Visualize Semantic Segmentation with Legend

[wkentaro]

def draw_label(label, img=None, label_names=None, colormap=None, **kwargs):
    """Draw pixel-wise label with colorization and label names.
    label: ndarray, (H, W)
        Pixel-wise labels to colorize.
    img: ndarray, (H, W, 3), optional
        Image on which the colorized label will be drawn.
    label_names: iterable
        List of label names.
    """
    import matplotlib.pyplot as plt

    backend_org = plt.rcParams['backend']
    plt.switch_backend('agg')

    plt.subplots_adjust(left=0, right=1, top=1, bottom=0,
                        wspace=0, hspace=0)
    plt.margins(0, 0)
    plt.gca().xaxis.set_major_locator(plt.NullLocator())
    plt.gca().yaxis.set_major_locator(plt.NullLocator())

    if label_names is None:
        label_names = [str(l) for l in range(label.max() + 1)]

    colormap = _validate_colormap(colormap, len(label_names))

    label_viz = label2rgb(
        label, img, n_labels=len(label_names), colormap=colormap, **kwargs
    )
    plt.imshow(label_viz)
    plt.axis('off')

    plt_handlers = []
    plt_titles = []
    for label_value, label_name in enumerate(label_names):
        if label_value not in label:
            continue
        fc = colormap[label_value]
        p = plt.Rectangle((0, 0), 1, 1, fc=fc)
        plt_handlers.append(p)
        plt_titles.append('{value}: {name}'
                          .format(value=label_value, name=label_name))
    plt.legend(plt_handlers, plt_titles, loc='lower right', framealpha=.5)

    f = io.BytesIO()
    plt.savefig(f, bbox_inches='tight', pad_inches=0)
    plt.cla()
    plt.close()

    plt.switch_backend(backend_org)

    out_size = (label_viz.shape[1], label_viz.shape[0])
    out = PIL.Image.open(f).resize(out_size, PIL.Image.BILINEAR).convert('RGB')
    out = np.asarray(out)
    return out

[wkentaro]

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