lsst.afw.display.rgb.AsinhMapping Class Reference

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

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

Public Member Functions
def	__init__
def	mapIntensityToUint8
Public Member Functions inherited from lsst.afw.display.rgb.Mapping
def	__init__
	Create a mapping. More...
def	makeRgbImage
	Convert 3 arrays, imageR, imageG, and imageB into a numpy RGB image. More...
def	intensity
	Return the total intensity from the red, blue, and green intensities. More...
def	mapIntensityToUint8

Private Attributes
	_slope
	_soften

Detailed Description

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

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

This reduces to a linear stretch if Q == 0

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

Definition at line 77 of file rgb.py.

Constructor & Destructor Documentation

def lsst.afw.display.rgb.AsinhMapping.__init__	(		self,
			min,
			range,
			Q
	)

Definition at line 87 of file rgb.py.

    def __init__(self, min, range, Q):
        Mapping.__init__(self, min)

        epsilon = 1.0/2**23            # 32bit floating point machine epsilon; sys.float_info.epsilon is 64bit
        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(range);