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

[Laurent Pinchart]

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

Laurent Pinchart