Deploy Python face recognition model on Heroku and use it from Flutter ①

We have deployed Python's powerful facial recognition model on Heroku so that it can be called from a mobile app.

Part 1 will introduce the code on the Python side and deployment to Heroku, and Part 2 will introduce the part that calls the deployed process with Flutter.

Please refer to the following article for the call part in the second Flutter. Deploy Python face recognition model to Heroku and use it from Flutter②

About the poster of this article

We are tweeting about application development utilizing face recognition on Twitter.

The diary of application development is serialized in note.

Face recognition model

Library used

I am using Python face_recognition.

The documentation is very rich and very easy to use. With an accuracy of 99.38% in the benchmark, you can expect performance equal to or better than humans.

Other libraries used

I don't think too much about it, but I chose the one that seems to be lightweight and is often used on Heroku.

--Web development framework: Flask --HTTP server: Gunicorn

Python source code commentary

It's the minimum necessary, but you can see the gist.

import face_recognition
from flask import Flask, jsonify, request, redirect
app = Flask(__name__)
ALLOWED_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif'}

First, import the required libraries and declare constants. The variable name of app is also used when starting Gunicorn.

def hello_world():
    return 'hello'

When called as root, it simply displays only hello. This is useful for checking if the server is alive.

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

When the image file is sent, make sure that the extension of the file is png, jpg, jpeg, or gif. Other than these, face recognition processing is excluded.

@app.route('/embedding', methods=['GET', 'POST'])
def get_embedding():
    # Check if a valid image file was uploaded
    if request.method == 'POST':
        if 'file' not in request.files:
            print("file not in request.files")
            return redirect(request.url)

        file = request.files['file']

        if file.filename == '':
            print("file name is blank")
            return redirect(request.url)

This is the main face recognition processing unit. Call it with / embedding. Only when the input type is file and the file name is one of the above png, jpg, jpeg, gif by POST. Otherwise, redirect back to the caller. In that case, the response code will be 302.

        if file and allowed_file(file.filename):
            print("file found")

            # The image file seems valid! Detect faces and return the result.
            img = face_recognition.load_image_file(file)
            emb = face_recognition.face_encodings(img)[0]
            return jsonify(emb.tolist())

If it has been POSTed in the correct file format, have face_recognition read the file and use it to get the Embedding of the 128-dimensional Float. With this embedding, you can calculate the similarity with other faces. Since this part is implemented separately on the mobile application side, only the embedded facial feature amount information is returned on the Python side. The return value of face_recognition is a Numpy array, so you need to call tolist () to make it a Python array. I will return the Jsonized version of it.

    # If no valid image file was uploaded, show the file upload form:
    return '''
    <!doctype html>
    <h1>Please select image and upload</h1>
    <form method="POST" enctype="multipart/form-data">
      <input type="file" name="file">
      <input type="submit" value="Upload">

When called by GET, HTML for file upload is output so that the file can be uploaded directly.

if __name__ == "__main__":'')

In the main process, start Flask. By setting host to, you can use it with the URL of the Heroku deployment destination.

Operation check

pip install -r requirements.txt

The required libraries are put together in requirements.txt, so you can install them all together with the above command. This requirements.txt is also required when deploying to Heroku. Depending on the version, there was information that it could not be deployed successfully on Heroku unless it was installed in the order of cmake, dlib, face_recognition, so I wrote it in requirements.txt as follows.



Try launching it locally using gunicorn.

gunicorn run:app --log-file -

If it starts up successfully, you should see something like the following.

$ gunicorn run:app --log-file -
[2020-05-15 09:02:24 +0900] [11143] [INFO] Starting gunicorn 20.0.4
[2020-05-15 09:02:24 +0900] [11143] [INFO] Listening at: (11143)
[2020-05-15 09:02:24 +0900] [11143] [INFO] Using worker: sync
[2020-05-15 09:02:24 +0900] [11146] [INFO] Booting worker with pid: 11146

Let's open in your browser. If "hello`" is displayed, it is successful.

Next, when you access, you will see the HTML for file selection as shown below. Try uploading a human face image file.


If you see an array of 128 Float as shown below, you are successful. This is the content of Embedding, which is the feature of the uploaded image.


Cloud environment

Using Heroku

I chose Heroku as the destination for deploying the web service. I chose Heroku because it's available in Python, it's easy to deploy and scale, and I felt it was reasonably priced. You can use it for free if you use it as a trial.

As a countermeasure, I also considered Firebase's Cloud Function, but since this model will take some load to load, I thought that the VM type that is always running is better than the Cloud Function that is started every time.

If Heroku is also a free version, the instance will drop if it is not used for 30 minutes and it will start when calling, but if you use the paid version, the instance will not drop. You can move to the paid version if necessary.

Deploy to Heroku

Deploying is not difficult. You can register as a user on Heroku and follow the setup steps below.

Install Heroku command line tools.

sudo snap install heroku --classic

Log in to Heroku. The browser will be launched and you can log in from the browser.

heroku login

Register the app on Heroku. The app will be registered with a suitable name and can be confirmed on the Heroku dashboard.

heroku create

Create a Procfile. This file is a file that teaches Heroku how to start the server. Write the instruction to start gunicorn as WEB as follows.

web: gunicorn run:app --log-file -

That's all for preparation. Then push it to heroku's repository with the git command and it will be deployed.

git push heroku master

Now it will be deployed on Heroku and the URL will be displayed, so please access that URL and check that it works.

Please note that the first deployment will take a considerable amount of time. Especially since dlib is a library written in C ++ and needs to be compiled, I had to wait a long time to complete the installation. It may have taken about 30 minutes. If it doesn't end with an error, feel free to wait.

Next time, I would like to introduce the part that calls this WEB service from Flutter.

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