[libcamera-devel] [PATCH] ipa: rpi: Allow the mean of an empty histogram interval

[Naushir Patuck]

Hi Nick,

Thanks for the patch.

On Wed, 6 Dec 2023 at 17:27, Nick Hollinghurst via libcamera-devel
<libcamera-devel at lists.libcamera.org> wrote:
>
> Don't assert when taking the weighted mean of a zero-width or
> zero-weight interval; return its upper bound. That is certainly
> correct in the zero-width case, and plausible otherwise.
>
> Signed-off-by: Nick Hollinghurst <nick.hollinghurst at raspberrypi.com>

Reviewed-by: Naushir Patuck <naush at raspberrypi.com>

> ---
>  src/ipa/rpi/controller/histogram.cpp | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/src/ipa/rpi/controller/histogram.cpp b/src/ipa/rpi/controller/histogram.cpp
> index 0a27ba2c..78116141 100644
> --- a/src/ipa/rpi/controller/histogram.cpp
> +++ b/src/ipa/rpi/controller/histogram.cpp
> @@ -47,7 +47,7 @@ double Histogram::quantile(double q, int first, int last) const
>
>  double Histogram::interBinMean(double binLo, double binHi) const
>  {
> -       assert(binHi > binLo);
> +       assert(binHi >= binLo);
>         double sumBinFreq = 0, cumulFreq = 0;
>         for (double binNext = floor(binLo) + 1.0; binNext <= ceil(binHi);
>              binLo = binNext, binNext += 1.0) {
> @@ -57,13 +57,19 @@ double Histogram::interBinMean(double binLo, double binHi) const
>                 sumBinFreq += bin * freq;
>                 cumulFreq += freq;
>         }
> +
> +       if (cumulFreq == 0) {
> +               /* interval had zero width or contained no weight? */
> +               return binHi;
> +       }
> +
>         /* add 0.5 to give an average for bin mid-points */
>         return sumBinFreq / cumulFreq + 0.5;
>  }
>
>  double Histogram::interQuantileMean(double qLo, double qHi) const
>  {
> -       assert(qHi > qLo);
> +       assert(qHi >= qLo);
>         double pLo = quantile(qLo);
>         double pHi = quantile(qHi, (int)pLo);
>         return interBinMean(pLo, pHi);
> --
> 2.39.2
>