"""
A module that provides functions for manipulating bit masks and data quality
(DQ) arrays.
"""
import sys
import warnings
import numbers
import numpy as np
__all__ = ['bitfield_to_boolean_mask', 'interpret_bit_flags']
_MAX_UINT_TYPE = np.maximum_sctype(np.uint)
_SUPPORTED_FLAGS = int(np.bitwise_not(
0, dtype=_MAX_UINT_TYPE, casting='unsafe'
))
def _is_bit_flag(n):
"""
Verifies if the input number is a bit flag (i.e., an integer number that is
an integer power of 2).
Parameters
----------
n : int
A positive integer number. Non-positive integers are considered not to
be "flags".
Returns
-------
bool
``True`` if input ``n`` is a bit flag and ``False`` if it is not.
"""
if n < 1:
return False
return bin(n).count('1') == 1
def _is_int(n):
return (
(isinstance(n, numbers.Integral) and not isinstance(n, bool)) or
(isinstance(n, np.generic) and np.issubdtype(n, np.integer))
)
[docs]def interpret_bit_flags(bit_flags, flip_bits=None):
"""
Converts input bit flags to a single integer value (bit mask) or `None`.
When input is a list of flags (either a Python list of integer flags or a
sting of comma- or '+'-separated list of flags), the returned bit mask
is obtained by summing input flags.
.. note::
In order to flip the bits of the returned bit mask,
for input of `str` type, prepend '~' to the input string. '~' must
be prepended to the *entire string* and not to each bit flag! For
input that is already a bit mask or a Python list of bit flags, set
``flip_bits`` for `True` in order to flip the bits of the returned
bit mask.
Parameters
----------
bit_flags : int, str, list, None
An integer bit mask or flag, `None`, a string of comma- or
'+'-separated list of integer bit flags, or a Python list of integer
bit flags. If ``bit_flags`` is a `str` and if it is prepended with '~',
then the output bit mask will have its bits flipped (compared to simple
sum of input flags). For input ``bit_flags`` that is already a bit mask
or a Python list of bit flags, bit-flipping can be controlled through
``flip_bits`` parameter.
flip_bits : bool, None
Indicates whether or not to flip the bits of the returned bit mask
obtained from input bit flags. This parameter must be set to `None`
when input ``bit_flags`` is either `None` or a Python list of flags.
Returns
-------
bitmask : int or None
Returns an integer bit mask formed from the input bit value or `None`
if input ``bit_flags`` parameter is `None` or an empty string.
If input string value was prepended with '~' (or ``flip_bits`` was set
to `True`), then returned value will have its bits flipped
(inverse mask).
Examples
--------
>>> from astropy.nddata.bitmask import interpret_bit_flags
>>> "{0:016b}".format(0xFFFF & interpret_bit_flags(28))
'0000000000011100'
>>> "{0:016b}".format(0xFFFF & interpret_bit_flags('4,8,16'))
'0000000000011100'
>>> "{0:016b}".format(0xFFFF & interpret_bit_flags('~4,8,16'))
'1111111111100011'
>>> "{0:016b}".format(0xFFFF & interpret_bit_flags('~(4+8+16)'))
'1111111111100011'
>>> "{0:016b}".format(0xFFFF & interpret_bit_flags([4, 8, 16]))
'0000000000011100'
>>> "{0:016b}".format(0xFFFF & interpret_bit_flags([4, 8, 16], flip_bits=True))
'1111111111100011'
"""
has_flip_bits = flip_bits is not None
flip_bits = bool(flip_bits)
allow_non_flags = False
if _is_int(bit_flags):
return (~int(bit_flags) if flip_bits else int(bit_flags))
elif bit_flags is None:
if has_flip_bits:
raise TypeError(
"Keyword argument 'flip_bits' must be set to 'None' when "
"input 'bit_flags' is None."
)
return None
elif isinstance(bit_flags, str):
if has_flip_bits:
raise TypeError(
"Keyword argument 'flip_bits' is not permitted for "
"comma-separated string lists of bit flags. Prepend '~' to "
"the string to indicate bit-flipping."
)
bit_flags = str(bit_flags).strip()
if bit_flags.upper() in ['', 'NONE', 'INDEF']:
return None
# check whether bitwise-NOT is present and if it is, check that it is
# in the first position:
bitflip_pos = bit_flags.find('~')
if bitflip_pos == 0:
flip_bits = True
bit_flags = bit_flags[1:].lstrip()
else:
if bitflip_pos > 0:
raise ValueError("Bitwise-NOT must precede bit flag list.")
flip_bits = False
# basic check for correct use of parenthesis:
while True:
nlpar = bit_flags.count('(')
nrpar = bit_flags.count(')')
if nlpar == 0 and nrpar == 0:
break
if nlpar != nrpar:
raise ValueError("Unbalanced parantheses in bit flag list.")
lpar_pos = bit_flags.find('(')
rpar_pos = bit_flags.rfind(')')
if lpar_pos > 0 or rpar_pos < (len(bit_flags) - 1):
raise ValueError("Incorrect syntax (incorrect use of "
"parenthesis) in bit flag list.")
bit_flags = bit_flags[1:-1].strip()
if ',' in bit_flags:
bit_flags = bit_flags.split(',')
elif '+' in bit_flags:
bit_flags = bit_flags.split('+')
else:
if bit_flags == '':
raise ValueError(
"Empty bit flag lists not allowed when either bitwise-NOT "
"or parenthesis are present."
)
bit_flags = [bit_flags]
allow_non_flags = len(bit_flags) == 1
elif hasattr(bit_flags, '__iter__'):
if not all([_is_int(flag) for flag in bit_flags]):
raise TypeError("Each bit flag in a list must be an integer.")
else:
raise TypeError("Unsupported type for argument 'bit_flags'.")
bitset = set(map(int, bit_flags))
if len(bitset) != len(bit_flags):
warnings.warn("Duplicate bit flags will be ignored")
bitmask = 0
for v in bitset:
if not _is_bit_flag(v) and not allow_non_flags:
raise ValueError("Input list contains invalid (not powers of two) "
"bit flag: {:d}".format(v))
bitmask += v
if flip_bits:
bitmask = ~bitmask
return bitmask
[docs]def bitfield_to_boolean_mask(bitfield, ignore_flags=0, flip_bits=None,
good_mask_value=False, dtype=np.bool_):
"""
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 : numpy.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 : int, str, list, None (Default = 0)
An integer bit mask, a Python list of bit flags, a comma- or
'+'-separated string list of integer bit flags that indicate what
bits in the input ``bitfield`` should be *ignored* (i.e., zeroed), or
`None`.
| 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
'+'-separated list of integer bit flags that should be added together
to create an integer bit mask. For example, both ``'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 interpretted as an
integer bit mask. For example, instead of ``'4,8'`` one could
simply provide string ``'12'``.
.. 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, None (Default = 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 : int, bool (Default = 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.
Returns
-------
mask : numpy.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
>>> dqbits = np.asarray([[0, 0, 1, 2, 0, 8, 12, 0],
... [10, 4, 0, 0, 0, 16, 6, 0]])
>>> bitmask.bitfield_to_boolean_mask(dqbits, 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(dqbits, 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(dqbits, 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(dqbits, 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(dqbits, 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(dqbits, 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(dqbits, 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]])
"""
bitfield = np.asarray(bitfield)
if not np.issubdtype(bitfield.dtype, np.integer):
raise TypeError("Input bitfield array must be of integer type.")
ignore_mask = interpret_bit_flags(ignore_flags, flip_bits=flip_bits)
if ignore_mask is None:
if good_mask_value:
mask = np.ones_like(bitfield, dtype=dtype)
else:
mask = np.zeros_like(bitfield, dtype=dtype)
return mask
# filter out bits beyond the maximum supported by the data type:
ignore_mask = ignore_mask & _SUPPORTED_FLAGS
# invert the "ignore" mask:
ignore_mask = np.bitwise_not(ignore_mask, dtype=bitfield.dtype,
casting='unsafe')
mask = np.empty_like(bitfield, dtype=np.bool_)
np.bitwise_and(bitfield, ignore_mask, out=mask, casting='unsafe')
if good_mask_value:
np.logical_not(mask, out=mask)
return mask.astype(dtype=dtype, subok=False, copy=False)