[libcamera-devel] [PATCH 01/13] ipa: ipu3: awb: Set a threshold for the green saturation

[Kieran Bingham]

Quoting Jean-Michel Hautbois (2021-10-13 16:41:13)
> We can have a saturation ratio per cell, giving the percentage of pixels
> over a threshold within a cell where 100% is set to 0xff.
> 
> The parameter structure 'ipu3_uapi_awb_config_s' contains four fields to
> set the threshold, one per channel.
> The blue field is also used to configure the ImgU and make it calculate
> the saturation ratio or not.
> 
> Set a green value saturated when it is more than 230 (90% of the maximum
> value 255, coded as 8191).

Why do we only determine a lower saturation on one component?

Shouldn't they be balanced (perhaps in accordance with the white balance
somehow?).


> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/ipa/ipu3/algorithms/awb.cpp | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp
> index e2b18336..5574bd44 100644
> --- a/src/ipa/ipu3/algorithms/awb.cpp
> +++ b/src/ipa/ipu3/algorithms/awb.cpp
> @@ -326,9 +326,9 @@ void Awb::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
>  
>  void Awb::prepare(IPAContext &context, ipu3_uapi_params *params)
>  {
> -       params->acc_param.awb.config.rgbs_thr_gr = 8191;
> +       params->acc_param.awb.config.rgbs_thr_gr = (90 * 8191 / 100);
>         params->acc_param.awb.config.rgbs_thr_r = 8191;
> -       params->acc_param.awb.config.rgbs_thr_gb = 8191;
> +       params->acc_param.awb.config.rgbs_thr_gb = (90 * 8191 / 100);
>         params->acc_param.awb.config.rgbs_thr_b = IPU3_UAPI_AWB_RGBS_THR_B_INCL_SAT
>                                                | IPU3_UAPI_AWB_RGBS_THR_B_EN
>                                                | 8191;

That's interesting that thr_b has those enable flags. Do they apply
only to B? or does that enable all of them?

I wonder if a helper function would make the values clearer:

(Awb private:)
uint16_t Awb::Threshold(float value)
{
	/* AWB Thresholds are represented in FixedPoint 3.13 */
	constexpr uint16_t kFixedPoint3_13 = 8191;

	return value * kFixedPoint3_13;
}


void Awb::prepare(IPAContext &context, ipu3_uapi_params *params)
{
	/*
	 * Green saturation thresholds are reduced because...
	 */
	params->acc_param.awb.config.rgbs_thr_r = Threshold(1.0);
	params->acc_param.awb.config.rgbs_thr_gr = Threshold(0.9);
	params->acc_param.awb.config.rgbs_thr_gb = Threshold(0.9);
	params->acc_param.awb.config.rgbs_thr_b = Threshold(1.0);

	/* Enable saturation inclusion on thr_b because ... */
	params->acc_param.awb.config.rgbs_thr_b |= IPU3_UAPI_AWB_RGBS_THR_B_INCL_SAT |
					 	   IPU3_UAPI_AWB_RGBS_THR_B_EN;
	...
}



> -- 
> 2.30.2
>