[libcamera-devel] [PATCH v2 07/13] ipa: ipu3: agc: Change analogue gain limits

[Laurent Pinchart]

Hi Jean-Michel,

Thank you for the patch.

On Wed, Oct 20, 2021 at 05:46:01PM +0200, Jean-Michel Hautbois wrote:
> The gains is currently set as a uint32_t while the analogue gain is

s/gains/gain/

> passed as a double. We also have a default maximum analogue gain of 15
> which is quite high for a number of sensors.
> 
> Use a maximum value of 8 which should really be configured by the IPA
> and not fixed as it is now. While at it make it a double.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 8e1b6d8c..1bae1eb9 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -30,14 +30,10 @@ static constexpr uint32_t kInitialFrameMinAECount = 4;
>  /* Number of frames to wait between new gain/exposure estimations */
>  static constexpr uint32_t kFrameSkipCount = 6;
>  
> -/* Maximum ISO value for analogue gain */
> -static constexpr uint32_t kMinISO = 100;
> -static constexpr uint32_t kMaxISO = 1500;
> -
>  /* Maximum analogue gain value
>   * \todo grab it from a camera helper */
> -static constexpr uint32_t kMinGain = kMinISO / 100;
> -static constexpr uint32_t kMaxGain = kMaxISO / 100;
> +static constexpr double kMinGain = 1.0;
> +static constexpr double kMaxGain = 8.0;
>  
>  /* Histogram constants */
>  static constexpr uint32_t knumHistogramBins = 256;
> @@ -165,9 +161,11 @@ void Agc::lockExposureGain(uint32_t &exposure, double &gain)
>  							minExposureLines_,
>  							maxExposureLines_);
>  			newExposure = currentExposure_ / exposure;
> -			gain = std::clamp(static_cast<uint32_t>(gain * currentExposure_ / newExposure), kMinGain, kMaxGain);
> +			gain = std::clamp(gain * currentExposure_ / newExposure,
> +					  kMinGain, kMaxGain);
>  		} else if (currentShutter >= maxShutterSpeed) {
> -			gain = std::clamp(static_cast<uint32_t>(gain * currentExposure_ / currentExposureNoDg_), kMinGain, kMaxGain);
> +			gain = std::clamp(gain * currentExposure_ / currentExposureNoDg_,
> +					  kMinGain, kMaxGain);
>  			newExposure = currentExposure_ / gain;
>  			exposure = std::clamp<uint32_t>(exposure * currentExposure_ / newExposure,
>  							minExposureLines_,

-- 
Regards,

Laurent Pinchart