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from __future__ import division
import numpy as np
from chainercv.visualizations.colormap import voc_colormap
from chainercv.visualizations import vis_image
def vis_semantic_segmentation(
img, label, label_names=None,
label_colors=None, ignore_label_color=(0, 0, 0), alpha=1,
all_label_names_in_legend=False, ax=None):
"""Visualize a semantic segmentation.
>>> from chainercv.datasets import VOCSemanticSegmentationDataset
>>> from chainercv.datasets \
... import voc_semantic_segmentation_label_colors
>>> from chainercv.datasets \
... import voc_semantic_segmentation_label_names
>>> from chainercv.visualizations import vis_semantic_segmentation
>>> import matplotlib.pyplot as plt
>>> dataset = VOCSemanticSegmentationDataset()
>>> img, label = dataset[60]
>>> ax, legend_handles = vis_semantic_segmentation(
... img, label,
... label_names=voc_semantic_segmentation_label_names,
... label_colors=voc_semantic_segmentation_label_colors,
... alpha=0.9)
>>> ax.legend(handles=legend_handles, bbox_to_anchor=(1, 1), loc=2)
img (~numpy.ndarray): See the table below. If this is :obj:`None`,
no image is displayed.
label (~numpy.ndarray): See the table below.
label_names (iterable of strings): Name of labels ordered according
to label ids.
label_colors: (iterable of tuple): An iterable of colors for regular
Each color is RGB format and the range of its values is
:math:`[0, 255]`.
If :obj:`colors` is :obj:`None`, the default color map is used.
ignore_label_color (tuple): Color for ignored label.
This is RGB format and the range of its values is :math:`[0, 255]`.
The default value is :obj:`(0, 0, 0)`.
alpha (float): The value which determines transparency of the figure.
The range of this value is :math:`[0, 1]`. If this
value is :obj:`0`, the figure will be completely transparent.
The default value is :obj:`1`. This option is useful for
overlaying the label on the source image.
all_label_names_in_legend (bool): Determines whether to include
all label names in a legend. If this is :obj:`False`,
the legend does not contain the names of unused labels.
An unused label is defined as a label that does not appear in
The default value is :obj:`False`.
ax (matplotlib.axes.Axis): The visualization is displayed on this
axis. If this is :obj:`None` (default), a new axis is created.
.. csv-table::
:header: name, shape, dtype, format
:obj:`img`, ":math:`(3, H, W)`", :obj:`float32`, \
"RGB, :math:`[0, 255]`"
:obj:`label`, ":math:`(H, W)`", :obj:`int32`, \
":math:`[-1, \#class - 1]`"
matploblib.axes.Axes and list of matplotlib.patches.Patch:
Returns :obj:`ax` and :obj:`legend_handles`.
:obj:`ax` is an :class:`matploblib.axes.Axes` with the plot.
It can be used for further tweaking.
:obj:`legend_handles` is a list of legends. It can be passed
:func:`matploblib.pyplot.legend` to show a legend.
import matplotlib
from matplotlib.patches import Patch
if label_names is not None:
n_class = len(label_names)
elif label_colors is not None:
n_class = len(label_colors)
n_class = label.max() + 1
if label_colors is not None and not len(label_colors) == n_class:
raise ValueError(
'The size of label_colors is not same as the number of classes')
if label.max() >= n_class:
raise ValueError('The values of label exceed the number of classes')
# Returns newly instantiated matplotlib.axes.Axes object if ax is None
ax = vis_image(img, ax=ax)
if label_names is None:
label_names = [str(l) for l in range(label.max() + 1)]
if label_colors is None:
label_colors = voc_colormap(list(range(n_class)))
# [0, 255] -> [0, 1]
label_colors = np.array(label_colors) / 255
cmap = matplotlib.colors.ListedColormap(label_colors)
canvas_img = cmap(label / (n_class - 1), alpha=alpha)
# [0, 255] -> [0, 1]
ignore_label_color = np.array(ignore_label_color) / 255,
canvas_img[label < 0, :3] = ignore_label_color
legend_handles = []
if all_label_names_in_legend:
legend_labels = [l for l in np.unique(label) if l >= 0]
legend_labels = range(n_class)
for l in legend_labels:
Patch(color=cmap(l / (n_class - 1)), label=label_names[l]))
return ax, legend_handles