Python PIL 调整大小是否保持纵横比？

Question

Does PIL resize to the exact dimensions I give it no matter what? Or will it try to keep the aspect ratio if I give it something like the Image.ANTIALIAS argument?

Answer 1

Yes it will keep aspect ratio using thumbnail method:

image = Image.open(source_path)
image.thumbnail(size, Image.ANTIALIAS)
image.save(dest_path, "JPEG")

Answer 2

How do I resize an image using PIL and maintain its aspect ratio?

Image.resize from PIL will do exactly as told. No behind scenes aspect ratio stuff.

Answer 3

最近的 Pillow 版本（自 8.3 起）具有以下方法来调整图像大小以适应给定的框并保持纵横比。

image = ImageOps.contain(image, (2048,2048))

Answer 4

Yes. the thumbnail() method is what is needed here... One thing that hasn't been mentioned in this or other posts on the topic is that 'size' must be either a list or tuple. So, to resize to a maximum dimension of 500 pixels, you would call: image.thumbnail((500,500), Image.ANTIALIAS)

See also this post on the subject: How do I resize an image using PIL and maintain its aspect ratio?

Answer 5

No, it does not. But you can do something like the following:

im = PIL.Image.open("email.jpg"))
width, height = im.size
im = im.resize((width//2, height//2))

Here the height and width are divided by the same number, keeping the same aspect ratio.

Answer 6

Okay, so this requires a couple of lines of code to get what you want.

First you find the ratio, then you fix a dimension of the image that you want (height or width). In my case, I wanted height as 100px and let the width adjust accordingly, and finally use that ratio to find new height or new width.

So first find the dimensions:

width, height = logo_img.size
ratio = width / height
      

Then, fix one of the dimension:

new_height = 100

Then find new width for that height:

new_width = int(ratio * new_height)
            
logo_img = logo_img.resize((new_width, new_height))

Answer 7

It depends on your demand, if you want you can set a fixed height and width or if you want you can resize it with aspect-ratio.

For the aspect-ratio-wise resize you can try with the below codes :

To make the new image half the width and half the height of the original image:

from PIL import Image
im = Image.open("image.jpg")
resized_im = im.resize((round(im.size[0]*0.5), round(im.size[1]*0.5)))
        
#Save the cropped image
resized_im.save('resizedimage.jpg')

To resize with fixed width and ratio wise dynamic height :

from PIL import Image
new_width = 300
im = Image.open("img/7.jpeg")
concat = int(new_width/float(im.size[0]))
size = int((float(im.size[1])*float(concat)))
resized_im = im.resize((new_width,size), Image.ANTIALIAS)
#Save the cropped image
resized_im.save('resizedimage.jpg')

Answer 8

Recent versions of Pillow have some useful methods in PIL.ImageOps .

Depending on exactly what you're trying to achieve, you may be looking for one of these:

• ImageOps.fit(image, size [, …]) (docs) – resizes your image, maintaining its aspect ratio, and crops it to fit the given size

• ImageOps.contain(image, size [, …]) (docs) – resizes your image, maintaining its aspect ratio, so that it fits within the given size

Answer 9

One complete example:

import PIL.Image


class ImageUtils(object):
    @classmethod
    def resize_image(cls, image: PIL.Image.Image, width=None, height=None) -> PIL.Image.Image:
        if height is None and width is not None:
            height = image.height * width // image.width
        elif width is None and height is not None:
            width = image.width * height // image.height
        elif height is None and width is None:
            raise RuntimeError("At lease one of width and height must be present")
        return image.resize((width, height))


def main():
    ImageUtils.resize_image(PIL.Image.open("old.png"), width=100).save("new.png")


if __name__ == '__main__':
    main()

Answer 10

我认为以下是最简单的方法：

Img1 = img.resize((img.size),PIL.Image.ANTIALIAS)