AWS Lambda中Pillow图片缩放逻辑错误：生成同尺寸图片求助

我一眼就看出问题所在啦——你在使用Pillow的resize()方法时犯了一个非常常见的小疏忽！

问题根源 #

Pillow的Image.resize()方法不会直接修改原图像对象，它会返回一个调整尺寸后的新图像实例。你当前的代码里只是调用了image.resize(dim)，但没有将这个返回的新图像赋值给变量，最后保存的依然是原始尺寸的图片，这就导致两张输出图的尺寸完全一致，和你预期的两种尺寸不符。

修复后的代码 #

只需要修改两个缩放函数，把resize()返回的新图像赋值给变量后再保存即可：

from __future__ import print_function
import boto3
import os
import sys
import uuid
from PIL import Image
import PIL.Image

s3_client = boto3.client('s3')

def resize_image_DOG(image_path, resized_path):
    with Image.open(image_path) as image:
        dim=(3840,2160)
        # 接收resize返回的新图像实例
        resized_image = image.resize(dim)
        resized_image.save(resized_path)

def resize_image_CAT(image_path, resized_path):
    with Image.open(image_path) as image:
        dim=(1920,1080)
        resized_image = image.resize(dim)
        resized_image.save(resized_path)

def handler(event, context):
    for record in event['Records']:
        bucket = record['s3']['bucket']['name']
        key = record['s3']['object']['key']
        download_path = '/tmp/{}{}'.format(uuid.uuid4(), key)
        upload_path_1 = '/tmp/resized-{}{}'.format('test1',key)
        upload_path_2 = '/tmp/resized-{}{}'.format('test2',key)
        s3_client.download_file(bucket, key, download_path)
        resize_image_DOG(download_path, upload_path_1)
        resize_image_CAT(download_path, upload_path_2)
        s3_client.upload_file(upload_path_1, '{}resized'.format(bucket), key+'xxxhdpi-3840*2160'+'.png')
        s3_client.upload_file(upload_path_2, '{}resized'.format(bucket), key+'xxxhdpi-1920*1080'+'.png')

额外优化提示 #

如果需要提升缩放后图片的质量，可以给resize()方法加上重采样参数（推荐使用LANCZOS算法，适合缩小或放大图像时保持清晰度）：

• 对于Pillow 9.1.0及以上版本：resized_image = image.resize(dim, resample=Image.Resampling.LANCZOS)
• 对于旧版本Pillow：resized_image = image.resize(dim, resample=Image.LANCZOS)

这样修改后，你上传到S3的两张图片就会分别是3840×2160和1920×1080的尺寸啦！

内容的提问来源于stack exchange，提问作者Nishant Singh