[libcamera-devel] [PATCH 12/13] ipa: ipu3: agc: Increase IIR filter speed

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-10-13 16:41:24)
> The filter used is an infinite response filter which is controlled by
> the speed variable. It is used to limit the gap between two exposure
> values, and avoid nasty oscillations. The higher the speed, the less the
> result oscillates.

Does that also mean it will take longer to obtain a good exposure?

> As we are only calculating the exposure every 6 frames, as controled by
> the 'kFrameSkipCount' constant, we can increase the speed, to avoid a
> slow response (it can be more than 1 second to get a stable enough
> output).

Are we able to move towards calculating on every frame? or would that
cause more oscillations? If so that implies to me that we're using the
wrong inputs to perform the calculations.

But ... although we might need to do further investigations on the
inputs if we hit oscillations, I don't think this is a problem if it's a
short term gain.

But if we do need to do more work to improve the calculatoins to allow
us to run the calculations faster, then we might need to record a todo
somewhere.


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


> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index b922bcdf..81eaf436 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -92,7 +92,7 @@ void Agc::processBrightness(const ipu3_uapi_stats_3a *stats,
>  
>  void Agc::filterExposure()
>  {
> -       double speed = 0.2;
> +       double speed = 0.9;
>         if (filteredExposure_ == 0s) {
>                 /* DG stands for digital gain.*/
>                 filteredExposure_ = currentExposure_;
> -- 
> 2.30.2
>