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

Question

Is there an obvious way to do this that I'm missing? I'm just trying to make thumbnails.

Solution 1

Define a maximum size. Then, compute a resize ratio by taking min(maxwidth/width, maxheight/height).

The proper size is oldsize*ratio.

There is of course also a library method to do this: the method Image.thumbnail.
Below is an (edited) example from the PIL documentation.

import os, sys
import Image

size = 128, 128

for infile in sys.argv[1:]:
    outfile = os.path.splitext(infile)[0] + ".thumbnail"
    if infile != outfile:
        try:
            im = Image.open(infile)
            im.thumbnail(size, Image.ANTIALIAS)
            im.save(outfile, "JPEG")
        except IOError:
            print "cannot create thumbnail for '%s'" % infile

Solution 2

This script will resize an image (somepic.jpg) using PIL (Python Imaging Library) to a width of 300 pixels and a height proportional to the new width. It does this by determining what percentage 300 pixels is of the original width (img.size[0]) and then multiplying the original height (img.size[1]) by that percentage. Change "basewidth" to any other number to change the default width of your images.

from PIL import Image

basewidth = 300
img = Image.open('somepic.jpg')
wpercent = (basewidth/float(img.size[0]))
hsize = int((float(img.size[1])*float(wpercent)))
img = img.resize((basewidth,hsize), Image.ANTIALIAS)
img.save('somepic.jpg')

Solution 3

I also recommend using PIL's thumbnail method, because it removes all the ratio hassles from you.

One important hint, though: Replace

im.thumbnail(size)

with

im.thumbnail(size,Image.ANTIALIAS)

by default, PIL uses the Image.NEAREST filter for resizing which results in good performance, but poor quality.

Solution 4

Based in @tomvon, I finished using the following (pick your case):

a) Resizing height (I know the new width, so I need the new height)

new_width  = 680
new_height = new_width * height / width 

b) Resizing width (I know the new height, so I need the new width)

new_height = 680
new_width  = new_height * width / height

Then just:

img = img.resize((new_width, new_height), Image.ANTIALIAS)

Solution 5

from PIL import Image

img = Image.open('/your image path/image.jpg') # image extension *.png,*.jpg
new_width  = 200
new_height = 300
img = img.resize((new_width, new_height), Image.ANTIALIAS)
img.save('output image name.png') # format may what you want *.png, *jpg, *.gif

View more solutions

Comments

[tomvon]

If you are using this script in Zope as an External method you will need the line "from PIL import Image" to avoid namespace clashes with Zope's "Image".

[gnud]

Like it says, the example was from the pil documentation, and that example (still) doesn't use the antialias flag. Since it's probably what most people would want, though, I added it.

[eugene]

PIL sets the height of the new image to the size given(128 here) and calculate the width to keep the aspect ratio. Is there a way to fix the width instead of height? maybe I'll ask this in separate question.

[gnud]

@Eugene: try something like s= img.size(); ratio = MAXWIDTH/s[0]; newimg = img.resize((s[0]*ratio, s[1]*ratio), Image.ANTIALIAS)? (that's for floating point division though :)

[mt88]

Does using the above guarantee that the final saved image will be 128x128?

[Joshmaker]

Note that ANTIALIAS is no longer preferred for users of the popular Pillow fork of PIL. pillow.readthedocs.org/en/3.0.x/releasenotes/…

[Zacharious]

Your variables are all mixed up. Your post says resizing width, and then resizes height. And in the resize call, you are using the new_width for both height and width?

[Mark]

To build on that, ANTIALIAS is not needed from Pillow 2.5 and above.

[Mo Beigi]

Suggested a fix for that @Zachafer

[So S]

The Python 3 documentation for PIL says that thumbnail only works if the resulting image is smaller than the original one. Because of that I would guess that using resize is the better way.

[imrek]

This code gets me a 0 byte output file sompic.jpg. Why does this happen? I'm using Python 3.x

[imrek]

– Update: the same happens in Python 2.7.

[imrek]

I may have figured out. If you are saving a .jpeg, use img.save('sompic.jpg', 'JPEG').

[Fred Wu]

nit: there is no PIL.Image.ANTIALIAS option for resize, should actually be PIL.Image.LANCZOS, although they are both 1 in value, see pillow.readthedocs.io/en/3.1.x/reference/…

[Jose Luis de la Rosa]

The solution provided by @tomvon worked better for me because included how to calculate the ratio

[Daniel Möller]

Differences between thumbnail and resize?

[codezjx]

By default PIL save() method is poor quality, you can use image.save(file_path, quality=quality_value) to change the quality.

[Arpit Singh]

Can we crop the image in the same way?

[gnud]

@ArpitSingh to crop, use the Image.crop method - pillow.readthedocs.io/en/3.1.x/reference/…

[J'e]

@FredWu PIL.Image.ANTIALIAS is in PIL version 1.1.7. This comes with Anaconda3 v5.x

[pnd]

the docs say: In Pillow 2.5 the default filter for thumbnail() was changed from NEAREST to ANTIALIAS

[Marc Maxmeister]

tested and WORKED with python 2.7.15, and also works with 'PNG' files without need for editing

[Anytoe]

resize_contain looks actually quite useful!

[burny]

This does not keep the aspect ratio of the source image. It forces the image to 200x300 and will result in a squeezed or stretched image.

[burny]

With this, you can only decrease the size of an image. It is not possible to increase the size with Image.thumbnail.

[Black Thunder]

Better convert them to integer

[AMC]

This does not answer the question in any way.

[Ronen Ness]

This rotate some images (more info and solution here stackoverflow.com/questions/4228530/…)

[Anthony]

What is display() and where is it located?

[Qinjie]

@Anthony, display() is an iPython function and can be used in Jupyter Notebook to display images.

[max]

Unfortunately, this does not answer to the question, which explicitly addresses the library PIL -- and it does not keep the aspect ratio!. Further, you may provide a sort description of your approach to explain your thoughts

[Boz]

Could've just used .thumbnail from PIL, your solution doesn't work on increasing size, just decreasing.

[Robin]

Got error : integer argument expected, got float

[Robin]

Wrong answer for the op. The question was 'How do I resize an image using PIL and maintain its ASPECT RATIO?"

[Robin]

This works fine. Instead of saving the image with a new name, can I pass it directly to a canvas or frame?

[Robin]

I like the image.show()