[libcamera-devel] [PATCH 0/1] DigitalGain control

[David Plowman]

Hi everyone

I wanted to raise a topic on which there was already some discussion a
few weeks back, prompted by my noticing a gap in the metadata that we
provide with images.

My observation was that I couldn't correctly set the ISO value in my
JPEG files because we don't report how much digital gain has been
supplied by the image processing pipeline. To address this problem, it
seemed as good a way as any actually to include a proposal for a new
DigitalGain control (see the associated patch). Nevertheless, I think
there's a discussion to be had first. Notably:

* Should we let the pipeline report a single global "digital gain"
  value or, given that different gains may be applied to the colour
  channels, should we report three gain values instead?

* In the Pi world I'd like this to be a read-only control, i.e. you
  can't force the pipeline digital gain to a particular value, as our
  AGC doesn't work like that. But there may be platforms that do allow
  you to set the digital gain.

* You could imagine this being "per-stream". I think it's another case
  of "practically everyone will just want a single value", though
  technically you might be able to imagine some platform and use-cases
  where different outputs might reflect different digital gains.

* There's a question about digital gain being applied by the sensor
  itself, but I'm inclined to view that as a separate topic. The issue
  at hand, at least for me, is being able to distinguish the gain
  applied by the sensor, and which we see in the raw frames, from that
  applied by the ISP, which appears in the JPEGs.

You may have other comments too - so everyone's thoughts would be much
appreciated.

Thanks!
David

David Plowman (1):
  libcamera: controls: Add DigitalGain control

 src/libcamera/control_ids.yaml | 11 +++++++++++
 1 file changed, 11 insertions(+)

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2.20.1