图像base64与numpy array之间的转换

https://blog.youkuaiyun.com/qian1122221/article/details/84567715

https://blog.youkuaiyun.com/wangjian1204/article/details/84445334

环境python3.6

import base64
import cv2
import numpy as np

1.base64 string to numpy array

image_string = request_data['image']
img_data = base64.b64decode(image_string)
nparr = np.fromstring(img_data, np.uint8)
img_np = cv2.imdecode(nparr, cv2.IMREAD_COLOR)

2. numpy array to base64 string

retval, buffer = cv2.imencode('.jpg', pic_img)
pic_str = base64.b64encode(buffer)
pic_str = pic_str.decode()

3. image file to base64 directly

with open(img_path, "rb") as image_file:
    encoded_image = base64.b64encode(image_file.read())
    req_file = encoded_image.decode('utf-8')

4. post request using the base64 string as part of json parameters

import requests
import json
with open(img_path, "rb") as image_file:
    encoded_image = base64.b64encode(image_file.read())
    req_file = encoded_image.decode('utf-8')
#json format parameters
post_dict = {"image": req_file, "type": 0}
headers = {
    'Content-Type': 'application/json',  # This is important
}
response = requests.post(url, data=json.dumps(post_dict), headers=headers)
 
#the host using jsonify(from flask) to return the result
result = json.loads(response.content.decode('utf8'))
pic_str = result['data']['pic_str']
pic_str = pic_str.encode('utf-8')
jpg_original = base64.b64decode(pic_str)
jpg_as_np = np.frombuffer(jpg_original, dtype=np.uint8)
image_buffer = cv2.imdecode(jpg_as_np, flags=1)
cv2.imshow("asd", image_buffer)
cv2.waitKey(0)

---

OpenCV图像转base64
OpenCV图像的数据类型也是numpy 2维数组，OpenCV提供了cv2.imencode这两个函数来把图片编码成流数据，放到内存缓存中，函数cv2.imdecode可以从编码的数据流恢复到numpy数组：

   # OpenCV 图像转base64编码
img = cv2.imread('data/laska.png')
img_str = cv2.imencode('.jpg', img)[1].tostring()  # 将图片编码成流数据，放到内存缓存中，然后转化成string格式
b64_code = base64.b64encode(img_str) # 编码成base64

# 从base64编码恢复OpenCV图像
str_decode = base64.b64decode(b64_code)
nparr = np.fromstring(str_decode, np.uint8)
# img_restore = cv2.imdecode(nparr, cv2.CV_LOAD_IMAGE_COLOR) for python 2
img_restore = cv2.imdecode(nparr, cv2.IMREAD_COLOR)

numpy 1维或者2维数组转base64
对于普通的1维或者2维numpy数组，还可以用ByteIO进行编码。

   # numpy数组转base64编码
arr = np.arange(12).reshape(3, 4)
bytesio = BytesIO()
np.savetxt(bytesio, arr) # 只支持1维或者2维数组，numpy数组转化成字节流
content = bytesio.getvalue()  # 获取string字符串表示
print(content)
b64_code = base64.b64encode(content)
 
# 从base64编码恢复numpy数组
b64_decode = base64.b64decode(b64_code)
arr = np.loadtxt(BytesIO(b64_decode))
print(arr)

用于HTTP传输的时候通常会用base64.urlsafe_b64encode来代替base64.b64encode，base64.urlsafe_b64decode代替base64.b64decode。两者的区别在于base64.urlsafe_b64encode会把+用-代替，/用_代替，避免URL把+``/当成特殊字符解析了。