mirror of
https://github.com/wassname/scikit-image.git
synced 2026-06-28 02:47:01 +08:00
Juan Nunez-Iglesias
159 lines
4.7 KiB
Python
159 lines
4.7 KiB
Python
from collections import namedtuple
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import numpy as np
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import warnings
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import matplotlib.pyplot as plt
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from skimage.util import dtype as dtypes
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_default_colormap = 'gray'
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_nonstandard_colormap = 'cubehelix'
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_diverging_colormap = 'RdBu'
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ImageProperties = namedtuple('ImageProperties',
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['signed', 'out_of_range_float',
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'low_dynamic_range', 'unsupported_dtype'])
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def _get_image_properties(image):
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"""Determine nonstandard properties of an input image.
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Parameters
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----------
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image : array
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The input image.
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Returns
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-------
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ip : ImageProperties named tuple
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The properties of the image:
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- signed: whether the image has negative values.
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- out_of_range_float: if the image has floating point data
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outside of [-1, 1].
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- low_dynamic_range: if the image is in the standard image
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range (e.g. [0, 1] for a floating point image) but its
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dynamic range would be too small to display with standard
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image ranges.
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- unsupported_dtype: if the image data type is not a
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standard skimage type, e.g. ``numpy.uint64``.
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"""
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immin, immax = np.min(image), np.max(image)
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imtype = image.dtype.type
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try:
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lo, hi = dtypes.dtype_range[imtype]
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except KeyError:
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lo, hi = immin, immax
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signed = immin < 0
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out_of_range_float = (np.issubdtype(image.dtype, np.float) and
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(immin < lo or immax > hi))
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low_dynamic_range = (immin != immax and
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(float(immax - immin) / (hi - lo)) < (1. / 255))
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unsupported_dtype = image.dtype not in dtypes._supported_types
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ip = ImageProperties(signed, out_of_range_float,
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low_dynamic_range, unsupported_dtype)
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return ip
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def _raise_warnings(image_properties):
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"""Raise the appropriate warning for each nonstandard image type.
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Parameters
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----------
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image_properties : ImageProperties named tuple
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The properties of the considered image.
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"""
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ip = image_properties
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if ip.unsupported_dtype:
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warnings.warn("Non-standard image type; displaying image with "
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"stretched contrast.")
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if ip.low_dynamic_range:
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warnings.warn("Low image dynamic range; displaying image with "
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"stretched contrast.")
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if ip.out_of_range_float:
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warnings.warn("Float image out of standard range; displaying image "
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"with stretched contrast.")
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def _get_display_range(image):
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"""Return the display range for a given set of image properties.
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Parameters
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----------
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image : array
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The input image.
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Returns
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-------
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lo, hi : same type as immin, immax
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The display range to be used for the input image.
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cmap : string
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The name of the colormap to use.
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"""
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ip = _get_image_properties(image)
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immin, immax = np.min(image), np.max(image)
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if ip.signed:
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magnitude = max(abs(immin), abs(immax))
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lo, hi = -magnitude, magnitude
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cmap = _diverging_colormap
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elif any(ip):
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_raise_warnings(ip)
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lo, hi = immin, immax
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cmap = _nonstandard_colormap
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else:
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lo = 0
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imtype = image.dtype.type
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hi = dtypes.dtype_range[imtype][1]
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cmap = _default_colormap
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return lo, hi, cmap
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def imshow(im, *args, **kwargs):
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"""Show the input image and return the current axes.
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By default, the image is displayed in greyscale, rather than
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the matplotlib default colormap, 'jet'.
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Images are assumed to have standard range for their type. For
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example, if a floating point image has values in [0, 0.5], the
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most intense color will be gray50, not white.
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If the image exceeds the standard range, or if the range is too
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small to display, we fall back on displaying exactly the range of
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the input image, along with a colorbar to clearly indicate that
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this range transformation has occurred.
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For signed images, we use a diverging colormap centered at 0.
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Parameters
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----------
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im : array, shape (M, N[, 3])
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The image to display.
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*args, **kwargs : positional and keyword arguments
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These are passed directly to `matplotlib.pyplot.imshow`.
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Returns
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-------
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ax_im : `matplotlib.pyplot.AxesImage`
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The `AxesImage` object returned by `plt.imshow`.
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"""
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lo, hi, cmap = _get_display_range(im)
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kwargs.setdefault('interpolation', 'nearest')
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kwargs.setdefault('cmap', cmap)
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kwargs.setdefault('vmin', lo)
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kwargs.setdefault('vmax', hi)
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ax_im = plt.imshow(im, *args, **kwargs)
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if cmap != _default_colormap:
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plt.colorbar()
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return ax_im
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imread = plt.imread
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show = plt.show
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def _app_show():
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show()
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