libipa: camera_sensor_helper: Add quantizeGain() function

Add a small utility function that calculates the quantized gain that
gets applied by a sensor when the gain code is set to gainCode(gain).
This is needed by algorithms to calculate a digital correction gain that
gets applied to mitigate the error introduce by quantization.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Isaac Scott <isaac.scott@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/ipa/libipa/camera_sensor_helper.cpp

@@ -131,6 +131,29 @@ double CameraSensorHelper::gain(uint32_t gainCode) const
 	}
 }
 
+/**
+ * \brief Quantize the given gain value
+ * \param[in] _gain The real gain
+ * \param[out] quantizationGain The gain that is lost due to quantization
+ *
+ * This function returns the actual gain that is applied when the sensor's gain
+ * is set to gainCode(_gain).
+ *
+ * It shall be guaranteed that gainCode(_gain) == gainCode(quantizeGain(_gain)).
+ *
+ * If \a quantizationGain is provided it is populated with the gain that must be
+ * applied on top to correct for the losses due to quantization.
+ *
+ * \return The quantized real gain
+ */
+double CameraSensorHelper::quantizeGain(double _gain, double *quantizationGain) const
+{
+	double g = gain(gainCode(_gain));
+	if (quantizationGain)
+		*quantizationGain = _gain / g;
+	return g;
+}
+
 /**
  * \struct CameraSensorHelper::AnalogueGainLinear
  * \brief Analogue gain constants for the linear gain model

src/ipa/libipa/camera_sensor_helper.h

@@ -29,6 +29,7 @@ public:
 	std::optional<int16_t> blackLevel() const { return blackLevel_; }
 	virtual uint32_t gainCode(double gain) const;
 	virtual double gain(uint32_t gainCode) const;
+	double quantizeGain(double gain, double *quantizationGain) const;
 
 protected:
 	struct AnalogueGainLinear {