[libcamera-devel] [PATCH v3 5/5] ipa: raspberrypi: Normalise region sums to 16-bits

[Kieran Bingham]

Quoting Naushir Patuck via libcamera-devel (2022-12-13 11:48:36)
> The VC4 ISP uses a pipeline bit-depth of 13-bits. The AGC algorithm needs to
> know this bit-depth when computing the Y value for the image.
> 
> Instead of hardcoding the VC4 bit-depth in the AGC source code, normalise all
> region sums to 16-bits when filling the Statistics structure. AWB and ALSC are
> agnostic about pipeline depth, so do not need changing.

pipeline bit-depth to not confuse pipeline depth with the number of
buffers as this term has been used for previously?

> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> ---
>  src/ipa/raspberrypi/controller/rpi/agc.cpp | 10 ++++------
>  src/ipa/raspberrypi/raspberrypi.cpp        | 16 ++++++++++------
>  2 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/src/ipa/raspberrypi/controller/rpi/agc.cpp b/src/ipa/raspberrypi/controller/rpi/agc.cpp
> index 868c30f03d66..7ec8292d32ff 100644
> --- a/src/ipa/raspberrypi/controller/rpi/agc.cpp
> +++ b/src/ipa/raspberrypi/controller/rpi/agc.cpp
> @@ -28,8 +28,6 @@ LOG_DEFINE_CATEGORY(RPiAgc)
>  
>  #define NAME "rpi.agc"
>  
> -static constexpr unsigned int PipelineBits = 13; /* seems to be a 13-bit pipeline */
> -
>  int AgcMeteringMode::read(const libcamera::YamlObject &params)
>  {
>         const YamlObject &yamlWeights = params["weights"];
> @@ -593,9 +591,9 @@ static double computeInitialY(StatisticsPtr &stats, AwbStatus const &awb,
>         double rSum = 0, gSum = 0, bSum = 0, pixelSum = 0;
>         for (unsigned int i = 0; i < stats->agcRegions.numRegions(); i++) {
>                 auto &region = stats->agcRegions.get(i);
> -               double rAcc = std::min<double>(region.val.rSum * gain, ((1 << PipelineBits) - 1) * region.counted);
> -               double gAcc = std::min<double>(region.val.gSum * gain, ((1 << PipelineBits) - 1) * region.counted);
> -               double bAcc = std::min<double>(region.val.bSum * gain, ((1 << PipelineBits) - 1) * region.counted);
> +               double rAcc = std::min<double>(region.val.rSum * gain, ((1 << 16) - 1) * region.counted);
> +               double gAcc = std::min<double>(region.val.gSum * gain, ((1 << 16) - 1) * region.counted);
> +               double bAcc = std::min<double>(region.val.bSum * gain, ((1 << 16) - 1) * region.counted);

1 << 16 - 1 now looks a bit 'magic', and it may not be clear to a
reader what it's refering to?

Before it referenced PipelineBits so it was clearer. I expect this
  ((1 << 16) - 1)

could be a constexpr somewhere at the top of the file, or a helper to
wrap the scaling of region.counted?


Hrm ... it 'was' already a constexpr at the top...
Is there a reason you chose to hardcode the value here instead of update
(/and or rename) the existing PipelineBits ?

Aside from that:


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


>                 rSum += rAcc * weights[i];
>                 gSum += gAcc * weights[i];
>                 bSum += bAcc * weights[i];
> @@ -608,7 +606,7 @@ static double computeInitialY(StatisticsPtr &stats, AwbStatus const &awb,
>         double ySum = rSum * awb.gainR * .299 +
>                       gSum * awb.gainG * .587 +
>                       bSum * awb.gainB * .114;
> -       return ySum / pixelSum / (1 << PipelineBits);
> +       return ySum / pixelSum / (1 << 16);
>  }
>  
>  /*
> diff --git a/src/ipa/raspberrypi/raspberrypi.cpp b/src/ipa/raspberrypi/raspberrypi.cpp
> index cff079bbafb3..50fdeb4f0478 100644
> --- a/src/ipa/raspberrypi/raspberrypi.cpp
> +++ b/src/ipa/raspberrypi/raspberrypi.cpp
> @@ -1154,11 +1154,15 @@ RPiController::StatisticsPtr IPARPi::fillStatistics(bcm2835_isp_stats *stats) co
>         /* RGB histograms are not used, so do not populate them. */
>         statistics->yHist = std::move(RPiController::Histogram(stats->hist[0].g_hist, NUM_HISTOGRAM_BINS));
>  
> +       /*
> +        * All region sums are based on a 13-bit pipeline bit-depth. Normalise
> +        * this to 16-bits for the AGC/AWB/ALSC algorithms.
> +        */
>         statistics->awbRegions.init({ DEFAULT_AWB_REGIONS_X, DEFAULT_AWB_REGIONS_Y });
>         for (i = 0; i < statistics->awbRegions.numRegions(); i++)
> -               statistics->awbRegions.set(i, { { stats->awb_stats[i].r_sum,
> -                                                 stats->awb_stats[i].g_sum,
> -                                                 stats->awb_stats[i].b_sum },
> +               statistics->awbRegions.set(i, { { stats->awb_stats[i].r_sum << 3,
> +                                                 stats->awb_stats[i].g_sum << 3,
> +                                                 stats->awb_stats[i].b_sum << 3 },
>                                                 stats->awb_stats[i].counted,
>                                                 stats->awb_stats[i].notcounted });
>  
> @@ -1168,9 +1172,9 @@ RPiController::StatisticsPtr IPARPi::fillStatistics(bcm2835_isp_stats *stats) co
>          */
>         statistics->agcRegions.init(15);
>         for (i = 0; i < statistics->agcRegions.numRegions(); i++)
> -               statistics->agcRegions.set(i, { { stats->agc_stats[i].r_sum,
> -                                                 stats->agc_stats[i].g_sum,
> -                                                 stats->agc_stats[i].b_sum },
> +               statistics->agcRegions.set(i, { { stats->agc_stats[i].r_sum << 3,
> +                                                 stats->agc_stats[i].g_sum << 3,
> +                                                 stats->agc_stats[i].b_sum << 3 },
>                                                 stats->agc_stats[i].counted,
>                                                 stats->awb_stats[i].notcounted });
>  
> -- 
> 2.25.1
>