[libcamera-devel] [PATCH 3/4] libipa: camera_sensor_helper: Add IMX290 helper

[Laurent Pinchart]

The IMX290 is a Sony sensor that expresses its gain in 0.3dB units. It
thus maps to the exponential gain model.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/ipa/libipa/camera_sensor_helper.cpp | 31 +++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
index 7bb999e19102..136b9f6bc3c5 100644
--- a/src/ipa/libipa/camera_sensor_helper.cpp
+++ b/src/ipa/libipa/camera_sensor_helper.cpp
@@ -332,6 +332,26 @@ std::vector<CameraSensorHelperFactory *> &CameraSensorHelperFactory::factories()
 
 #ifndef __DOXYGEN__
 
+/*
+ * Helper function to compute the m parameter of the exponential gain model
+ * when the gain code is expressed in dB.
+ */
+static constexpr double expGainDb(double step)
+{
+	constexpr double log2_10 = 3.321928094887362;
+
+	/*
+	 * The gain code is expressed in step * dB (e.g. in 0.1 dB steps):
+	 *
+	 * G_code = G_dB/step = 20/step*log10(G_linear)
+	 *
+	 * Inverting the formula, we get
+	 *
+	 * G_linear = 10^(step/20*G_code) = 2^(log2(10)*step/20*G_code)
+	 */
+	return log2_10 * step / 20;
+}
+
 class CameraSensorHelperImx219 : public CameraSensorHelper
 {
 public:
@@ -354,6 +374,17 @@ public:
 };
 REGISTER_CAMERA_SENSOR_HELPER("imx258", CameraSensorHelperImx258)
 
+class CameraSensorHelperImx290 : public CameraSensorHelper
+{
+public:
+	CameraSensorHelperImx290()
+	{
+		gainType_ = AnalogueGainExponential;
+		gainConstants_.exp = { 1.0, expGainDb(0.3) };
+	}
+};
+REGISTER_CAMERA_SENSOR_HELPER("imx290", CameraSensorHelperImx290)
+
 class CameraSensorHelperOv2740 : public CameraSensorHelper
 {
 public:
-- 
Regards,

Laurent Pinchart