Camera knobs and dials...

[Jonathan Corbet]

Jim Gettys <jg at laptop.org> wrote:

> To do so, they need to be
> able to use the device in as linear a fashion (photometrically) as
> possible: disable gain control, black point processing, color balancing,
> etc, which from looking at the sensor spec appears to be possible from a
> quick perusal.  Such sensors do a remarkable amount of signal processing
> internally these days.
> 
> I know V4L has facilities for controlling (most of) these features, that
> you are hooking up in the sensor driver right now.  Does V4L also have
> facilities for completely disabling these features?  Are there any
> features of the chip that V4L does not support?

V4L2 has a fair number of predefined controls, there's a list at:

  http://v4l2spec.bytesex.org/spec/x488.htm#CONTROL-ID

Some of them do what they want - disabling white balance, auto exposure
control, etc.  There is also a way to add driver-specific controls for
the ones that are missing.  So all of this can be handled.

If it seems that any of those settings should be turned into standard
V4L2 controls, that's easy enough to make happen.

The big challenge is a story you've heard from me for a while:
translating those controls into an appropriate set of OV7670 register
settings.  I have come to the conclusion that those settings really
constitute a form of opaque firmware, and, without cooperation from 
OmniVision, they can be hard to get right.  There's a lot of registers
simply marked "reserved" in the spec, and there are undocumented 
ordering issues as well.  It can all be done, eventually.

jon