python 遍历文件夹里的图片

Question

python 主程序遍历文件夹里的图片后，调用自定义的 process_image()方法，进入后运行到图像灰度化时，提示image为空None，想不明白，是遍历的结果有错，还是参数传递有错，或是什么？这里好像传入的图片列表路径，而我正真要的是图片路径下的图片数据。请教教我，或请您给看看哪里有写的不对的地方，谢谢各位大老诗

下面是python代码

import cv2
import os


def process_image(image_path):
    # 读取图片
    img = cv2.imread(image_path)
    # 获取前景部分
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    ret, thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)
    contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
    cnt = max(contours, key=cv2.contourArea)
    x, y, w, h = cv2.boundingRect(cnt)
    foreground = img[y:y + h, x:x + w]
    # 统一改变背景颜色为黑色
    background = cv2.imread('black.jpg')
    background = cv2.resize(background, (w, h))
    foreground = cv2.resize(foreground, (w, h))
    mask = cv2.cvtColor(foreground, cv2.COLOR_BGR2GRAY)
    ret, thresh = cv2.threshold(mask, 10, 255, cv2.THRESH_BINARY)
    mask_inv = cv2.bitwise_not(thresh)
    img1_bg = cv2.bitwise_and(background, background, mask=thresh)
    img2_fg = cv2.bitwise_and(foreground, foreground, mask=mask_inv)
    dst = cv2.add(img1_bg, img2_fg)
    # 统一改变图片分辨率为24*24
    dst = cv2.resize(dst, (24, 24))
    # 返回处理后的图片
    return dst

    # 读取文件目录中的每一个文件
    path = 'image_folder/'
    for filename in os.listdir(path):
        if filename.endswith('.jpg'):
            image_path = os.path.join(path, filename)
            # 处理图片
            processed_image = process_image(image_path)
            # 保存处理后的图片
            cv2.imwrite(os.path.join(path, 'processed_' + filename), processed_image)


if __name__ == '__main__':
    # 读取文件夹中的所有文件
    folder_path = 'D:/PyCharm_Projects/lab/imagefile'  # 给相对路径下的文件夹赋值一个变量名
    file_list = os.listdir(folder_path)  # 将文件夹变量名及内部文件转为python列表的格式

    # 遍历文件列表
    for i, fileNames in enumerate(file_list):
        # 调用获取图片前景部分，并统一改变背景颜色为黑色，和统一改变图片分辨率为24*24的函数
        process_image(fileNames)

报错：

PyDev console: starting.
Python 3.7.9 (tags/v3.7.9:13c94747c7, Aug 17 2020, 18:58:18) [MSC v.1900 64 bit (AMD64)] on win32
runfile('D:/PyCharm_Projects/lab/heoll.py', wdir='D:/PyCharm_Projects/lab')
None
Traceback (most recent call last):
  File "C:\Users\Administrator\AppData\Local\Programs\Python\Python37\lib\code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "D:\PyCharm2021.3\PyCharm 2021.3\plugins\python\helpers\pydev\_pydev_bundle\pydev_umd.py", line 198, in runfile
    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script
  File "D:\PyCharm2021.3\PyCharm 2021.3\plugins\python\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "D:/PyCharm_Projects/lab/heoll.py", line 48, in <module>
    process_image(fileNames)
  File "D:/PyCharm_Projects/lab/heoll.py", line 10, in process_image
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
cv2.error: OpenCV(3.4.8) C:\projects\opencv-python\opencv\modules\imgproc\src\color.cpp:182: error: (-215:Assertion failed) !_src.empty() in function

Answer 1

查了好多，终于参考这位博主的文章，已解决。谢谢，各位！

http://t.csdn.cn/ChY9L
但还是不太明白，为什么自定义函数传入参数要有双斜杠？

    dir_path = "D:/PyCharm_Projects/lab/imgfile/"
    files = os.listdir(dir_path)
    for file in files:
        print(file)
        # 调用自定义函数
        process_image(dir_path + "\\" + file)