[libcamera-devel] [PATCH v5 30/33] 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>
Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
---
 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 139c8239504f..59664d09b84c 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