lsst::meas::base::BlendednessAlgorithm Class Reference

Compute metrics that measure how blended objects are. More...

#include <Blendedness.h>

Inheritance diagram for lsst::meas::base::BlendednessAlgorithm:

Public Types
typedef BlendednessControl	Control

Public Member Functions
	BlendednessAlgorithm (Control const &ctrl, std::string const &name, afw::table::Schema &schema)
void	measureChildPixels (afw::image::MaskedImage< float > const &image, afw::table::SourceRecord &child) const
void	measureParentPixels (afw::image::MaskedImage< float > const &image, afw::table::SourceRecord &child) const
virtual void	measure (afw::table::SourceRecord &measRecord, afw::image::Exposure< float > const &exposure) const
	Called to measure a single child source in an image.
virtual void	fail (afw::table::SourceRecord &measRecord, MeasurementError *error=nullptr) const
	Handle an exception thrown by the current algorithm by setting flags in the given record.
void	measureForced (afw::table::SourceRecord &measRecord, afw::image::Exposure< float > const &exposure, afw::table::SourceRecord const &refRecord, afw::geom::SkyWcs const &refWcs) const override
	Called to measure a single child source in an image.
void	measureNForced (afw::table::SourceCatalog const &measCat, afw::image::Exposure< float > const &exposure, afw::table::SourceCatalog const &refRecord, afw::geom::SkyWcs const &refWcs) const override
	Called to simultaneously measure all children in a deblend family, in a single image.
virtual void	measureN (afw::table::SourceCatalog const &measCat, afw::image::Exposure< float > const &exposure) const
	Called to simultaneously measure all children in a deblend family, in a single image.
std::string	getLogName () const

Static Public Member Functions
static FlagDefinitionList const &	getFlagDefinitions ()
static float	computeAbsExpectation (float data, float variance)
	Compute the posterior expectation value of the true instrumental flux in a pixel from its (Gaussian) likelihood and a flat nonnegative prior.
static float	computeAbsBias (float mu, float variance)
	Compute the bias induced by using the absolute value of a pixel instead of its value.

Static Public Attributes
static FlagDefinition const	FAILURE = flagDefinitions.addFailureFlag()
static FlagDefinition const	NO_CENTROID
static FlagDefinition const	NO_SHAPE

Protected Attributes
std::string	_logName

Detailed Description

Compute metrics that measure how blended objects are.

Blendedness is initialized once for a given Schema, then run repeatedly by calls to measureChildPixels and measureParentPixels (in any order, possibly with multiple sources interleaved). Since it needs access to both the image with with noise and the noise replaced children it cannot use the standard plugin interface.

Definition at line 66 of file Blendedness.h.

Member Typedef Documentation

Control

typedef BlendednessControl lsst::meas::base::BlendednessAlgorithm::Control

Definition at line 74 of file Blendedness.h.

Constructor & Destructor Documentation

BlendednessAlgorithm()

lsst::meas::base::BlendednessAlgorithm::BlendednessAlgorithm	(	Control const &	ctrl,
		std::string const &	name,
		afw::table::Schema &	schema )

Definition at line 195 of file Blendedness.cc.

        : _ctrl(ctrl) {
    if (_ctrl.doOld) {
        _old = schema.addField<double>(
                schema.join(name, "old"),
                "Blendedness from dot products: (child.dot(parent)/child.dot(child) - 1)");
    }
    if (_ctrl.doFlux) {
        _raw = schema.addField<double>(
                schema.join(name, "raw"),
                "Measure of how much the flux is affected by neighbors: "
                "(1 - child_instFlux/parent_instFlux).  Operates on the \"raw\" pixel values.");
        _instFluxChildRaw = schema.addField<double>(
                schema.join(name, "raw_child_instFlux"),
                "Instrumental flux of the child, measured with a Gaussian weight matched to the child.  "
                "Operates on the \"raw\" pixel values.", "count");
        _instFluxParentRaw = schema.addField<double>(
                schema.join(name, "raw_parent_instFlux"),
                "Instrumental flux of the parent, measured with a Gaussian weight matched to the child.  "
                "Operates on the \"raw\" pixel values.", "count");
        _abs = schema.addField<double>(
                schema.join(name, "abs"),
                "Measure of how much the flux is affected by neighbors: "
                "(1 - child_instFlux/parent_instFlux).  "
                "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value.  "
                "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.");
        _instFluxChildAbs = schema.addField<double>(
                schema.join(name, "abs_child_instFlux"),
                "Instrumental flux of the child, measured with a Gaussian weight matched to the child.  "
                "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value.  "
                "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.", "count");
        _instFluxParentAbs = schema.addField<double>(
                schema.join(name, "abs_parent_instFlux"),
                "Instrumental flux of the parent, measured with a Gaussian weight matched to the child.  "
                "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value.  "
                "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.", "count");
    }
    if (_ctrl.doShape) {
        _shapeChildRaw = ShapeResultKey::addFields(
                schema, schema.join(name, "raw_child"),
                "Shape of the child, measured with a Gaussian weight matched to the child.  "
                "Operates on the \"raw\" pixel values.", NO_UNCERTAINTY);
        _shapeParentRaw = ShapeResultKey::addFields(
                schema, schema.join(name, "raw_parent"),
                "Shape of the parent, measured with a Gaussian weight matched to the child.  "
                "Operates on the \"raw\" pixel values.", NO_UNCERTAINTY);
        _shapeChildAbs = ShapeResultKey::addFields(
                schema, schema.join(name, "abs_child"),
                "Shape of the child, measured with a Gaussian weight matched to the child.  "
                "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value.  "
                "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.",
                NO_UNCERTAINTY);
        _shapeParentAbs = ShapeResultKey::addFields(
                schema, schema.join(name, "abs_parent"),
                "Shape of the parent, measured with a Gaussian weight matched to the child.  "
                "Operates on the absolute value of the pixels to try to obtain a \"de-noised\" value.  "
                "See section 4.9.11 of Bosch et al. 2018, PASJ, 70, S5 for details.",
                NO_UNCERTAINTY);
    }
    if (_ctrl.doShape || _ctrl.doFlux) {
        _flagHandler = FlagHandler::addFields(schema, name, getFlagDefinitions());
    }
}

Member Function Documentation

computeAbsBias()

float lsst::meas::base::BlendednessAlgorithm::computeAbsBias ( float mu, float variance )

static

Compute the bias induced by using the absolute value of a pixel instead of its value.

The computation assumes the true distribution for the pixel is a Gaussian with mean mu and the given variance. To compute mu from the data, use computeAbsExpectation.

This computes

\[ \sqrt{\frac{2}{\pi}}\sigma e^{-\frac{\mu^2}{2\sigma^2}} - \mu\,\mathrm{erfc}\left(\frac{\mu}{\sqrt{2}\sigma}\right) \]

where \(\mu\) is the mean of the underlying distribution and \(\sigma^2\) is its variance. See section 4.9.11 of Bosch, J. et al. 2018, PASJ, 70, S5 for further details.

Definition at line 270 of file Blendedness.cc.

                                                                   {
    return (std::sqrt(2.0f * variance / boost::math::constants::pi<float>()) *
            std::exp(-0.5f * (mu * mu) / variance)) -
           mu * std::erfc(mu / std::sqrt(2.0f * variance));
}

computeAbsExpectation()

float lsst::meas::base::BlendednessAlgorithm::computeAbsExpectation ( float data, float variance )

static

Compute the posterior expectation value of the true instrumental flux in a pixel from its (Gaussian) likelihood and a flat nonnegative prior.

This computes

\[ \frac{\int_0^\infty f \frac{1}{\sqrt{2\pi}\sigma} e^{-\frac{(f-z)^2}{2\sigma^2}} df} {\int_0^\infty \frac{1}{\sqrt{2\pi}\sigma} e^{-\frac{(f-z)^2}{2\sigma^2}} df} \]

where \(z\) is the (noisy) pixel value and \(\sigma^2\) is the pixel variance. This approaches \(z\) when \(z \gg \sigma\) and \(0\) when \(z \ll -\sigma\).

We use single precision here for performance reasons; this function is called in a loop over single-precision pixels, and relies on a number of calls to exp and erfc, which are much faster in single precision.

Definition at line 260 of file Blendedness.cc.

                                                                            {
    float normalization = 0.5f * std::erfc(-data / std::sqrt(2.0f * variance));
    if (!(normalization > 0)) {
        // avoid division by zero; we know the limit at data << -sigma -> 0.
        return 0.0;
    }
    return data + (std::sqrt(0.5f * variance / boost::math::constants::pi<float>()) *
                   std::exp(-0.5f * (data * data) / variance) / normalization);
}

fail()

virtual void lsst::meas::base::BlendednessAlgorithm::fail ( afw::table::SourceRecord & measRecord, MeasurementError * error = nullptr ) const

inlinevirtual

Handle an exception thrown by the current algorithm by setting flags in the given record.

fail() is called by the measurement framework when an exception is allowed to propagate out of one the algorithm's measure() methods. It should generally set both a general failure flag for the algorithm as well as a specific flag indicating the error condition, if possible. To aid in this, if the exception was an instance of MeasurementError, it will be passed in, carrying information about what flag to set.

An algorithm can also to chose to set flags within its own measure() methods, and then just return, rather than throw an exception. However, fail() should be implemented even when all known failure modes do not throw exceptions, to ensure that unexpected exceptions thrown in lower-level code are properly handled.

Implements lsst::meas::base::BaseAlgorithm.

Definition at line 123 of file Blendedness.h.

{}

getFlagDefinitions()

FlagDefinitionList const & lsst::meas::base::BlendednessAlgorithm::getFlagDefinitions ( )

static

Definition at line 49 of file Blendedness.cc.

{ return flagDefinitions; }

getLogName()

std::string lsst::meas::base::BaseAlgorithm::getLogName ( ) const

inlineinherited

Definition at line 66 of file Algorithm.h.

{ return _logName; }

measure()

virtual void lsst::meas::base::BlendednessAlgorithm::measure ( afw::table::SourceRecord & measRecord, afw::image::Exposure< float > const & exposure ) const

inlinevirtual

Called to measure a single child source in an image.

Before this method is called, all neighbors will be replaced with noise, using the outputs of the deblender. Outputs should be saved in the given SourceRecord, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

Implements lsst::meas::base::SingleFrameAlgorithm.

Definition at line 120 of file Blendedness.h.

                                                                        {}

measureChildPixels()

void lsst::meas::base::BlendednessAlgorithm::measureChildPixels	(	afw::image::MaskedImage< float > const &	image,
		afw::table::SourceRecord &	child ) const

Definition at line 346 of file Blendedness.cc.

                                                                                 {
    _measureMoments(image, child, _instFluxChildRaw, _instFluxChildAbs, _shapeChildRaw, _shapeChildAbs);
}

measureForced()

void lsst::meas::base::SimpleAlgorithm::measureForced ( afw::table::SourceRecord & measRecord, afw::image::Exposure< float > const & exposure, afw::table::SourceRecord const & refRecord, afw::geom::SkyWcs const & refWcs ) const

inlineoverridevirtualinherited

Called to measure a single child source in an image.

Before this method is called, all neighbors will be replaced with noise, using the outputs of the deblender. Outputs should be saved in the given SourceRecord, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

Implements lsst::meas::base::ForcedAlgorithm.

Reimplemented in lsst::meas::extensions::photometryKron::KronFluxAlgorithm.

Definition at line 172 of file Algorithm.h.

                                                                           {
        measure(measRecord, exposure);
    }

measureN()

void lsst::meas::base::SingleFrameAlgorithm::measureN ( afw::table::SourceCatalog const & measCat, afw::image::Exposure< float > const & exposure ) const

virtualinherited

Called to simultaneously measure all children in a deblend family, in a single image.

Outputs should be saved in the given SourceCatalog, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

The default implementation simply throws an exception, indicating that simultaneous measurement is not supported.

Definition at line 31 of file Algorithm.cc.

                                                                                   {
    throw LSST_EXCEPT(pex::exceptions::LogicError, "measureN not implemented for this algorithm");
}

measureNForced()

void lsst::meas::base::SimpleAlgorithm::measureNForced ( afw::table::SourceCatalog const & measCat, afw::image::Exposure< float > const & exposure, afw::table::SourceCatalog const & refRecord, afw::geom::SkyWcs const & refWcs ) const

inlineoverridevirtualinherited

Called to simultaneously measure all children in a deblend family, in a single image.

Outputs should be saved in the given SourceCatalog, which can also be used to obtain centroid (see SafeCentroidExtractor) and shape (see SafeShapeExtractor) information.

The default implementation simply throws an exception, indicating that simultaneous measurement is not supported.

Reimplemented from lsst::meas::base::ForcedAlgorithm.

Definition at line 179 of file Algorithm.h.

                                                                            {
        measureN(measCat, exposure);
    }

measureParentPixels()

void lsst::meas::base::BlendednessAlgorithm::measureParentPixels	(	afw::image::MaskedImage< float > const &	image,
		afw::table::SourceRecord &	child ) const

Definition at line 351 of file Blendedness.cc.

                                                                                  {
    if (_ctrl.doOld) {
        child.set(_old, computeOldBlendedness(child.getFootprint(), *image.getImage()));
    }
    _measureMoments(image, child, _instFluxParentRaw, _instFluxParentAbs, _shapeParentRaw, _shapeParentAbs);
    if (_ctrl.doFlux) {
        child.set(_raw, 1.0 - child.get(_instFluxChildRaw) / child.get(_instFluxParentRaw));
        child.set(_abs, 1.0 - child.get(_instFluxChildAbs) / child.get(_instFluxParentAbs));
        if (child.get(_instFluxParentAbs) == 0.0) {
            // We can get NaNs in the absolute measure if both parent and child have only negative
            // biased-corrected instFluxes (which we clip to zero).  We can't really recover from this,
            // so we should set the flag.
            _flagHandler.setValue(child, FAILURE.number, true);
        }
    }
}

Member Data Documentation

_logName

std::string lsst::meas::base::BaseAlgorithm::_logName

protectedinherited

Definition at line 69 of file Algorithm.h.

FAILURE

FlagDefinition const lsst::meas::base::BlendednessAlgorithm::FAILURE = flagDefinitions.addFailureFlag()

static

Definition at line 70 of file Blendedness.h.

NO_CENTROID

FlagDefinition const lsst::meas::base::BlendednessAlgorithm::NO_CENTROID

static

Initial value:

=
        flagDefinitions.add("flag_noCentroid", "Object has no centroid")

Definition at line 71 of file Blendedness.h.

NO_SHAPE

FlagDefinition const lsst::meas::base::BlendednessAlgorithm::NO_SHAPE

static

Initial value:

=
        flagDefinitions.add("flag_noShape", "Object has no shape")

Definition at line 72 of file Blendedness.h.

---

The documentation for this class was generated from the following files:

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-9.0.0/Linux64/meas_base/g217e2c1bcf+73dee94bd0/include/lsst/meas/base/Blendedness.h
• /j/snowflake/release/lsstsw/stack/lsst-scipipe-9.0.0/Linux64/meas_base/g217e2c1bcf+73dee94bd0/src/Blendedness.cc