[libcamera-devel] [PATCH 1/4] libcamera: controls: Add focus Figure of Merit (FoM) control

[Laurent Pinchart]

Hi Naush,

Thank you for the patch.

On Fri, Jun 26, 2020 at 11:25:28AM +0100, Naushir Patuck wrote:
> Provide a control to allow the IPA to return a FoM to indicate how
> in-focus a scene is. Note, this is not to be used as a means to
> implement a focus algorithm by the application, rather an indication of
> how in-focus a scene is.
> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> ---
>  src/libcamera/control_ids.yaml | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> index 8c3e4c72..b46693ec 100644
> --- a/src/libcamera/control_ids.yaml
> +++ b/src/libcamera/control_ids.yaml
> @@ -251,4 +251,15 @@ controls:
>          higher than anyone could reasonably want. Negative values are
>          not allowed. Note also that sharpening is not applied to raw
>          streams.
> +
> +  - FocusFoM:
> +      type: int32_t
> +      description: |
> +        Reports a Figure of Merit (FoM) to indicate how in-focus the frame is.
> +        A larger FocusFoM value indicates a more in-focus frame. This control
> +        depends on the IPA to gather ISP statistics from the defined focus
> +        region, and combine them in a suitable way to generate a FocusFoM value.
> +        In this respect, it is not necessarily aimed a providing a way to
> +        implement a focus algorithm by the application, rather an indication of
> +        how in-focus a frame is.

Do you think this would be sufficient for applications, or would it be
better to use an array control that would return an array of values ?
Looking a 4/4 your ISP returns a grid of 4x3 values, so that could fit
in a control without a large performance impact.

This leads to the next question of whether we should then report all
statistics in a buffer instead, and possibly even standardize the
statistics format. That could open pandora's box though, it's a rabbit
hole that could end up being pretty deep. I tried to look around for
other implementations, and there's support for histogram and focus
(sharpness) data in the Android camera HAL API, but marked as
"future". It seems to have been work in progress pretty much from the
start, without much interest in finalizing it. Looking at OpenKCam could
be interesting too, but there's no public spec I could find. Are you
aware of any other attempt at standardizing something in this area ?

>  ...

-- 
Regards,

Laurent Pinchart