Cloud Functions to resize images using OpenCV with Cloud Storage triggers

This is a sample using python when you want to create a thumbnail of an uploaded image using a Cloud storage trigger in Cloud functions of GCP.

--The GCS trigger will also fire on the object uploaded by this script, so you need to include some logic to prevent it from looping. ――It is assumed that all the objects that come into this bucket are images. If other files come in, there is logic to repel --cv2.imwrite () does not work well without the extension, so you need to set it in the file name ――Since it is a thumbnail, I think that there are many requests such as a square with a height and width of 300px ...

requirements.txt

google-cloud-storage==1.28.1
opencv-python==4.2.0.32

# -*- coding: utf-8 -*-
import tempfile
import os
import cv2
from google.cloud import storage


NEW_FILE_PREFIX="thumbnail_"
client = storage.Client()


def main(event, context):
    """Triggered by a change to a Cloud Storage bucket.
    Args:
         event (dict): Event payload.
         context (google.cloud.functions.Context): Metadata for the event.
    """
    name = event['name']
    bucket = event['bucket']

    _, _name = os.path.split(name)
    if _name.startswith(NEW_FILE_PREFIX):
        print(f"Blob {name} is already resized.")
        return

    file_name = download(bucket, name)
    resize(file_name)
    upload(bucket, name, file_name)

    os.remove(file_name)


def download(bucket, blob_name):
    blob = client.bucket(bucket).blob(blob_name)
    _, _ext = os.path.splitext(blob.name)
    _, temp_local_filename = tempfile.mkstemp(suffix=_ext)
    blob.download_to_filename(temp_local_filename)
    print(f"Blob {blob_name} downloaded to {temp_local_filename}.")
    return temp_local_filename


def upload(bucket, blob_name, file_name):
    _dir, _name = os.path.split(blob_name)
    new_file_name = os.path.join(_dir, NEW_FILE_PREFIX + _name)
    new_blob = client.bucket(bucket).blob(new_file_name)
    new_blob.upload_from_filename(file_name)
    print(f'New image uploaded to: gs://{bucket}/{new_file_name}')


def resize(file_name):
    img = cv2.imread(file_name)
    height = img.shape[0]
    width = img.shape[1]
    print(f"Old blob width {width}, height {height}")

    dst = cv2.resize(img, (int(width/2), int(height/2)))
    cv2.imwrite(file_name, dst) # requierd ext
    print(f"New blob width {dst.shape[0]}, height {dst.shape[1]}")
    return file_name

Referenced --Upload Objects -Download Objects -ImageMagick Tutorial

• Image Processing using Google Cloud Functions