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"""skimage's `rescale_intensity` that takes and returns dask arrays."""
import warnings
import numpy as np
import skimage
from packaging.version import Version
from skimage.exposure.exposure import _output_dtype, intensity_range
def rescale_intensity(image, in_range="image", out_range="dtype"):
"""Return image after stretching or shrinking its intensity levels.
The desired intensity range of the input and output, `in_range` and
`out_range` respectively, are used to stretch or shrink the intensity range
of the input image. See examples below.
Parameters
----------
image : array
Image array.
in_range, out_range : str or 2-tuple, optional
Min and max intensity values of input and output image.
The possible values for this parameter are enumerated below.
'image'
Use image min/max as the intensity range.
'dtype'
Use min/max of the image's dtype as the intensity range.
dtype-name
Use intensity range based on desired `dtype`. Must be valid key
in `DTYPE_RANGE`.
2-tuple
Use `range_values` as explicit min/max intensities.
Returns
-------
out : array
Image array after rescaling its intensity. This image is the same dtype
as the input image.
Notes
-----
.. versionchanged:: 0.17
The dtype of the output array has changed to match the input dtype, or
float if the output range is specified by a pair of floats.
See Also
--------
equalize_hist
Examples
--------
By default, the min/max intensities of the input image are stretched to
the limits allowed by the image's dtype, since `in_range` defaults to
'image' and `out_range` defaults to 'dtype':
>>> image = np.array([51, 102, 153], dtype=np.uint8)
>>> rescale_intensity(image)
array([ 0, 127, 255], dtype=uint8)
It's easy to accidentally convert an image dtype from uint8 to float:
>>> 1.0 * image
array([ 51., 102., 153.])
Use `rescale_intensity` to rescale to the proper range for float dtypes:
>>> image_float = 1.0 * image
>>> rescale_intensity(image_float)
array([0. , 0.5, 1. ])
To maintain the low contrast of the original, use the `in_range` parameter:
>>> rescale_intensity(image_float, in_range=(0, 255))
array([0.2, 0.4, 0.6])
If the min/max value of `in_range` is more/less than the min/max image
intensity, then the intensity levels are clipped:
>>> rescale_intensity(image_float, in_range=(0, 102))
array([0.5, 1. , 1. ])
If you have an image with signed integers but want to rescale the image to
just the positive range, use the `out_range` parameter. In that case, the
output dtype will be float:
>>> image = np.array([-10, 0, 10], dtype=np.int8)
>>> rescale_intensity(image, out_range=(0, 127))
array([ 0. , 63.5, 127. ])
To get the desired range with a specific dtype, use ``.astype()``:
>>> rescale_intensity(image, out_range=(0, 127)).astype(np.int8)
array([ 0, 63, 127], dtype=int8)
If the input image is constant, the output will be clipped directly to the
output range:
>>> image = np.array([130, 130, 130], dtype=np.int32)
>>> rescale_intensity(image, out_range=(0, 127)).astype(np.int32)
array([127, 127, 127], dtype=int32)
"""
args = ()
if Version(skimage.__version__) >= Version("0.19.0"):
args = (image.dtype,)
if out_range in ["dtype", "image"]:
out_dtype = _output_dtype(image.dtype.type, *args)
else:
out_dtype = _output_dtype(out_range, *args)
imin, imax = map(float, intensity_range(image, in_range))
omin, omax = map(
float, intensity_range(image, out_range, clip_negative=(imin >= 0))
)
if np.any(np.isnan([imin, imax, omin, omax])):
warnings.warn(
"One or more intensity levels are NaN. Rescaling will broadcast "
"NaN to the full image. Provide intensity levels yourself to "
"avoid this. E.g. with np.nanmin(image), np.nanmax(image).",
stacklevel=2,
)
image = np.clip(image, imin, imax)
if imin != imax:
image = (image - imin) / (imax - imin)
return (image * (omax - omin) + omin).astype(dtype=out_dtype)
else:
return np.clip(image, omin, omax).astype(out_dtype)
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