[libcamera-devel] [PATCH v2] ipa: ipu3: agc: Limit the number of saturated cells

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-11-04 11:36:21)
> When the histogram is calculated, we check if a cell is saturated or not
> before cumulating its green value. This is wrong, and it can lead to an
> empty histogram in case of a fully saturated frame.
> 
> Use a constant to limit the amount of pixels within a cell before
> considering it saturated. If at the end of the loop we still have an
> empty histogram, then make it a fully saturated one.
> 
> Bug: https://bugs.libcamera.org/show_bug.cgi?id=84
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/agc.cpp | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index b5d736c1..dcdfb95c 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -63,6 +63,12 @@ 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 * 50 / 100;

I think I see in your latest series that this is now set to 20%, Can i
assume this version of the patch is superseeded?

Should this 'fix' be integrated separately from the large control series
as it fixes a known bug?

--
Kieran

> +
>  Agc::Agc()
>         : frameCount_(0), lastFrame_(0), iqMean_(0.0), lineDuration_(0s),
>           minExposureLines_(0), maxExposureLines_(0), filteredExposure_(0s),
> @@ -124,7 +130,7 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
>                                         &stats->awb_raw_buffer.meta_data[cellPosition]
>                                 );
>  
> -                       if (cell->sat_ratio == 0) {
> +                       if (cell->sat_ratio <= kMinCellsPerZoneRatio) {
>                                 uint8_t gr = cell->Gr_avg;
>                                 uint8_t gb = cell->Gb_avg;
>                                 /*
> @@ -137,8 +143,14 @@ void Agc::measureBrightness(const ipu3_uapi_stats_3a *stats,
>                 }
>         }
>  
> +       Histogram cumulativeHist = Histogram(Span<uint32_t>(hist));
>         /* Estimate the quantile mean of the top 2% of the histogram */
> -       iqMean_ = Histogram(Span<uint32_t>(hist)).interQuantileMean(0.98, 1.0);
> +       if (cumulativeHist.total() == 0) {
> +               /* Force the value as histogram is empty */
> +               iqMean_ = knumHistogramBins - 0.5;
> +       } else {
> +               iqMean_ = cumulativeHist.interQuantileMean(0.98, 1.0);
> +       }
>  }
>  
>  /**
> -- 
> 2.32.0
>