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- bitfield_to_boolean_mask

# bitfield_to_boolean_mask

astropy.nddata.bitmask.bitfield_to_boolean_mask(bitfield, ignore_flags=None, flip_bits=None, good_mask_value=False, dtype=numpy.bool_)

  Converts an array of bit fields to a boolean (or integer) mask array according to a bit mask constructed from the supplied bit flags (see `ignore_flags` parameter).

  This function is particularly useful to convert data quality arrays to boolean masks with selective filtering of DQ flags.

  Parameters:
    bitfield `ndarray`

      An array of bit flags. By default, values different from zero are interpreted as “bad” values and values equal to zero are considered as “good” values. However, see `ignore_flags` parameter on how to selectively ignore some bits in the `bitfield` array data.

    ignore_flags `python:int`, `python:str`, `python:list`, `python:None` (default = 0)

      An integer bit mask, `None`, a Python list of bit flags, a comma-, or `'|'`-separated, `'+'`-separated string list of integer bit flags or mnemonic flag names that indicate what bits in the input `bitfield` should be ignored (i.e., zeroed), or `None`.

      Note

      When `bit_flags` is a list of flag names, the `flag_name_map` parameter must be provided.

      Setting `ignore_flags` to `None` effectively will make `bitfield_to_boolean_mask` interpret all `bitfield` elements as “good” regardless of their value.
      When `ignore_flags` argument is an integer bit mask, it will be combined using bitwise-NOT and bitwise-AND with each element of the input `bitfield` array (`~ignore_flags & bitfield`). If the resultant bitfield element is non-zero, that element will be interpreted as a “bad” in the output boolean mask and it will be interpreted as “good” otherwise. `flip_bits` parameter may be used to flip the bits (`bitwise-NOT`) of the bit mask thus effectively changing the meaning of the `ignore_flags` parameter from “ignore” to “use only” these flags.

      Note

      Setting `ignore_flags` to 0 effectively will assume that all non-zero elements in the input `bitfield` array are to be interpreted as “bad”.

      When `ignore_flags` argument is a Python list of integer bit flags, these flags are added together to create an integer bit mask. Each item in the list must be a flag, i.e., an integer that is an integer power of 2. In order to flip the bits of the resultant bit mask, use `flip_bits` parameter.
      Alternatively, `ignore_flags` may be a string of comma- or `'+'``(or ``'|'`)-separated list of integer bit flags that should be added (bitwise OR) together to create an integer bit mask. For example, both `'4,8'`, `'4|8'`, and `'4+8'` are equivalent and indicate that bit flags 4 and 8 in the input `bitfield` array should be ignored when generating boolean mask.

      Note

      `'None'`, `'INDEF'`, and empty (or all white space) strings are special values of string `ignore_flags` that are interpreted as `None`.

      Note

      Each item in the list must be a flag, i.e., an integer that is an integer power of 2. In addition, for convenience, an arbitrary single integer is allowed and it will be interpreted as an integer bit mask. For example, instead of `'4,8'` one could simply provide string `'12'`.

      Note

      Only one flag separator is supported at a time. `ignore_flags` string should not mix `','`, `'+'`, and `'|'` separators.

      Note

      When `ignore_flags` is a `str` and when it is prepended with ‘~’, then the meaning of `ignore_flags` parameters will be reversed: now it will be interpreted as a list of bit flags to be used (or not ignored) when deciding which elements of the input `bitfield` array are “bad”. Following this convention, an `ignore_flags` string value of `'~0'` would be equivalent to setting `ignore_flags=None`.

      Warning

      Because prepending ‘~’ to a string `ignore_flags` is equivalent to setting `flip_bits` to `True`, `flip_bits` cannot be used with string `ignore_flags` and it must be set to `None`.

    flip_bits bool, `python:None` (default = `python:None`)

      Specifies whether or not to invert the bits of the bit mask either supplied directly through `ignore_flags` parameter or built from the bit flags passed through `ignore_flags` (only when bit flags are passed as Python lists of integer bit flags). Occasionally, it may be useful to consider only specific bit flags in the `bitfield` array when creating a boolean mask as opposed to ignoring specific bit flags as `ignore_flags` behaves by default. This can be achieved by inverting/flipping the bits of the bit mask created from `ignore_flags` flags which effectively changes the meaning of the `ignore_flags` parameter from “ignore” to “use only” these flags. Setting `flip_bits` to `None` means that no bit flipping will be performed. Bit flipping for string lists of bit flags must be specified by prepending ‘~’ to string bit flag lists (see documentation for `ignore_flags` for more details).

      Warning

      This parameter can be set to either `True` or `False` ONLY when `ignore_flags` is either an integer bit mask or a Python list of integer bit flags. When `ignore_flags` is either `None` or a string list of flags, `flip_bits` MUST be set to `None`.

    good_mask_value `python:int`, bool (default = `python:False`)

      This parameter is used to derive the values that will be assigned to the elements in the output boolean mask array that correspond to the “good” bit fields (that are 0 after zeroing bits specified by `ignore_flags`) in the input `bitfield` array. When `good_mask_value` is non-zero or `numpy.True_` then values in the output boolean mask array corresponding to “good” bit fields in `bitfield` will be `numpy.True_` (if `dtype` is `numpy.bool_`) or 1 (if `dtype` is of numerical type) and values of corresponding to “bad” flags will be `numpy.False_` (or 0). When `good_mask_value` is zero or `numpy.False_` then the values in the output boolean mask array corresponding to “good” bit fields in `bitfield` will be `numpy.False_` (if `dtype` is `numpy.bool_`) or 0 (if `dtype` is of numerical type) and values of corresponding to “bad” flags will be `numpy.True_` (or 1).

    dtype data-type (default = `numpy.bool_`)

      The desired data-type for the output binary mask array.

    flag_name_map `BitFlagNameMap`

      A `BitFlagNameMap` object that provides mapping from mnemonic bit flag names to integer bit values in order to translate mnemonic flags to numeric values when `bit_flags` that are comma- or ‘+’-separated list of menmonic bit flag names.

  Returns:
    mask `ndarray`

      Returns an array of the same dimensionality as the input `bitfield` array whose elements can have two possible values, e.g., `numpy.True_` or `numpy.False_` (or 1 or 0 for integer `dtype`) according to values of to the input `bitfield` elements, `ignore_flags` parameter, and the `good_mask_value` parameter.

  Examples

      >>> from astropy.nddata import bitmask
      >>> import numpy as np
      >>> dqarr = np.asarray([[0, 0, 1, 2, 0, 8, 12, 0],
      ...                     [10, 4, 0, 0, 0, 16, 6, 0]])
      >>> flag_map = bitmask.extend_bit_flag_map(
      ...     'ST_DQ', CR=2, CLOUDY=4, RAINY=8, HOT=16, DEAD=32
      ... )
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags=0,
      ...                                  dtype=int)
      array([[0, 0, 1, 1, 0, 1, 1, 0],
             [1, 1, 0, 0, 0, 1, 1, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags=0,
      ...                                  dtype=bool)
      array([[False, False,  True,  True, False,  True,  True, False],
             [ True,  True, False, False, False,  True,  True, False]]...)
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags=6,
      ...                                  good_mask_value=0, dtype=int)
      array([[0, 0, 1, 0, 0, 1, 1, 0],
             [1, 0, 0, 0, 0, 1, 0, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags=~6,
      ...                                  good_mask_value=0, dtype=int)
      array([[0, 0, 0, 1, 0, 0, 1, 0],
             [1, 1, 0, 0, 0, 0, 1, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags=6, dtype=int,
      ...                                  flip_bits=True, good_mask_value=0)
      array([[0, 0, 0, 1, 0, 0, 1, 0],
             [1, 1, 0, 0, 0, 0, 1, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags='~(2+4)',
      ...                                  good_mask_value=0, dtype=int)
      array([[0, 0, 0, 1, 0, 0, 1, 0],
             [1, 1, 0, 0, 0, 0, 1, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags=[2, 4],
      ...                                  flip_bits=True, good_mask_value=0,
      ...                                  dtype=int)
      array([[0, 0, 0, 1, 0, 0, 1, 0],
             [1, 1, 0, 0, 0, 0, 1, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags='~(CR,CLOUDY)',
      ...                                  good_mask_value=0, dtype=int,
      ...                                  flag_name_map=flag_map)
      array([[0, 0, 0, 1, 0, 0, 1, 0],
             [1, 1, 0, 0, 0, 0, 1, 0]])
      >>> bitmask.bitfield_to_boolean_mask(dqarr, ignore_flags='~(CR+CLOUDY)',
      ...                                  good_mask_value=0, dtype=int,
      ...                                  flag_name_map=flag_map)
      array([[0, 0, 0, 1, 0, 0, 1, 0],
             [1, 1, 0, 0, 0, 0, 1, 0]])