Re: [RFC] snapshot mode, flash capabilities and control

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On Mon, 28 Feb 2011, Laurent Pinchart wrote:

> > > > I don't think snapshot capture is *that* special. I don't expect most
> > > > embedded SoCs to implement snapshot capture in hardware. What usually
> > > > happens is that the hardware provides some support (like two independent
> > > > video streams for instance, or the ability to capture a given number of
> > > > frames) and the scheduling is performed in userspace. Good quality
> > > > snapshot capture requires complex algorithms and involves several
> > > > hardware pieces (ISP, flash controller, lens controller, ...), so it
> > > > can't be implemented in the kernel.
> > > 
> > > I agree.
> > 
> > Right, but sensors do need it. It is not enough to just tell the sensor -
> > a per-frame flash is used and let the driver figure out, that it has to
> > switch to snapshot mode. The snapshot mode has other effects too, e.g., on
> > some sensors it enables the external trigger pin, which some designs might
> > want to use also without a flash. Maybe there are also some other side
> > effects of such snapshot modes on some other sensors, that I'm not aware
> > of.
> 
> This makes me wonder if we need a snapshot mode at all. Why should we tie 
> flash, capture trigger (and other such options that you're not aware of yet 
> :-)) together under a single high-level control (in the general sense, not to 
> be strictly taken as a V4L2 CID) ? Wouldn't it be better to expose those 
> features individually instead ? User might want to use the flash in video 
> capture mode for a stroboscopic effect for instance.

So, you'd also need a separate control for external exposure, there are 
also sensors, that can be configured to different shutter / exposure / 
readout sequence controlling... No, we don't have to support all that 
variety, but we have to be aware of it, while making decisions;)

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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