[libcamera-devel] [RFC PATCH 1/2] ipa: rkisp1: awb: add support for RGB means

[Quentin Schulz]

From: Quentin Schulz <quentin.schulz at theobroma-systems.com>

RkISP actually supports two modes for color means, RGB and YCbCr. The
variables where the means are stored are identically named regardless of
the color means mode that's been selected.

Since the gains are computed in RGB mode, a conversion needs to be done
when the mode is YCbCr, which is unnecessary when RGB mode is selected.

This adds support for RGB means mode too, by checking at runtime which
mode is selected at a given time.

Cc: Quentin Schulz <foss+libcamera at 0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz at theobroma-systems.com>
---

To be decided if we want to keep supporting both modes or only one?
(Given that at the moment we harcode which mode is used at compile time,
 I'm not sure it's worth keeping dead code around)

 src/ipa/rkisp1/algorithms/awb.cpp | 57 ++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 24 deletions(-)

diff --git a/src/ipa/rkisp1/algorithms/awb.cpp b/src/ipa/rkisp1/algorithms/awb.cpp
index be4585c6..df749b9b 100644
--- a/src/ipa/rkisp1/algorithms/awb.cpp
+++ b/src/ipa/rkisp1/algorithms/awb.cpp
@@ -124,30 +124,39 @@ void Awb::process([[maybe_unused]] IPAContext &context, const rkisp1_stat_buffer
 	const rkisp1_cif_isp_stat *params = &stats->params;
 	const rkisp1_cif_isp_awb_stat *awb = &params->awb;
 	IPAFrameContext &frameContext = context.frameContext;
-
-	/* Get the YCbCr mean values */
-	double yMean = awb->awb_mean[0].mean_y_or_g;
-	double crMean = awb->awb_mean[0].mean_cr_or_r;
-	double cbMean = awb->awb_mean[0].mean_cb_or_b;
-
-	/*
-	 * Convert from YCbCr to RGB.
-	 * The hardware uses the following formulas:
-	 * Y = 16 + 0.2500 R + 0.5000 G + 0.1094 B
-	 * Cb = 128 - 0.1406 R - 0.2969 G + 0.4375 B
-	 * Cr = 128 + 0.4375 R - 0.3750 G - 0.0625 B
-	 *
-	 * The inverse matrix is thus:
-	 * [[1,1636, -0,0623,  1,6008]
-	 *  [1,1636, -0,4045, -0,7949]
-	 *  [1,1636,  1,9912, -0,0250]]
-	 */
-	yMean -= 16;
-	cbMean -= 128;
-	crMean -= 128;
-	double redMean = 1.1636 * yMean - 0.0623 * cbMean + 1.6008 * crMean;
-	double greenMean = 1.1636 * yMean - 0.4045 * cbMean - 0.7949 * crMean;
-	double blueMean = 1.1636 * yMean + 1.9912 * cbMean - 0.0250 * crMean;
+	double greenMean;
+	double redMean;
+	double blueMean;
+
+	if (params->meas.awb_meas_config.awb_mode == RKISP1_CIF_ISP_AWB_MODE_RGB) {
+		greenMean = awb->awb_mean[0].mean_y_or_g;
+		redMean = awb->awb_mean[0].mean_cr_or_r;
+		blueMean = awb->awb_mean[0].mean_cb_or_b;
+	} else {
+		/* Get the YCbCr mean values */
+		double yMean = awb->awb_mean[0].mean_y_or_g;
+		double crMean = awb->awb_mean[0].mean_cr_or_r;
+		double cbMean = awb->awb_mean[0].mean_cb_or_b;
+
+		/*
+		 * Convert from YCbCr to RGB.
+		 * The hardware uses the following formulas:
+		 * Y = 16 + 0.2500 R + 0.5000 G + 0.1094 B
+		 * Cb = 128 - 0.1406 R - 0.2969 G + 0.4375 B
+		 * Cr = 128 + 0.4375 R - 0.3750 G - 0.0625 B
+		 *
+		 * The inverse matrix is thus:
+		 * [[1,1636, -0,0623,  1,6008]
+		 *  [1,1636, -0,4045, -0,7949]
+		 *  [1,1636,  1,9912, -0,0250]]
+		 */
+		yMean -= 16;
+		cbMean -= 128;
+		crMean -= 128;
+		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;
+	}
 
 	/* Estimate the red and blue gains to apply in a grey world. */
 	double redGain = greenMean / (redMean + 1);
-- 
2.35.3