烧瓶上传灰度图答案

【问题标题】：flask upload grayscale image烧瓶上传灰度图
【发布时间】：2020-09-22 04:20:12
【问题描述】：

我正在研究烧瓶。当我选择一个图像文件时，我想通过 cv2 转换该图像灰度。但cv2.imread 无法读取变量。我制作新功能或添加一些代码行？我认为html没有什么可改变的应用程序.py

from flask import Flask, render_template, request, redirect, url_for,send_from_directory
from werkzeug.utils import secure_filename
import os

FOLDER_PATH = os.path.join('C:\\Users\\teran\\Desktop\\Ps_Sd\\uploads\\')
ALLOWED_EXTENSIONS = set([ 'png','PNG', 'jpg', 'jpeg'])

app = Flask(__name__)
app.config['UPLOAD_FOLDER'] = FOLDER_PATH

def allowed_file(filename):
    return '.' in filename and \
            filename.rsplit('.', 1)[1] in ALLOWED_EXTENSIONS

@app.route('/', methods=['GET', 'POST'])
def upload_file():
    if request.method == 'POST':
        file = request.files['file']
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
            return redirect(url_for('uploaded_file', filename=filename))
    return render_template('upload.html')
  
@app.route('/show/<filename>')
def uploaded_file(filename):
    filename = 'http://localhost:5000/uploads/' + filename
    return render_template('upload.html', filename=filename)

@app.route('/uploads/<filename>')
def send_file(filename):
    return send_from_directory(FOLDER_PATH, filename)
if __name__ == '__main__':
    app.run(debug=True)

【问题讨论】：

标签： python flask

【解决方案1】：

您需要按照this answer 中的说明使用cv2.imdecode 函数，然后使用c2.imencode 将其恢复为可写流。

所以我会创建一个函数来创建灰度图像，例如：

import cv2
import numpy as np

def make_grayscale(in_stream):
    # Credit: https://stackoverflow.com/a/34475270

    #use numpy to construct an array from the bytes
    arr = np.fromstring(in_stream, dtype='uint8')

    #decode the array into an image
    img = cv2.imdecode(arr, cv2.IMREAD_UNCHANGED)

    # Make grayscale
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    
    _, out_stream = cv2.imencode('.PNG', gray)

    return out_stream

然后，如果您想在上传时将该图像更改为灰度（将其以灰度保存在您的服务器上），您可以修改上传代码，使其看起来更像：

# ...
        if file and allowed_file(file.filename):
            filename = secure_filename(file.filename)
            file_data = make_grayscale(file.read())

            with open(os.path.join(app.config['UPLOAD_FOLDER'], filename),
                      'wb') as f:
                f.write(file_data)

            return redirect(url_for('uploaded_file', filename=filename))
# ...

附带说明，您可能应该知道，使用最初上传的文件名来命名文件可能会导致以后出现问题，我已经在另一个关于 handling duplicate filenames 的答案中介绍了这些问题。

【讨论】：