fr/fr_env/lib/python3.8/site-packages/skimage/util/_invert.py

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2021-02-17 12:26:31 +05:30
import numpy as np
from .dtype import dtype_limits
def invert(image, signed_float=False):
"""Invert an image.
Invert the intensity range of the input image, so that the dtype maximum
is now the dtype minimum, and vice-versa. This operation is
slightly different depending on the input dtype:
- unsigned integers: subtract the image from the dtype maximum
- signed integers: subtract the image from -1 (see Notes)
- floats: subtract the image from 1 (if signed_float is False, so we
assume the image is unsigned), or from 0 (if signed_float is True).
See the examples for clarification.
Parameters
----------
image : ndarray
Input image.
signed_float : bool, optional
If True and the image is of type float, the range is assumed to
be [-1, 1]. If False and the image is of type float, the range is
assumed to be [0, 1].
Returns
-------
inverted : ndarray
Inverted image.
Notes
-----
Ideally, for signed integers we would simply multiply by -1. However,
signed integer ranges are asymmetric. For example, for np.int8, the range
of possible values is [-128, 127], so that -128 * -1 equals -128! By
subtracting from -1, we correctly map the maximum dtype value to the
minimum.
Examples
--------
>>> img = np.array([[100, 0, 200],
... [ 0, 50, 0],
... [ 30, 0, 255]], np.uint8)
>>> invert(img)
array([[155, 255, 55],
[255, 205, 255],
[225, 255, 0]], dtype=uint8)
>>> img2 = np.array([[ -2, 0, -128],
... [127, 0, 5]], np.int8)
>>> invert(img2)
array([[ 1, -1, 127],
[-128, -1, -6]], dtype=int8)
>>> img3 = np.array([[ 0., 1., 0.5, 0.75]])
>>> invert(img3)
array([[1. , 0. , 0.5 , 0.25]])
>>> img4 = np.array([[ 0., 1., -1., -0.25]])
>>> invert(img4, signed_float=True)
array([[-0. , -1. , 1. , 0.25]])
"""
if image.dtype == 'bool':
inverted = ~image
elif np.issubdtype(image.dtype, np.unsignedinteger):
max_val = dtype_limits(image, clip_negative=False)[1]
inverted = np.subtract(max_val, image, dtype=image.dtype)
elif np.issubdtype(image.dtype, np.signedinteger):
inverted = np.subtract(-1, image, dtype=image.dtype)
else: # float dtype
if signed_float:
inverted = -image
else:
inverted = np.subtract(1, image, dtype=image.dtype)
return inverted