[libcamera-devel] [PATCH v2] ipa: ipu3: agc: Remove the threshold for the histogram calculation

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-11-16 15:24:44)
> Until commit f8f07f9468c6 (ipa: ipu3: agc: Improve gain calculation)
> the gain to apply on the exposure value was only using the histogram.
> Now that the global brightness of the frame is estimated too, we don't
> need to remove part of the saturated pixels from the equation anymore.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
> v2: - remove the empty histogram test
>     - don't take Kieran's R-B tag as it needs testing again

Retested. No issues/blackouts on covered lens. Copes with backlights.

I can certainly see the small subtle changes when the brightness is
changed by covering a backlight - but I don't think there's anything
inappropriate there.

Tested-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 32 +++++++++-----------------------
>  1 file changed, 9 insertions(+), 23 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index 4e424857..bd02c474 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -58,12 +58,6 @@ static constexpr uint32_t knumHistogramBins = 256;
>  /* Target value to reach for the top 2% of the histogram */
>  static constexpr double kEvGainTarget = 0.5;
>  
> -/*
> - * Maximum ratio of saturated pixels in a cell for the cell to be considered
> - * non-saturated and counted by the AGC algorithm.
> - */
> -static constexpr uint32_t kMinCellsPerZoneRatio = 255 * 20 / 100;
> -
>  /* Number of frames to wait before calculating stats on minimum exposure */
>  static constexpr uint32_t kNumStartupFrames = 10;
>  
> @@ -133,27 +127,19 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
>                                         &stats->awb_raw_buffer.meta_data[cellPosition]
>                                 );
>  
> -                       if (cell->sat_ratio <= kMinCellsPerZoneRatio) {
> -                               uint8_t gr = cell->Gr_avg;
> -                               uint8_t gb = cell->Gb_avg;
> -                               /*
> -                                * Store the average green value to estimate the
> -                                * brightness. Even the overexposed pixels are
> -                                * taken into account.
> -                                */
> -                               hist[(gr + gb) / 2]++;
> -                       }
> +                       uint8_t gr = cell->Gr_avg;
> +                       uint8_t gb = cell->Gb_avg;
> +                       /*
> +                        * Store the average green value to estimate the
> +                        * brightness. Even the overexposed pixels are
> +                        * taken into account.
> +                        */
> +                       hist[(gr + gb) / 2]++;
>                 }
>         }
>  
> -       Histogram cumulativeHist = Histogram(Span<uint32_t>(hist));
>         /* Estimate the quantile mean of the top 2% of the histogram */
> -       if (cumulativeHist.total() == 0) {
> -               /* Force the value as histogram is empty */
> -               iqMean_ = knumHistogramBins - 0.5;
> -       } else {
> -               iqMean_ = cumulativeHist.interQuantileMean(0.98, 1.0);
> -       }
> +       iqMean_ = Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
>  }
>  
>  /**
> -- 
> 2.32.0
>