lsst.pipe.drivers.background Namespace Reference

Classes
class	BackgroundConfig
class	FocalPlaneBackground
class	FocalPlaneBackgroundConfig
class	MaskObjectsConfig
class	MaskObjectsTask
class	SkyMeasurementConfig
class	SkyMeasurementTask
class	SkyStatsConfig

Functions
def	robustMean (array, rej=3.0)
def	interpolate1D (method, xSample, ySample, xInterp)
def	interpolateBadPixels (array, isBad, interpolationStyle)
def	smoothArray (array, bad, sigma)

Function Documentation

interpolate1D()

def lsst.pipe.drivers.background.interpolate1D	(		method,
			xSample,
			ySample,
			xInterp
	)

Interpolate in one dimension

Interpolates the curve provided by `xSample` and `ySample` at
the positions of `xInterp`. Automatically backs off the
interpolation method to achieve successful interpolation.

Parameters
----------
method : `lsst.afw.math.Interpolate.Style`
    Interpolation method to use.
xSample : `numpy.ndarray`
    Vector of ordinates.
ySample : `numpy.ndarray`
    Vector of coordinates.
xInterp : `numpy.ndarray`
    Vector of ordinates to which to interpolate.

Returns
-------
yInterp : `numpy.ndarray`
    Vector of interpolated coordinates.

Definition at line 377 of file background.py.

def interpolate1D(method, xSample, ySample, xInterp):
    """Interpolate in one dimension

    Interpolates the curve provided by `xSample` and `ySample` at
    the positions of `xInterp`. Automatically backs off the
    interpolation method to achieve successful interpolation.

    Parameters
    ----------
    method : `lsst.afw.math.Interpolate.Style`
        Interpolation method to use.
    xSample : `numpy.ndarray`
        Vector of ordinates.
    ySample : `numpy.ndarray`
        Vector of coordinates.
    xInterp : `numpy.ndarray`
        Vector of ordinates to which to interpolate.

    Returns
    -------
    yInterp : `numpy.ndarray`
        Vector of interpolated coordinates.

    """
    if len(xSample) == 0:
        return numpy.ones_like(xInterp)*numpy.nan
    try:
        return afwMath.makeInterpolate(xSample.astype(float), ySample.astype(float),
                                       method).interpolate(xInterp.astype(float))
    except Exception:
        if method == afwMath.Interpolate.CONSTANT:
            # We've already tried the most basic interpolation and it failed
            return numpy.ones_like(xInterp)*numpy.nan
        newMethod = afwMath.lookupMaxInterpStyle(len(xSample))
        if newMethod == method:
            newMethod = afwMath.Interpolate.CONSTANT
        return interpolate1D(newMethod, xSample, ySample, xInterp)

interpolateBadPixels()

def lsst.pipe.drivers.background.interpolateBadPixels	(		array,
			isBad,
			interpolationStyle
	)

Interpolate bad pixels in an image array

The bad pixels are modified in the array.

Parameters
----------
array : `numpy.ndarray`
    Image array with bad pixels.
isBad : `numpy.ndarray` of type `bool`
    Boolean array indicating which pixels are bad.
interpolationStyle : `str`
    Style for interpolation (see `lsst.afw.math.Background`);
    supported values are CONSTANT, LINEAR, NATURAL_SPLINE,
    AKIMA_SPLINE.

Definition at line 416 of file background.py.

def interpolateBadPixels(array, isBad, interpolationStyle):
    """Interpolate bad pixels in an image array

    The bad pixels are modified in the array.

    Parameters
    ----------
    array : `numpy.ndarray`
        Image array with bad pixels.
    isBad : `numpy.ndarray` of type `bool`
        Boolean array indicating which pixels are bad.
    interpolationStyle : `str`
        Style for interpolation (see `lsst.afw.math.Background`);
        supported values are CONSTANT, LINEAR, NATURAL_SPLINE,
        AKIMA_SPLINE.
    """
    if numpy.all(isBad):
        raise RuntimeError("No good pixels in image array")
    height, width = array.shape
    xIndices = numpy.arange(width, dtype=float)
    yIndices = numpy.arange(height, dtype=float)
    method = afwMath.stringToInterpStyle(interpolationStyle)
    isGood = ~isBad
    for y in range(height):
        if numpy.any(isBad[y, :]) and numpy.any(isGood[y, :]):
            array[y][isBad[y]] = interpolate1D(method, xIndices[isGood[y]], array[y][isGood[y]],
                                               xIndices[isBad[y]])

    isBad = numpy.isnan(array)
    isGood = ~isBad
    for x in range(width):
        if numpy.any(isBad[:, x]) and numpy.any(isGood[:, x]):
            array[:, x][isBad[:, x]] = interpolate1D(method, yIndices[isGood[:, x]],
                                                     array[:, x][isGood[:, x]], yIndices[isBad[:, x]])

robustMean()

def lsst.pipe.drivers.background.robustMean	(		array,
			rej = 3.0
	)

Measure a robust mean of an array

Parameters
----------
array : `numpy.ndarray`
    Array for which to measure the mean.
rej : `float`
    k-sigma rejection threshold.

Returns
-------
mean : `array.dtype`
    Robust mean of `array`.

Definition at line 18 of file background.py.

def robustMean(array, rej=3.0):
    """Measure a robust mean of an array

    Parameters
    ----------
    array : `numpy.ndarray`
        Array for which to measure the mean.
    rej : `float`
        k-sigma rejection threshold.

    Returns
    -------
    mean : `array.dtype`
        Robust mean of `array`.
    """
    q1, median, q3 = numpy.percentile(array, [25.0, 50.0, 100.0])
    good = numpy.abs(array - median) < rej*0.74*(q3 - q1)
    return array[good].mean()

smoothArray()

def lsst.pipe.drivers.background.smoothArray	(		array,
			bad,
			sigma
	)

Gaussian-smooth an array while ignoring bad pixels

It's not sufficient to set the bad pixels to zero, as then they're treated
as if they are zero, rather than being ignored altogether. We need to apply
a correction to that image that removes the effect of the bad pixels.

Parameters
----------
array : `numpy.ndarray` of floating-point
    Array to smooth.
bad : `numpy.ndarray` of `bool`
    Flag array indicating bad pixels.
sigma : `float`
    Gaussian sigma.

Returns
-------
convolved : `numpy.ndarray`
    Smoothed image.

Definition at line 848 of file background.py.

def smoothArray(array, bad, sigma):
    """Gaussian-smooth an array while ignoring bad pixels

    It's not sufficient to set the bad pixels to zero, as then they're treated
    as if they are zero, rather than being ignored altogether. We need to apply
    a correction to that image that removes the effect of the bad pixels.

    Parameters
    ----------
    array : `numpy.ndarray` of floating-point
        Array to smooth.
    bad : `numpy.ndarray` of `bool`
        Flag array indicating bad pixels.
    sigma : `float`
        Gaussian sigma.

    Returns
    -------
    convolved : `numpy.ndarray`
        Smoothed image.
    """
    convolved = gaussian_filter(numpy.where(bad, 0.0, array), sigma, mode="constant", cval=0.0)
    denominator = gaussian_filter(numpy.where(bad, 0.0, 1.0), sigma, mode="constant", cval=0.0)
    return convolved/denominator

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