def flood1(image, delta):
    """
    Create a blue label image by manual threshold of input image.

    Keyword Arguments:
    -----------------
    image -- the image
    delta -- the threshold value (min 0, max 255)

    """
    new_level = delta
    label_image = image <= new_level
    label_image = label_image.astype(int)*13  # label 13 is blue in napari
    return(label_image, new_level)