[libcamera-devel] [PATCH v4 25/32] ipa: rkisp1: awb: Use frame context to fix gains calculations

[Kieran Bingham]

Quoting Laurent Pinchart via libcamera-devel (2022-09-08 02:41:53)
> The AWB statistics are computed after the ISP applies the colour gains.
> This means that the red, green and blue means do not match the data
> coming directly from the sensor, but are multiplied by the colour gains
> that were used for the frame on which the statistics have been computed.
> The AWB algorithm needs to take this into account when calculating the
> colour gains for the next frame. Do so by dividing the means by the
> gains that were applied to the frame, retrieved from the frame context.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  src/ipa/rkisp1/algorithms/awb.cpp | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/src/ipa/rkisp1/algorithms/awb.cpp b/src/ipa/rkisp1/algorithms/awb.cpp
> index bb0f6c27fc7d..b711e93b73ba 100644
> --- a/src/ipa/rkisp1/algorithms/awb.cpp
> +++ b/src/ipa/rkisp1/algorithms/awb.cpp
> @@ -207,6 +207,15 @@ void Awb::process(IPAContext &context,
>         double greenMean = 1.1636 * yMean - 0.4045 * cbMean - 0.7949 * crMean;
>         double blueMean = 1.1636 * yMean + 1.9912 * cbMean - 0.0250 * crMean;
>  
> +       /*
> +        * The ISP computes the AWB means after applying the colour gains,
> +        * divide by the gains that were used to get the raw means from the
> +        * sensor.
> +        */
> +       redMean /= frameContext.awb.gains.red;
> +       greenMean /= frameContext.awb.gains.green;
> +       blueMean /= frameContext.awb.gains.blue;
> +

Sounds so easy now I see it in code.

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

>         frameContext.awb.temperatureK = estimateCCT(redMean, greenMean, blueMean);
>  
>         /* Estimate the red and blue gains to apply in a grey world. */
> -- 
> Regards,
> 
> Laurent Pinchart
>