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.

Answer 1

My ugly example.

Function get file like: "pic[0-9a-z].[extension]", resize them to 120x120, moves section to center and save to "ico[0-9a-z].[extension]", works with portrait and landscape:

def imageResize(filepath):
    from PIL import Image
    file_dir=os.path.split(filepath)
    img = Image.open(filepath)

    if img.size[0] > img.size[1]:
        aspect = img.size[1]/120
        new_size = (img.size[0]/aspect, 120)
    else:
        aspect = img.size[0]/120
        new_size = (120, img.size[1]/aspect)
    img.resize(new_size).save(file_dir[0]+'/ico'+file_dir[1][3:])
    img = Image.open(file_dir[0]+'/ico'+file_dir[1][3:])

    if img.size[0] > img.size[1]:
        new_img = img.crop( (
            (((img.size[0])-120)/2),
            0,
            120+(((img.size[0])-120)/2),
            120
        ) )
    else:
        new_img = img.crop( (
            0,
            (((img.size[1])-120)/2),
            120,
            120+(((img.size[1])-120)/2)
        ) )

    new_img.save(file_dir[0]+'/ico'+file_dir[1][3:])

Answer 2

I resizeed the image in such a way and it's working very well

from io import BytesIO
from django.core.files.uploadedfile import InMemoryUploadedFile
import os, sys
from PIL import Image


def imageResize(image):
    outputIoStream = BytesIO()
    imageTemproaryResized = imageTemproary.resize( (1920,1080), Image.ANTIALIAS) 
    imageTemproaryResized.save(outputIoStream , format='PNG', quality='10') 
    outputIoStream.seek(0)
    uploadedImage = InMemoryUploadedFile(outputIoStream,'ImageField', "%s.jpg" % image.name.split('.')[0], 'image/jpeg', sys.getsizeof(outputIoStream), None)

    ## For upload local folder
    fs = FileSystemStorage()
    filename = fs.save(uploadedImage.name, uploadedImage)

Answer 3

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

Answer 4

from PIL import Image
from resizeimage import resizeimage

def resize_file(in_file, out_file, size):
    with open(in_file) as fd:
        image = resizeimage.resize_thumbnail(Image.open(fd), size)
    image.save(out_file)
    image.close()

resize_file('foo.tif', 'foo_small.jpg', (256, 256))

I use this library:

pip install python-resize-image

Answer 5

I was trying to resize some images for a slideshow video and because of that, I wanted not just one max dimension, but a max width and a max height (the size of the video frame).
And there was always the possibility of a portrait video...
The Image.thumbnail method was promising, but I could not make it upscale a smaller image.

So after I couldn't find an obvious way to do that here (or at some other places), I wrote this function and put it here for the ones to come:

from PIL import Image

def get_resized_img(img_path, video_size):
    img = Image.open(img_path)
    width, height = video_size  # these are the MAX dimensions
    video_ratio = width / height
    img_ratio = img.size[0] / img.size[1]
    if video_ratio >= 1:  # the video is wide
        if img_ratio <= video_ratio:  # image is not wide enough
            width_new = int(height * img_ratio)
            size_new = width_new, height
        else:  # image is wider than video
            height_new = int(width / img_ratio)
            size_new = width, height_new
    else:  # the video is tall
        if img_ratio >= video_ratio:  # image is not tall enough
            height_new = int(width / img_ratio)
            size_new = width, height_new
        else:  # image is taller than video
            width_new = int(height * img_ratio)
            size_new = width_new, height
    return img.resize(size_new, resample=Image.LANCZOS)

Answer 6

Open your image file

from PIL import Image
im = Image.open("image.png")

Use PIL Image.resize(size, resample=0) method, where you substitute (width, height) of your image for the size 2-tuple.

This will display your image at original size:

display(im.resize((int(im.size[0]),int(im.size[1])), 0) )

This will display your image at 1/2 the size:

display(im.resize((int(im.size[0]/2),int(im.size[1]/2)), 0) )

This will display your image at 1/3 the size:

display(im.resize((int(im.size[0]/3),int(im.size[1]/3)), 0) )

This will display your image at 1/4 the size:

display(im.resize((int(im.size[0]/4),int(im.size[1]/4)), 0) )

etc etc