2, with the expansion board:
	https://www.isee.biz/products/igep-processor-boards/igepv2-dm3730
	https://www.isee.biz/products/igep-expansion-boards/igepv2-expansion

The expansion board comes with a tvp5150 analog TV demod. So, with
this device, I can simply connect it to a composite input signal.
I have some sources here that I can use to test it.

Thanks,
Mauro