[libcamera-devel] [PATCH] ipa: ipu3: agc: Clamp shutter speed

[Laurent Pinchart]

Hi Jean-Michel,

Thank you for the patch.

On Tue, Oct 26, 2021 at 10:21:42AM +0200, Jean-Michel Hautbois wrote:
> In case the maximum exposure received from the sensor is very high, we
> can have a very high shutter speed with a small analogue gain, and it
> may result in very slow framerate. We are not really supporting it for
> the moment, so clamp the shutter speed to an arbitrary value of 60ms.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 6c151232..5927b5d3 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -34,6 +34,9 @@ static constexpr uint32_t kFrameSkipCount = 6;
>  static constexpr double kMinAnalogueGain = 1.0;
>  static constexpr double kMaxAnalogueGain = 8.0;
>  
> +/* Maximum shutter speed allowed */

/* \todo Honour the FrameDurationLimits control instead of hardcoding a limit */

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> +static constexpr utils::Duration kMaxShutterSpeed = 60ms;
> +
>  /* Histogram constants */
>  static constexpr uint32_t knumHistogramBins = 256;
>  static constexpr double kEvGainTarget = 0.5;
> @@ -54,7 +57,8 @@ int Agc::configure(IPAContext &context, const IPAConfigInfo &configInfo)
>  
>  	/* \todo replace the exposure in lines storage with time based ones. */
>  	minExposureLines_ = context.configuration.agc.minShutterSpeed / lineDuration_;
> -	maxExposureLines_ = context.configuration.agc.maxShutterSpeed / lineDuration_;
> +	maxExposureLines_ = std::min(context.configuration.agc.maxShutterSpeed / lineDuration_,
> +				     kMaxShutterSpeed / lineDuration_);
>  
>  	minAnalogueGain_ = std::max(context.configuration.agc.minAnalogueGain, kMinAnalogueGain);
>  	maxAnalogueGain_ = std::min(context.configuration.agc.maxAnalogueGain, kMaxAnalogueGain);

-- 
Regards,

Laurent Pinchart