FixedScaleOffset

class numcodecs.fixedscaleoffset.FixedScaleOffset(offset, scale, dtype, astype=None)[source]

Simplified version of the scale-offset filter available in HDF5. Applies the transformation (x - offset) * scale to all chunks. Results are rounded to the nearest integer but are not packed according to the minimum number of bits.

Parameters:
offset : float

Value to subtract from data.

scale : int

Value to multiply by data.

dtype : dtype

Data type to use for decoded data.

astype : dtype, optional

Data type to use for encoded data.

Notes

If astype is an integer data type, please ensure that it is sufficiently large to store encoded values. No checks are made and data may become corrupted due to integer overflow if astype is too small.

Examples

>>> import numcodecs
>>> import numpy as np
>>> x = np.linspace(1000, 1001, 10, dtype='f8')
>>> x
array([1000.        , 1000.11111111, 1000.22222222, 1000.33333333,
       1000.44444444, 1000.55555556, 1000.66666667, 1000.77777778,
       1000.88888889, 1001.        ])
>>> codec = numcodecs.FixedScaleOffset(offset=1000, scale=10, dtype='f8', astype='u1')
>>> y1 = codec.encode(x)
>>> y1
array([ 0,  1,  2,  3,  4,  6,  7,  8,  9, 10], dtype=uint8)
>>> z1 = codec.decode(y1)
>>> z1
array([1000. , 1000.1, 1000.2, 1000.3, 1000.4, 1000.6, 1000.7,
       1000.8, 1000.9, 1001. ])
>>> codec = numcodecs.FixedScaleOffset(offset=1000, scale=10**2, dtype='f8', astype='u1')
>>> y2 = codec.encode(x)
>>> y2
array([ 0,  11,  22,  33,  44,  56,  67,  78,  89, 100], dtype=uint8)
>>> z2 = codec.decode(y2)
>>> z2
array([1000.  , 1000.11, 1000.22, 1000.33, 1000.44, 1000.56,
       1000.67, 1000.78, 1000.89, 1001.  ])
>>> codec = numcodecs.FixedScaleOffset(offset=1000, scale=10**3, dtype='f8', astype='u2')
>>> y3 = codec.encode(x)
>>> y3
array([ 0,  111,  222,  333,  444,  556,  667,  778,  889, 1000], dtype=uint16)
>>> z3 = codec.decode(y3)
>>> z3
array([1000.   , 1000.111, 1000.222, 1000.333, 1000.444, 1000.556,
       1000.667, 1000.778, 1000.889, 1001.   ])
codec_id = 'fixedscaleoffset'
encode(buf)[source]

Encode data in buf.

Parameters:
buf : buffer-like

Data to be encoded. May be any object supporting the new-style buffer protocol.

Returns:
enc : buffer-like

Encoded data. May be any object supporting the new-style buffer protocol.

decode(buf, out=None)[source]

Decode data in buf.

Parameters:
buf : buffer-like

Encoded data. May be any object supporting the new-style buffer protocol.

out : buffer-like, optional

Writeable buffer to store decoded data. N.B. if provided, this buffer must be exactly the right size to store the decoded data.

Returns:
dec : buffer-like

Decoded data. May be any object supporting the new-style buffer protocol.

get_config()[source]

Return a dictionary holding configuration parameters for this codec. Must include an ‘id’ field with the codec identifier. All values must be compatible with JSON encoding.

classmethod from_config(config)

Instantiate codec from a configuration object.