[libcamera-devel] [PATCH v2 1/2] libcamera: camera: Add a mode sensitivity field

[Kieran Bingham]

Quoting David Plowman (2021-09-22 14:29:14)
> The modeSensitivity field is a number that describes how sensitive the
> selected sensor mode is compared to other readout modes of the same
> sensor. For example, a binned mode might have twice the sensitivity of
> the full resolution mode, meaning you would get double the signal
> level for the same exposure and gains.

Is there a way to define which is the 'base' level?

Or does it not matter, as it's all relative (but relative to what I
guess is my question).

I.e. Does it matter, or is it necessary to know that Mode A is 'half' as
sensitive as Mode B?

In fact, I think that's already a given as whatever the pipeline handler
does will be relative. I.e. it would be about comparing the value
against other configurations not a standalone value.

> 
> Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
> ---
>  include/libcamera/camera.h |  2 ++
>  src/libcamera/camera.cpp   | 16 +++++++++++++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/include/libcamera/camera.h b/include/libcamera/camera.h
> index 601ee46e..3314c06b 100644
> --- a/include/libcamera/camera.h
> +++ b/include/libcamera/camera.h
> @@ -66,6 +66,8 @@ public:
>  
>         Transform transform;
>  
> +       float modeSensitivity;
> +
>  protected:
>         CameraConfiguration();
>  
> diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp
> index 71809bcd..8d795dff 100644
> --- a/src/libcamera/camera.cpp
> +++ b/src/libcamera/camera.cpp
> @@ -156,7 +156,7 @@ LOG_DECLARE_CATEGORY(Camera)
>   * \brief Create an empty camera configuration
>   */
>  CameraConfiguration::CameraConfiguration()
> -       : transform(Transform::Identity), config_({})
> +       : transform(Transform::Identity), modeSensitivity(1.0), config_({})
>  {
>  }
>  
> @@ -327,6 +327,20 @@ std::size_t CameraConfiguration::size() const
>   * may adjust this field at its discretion if the selection is not supported.
>   */
>  
> +/**
> + * \var CameraConfiguration::modeSensitivity
> + * \brief The relative sensitivity of the chosen sensor mode
> + *
> + * Some sensors have readout modes with different sensitivities. For example,
> + * a binned camera mode might, with the same exposure and gains, produce
> + * twice the signal level of the full resolution readout. This would be
> + * signalled by the binned mode, when it is chosen, indicating a value here
> + * that is twice that of the full resolution mode.
> + *
> + * This value should only be read, and not set, by the user. It will be
> + * valid after the configure method has reteurned successfully.
> + */
> +

I bet we've discussed this in the past, but I can't recall. If there are
more of these properties, I would suspect they should be in a
ControlList somehow - but if there's not expected to be many, an
explicit field is fine to me, and I can see the importance of conveying
this information.


I was also going to say perhaps we need some testing on this in
lc-compliance, but given that the default is 1.0 for all camera
configurations - I think that's fine. It wouldn't be something we could
easily test anyway.

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>



>  /**
>   * \var CameraConfiguration::config_
>   * \brief The vector of stream configurations
> -- 
> 2.20.1
>