Some useful functions with opencv.

opencv_debug.py

import cv2
import matplotlib.pyplot as plt
import numpy as np
import numpy.typing as npt
from imutils import opencv2matplotlib

from opencv_utils import cvt_single_color


def show(image: npt.NDArray, contours=None):
    """
    Show image for debugging.

    :param image: The image to show.
    :param contours: Optional contours.
    """
    if contours is None:
        to_show = image
    else:
        to_show = image.copy()
        cv2.drawContours(
            to_show, contours, -1, _get_contour_color(image), image.shape[0] // 100
        )
    plt.figure()
    plt.imshow(opencv2matplotlib(to_show))


def _get_contour_color(image: npt.NDArray) -> tuple[int, int, int]:
    """
    Get a proper color for the contour.

    :param image: The image.
    :return: A BGR color for the contour.
    """
    # get hsv of center pixel
    h, w = image.shape[:2]
    center = image[h // 2, w // 2]
    hsv = cvt_single_color(center, cv2.COLOR_BGR2HSV)

    # use red contour for green image
    if np.all((40, 40, 40) <= hsv) and np.all(hsv <= (70, 255, 255)):
        return 0, 0, 255
    # green for others
    return 0, 255, 0

opencv_utils.py

import itertools
import os
import shutil
import tempfile

import cv2
import numpy as np


def cvt_single_color(src, code, np_type=np.uint8):
    """
    Single color conversion.

    :param src: The source color.
    :param code: Something like cv2.COLOR_BGR2HSV.
    :param np_type: np.uint8 or np.float32 or something else.
    :return: The converted color.
    """
    return cv2.cvtColor(np_type([[src]]), code)[0][0]


def cv_read(path, *args):
    """
    Read from a path with Unicode characters.

    :param path: path of a single image or a directory which contains images
    :param args: other args passed to cv2.imread
    :return: a single image or a list of images
    """
    with tempfile.TemporaryDirectory() as tmp_dir:
        if os.path.isdir(path):
            shutil.copytree(path, tmp_dir, dirs_exist_ok=True)
        elif os.path.isfile(path):
            shutil.copy(path, tmp_dir)
        else:
            raise FileNotFoundError

        img_arr = [
            cv2.imread(os.path.join(tmp_dir, img), *args) for img in os.listdir(tmp_dir)
        ]

        return img_arr if os.path.isdir(path) else img_arr[0]


def show_images(images, *, delay=200, cycle=False):
    """Show images as slides."""
    for img in itertools.cycle(images) if cycle else images:
        cv2.imshow("", img)
        cv2.waitKey(delay)