lsst.afw.display.rgb._rgbContinued.AsinhMapping Class Reference

Inheritance diagram for lsst.afw.display.rgb._rgbContinued.AsinhMapping:

Public Member Functions
	__init__ (self, minimum, dataRange, Q=8)
	mapIntensityToUint8 (self, intensity)

Protected Attributes
	_slope
	_soften

Detailed Description

A mapping for an asinh stretch (preserving colours independent of brightness)

x = asinh(Q (I - minimum)/range)/Q

Notes
-----
This reduces to a linear stretch if Q == 0

See http://adsabs.harvard.edu/abs/2004PASP..116..133L

Definition at line 282 of file _rgbContinued.py.

Constructor & Destructor Documentation

__init__()

lsst.afw.display.rgb._rgbContinued.AsinhMapping.__init__	(		self,
			minimum,
			dataRange,
			Q = 8 )

Reimplemented from lsst.afw.display.rgb._rgbContinued.Mapping.

Reimplemented in lsst.afw.display.rgb._rgbContinued.AsinhZScaleMapping.

Definition at line 294 of file _rgbContinued.py.

    def __init__(self, minimum, dataRange, Q=8):
        Mapping.__init__(self, minimum)
 
        # 32bit floating point machine epsilon; sys.float_info.epsilon is 64bit
        epsilon = 1.0/2**23
        if abs(Q) < epsilon:
            Q = 0.1
        else:
            Qmax = 1e10
            if Q > Qmax:
                Q = Qmax
 
        if False:
            self._slope = self._uint8Max/Q  # gradient at origin is self._slope
        else:
            frac = 0.1                  # gradient estimated using frac*range is _slope
            self._slope = frac*self._uint8Max/np.arcsinh(frac*Q)
 
        self._soften = Q/float(dataRange)
 

Member Function Documentation

mapIntensityToUint8()

lsst.afw.display.rgb._rgbContinued.AsinhMapping.mapIntensityToUint8	(		self,
			intensity )

Return an array which, when multiplied by an image, returns that image mapped to the range of a
uint8, [0, 255] (but not converted to uint8)

The intensity is assumed to have had minimum subtracted (as that can be done per-band)

Reimplemented from lsst.afw.display.rgb._rgbContinued.Mapping.

Definition at line 314 of file _rgbContinued.py.

    def mapIntensityToUint8(self, intensity):
        """Return an array which, when multiplied by an image, returns that image mapped to the range of a
        uint8, [0, 255] (but not converted to uint8)
 
        The intensity is assumed to have had minimum subtracted (as that can be done per-band)
        """
        with np.errstate(invalid='ignore', divide='ignore'):  # n.b. np.where can't and doesn't short-circuit
            return np.where(intensity <= 0, 0, np.arcsinh(intensity*self._soften)*self._slope/intensity)
 
 

Member Data Documentation

_slope

lsst.afw.display.rgb._rgbContinued.AsinhMapping._slope

protected

Definition at line 307 of file _rgbContinued.py.

_soften

lsst.afw.display.rgb._rgbContinued.AsinhMapping._soften

protected

Definition at line 312 of file _rgbContinued.py.

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

• /j/snowflake/release/lsstsw/stack/lsst-scipipe-9.0.0/Linux64/afw/gef2f8181fd+3031e3cf99/python/lsst/afw/display/rgb/_rgbContinued.py