[libcamera-devel] [PATCH v4 29/32] ipa: rkisp1: awb: Prevent RGB means from being negative

[Laurent Pinchart]

Due to hardware rounding errors in the YCbCr means, the calculated RGB
means may be negative. This would lead to negative gains, messing up
calculation. Prevent this by clamping the means to positive values.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/ipa/rkisp1/algorithms/awb.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/ipa/rkisp1/algorithms/awb.cpp b/src/ipa/rkisp1/algorithms/awb.cpp
index ed91e9277a16..de54c4d24650 100644
--- a/src/ipa/rkisp1/algorithms/awb.cpp
+++ b/src/ipa/rkisp1/algorithms/awb.cpp
@@ -242,6 +242,16 @@ void Awb::process(IPAContext &context,
 		redMean = 1.1636 * yMean - 0.0623 * cbMean + 1.6008 * crMean;
 		greenMean = 1.1636 * yMean - 0.4045 * cbMean - 0.7949 * crMean;
 		blueMean = 1.1636 * yMean + 1.9912 * cbMean - 0.0250 * crMean;
+
+		/*
+		 * Due to hardware rounding errors in the YCbCr means, the
+		 * calculated RGB means may be negative. This would lead to
+		 * negative gains, messing up calculation. Prevent this by
+		 * clamping the means to positive values.
+		 */
+		redMean = std::max(redMean, 0.0);
+		greenMean = std::max(greenMean, 0.0);
+		blueMean = std::max(blueMean, 0.0);
 	}
 
 	/*
-- 
Regards,

Laurent Pinchart