[libcamera-devel] [PATCH v2 01/13] ipa: ipu3: awb: Set a threshold for the green saturation

[Jean-Michel Hautbois]

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). As this is the only channel used for AGC,
there is no need to apply it to the other ones.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
 src/ipa/ipu3/algorithms/awb.cpp | 29 +++++++++++++++++++++++------
 src/ipa/ipu3/algorithms/awb.h   |  1 +
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp
index 809de66a..e44bbd6c 100644
--- a/src/ipa/ipu3/algorithms/awb.cpp
+++ b/src/ipa/ipu3/algorithms/awb.cpp
@@ -328,14 +328,31 @@ void Awb::process(IPAContext &context, const ipu3_uapi_stats_3a *stats)
 	context.frameContext.awb.gains.red = asyncResults_.redGain;
 }
 
+constexpr uint16_t Awb::Threshold(float value)
+{
+	/* AWB Thresholds are in the range [0, 8191] */
+	constexpr uint16_t kMaxThreshold = 8191;
+
+	return value * kMaxThreshold;
+}
+
 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_r = 8191;
-	params->acc_param.awb.config.rgbs_thr_gb = 8191;
-	params->acc_param.awb.config.rgbs_thr_b = IPU3_UAPI_AWB_RGBS_THR_B_INCL_SAT
-					       | IPU3_UAPI_AWB_RGBS_THR_B_EN
-					       | 8191;
+	/*
+	 * Green saturation thresholds are reduced because we are using the
+	 * green channel only in the exposure computation.
+	 */
+	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 for ImgU to update the
+	 * ipu3_uapi_awb_set_item->sat_ratio field.
+	 */
+	params->acc_param.awb.config.rgbs_thr_b |= IPU3_UAPI_AWB_RGBS_THR_B_INCL_SAT |
+						   IPU3_UAPI_AWB_RGBS_THR_B_EN;
 
 	const ipu3_uapi_grid_config &grid = context.configuration.grid.bdsGrid;
 
diff --git a/src/ipa/ipu3/algorithms/awb.h b/src/ipa/ipu3/algorithms/awb.h
index 3b81f600..b02d6b6c 100644
--- a/src/ipa/ipu3/algorithms/awb.h
+++ b/src/ipa/ipu3/algorithms/awb.h
@@ -70,6 +70,7 @@ private:
 	void clearAwbStats();
 	void awbGreyWorld();
 	uint32_t estimateCCT(double red, double green, double blue);
+	constexpr uint16_t Threshold(float value);
 
 	std::vector<RGB> zones_;
 	Accumulator awbStats_[kAwbStatsSizeX * kAwbStatsSizeY];
-- 
2.32.0