[libcamera-devel] [PATCH v2 08/12] ipa: ipu3: awb: Correct the gain multipliers

[Jean-Michel Hautbois]

The gains have a precision u3.13, range [0, 8[ which means that a gain
multiplier value of 1.0 is represented as a multiplication by 8192 in
the ImgU. Correct the gains as this was misunderstood in the first
place.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/ipa/ipu3/algorithms/awb.cpp | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/src/ipa/ipu3/algorithms/awb.cpp b/src/ipa/ipu3/algorithms/awb.cpp
index be764c79..c1ff9450 100644
--- a/src/ipa/ipu3/algorithms/awb.cpp
+++ b/src/ipa/ipu3/algorithms/awb.cpp
@@ -313,6 +313,7 @@ void Awb::awbGreyWorld()
 	/* Color temperature is not relevant in Grey world but still useful to estimate it :-) */
 	asyncResults_.temperatureK = estimateCCT(sumRed.R, sumRed.G, sumBlue.B);
 	asyncResults_.redGain = redGain;
+	/*Hardcode the green gain to 1.0. */
 	asyncResults_.greenGain = 1.0;
 	asyncResults_.blueGain = blueGain;
 }
@@ -376,15 +377,11 @@ void Awb::prepare(IPAContext &context, ipu3_uapi_params *params)
 							* params->acc_param.bnr.opt_center.x_reset;
 	params->acc_param.bnr.opt_center_sqr.y_sqr_reset = params->acc_param.bnr.opt_center.y_reset
 							* params->acc_param.bnr.opt_center.y_reset;
-	/*
-	 * Green gains should not be touched and considered 1.
-	 * Default is 16, so do not change it at all.
-	 * 4096 is the value for a gain of 1.0
-	 */
-	params->acc_param.bnr.wb_gains.gr = 16 * context.frameContext.awb.gains.green;
-	params->acc_param.bnr.wb_gains.r = 4096 * context.frameContext.awb.gains.red;
-	params->acc_param.bnr.wb_gains.b = 4096 * context.frameContext.awb.gains.blue;
-	params->acc_param.bnr.wb_gains.gb = 16 * context.frameContext.awb.gains.green;
+	/* Convert to u3.13 fixed point values */
+	params->acc_param.bnr.wb_gains.gr = 8192 * context.frameContext.awb.gains.green;
+	params->acc_param.bnr.wb_gains.r  = 8192 * context.frameContext.awb.gains.red;
+	params->acc_param.bnr.wb_gains.b  = 8192 * context.frameContext.awb.gains.blue;
+	params->acc_param.bnr.wb_gains.gb = 8192 * context.frameContext.awb.gains.green;
 
 	LOG(IPU3Awb, Debug) << "Color temperature estimated: " << asyncResults_.temperatureK;
 
-- 
2.30.2