api.py 文件源码

def binarize_image(image, method='li', **kwargs):
    """Binarize image using one of the available methods: 'isodata',
    'li', 'otsu', 'sauvola', and 'boolean'. Defaults to 'li'.
    Extra keyword arguments are passed in as is to the corresponding
    scikit-image thresholding function. The 'boolean' method refers to simple
    thresholding from a grey-scale image. If a 'threshold' kwarg is not passed
    to the 'boolean' method, 'li' thresholding is performed.
    For reference
    Sezgin M. and Sankur B. (2004) "Survey over Image Thresholding Techniques
    and Quantitative Performance Evaluation" Journal of Electronic Imaging,
    13(1): 146-165 DOI:10.1117/1.1631315
    """
    if image.ndim != 2:
        # image is not gray-scale
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    if np.unique(image).size == 2:
        # image is already binary
        return image
    boolean_threshold = kwargs.get('threshold', None)
    if method == 'boolean' and boolean_threshold:
        preprocessing.binarize(image, threshold=boolean_threshold, copy=False)
        return convert(image)
    if method not in ('sauvola', 'isodata', 'otsu', 'li'):
        method = 'li'
    thresh_func = getattr(filters.thresholding, "threshold_{}".format(method))
    threshold = thresh_func(image, **kwargs)
    # OpenCV can't write black and white images using boolean values, it needs
    # at least a 8bits 1-channel image ranged from 0 (black) to 255 (white)
    return convert(image <= threshold)