4 files changed, 50 insertions, 8 deletions
diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
index 782ff990..a1339c83 100644
--- a/src/ipa/libipa/camera_sensor_helper.cpp
+++ b/src/ipa/libipa/camera_sensor_helper.cpp
@@ -48,6 +48,33 @@ namespace ipa {
  */
 
 /**
+ * \fn CameraSensorHelper::blackLevel()
+ * \brief Fetch the black level of the sensor
+ *
+ * This function returns the black level of the sensor scaled to a 16bit pixel
+ * width. If it is unknown an empty optional is returned.
+ *
+ * \todo Fill the blanks and add pedestal values for all supported sensors. Once
+ * done, drop the std::optional<>.
+ *
+ * Black levels are typically the result of the following phenomena:
+ * - Pedestal added by the sensor to pixel values. They are typically fixed,
+ *   sometimes programmable and should be reported in datasheets (but
+ *   documentation is not always available).
+ * - Dark currents and other physical effects that add charge to pixels in the
+ *   absence of light. Those can depend on the integration time and the sensor
+ *   die temperature, and their contribution to pixel values depend on the
+ *   sensor gains.
+ *
+ * The pedestal is usually the value with the biggest contribution to the
+ * overall black level. In most cases it is either known before or in rare cases
+ * (there is not a single driver with such a control in the linux kernel) can be
+ * queried from the sensor. This function provides that fixed, known value.
+ *
+ * \return The black level of the sensor, or std::nullopt if not known
+ */
+
+/**
  * \brief Compute gain code from the analogue gain absolute value
  * \param[in] gain The real gain to pass
  *
@@ -205,6 +232,11 @@ double CameraSensorHelper::gain(uint32_t gainCode) const
  */
 
 /**
+ * \var CameraSensorHelper::blackLevel_
+ * \brief The black level of the sensor
+ */
+
+/**
  * \var CameraSensorHelper::gainType_
  * \brief The analogue gain model type
  */
@@ -396,6 +428,8 @@ class CameraSensorHelperImx219 : public CameraSensorHelper
 public:
 	CameraSensorHelperImx219()
 	{
+		/* From datasheet: 64 at 10bits. */
+		blackLevel_ = 4096;
 		gainType_ = AnalogueGainLinear;
 		gainConstants_.linear = { 0, 256, -1, 256 };
 	}
@@ -407,6 +441,8 @@ class CameraSensorHelperImx258 : public CameraSensorHelper
 public:
 	CameraSensorHelperImx258()
 	{
+		/* From datasheet: 0x40 at 10bits. */
+		blackLevel_ = 4096;
 		gainType_ = AnalogueGainLinear;
 		gainConstants_.linear = { 0, 512, -1, 512 };
 	}
@@ -456,6 +492,8 @@ class CameraSensorHelperImx335 : public CameraSensorHelper
 public:
 	CameraSensorHelperImx335()
 	{
+		/* From datasheet: 0x32 at 10bits. */
+		blackLevel_ = 3200;
 		gainType_ = AnalogueGainExponential;
 		gainConstants_.exp = { 1.0, expGainDb(0.3) };
 	}
@@ -515,6 +553,8 @@ class CameraSensorHelperOv4689 : public CameraSensorHelper
 public:
 	CameraSensorHelperOv4689()
 	{
+		/* From datasheet: 0x40 at 12bits. */
+		blackLevel_ = 1024;
 		gainType_ = AnalogueGainLinear;
 		gainConstants_.linear = { 1, 0, 0, 128 };
 	}
@@ -526,6 +566,8 @@ class CameraSensorHelperOv5640 : public CameraSensorHelper
 public:
 	CameraSensorHelperOv5640()
 	{
+		/* From datasheet: 0x10 at 10bits. */
+		blackLevel_ = 1024;
 		gainType_ = AnalogueGainLinear;
 		gainConstants_.linear = { 1, 0, 0, 16 };
 	}
diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
index 0d99073b..ac276e27 100644
--- a/src/ipa/libipa/camera_sensor_helper.h
+++ b/src/ipa/libipa/camera_sensor_helper.h
@@ -10,6 +10,7 @@
 #include <stdint.h>
 
 #include <memory>
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -25,6 +26,7 @@ public:
 	CameraSensorHelper() = default;
 	virtual ~CameraSensorHelper() = default;
 
+	std::optional<int16_t> blackLevel() const { return blackLevel_; }
 	virtual uint32_t gainCode(double gain) const;
 	virtual double gain(uint32_t gainCode) const;
 
@@ -51,6 +53,7 @@ protected:
 		AnalogueGainExpConstants exp;
 	};
 
+	std::optional<int16_t> blackLevel_;
 	AnalogueGainType gainType_;
 	AnalogueGainConstants gainConstants_;
 
diff --git a/src/ipa/libipa/exposure_mode_helper.cpp b/src/ipa/libipa/exposure_mode_helper.cpp
index 683a564a..7703becc 100644
--- a/src/ipa/libipa/exposure_mode_helper.cpp
+++ b/src/ipa/libipa/exposure_mode_helper.cpp
@@ -166,7 +166,7 @@ ExposureModeHelper::splitExposure(utils::Duration exposure) const
 		return { minShutter_, minGain_, exposure / (minShutter_ * minGain_) };
 
 	utils::Duration shutter;
-	double stageGain;
+	double stageGain = 1.0;
 	double gain;
 
 	for (unsigned int stage = 0; stage < gains_.size(); stage++) {
@@ -201,12 +201,9 @@ ExposureModeHelper::splitExposure(utils::Duration exposure) const
 	 * From here on all we can do is max out the shutter time, followed by
 	 * the analogue gain. If we still haven't achieved the target we send
 	 * the rest of the exposure time to digital gain. If we were given no
-	 * stages to use then set stageGain to 1.0 so that shutter time is maxed
-	 * before gain touched at all.
+	 * stages to use then the default stageGain of 1.0 is used so that
+	 * shutter time is maxed before gain is touched at all.
 	 */
-	if (gains_.empty())
-		stageGain = 1.0;
-
 	shutter = clampShutter(exposure / clampGain(stageGain));
 	gain = clampGain(exposure / shutter);
 
diff --git a/src/ipa/libipa/matrix.cpp b/src/ipa/libipa/matrix.cpp
index 7f000382..8346f0d3 100644
--- a/src/ipa/libipa/matrix.cpp
+++ b/src/ipa/libipa/matrix.cpp
@@ -122,8 +122,6 @@ namespace ipa {
  * \return Matrix sum of matrices \a m1 and \a m2
  */
 
-} /* namespace ipa */
-
 #ifndef __DOXYGEN__
 /*
  * The YAML data shall be a list of numerical values. Its size shall be equal
@@ -146,4 +144,6 @@ bool matrixValidateYaml(const YamlObject &obj, unsigned int size)
 }
 #endif /* __DOXYGEN__ */
 
+} /* namespace ipa */
+
 } /* namespace libcamera */