LogStretch

class astropy.visualization.LogStretch(a=1000.0)[source]

Bases: astropy.visualization.BaseStretch

A log stretch.

The stretch is given by:

\[y = \frac{\log{(a x + 1)}}{\log{(a + 1)}}\]
Parameters
afloat

The a parameter used in the above formula. a must be greater than 0. Default is 1000.

Attributes Summary

inverse

A stretch object that performs the inverse operation.

Methods Summary

__call__(values[, clip, out, invalid])

Transform values using this stretch.

Attributes Documentation

inverse

A stretch object that performs the inverse operation.

Methods Documentation

__call__(values, clip=True, out=None, invalid=None)[source]

Transform values using this stretch.

Parameters
valuesarray_like

The input values, which should already be normalized to the [0:1] range.

clipbool, optional

If True (default), values outside the [0:1] range are clipped to the [0:1] range.

outndarray, optional

If specified, the output values will be placed in this array (typically used for in-place calculations).

invalidNone or float, optional

Value to assign NaN values generated by this class. NaNs in the input values array are not changed. This option is generally used with matplotlib normalization classes, where the invalid value should map to the matplotlib colormap “under” value (i.e., any finite value < 0). If None, then NaN values are not replaced. This keyword has no effect if clip=True.

Returns
resultndarray

The transformed values.