[PATCH/RFC] libcamera: Rename "shutter speed" to "exposure time"
Naushir Patuck
naush at raspberrypi.com
Thu Oct 31 11:13:51 CET 2024
Hi Laurent,
On Mon, 28 Oct 2024 at 01:34, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>
> The terms "shutter" and "shutter speed" are used through libcamera to
> mean "exposure time". This is confusing, both due to "speed" being used
> as "time" while it should be the inverse (i.e. a maximum speed should
> correspond to the minimum time), and due to "shutter speed" and
> "exposure time" being used in different places with the same meaning.
>
> To improve clarity of the code base and the documentation, use "exposure
> time" consistently to replace "shutter speed".
>
> I'm sending this patch as an RFC to gather opinions before addressing a
> few remaining issues, regarding which I'd appreciate feedback as well:
>
> - The tuning data for the AgcMeanLuminance helper class still uses a
> "shutter" YAML element. I would ideally like to rename that too.
>
> - The ExposureModeHelper::splitExposure() function used to document that
> it splits "exposure time into shutter time and gain". I have reworded
> that to "split exposure into exposure time and gain", but I'm not
> entirely happy with the result as "exposure" has a defined meaning in
> photography (see https://en.wikipedia.org/wiki/Exposure_(photography))
> that is not expressed as a duration. It seems we need a better term
> here.
>
> - I haven't touched the Raspberry Pi IPA module. David, Naush, would you
> accept a rename there too ?
No objections from us to use either "shutter time" or "exposure time"
in the RPi IPA as part of this change. I would suggest leaving the
tuning JSON files as-is for now though as users will have custom files
in use.
Regards,
Naush
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
> src/ipa/ipu3/algorithms/agc.cpp | 26 ++--
> src/ipa/ipu3/algorithms/agc.h | 4 +-
> src/ipa/ipu3/ipa_context.cpp | 8 +-
> src/ipa/ipu3/ipa_context.h | 4 +-
> src/ipa/ipu3/ipu3.cpp | 10 +-
> src/ipa/libipa/agc_mean_luminance.cpp | 43 +++----
> src/ipa/libipa/agc_mean_luminance.h | 2 +-
> src/ipa/libipa/exposure_mode_helper.cpp | 152 ++++++++++++------------
> src/ipa/libipa/exposure_mode_helper.h | 14 +--
> src/ipa/rkisp1/algorithms/agc.cpp | 27 +++--
> src/ipa/rkisp1/ipa_context.cpp | 8 +-
> src/ipa/rkisp1/ipa_context.h | 4 +-
> src/ipa/rkisp1/rkisp1.cpp | 10 +-
> src/libcamera/control_ids_core.yaml | 14 +--
> 14 files changed, 163 insertions(+), 163 deletions(-)
>
> diff --git a/src/ipa/ipu3/algorithms/agc.cpp b/src/ipa/ipu3/algorithms/agc.cpp
> index c5f3d8f0ccac..ff0f857d378c 100644
> --- a/src/ipa/ipu3/algorithms/agc.cpp
> +++ b/src/ipa/ipu3/algorithms/agc.cpp
> @@ -33,7 +33,7 @@ namespace ipa::ipu3::algorithms {
> * \class Agc
> * \brief A mean-based auto-exposure algorithm
> *
> - * This algorithm calculates a shutter time and an analogue gain so that the
> + * This algorithm calculates an exposure time and an analogue gain so that the
> * average value of the green channel of the brightest 2% of pixels approaches
> * 0.5. The AWB gains are not used here, and all cells in the grid have the same
> * weight, like an average-metering case. In this metering mode, the camera uses
> @@ -51,13 +51,13 @@ LOG_DEFINE_CATEGORY(IPU3Agc)
> static constexpr double kMinAnalogueGain = 1.0;
>
> /* \todo Honour the FrameDurationLimits control instead of hardcoding a limit */
> -static constexpr utils::Duration kMaxShutterSpeed = 60ms;
> +static constexpr utils::Duration kMaxExposureTime = 60ms;
>
> /* Histogram constants */
> static constexpr uint32_t knumHistogramBins = 256;
>
> Agc::Agc()
> - : minShutterSpeed_(0s), maxShutterSpeed_(0s)
> + : minExposureTime_(0s), maxExposureTime_(0s)
> {
> }
>
> @@ -100,9 +100,9 @@ int Agc::configure(IPAContext &context,
> stride_ = configuration.grid.stride;
> bdsGrid_ = configuration.grid.bdsGrid;
>
> - minShutterSpeed_ = configuration.agc.minShutterSpeed;
> - maxShutterSpeed_ = std::min(configuration.agc.maxShutterSpeed,
> - kMaxShutterSpeed);
> + minExposureTime_ = configuration.agc.minExposureTime;
> + maxExposureTime_ = std::min(configuration.agc.maxExposureTime,
> + kMaxExposureTime);
>
> minAnalogueGain_ = std::max(configuration.agc.minAnalogueGain, kMinAnalogueGain);
> maxAnalogueGain_ = configuration.agc.maxAnalogueGain;
> @@ -115,7 +115,7 @@ int Agc::configure(IPAContext &context,
> context.activeState.agc.exposureMode = exposureModeHelpers().begin()->first;
>
> /* \todo Run this again when FrameDurationLimits is passed in */
> - setLimits(minShutterSpeed_, maxShutterSpeed_, minAnalogueGain_,
> + setLimits(minExposureTime_, maxExposureTime_, minAnalogueGain_,
> maxAnalogueGain_);
> resetFrameCount();
>
> @@ -222,20 +222,20 @@ void Agc::process(IPAContext &context, [[maybe_unused]] const uint32_t frame,
> double analogueGain = frameContext.sensor.gain;
> utils::Duration effectiveExposureValue = exposureTime * analogueGain;
>
> - utils::Duration shutterTime;
> + utils::Duration newExposureTime;
> double aGain, dGain;
> - std::tie(shutterTime, aGain, dGain) =
> + std::tie(newExposureTime, aGain, dGain) =
> calculateNewEv(context.activeState.agc.constraintMode,
> context.activeState.agc.exposureMode, hist,
> effectiveExposureValue);
>
> LOG(IPU3Agc, Debug)
> - << "Divided up shutter, analogue gain and digital gain are "
> - << shutterTime << ", " << aGain << " and " << dGain;
> + << "Divided up exposure time, analogue gain and digital gain are "
> + << newExposureTime << ", " << aGain << " and " << dGain;
>
> IPAActiveState &activeState = context.activeState;
> - /* Update the estimated exposure and gain. */
> - activeState.agc.exposure = shutterTime / context.configuration.sensor.lineDuration;
> + /* Update the estimated exposure time and gain. */
> + activeState.agc.exposure = newExposureTime / context.configuration.sensor.lineDuration;
> activeState.agc.gain = aGain;
>
> metadata.set(controls::AnalogueGain, frameContext.sensor.gain);
> diff --git a/src/ipa/ipu3/algorithms/agc.h b/src/ipa/ipu3/algorithms/agc.h
> index 411f4da0704e..890c271b4462 100644
> --- a/src/ipa/ipu3/algorithms/agc.h
> +++ b/src/ipa/ipu3/algorithms/agc.h
> @@ -42,8 +42,8 @@ private:
> Histogram parseStatistics(const ipu3_uapi_stats_3a *stats,
> const ipu3_uapi_grid_config &grid);
>
> - utils::Duration minShutterSpeed_;
> - utils::Duration maxShutterSpeed_;
> + utils::Duration minExposureTime_;
> + utils::Duration maxExposureTime_;
>
> double minAnalogueGain_;
> double maxAnalogueGain_;
> diff --git a/src/ipa/ipu3/ipa_context.cpp b/src/ipa/ipu3/ipa_context.cpp
> index 917d06541abe..fe455e0715c6 100644
> --- a/src/ipa/ipu3/ipa_context.cpp
> +++ b/src/ipa/ipu3/ipa_context.cpp
> @@ -92,11 +92,11 @@ namespace libcamera::ipa::ipu3 {
> * \var IPASessionConfiguration::agc
> * \brief AGC parameters configuration of the IPA
> *
> - * \var IPASessionConfiguration::agc.minShutterSpeed
> - * \brief Minimum shutter speed supported with the configured sensor
> + * \var IPASessionConfiguration::agc.minExposureTime
> + * \brief Minimum exposure time supported with the configured sensor
> *
> - * \var IPASessionConfiguration::agc.maxShutterSpeed
> - * \brief Maximum shutter speed supported with the configured sensor
> + * \var IPASessionConfiguration::agc.maxExposureTime
> + * \brief Maximum exposure time supported with the configured sensor
> *
> * \var IPASessionConfiguration::agc.minAnalogueGain
> * \brief Minimum analogue gain supported with the configured sensor
> diff --git a/src/ipa/ipu3/ipa_context.h b/src/ipa/ipu3/ipa_context.h
> index c85d1e34ea85..29f38b36a9a3 100644
> --- a/src/ipa/ipu3/ipa_context.h
> +++ b/src/ipa/ipu3/ipa_context.h
> @@ -33,8 +33,8 @@ struct IPASessionConfiguration {
> } af;
>
> struct {
> - utils::Duration minShutterSpeed;
> - utils::Duration maxShutterSpeed;
> + utils::Duration minExposureTime;
> + utils::Duration maxExposureTime;
> double minAnalogueGain;
> double maxAnalogueGain;
> } agc;
> diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
> index 10a8c86d8e64..e82287631146 100644
> --- a/src/ipa/ipu3/ipu3.cpp
> +++ b/src/ipa/ipu3/ipu3.cpp
> @@ -112,7 +112,7 @@ namespace ipa::ipu3 {
> * blue gains to apply to generate a neutral grey frame overall.
> *
> * AGC is handled by calculating a histogram of the green channel to estimate an
> - * analogue gain and shutter time which will provide a well exposed frame. A
> + * analogue gain and exposure time which will provide a well exposed frame. A
> * low-pass IIR filter is used to smooth the changes to the sensor to reduce
> * perceivable steps.
> *
> @@ -215,13 +215,13 @@ void IPAIPU3::updateSessionConfiguration(const ControlInfoMap &sensorControls)
>
> /*
> * When the AGC computes the new exposure values for a frame, it needs
> - * to know the limits for shutter speed and analogue gain.
> + * to know the limits for exposure time and analogue gain.
> * As it depends on the sensor, update it with the controls.
> *
> - * \todo take VBLANK into account for maximum shutter speed
> + * \todo take VBLANK into account for maximum exposure time
> */
> - context_.configuration.agc.minShutterSpeed = minExposure * context_.configuration.sensor.lineDuration;
> - context_.configuration.agc.maxShutterSpeed = maxExposure * context_.configuration.sensor.lineDuration;
> + context_.configuration.agc.minExposureTime = minExposure * context_.configuration.sensor.lineDuration;
> + context_.configuration.agc.maxExposureTime = maxExposure * context_.configuration.sensor.lineDuration;
> context_.configuration.agc.minAnalogueGain = camHelper_->gain(minGain);
> context_.configuration.agc.maxAnalogueGain = camHelper_->gain(maxGain);
> }
> diff --git a/src/ipa/libipa/agc_mean_luminance.cpp b/src/ipa/libipa/agc_mean_luminance.cpp
> index f97ef11771c4..d2d50001e51a 100644
> --- a/src/ipa/libipa/agc_mean_luminance.cpp
> +++ b/src/ipa/libipa/agc_mean_luminance.cpp
> @@ -89,10 +89,10 @@ static constexpr double kDefaultRelativeLuminanceTarget = 0.16;
> * \class AgcMeanLuminance
> * \brief A mean-based auto-exposure algorithm
> *
> - * This algorithm calculates a shutter time, analogue and digital gain such that
> - * the normalised mean luminance value of an image is driven towards a target,
> - * which itself is discovered from tuning data. The algorithm is a two-stage
> - * process.
> + * This algorithm calculates an exposure time, analogue and digital gain such
> + * that the normalised mean luminance value of an image is driven towards a
> + * target, which itself is discovered from tuning data. The algorithm is a
> + * two-stage process.
> *
> * In the first stage, an initial gain value is derived by iteratively comparing
> * the gain-adjusted mean luminance across the entire image against a target,
> @@ -109,7 +109,7 @@ static constexpr double kDefaultRelativeLuminanceTarget = 0.16;
> * stage is then clamped to the gain from this stage.
> *
> * The final gain is used to adjust the effective exposure value of the image,
> - * and that new exposure value is divided into shutter time, analogue gain and
> + * and that new exposure value is divided into exposure time, analogue gain and
> * digital gain according to the selected AeExposureMode. This class uses the
> * \ref ExposureModeHelper class to assist in that division, and expects the
> * data needed to initialise that class to be present in tuning data in a
> @@ -247,27 +247,27 @@ int AgcMeanLuminance::parseExposureModes(const YamlObject &tuningData)
> return -EINVAL;
> }
>
> - std::vector<uint32_t> shutters =
> + std::vector<uint32_t> exposureTimes =
> modeValues["shutter"].getList<uint32_t>().value_or(std::vector<uint32_t>{});
> std::vector<double> gains =
> modeValues["gain"].getList<double>().value_or(std::vector<double>{});
>
> - if (shutters.size() != gains.size()) {
> + if (exposureTimes.size() != gains.size()) {
> LOG(AgcMeanLuminance, Error)
> << "Shutter and gain array sizes unequal";
> return -EINVAL;
> }
>
> - if (shutters.empty()) {
> + if (exposureTimes.empty()) {
> LOG(AgcMeanLuminance, Error)
> << "Shutter and gain arrays are empty";
> return -EINVAL;
> }
>
> std::vector<std::pair<utils::Duration, double>> stages;
> - for (unsigned int i = 0; i < shutters.size(); i++) {
> + for (unsigned int i = 0; i < exposureTimes.size(); i++) {
> stages.push_back({
> - std::chrono::microseconds(shutters[i]),
> + std::chrono::microseconds(exposureTimes[i]),
> gains[i]
> });
> }
> @@ -283,7 +283,7 @@ int AgcMeanLuminance::parseExposureModes(const YamlObject &tuningData)
> /*
> * If we don't have any exposure modes in the tuning data we create an
> * ExposureModeHelper using an empty vector of stages. This will result
> - * in the ExposureModeHelper simply driving the shutter as high as
> + * in the ExposureModeHelper simply driving the exposure time as high as
> * possible before touching gain.
> */
> if (availableExposureModes.empty()) {
> @@ -338,8 +338,8 @@ int AgcMeanLuminance::parseExposureModes(const YamlObject &tuningData)
> * For the AeExposureMode control the data should contain a dictionary called
> * AeExposureMode containing per-mode setting dictionaries with the key being a
> * value from \ref controls::AeExposureModeNameValueMap. Each mode dict should
> - * contain an array of shutter times with the key "shutter" and an array of gain
> - * values with the key "gain", in this format:
> + * contain an array of exposure times with the key "shutter" and an array of
> + * gain values with the key "gain", in this format:
> *
> * \code{.unparsed}
> * algorithms:
> @@ -371,20 +371,20 @@ int AgcMeanLuminance::parseTuningData(const YamlObject &tuningData)
>
> /**
> * \brief Set the ExposureModeHelper limits for this class
> - * \param[in] minShutter Minimum shutter time to allow
> - * \param[in] maxShutter Maximum shutter time to allow
> + * \param[in] minExposureTime Minimum exposure time to allow
> + * \param[in] maxExposureTime Maximum ewposure time to allow
> * \param[in] minGain Minimum gain to allow
> * \param[in] maxGain Maximum gain to allow
> *
> * This function calls \ref ExposureModeHelper::setLimits() for each
> * ExposureModeHelper that has been created for this class.
> */
> -void AgcMeanLuminance::setLimits(utils::Duration minShutter,
> - utils::Duration maxShutter,
> +void AgcMeanLuminance::setLimits(utils::Duration minExposureTime,
> + utils::Duration maxExposureTime,
> double minGain, double maxGain)
> {
> for (auto &[id, helper] : exposureModeHelpers_)
> - helper->setLimits(minShutter, maxShutter, minGain, maxGain);
> + helper->setLimits(minExposureTime, maxExposureTime, minGain, maxGain);
> }
>
> /**
> @@ -513,7 +513,8 @@ utils::Duration AgcMeanLuminance::filterExposure(utils::Duration exposureValue)
> }
>
> /**
> - * \brief Calculate the new exposure value and splut it between shutter time and gain
> + * \brief Calculate the new exposure value and splut it between exposure time
> + * and gain
> * \param[in] constraintModeIndex The index of the current constraint mode
> * \param[in] exposureModeIndex The index of the current exposure mode
> * \param[in] yHist A Histogram from the ISP statistics to use in constraining
> @@ -523,9 +524,9 @@ utils::Duration AgcMeanLuminance::filterExposure(utils::Duration exposureValue)
> *
> * Calculate a new exposure value to try to obtain the target. The calculated
> * exposure value is filtered to prevent rapid changes from frame to frame, and
> - * divided into shutter time, analogue and digital gain.
> + * divided into exposure time, analogue and digital gain.
> *
> - * \return Tuple of shutter time, analogue gain, and digital gain
> + * \return Tuple of exposure time, analogue gain, and digital gain
> */
> std::tuple<utils::Duration, double, double>
> AgcMeanLuminance::calculateNewEv(uint32_t constraintModeIndex,
> diff --git a/src/ipa/libipa/agc_mean_luminance.h b/src/ipa/libipa/agc_mean_luminance.h
> index 576d28be8eb0..c41391cb0b73 100644
> --- a/src/ipa/libipa/agc_mean_luminance.h
> +++ b/src/ipa/libipa/agc_mean_luminance.h
> @@ -44,7 +44,7 @@ public:
>
> int parseTuningData(const YamlObject &tuningData);
>
> - void setLimits(utils::Duration minShutter, utils::Duration maxShutter,
> + void setLimits(utils::Duration minExposureTime, utils::Duration maxExposureTime,
> double minGain, double maxGain);
>
> std::map<int32_t, std::vector<AgcConstraint>> constraintModes()
> diff --git a/src/ipa/libipa/exposure_mode_helper.cpp b/src/ipa/libipa/exposure_mode_helper.cpp
> index 30da0c894044..f235316d3539 100644
> --- a/src/ipa/libipa/exposure_mode_helper.cpp
> +++ b/src/ipa/libipa/exposure_mode_helper.cpp
> @@ -14,9 +14,9 @@
> * \file exposure_mode_helper.h
> * \brief Helper class that performs computations relating to exposure
> *
> - * AEGC algorithms have a need to split exposure between shutter time, analogue
> + * AEGC algorithms have a need to split exposure between exposure time, analogue
> * and digital gain. Multiple implementations do so based on paired stages of
> - * shutter time and gain limits; provide a helper to avoid duplicating the code.
> + * exposure time and gain limits; provide a helper to avoid duplicating the code.
> */
>
> namespace libcamera {
> @@ -29,24 +29,24 @@ namespace ipa {
>
> /**
> * \class ExposureModeHelper
> - * \brief Class for splitting exposure into shutter time and total gain
> + * \brief Class for splitting exposure into exposure time and total gain
> *
> * The ExposureModeHelper class provides a standard interface through which an
> - * AEGC algorithm can divide exposure between shutter time and gain. It is
> - * configured with a set of shutter time and gain pairs and works by initially
> - * fixing gain at 1.0 and increasing shutter time up to the shutter time value
> + * AEGC algorithm can divide exposure between exposure time and gain. It is
> + * configured with a set of exposure time and gain pairs and works by initially
> + * fixing gain at 1.0 and increasing exposure time up to the exposure time value
> * from the first pair in the set in an attempt to meet the required exposure
> * value.
> *
> - * If the required exposure is not achievable by the first shutter time value
> + * If the required exposure is not achievable by the first exposure time value
> * alone it ramps gain up to the value from the first pair in the set. If the
> - * required exposure is still not met it then allows shutter time to ramp up to
> - * the shutter time value from the second pair in the set, and continues in this
> + * required exposure is still not met it then allows exposure time to ramp up to
> + * the exposure time value from the second pair in the set, and continues in this
> * vein until either the required exposure time is met, or else the hardware's
> - * shutter time or gain limits are reached.
> + * exposure time or gain limits are reached.
> *
> * This method allows users to strike a balance between a well-exposed image and
> - * an acceptable frame-rate, as opposed to simply maximising shutter time
> + * an acceptable frame-rate, as opposed to simply maximising exposure time
> * followed by gain. The same helpers can be used to perform the latter
> * operation if needed by passing an empty set of pairs to the initialisation
> * function.
> @@ -61,9 +61,9 @@ namespace ipa {
>
> /**
> * \brief Construct an ExposureModeHelper instance
> - * \param[in] stages The vector of paired shutter time and gain limits
> + * \param[in] stages The vector of paired exposure time and gain limits
> *
> - * The input stages are shutter time and _total_ gain pairs; the gain
> + * The input stages are exposure time and _total_ gain pairs; the gain
> * encompasses both analogue and digital gain.
> *
> * The vector of stages may be empty. In that case, the helper will simply use
> @@ -71,46 +71,46 @@ namespace ipa {
> */
> ExposureModeHelper::ExposureModeHelper(const Span<std::pair<utils::Duration, double>> stages)
> {
> - minShutter_ = 0us;
> - maxShutter_ = 0us;
> + minExposureTime_ = 0us;
> + maxExposureTime_ = 0us;
> minGain_ = 0;
> maxGain_ = 0;
>
> for (const auto &[s, g] : stages) {
> - shutters_.push_back(s);
> + exposureTimes_.push_back(s);
> gains_.push_back(g);
> }
> }
>
> /**
> - * \brief Set the shutter time and gain limits
> - * \param[in] minShutter The minimum shutter time supported
> - * \param[in] maxShutter The maximum shutter time supported
> + * \brief Set the exposure time and gain limits
> + * \param[in] minExposureTime The minimum exposure time supported
> + * \param[in] maxExposureTime The maximum exposure time supported
> * \param[in] minGain The minimum analogue gain supported
> * \param[in] maxGain The maximum analogue gain supported
> *
> - * This function configures the shutter time and analogue gain limits that need
> + * This function configures the exposure time and analogue gain limits that need
> * to be adhered to as the helper divides up exposure. Note that this function
> * *must* be called whenever those limits change and before splitExposure() is
> * used.
> *
> - * If the algorithm using the helpers needs to indicate that either shutter time
> + * If the algorithm using the helpers needs to indicate that either exposure time
> * or analogue gain or both should be fixed it can do so by setting both the
> * minima and maxima to the same value.
> */
> -void ExposureModeHelper::setLimits(utils::Duration minShutter,
> - utils::Duration maxShutter,
> +void ExposureModeHelper::setLimits(utils::Duration minExposureTime,
> + utils::Duration maxExposureTime,
> double minGain, double maxGain)
> {
> - minShutter_ = minShutter;
> - maxShutter_ = maxShutter;
> + minExposureTime_ = minExposureTime;
> + maxExposureTime_ = maxExposureTime;
> minGain_ = minGain;
> maxGain_ = maxGain;
> }
>
> -utils::Duration ExposureModeHelper::clampShutter(utils::Duration shutter) const
> +utils::Duration ExposureModeHelper::clampExposureTime(utils::Duration exposureTime) const
> {
> - return std::clamp(shutter, minShutter_, maxShutter_);
> + return std::clamp(exposureTime, minExposureTime_, maxExposureTime_);
> }
>
> double ExposureModeHelper::clampGain(double gain) const
> @@ -119,108 +119,108 @@ double ExposureModeHelper::clampGain(double gain) const
> }
>
> /**
> - * \brief Split exposure time into shutter time and gain
> - * \param[in] exposure Exposure time
> + * \brief Split exposure into exposure time and gain
> + * \param[in] exposure Exposure value
> *
> - * This function divides a given exposure time into shutter time, analogue and
> - * digital gain by iterating through stages of shutter time and gain limits. At
> - * each stage the current stage's shutter time limit is multiplied by the
> + * This function divides a given exposure into exposure time, analogue and
> + * digital gain by iterating through stages of exposure time and gain limits.
> + * At each stage the current stage's exposure time limit is multiplied by the
> * previous stage's gain limit (or 1.0 initially) to see if the combination of
> - * the two can meet the required exposure time. If they cannot then the current
> - * stage's shutter time limit is multiplied by the same stage's gain limit to
> + * the two can meet the required exposure. If they cannot then the current
> + * stage's exposure time limit is multiplied by the same stage's gain limit to
> * see if that combination can meet the required exposure time. If they cannot
> * then the function moves to consider the next stage.
> *
> - * When a combination of shutter time and gain _stage_ limits are found that are
> - * sufficient to meet the required exposure time, the function attempts to
> - * reduce shutter time as much as possible whilst fixing gain and still meeting
> - * the exposure time. If a _runtime_ limit prevents shutter time from being
> - * lowered enough to meet the exposure time with gain fixed at the stage limit,
> - * gain is also lowered to compensate.
> + * When a combination of exposure time and gain _stage_ limits are found that
> + * are sufficient to meet the required exposure, the function attempts to reduce
> + * exposure time as much as possible whilst fixing gain and still meeting the
> + * exposure. If a _runtime_ limit prevents exposure time from being lowered
> + * enough to meet the exposure with gain fixed at the stage limit, gain is also
> + * lowered to compensate.
> *
> - * Once the shutter time and gain values are ascertained, gain is assigned as
> + * Once the exposure time and gain values are ascertained, gain is assigned as
> * analogue gain as much as possible, with digital gain only in use if the
> * maximum analogue gain runtime limit is unable to accommodate the exposure
> * value.
> *
> - * If no combination of shutter time and gain limits is found that meets the
> - * required exposure time, the helper falls-back to simply maximising the
> - * shutter time first, followed by analogue gain, followed by digital gain.
> + * If no combination of exposure time and gain limits is found that meets the
> + * required exposure, the helper falls-back to simply maximising the exposure
> + * time first, followed by analogue gain, followed by digital gain.
> *
> - * \return Tuple of shutter time, analogue gain, and digital gain
> + * \return Tuple of exposure time, analogue gain, and digital gain
> */
> std::tuple<utils::Duration, double, double>
> ExposureModeHelper::splitExposure(utils::Duration exposure) const
> {
> - ASSERT(maxShutter_);
> + ASSERT(maxExposureTime_);
> ASSERT(maxGain_);
>
> bool gainFixed = minGain_ == maxGain_;
> - bool shutterFixed = minShutter_ == maxShutter_;
> + bool exposureTimeFixed = minExposureTime_ == maxExposureTime_;
>
> /*
> * There's no point entering the loop if we cannot change either gain
> - * nor shutter anyway.
> + * nor exposure time anyway.
> */
> - if (shutterFixed && gainFixed)
> - return { minShutter_, minGain_, exposure / (minShutter_ * minGain_) };
> + if (exposureTimeFixed && gainFixed)
> + return { minExposureTime_, minGain_, exposure / (minExposureTime_ * minGain_) };
>
> - utils::Duration shutter;
> + utils::Duration exposureTime;
> double stageGain = 1.0;
> double gain;
>
> for (unsigned int stage = 0; stage < gains_.size(); stage++) {
> double lastStageGain = stage == 0 ? 1.0 : clampGain(gains_[stage - 1]);
> - utils::Duration stageShutter = clampShutter(shutters_[stage]);
> + utils::Duration stageExposureTime = clampExposureTime(exposureTimes_[stage]);
> stageGain = clampGain(gains_[stage]);
>
> /*
> - * We perform the clamping on both shutter and gain in case the
> - * helper has had limits set that prevent those values being
> - * lowered beyond a certain minimum...this can happen at runtime
> - * for various reasons and so would not be known when the stage
> - * limits are initialised.
> + * We perform the clamping on both exposure time and gain in
> + * case the helper has had limits set that prevent those values
> + * being lowered beyond a certain minimum...this can happen at
> + * runtime for various reasons and so would not be known when
> + * the stage limits are initialised.
> */
>
> - if (stageShutter * lastStageGain >= exposure) {
> - shutter = clampShutter(exposure / clampGain(lastStageGain));
> - gain = clampGain(exposure / shutter);
> + if (stageExposureTime * lastStageGain >= exposure) {
> + exposureTime = clampExposureTime(exposure / clampGain(lastStageGain));
> + gain = clampGain(exposure / exposureTime);
>
> - return { shutter, gain, exposure / (shutter * gain) };
> + return { exposureTime, gain, exposure / (exposureTime * gain) };
> }
>
> - if (stageShutter * stageGain >= exposure) {
> - shutter = clampShutter(exposure / clampGain(stageGain));
> - gain = clampGain(exposure / shutter);
> + if (stageExposureTime * stageGain >= exposure) {
> + exposureTime = clampExposureTime(exposure / clampGain(stageGain));
> + gain = clampGain(exposure / exposureTime);
>
> - return { shutter, gain, exposure / (shutter * gain) };
> + return { exposureTime, gain, exposure / (exposureTime * gain) };
> }
> }
>
> /*
> - * From here on all we can do is max out the shutter time, followed by
> + * From here on all we can do is max out the exposure 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 the default stageGain of 1.0 is used so that
> - * shutter time is maxed before gain is touched at all.
> + * exposure time is maxed before gain is touched at all.
> */
> - shutter = clampShutter(exposure / clampGain(stageGain));
> - gain = clampGain(exposure / shutter);
> + exposureTime = clampExposureTime(exposure / clampGain(stageGain));
> + gain = clampGain(exposure / exposureTime);
>
> - return { shutter, gain, exposure / (shutter * gain) };
> + return { exposureTime, gain, exposure / (exposureTime * gain) };
> }
>
> /**
> - * \fn ExposureModeHelper::minShutter()
> - * \brief Retrieve the configured minimum shutter time limit set through
> + * \fn ExposureModeHelper::minExposureTime()
> + * \brief Retrieve the configured minimum exposure time limit set through
> * setLimits()
> - * \return The minShutter_ value
> + * \return The minExposureTime_ value
> */
>
> /**
> - * \fn ExposureModeHelper::maxShutter()
> - * \brief Retrieve the configured maximum shutter time set through setLimits()
> - * \return The maxShutter_ value
> + * \fn ExposureModeHelper::maxExposureTime()
> + * \brief Retrieve the configured maximum exposure time set through setLimits()
> + * \return The maxExposureTime_ value
> */
>
> /**
> diff --git a/src/ipa/libipa/exposure_mode_helper.h b/src/ipa/libipa/exposure_mode_helper.h
> index 85c665d7d187..c5be1b6703a8 100644
> --- a/src/ipa/libipa/exposure_mode_helper.h
> +++ b/src/ipa/libipa/exposure_mode_helper.h
> @@ -24,26 +24,26 @@ public:
> ExposureModeHelper(const Span<std::pair<utils::Duration, double>> stages);
> ~ExposureModeHelper() = default;
>
> - void setLimits(utils::Duration minShutter, utils::Duration maxShutter,
> + void setLimits(utils::Duration minExposureTime, utils::Duration maxExposureTime,
> double minGain, double maxGain);
>
> std::tuple<utils::Duration, double, double>
> splitExposure(utils::Duration exposure) const;
>
> - utils::Duration minShutter() const { return minShutter_; }
> - utils::Duration maxShutter() const { return maxShutter_; }
> + utils::Duration minExposureTime() const { return minExposureTime_; }
> + utils::Duration maxExposureTime() const { return maxExposureTime_; }
> double minGain() const { return minGain_; }
> double maxGain() const { return maxGain_; }
>
> private:
> - utils::Duration clampShutter(utils::Duration shutter) const;
> + utils::Duration clampExposureTime(utils::Duration exposureTime) const;
> double clampGain(double gain) const;
>
> - std::vector<utils::Duration> shutters_;
> + std::vector<utils::Duration> exposureTimes_;
> std::vector<double> gains_;
>
> - utils::Duration minShutter_;
> - utils::Duration maxShutter_;
> + utils::Duration minExposureTime_;
> + utils::Duration maxExposureTime_;
> double minGain_;
> double maxGain_;
> };
> diff --git a/src/ipa/rkisp1/algorithms/agc.cpp b/src/ipa/rkisp1/algorithms/agc.cpp
> index 301b7ec26508..40e5a8f481b2 100644
> --- a/src/ipa/rkisp1/algorithms/agc.cpp
> +++ b/src/ipa/rkisp1/algorithms/agc.cpp
> @@ -183,7 +183,7 @@ int Agc::configure(IPAContext &context, const IPACameraSensorInfo &configInfo)
> * except it's computed in the IPA and not here so we'd have to
> * recompute it.
> */
> - context.activeState.agc.maxFrameDuration = context.configuration.sensor.maxShutterSpeed;
> + context.activeState.agc.maxFrameDuration = context.configuration.sensor.maxExposureTime;
>
> /*
> * Define the measurement window for AGC as a centered rectangle
> @@ -194,8 +194,8 @@ int Agc::configure(IPAContext &context, const IPACameraSensorInfo &configInfo)
> context.configuration.agc.measureWindow.h_size = 3 * configInfo.outputSize.width / 4;
> context.configuration.agc.measureWindow.v_size = 3 * configInfo.outputSize.height / 4;
>
> - setLimits(context.configuration.sensor.minShutterSpeed,
> - context.configuration.sensor.maxShutterSpeed,
> + setLimits(context.configuration.sensor.minExposureTime,
> + context.configuration.sensor.maxExposureTime,
> context.configuration.sensor.minAnalogueGain,
> context.configuration.sensor.maxAnalogueGain);
>
> @@ -424,12 +424,12 @@ void Agc::process(IPAContext &context, [[maybe_unused]] const uint32_t frame,
> [](uint32_t x) { return x >> 4; });
> expMeans_ = { params->ae.exp_mean, context.hw->numAeCells };
>
> - utils::Duration maxShutterSpeed =
> + utils::Duration maxExposureTime =
> std::clamp(frameContext.agc.maxFrameDuration,
> - context.configuration.sensor.minShutterSpeed,
> - context.configuration.sensor.maxShutterSpeed);
> - setLimits(context.configuration.sensor.minShutterSpeed,
> - maxShutterSpeed,
> + context.configuration.sensor.minExposureTime,
> + context.configuration.sensor.maxExposureTime);
> + setLimits(context.configuration.sensor.minExposureTime,
> + maxExposureTime,
> context.configuration.sensor.minAnalogueGain,
> context.configuration.sensor.maxAnalogueGain);
>
> @@ -442,20 +442,21 @@ void Agc::process(IPAContext &context, [[maybe_unused]] const uint32_t frame,
> double analogueGain = frameContext.sensor.gain;
> utils::Duration effectiveExposureValue = exposureTime * analogueGain;
>
> - utils::Duration shutterTime;
> + utils::Duration newExposureTime;
> double aGain, dGain;
> - std::tie(shutterTime, aGain, dGain) =
> + std::tie(newExposureTime, aGain, dGain) =
> calculateNewEv(frameContext.agc.constraintMode,
> frameContext.agc.exposureMode,
> hist, effectiveExposureValue);
>
> LOG(RkISP1Agc, Debug)
> - << "Divided up shutter, analogue gain and digital gain are "
> - << shutterTime << ", " << aGain << " and " << dGain;
> + << "Divided up exposure time, analogue gain and digital gain are "
> + << newExposureTime << ", " << aGain << " and " << dGain;
>
> IPAActiveState &activeState = context.activeState;
> /* Update the estimated exposure and gain. */
> - activeState.agc.automatic.exposure = shutterTime / context.configuration.sensor.lineDuration;
> + activeState.agc.automatic.exposure = newExposureTime
> + / context.configuration.sensor.lineDuration;
> activeState.agc.automatic.gain = aGain;
>
> fillMetadata(context, frameContext, metadata);
> diff --git a/src/ipa/rkisp1/ipa_context.cpp b/src/ipa/rkisp1/ipa_context.cpp
> index 14d0c02a2b32..833e2cbb784f 100644
> --- a/src/ipa/rkisp1/ipa_context.cpp
> +++ b/src/ipa/rkisp1/ipa_context.cpp
> @@ -78,11 +78,11 @@ namespace libcamera::ipa::rkisp1 {
> * \var IPASessionConfiguration::sensor
> * \brief Sensor-specific configuration of the IPA
> *
> - * \var IPASessionConfiguration::sensor.minShutterSpeed
> - * \brief Minimum shutter speed supported with the sensor
> + * \var IPASessionConfiguration::sensor.minExposureTime
> + * \brief Minimum exposure time supported with the sensor
> *
> - * \var IPASessionConfiguration::sensor.maxShutterSpeed
> - * \brief Maximum shutter speed supported with the sensor
> + * \var IPASessionConfiguration::sensor.maxExposureTime
> + * \brief Maximum exposure time supported with the sensor
> *
> * \var IPASessionConfiguration::sensor.minAnalogueGain
> * \brief Minimum analogue gain supported with the sensor
> diff --git a/src/ipa/rkisp1/ipa_context.h b/src/ipa/rkisp1/ipa_context.h
> index e274d9b01e1c..5fc53011d9b4 100644
> --- a/src/ipa/rkisp1/ipa_context.h
> +++ b/src/ipa/rkisp1/ipa_context.h
> @@ -50,8 +50,8 @@ struct IPASessionConfiguration {
> } lsc;
>
> struct {
> - utils::Duration minShutterSpeed;
> - utils::Duration maxShutterSpeed;
> + utils::Duration minExposureTime;
> + utils::Duration maxExposureTime;
> double minAnalogueGain;
> double maxAnalogueGain;
>
> diff --git a/src/ipa/rkisp1/rkisp1.cpp b/src/ipa/rkisp1/rkisp1.cpp
> index 9e161cabdea4..69417b9ec6bf 100644
> --- a/src/ipa/rkisp1/rkisp1.cpp
> +++ b/src/ipa/rkisp1/rkisp1.cpp
> @@ -256,14 +256,14 @@ int IPARkISP1::configure(const IPAConfigInfo &ipaConfig,
>
> /*
> * When the AGC computes the new exposure values for a frame, it needs
> - * to know the limits for shutter speed and analogue gain.
> - * As it depends on the sensor, update it with the controls.
> + * to know the limits for exposure time and analogue gain. As it depends
> + * on the sensor, update it with the controls.
> *
> - * \todo take VBLANK into account for maximum shutter speed
> + * \todo take VBLANK into account for maximum exposure time
> */
> - context_.configuration.sensor.minShutterSpeed =
> + context_.configuration.sensor.minExposureTime =
> minExposure * context_.configuration.sensor.lineDuration;
> - context_.configuration.sensor.maxShutterSpeed =
> + context_.configuration.sensor.maxExposureTime =
> maxExposure * context_.configuration.sensor.lineDuration;
> context_.configuration.sensor.minAnalogueGain =
> context_.camHelper->gain(minGain);
> diff --git a/src/libcamera/control_ids_core.yaml b/src/libcamera/control_ids_core.yaml
> index 1b1bd9507d25..438a5d003750 100644
> --- a/src/libcamera/control_ids_core.yaml
> +++ b/src/libcamera/control_ids_core.yaml
> @@ -102,7 +102,7 @@ controls:
> Specify an exposure mode for the AE algorithm to use.
>
> The exposure modes specify how the desired total exposure is divided
> - between the shutter time and the sensor's analogue gain. They are
> + between the exposure time and the sensor's analogue gain. They are
> platform specific, and not all exposure modes may be supported.
> enum:
> - name: ExposureNormal
> @@ -135,8 +135,7 @@ controls:
> - ExposureTime:
> type: int32_t
> description: |
> - Exposure time (shutter speed) for the frame applied in the sensor
> - device.
> + Exposure time for the frame applied in the sensor device.
>
> This value is specified in micro-seconds.
>
> @@ -463,14 +462,13 @@ controls:
> values to be the same. Setting both values to 0 reverts to using the
> camera defaults.
>
> - The maximum frame duration provides the absolute limit to the shutter
> - speed computed by the AE algorithm and it overrides any exposure mode
> + The maximum frame duration provides the absolute limit to the exposure
> + time computed by the AE algorithm and it overrides any exposure mode
> setting specified with controls::AeExposureMode. Similarly, when a
> manual exposure time is set through controls::ExposureTime, it also
> gets clipped to the limits set by this control. When reported in
> - metadata, the control expresses the minimum and maximum frame
> - durations used after being clipped to the sensor provided frame
> - duration limits.
> + metadata, the control expresses the minimum and maximum frame durations
> + used after being clipped to the sensor provided frame duration limits.
>
> \sa AeExposureMode
> \sa ExposureTime
>
> base-commit: 80a7ccd3add45eb56fda6f1fb445017ac01fea7a
> prerequisite-patch-id: 19ba9a578d3e04662488c7189f88ffea94c769fe
> --
> Regards,
>
> Laurent Pinchart
>
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