全程使用openCV，没有PIL

代码：

 1 import base64
 2 import cv2
 3 import sys
 4 import numpy as np
 5 
 6 path = sys.argv[1]
 7 
 8 with open(path, "rb") as image_file:
 9     encodedImage = base64.b64encode(image_file.read())
10 imgBase64 = "data:image/jpeg;base64," + encodedImage
11 file = open('imgBase64.txt', 'wb')
12 file.write(imgBase64)
13 file.close()
14 
15 npArray = np.fromstring(encodedImage.decode('base64'), np.uint8)
16 image = cv2.imdecode(npArray, cv2.IMREAD_COLOR)
17 cv2.imwrite('img.jpeg',image)

读取图片转成base64字符串：

要注意用读文件的方式读取图片，不能用 cv2.imread()。我读取的是 jpeg图片，在网络传输时需要加上前缀 "data:image/jpeg;base64," 。

从base64字符串转为图片：

注意要先去掉前缀 "data:image/jpeg;base64," ， 然后再扔到decode函数中。以上是用openCV保存图片，也可以直接用保存文件的方式：

imgData = base64.b64decode(imgString.strip().replace("data:image/jpeg;base64,",''))
            
file = open('img.jpeg', 'wb')
file.write(imgData)
file.close()

参考： https://stackoverflow.com/questions/33754935/read-a-base-64-encoded-image-from-memory-using-opencv-python-library/54205640