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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?

arulmr
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frederix
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9 Answers9

53

Yes it will keep aspect ratio using thumbnail method:

image = Image.open(source_path)
image.thumbnail(size, Image.ANTIALIAS)
image.save(dest_path, "JPEG")
Maksym Kozlenko
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    ANTIALIAS method name update: As of 2.7.0, all resize methods are ANTIALIAS & the real (new) name for the specific ANTIALIAS filter is LANCZOS. (Tho antialias is currently left for backwards compatibility) https://pillow.readthedocs.io/en/3.0.x/releasenotes/2.7.0.html#antialias-renamed-to-lanczos – hbrannan Feb 22 '19 at 04:56
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    Note thought that the thumbnail method isn't equivalent in other regards - it won't blow up images to larger than they were, and it acts on the image object and doesn't return anything. – kloddant Nov 14 '19 at 22:54
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    Also note, this function modifies the `Image` object in place. If you need to use the full resolution image as well, apply this method to a `copy()` of the original image, per the [docs](https://pillow.readthedocs.io/en/stable/reference/Image.html#Image.thumbnail). – Viglione Mar 23 '22 at 18:28
21

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.

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Kugel
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  • the linked answer uses - im.thumbnail , is this suggested in general? Or just when working with thumbnails – baxx Apr 08 '21 at 10:12
7

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?

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Luke
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6

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.

Lahiru Karunaratne
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    you need to assign the im back. im.resize is not modifying the original image. `im = im.resize((width//2, height//2))` – York Yang Aug 13 '20 at 09:35
6

Recent Pillow version (since 8.3) have the following method to have an image resized to fit in given box with keeping aspect ratio.

image = ImageOps.contain(image, (2048,2048))
fabien-michel
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4

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))
Shreyas Vedpathak
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  • I get an error when I try your solution. I get "_tkinter.TclError: image "" doesn't exist. Any idea? – Robin Feb 23 '22 at 05:06
  • @Robin can you post more information about it? Like how are you loading the image, is the extension or path right? – Shreyas Vedpathak Feb 23 '22 at 13:30
  • @ Shreyas. Thank you. I am not trying to save the file. I want it to load on a canevas. The canevas takes a portion of the monitor, so I cannot have the image pass the border of the frame. Your solution works when I save the file, but not if I want to use the resized file in a canevas. Any idea if it is possible to redirect the resized image to a canevas with our code? – Robin Feb 23 '22 at 22:31
3

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')
Ruhul Amin
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1

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

talljosh
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-1

I think following is the easiest way to do:

Img1 = img.resize((img.size),PIL.Image.ANTIALIAS)
Salahuddin Ahmed
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Sourabh Verma
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