Resize image maintaining aspect ratio AND making portrait and landscape images exact same size?

问题

Currently I am using:

    os.chdir(album.path)
    images = glob.glob('*.*')

    # thumbs size
    size = 80,80

    for image in images:
        #create thumb
        file, ext = os.path.splitext(image)
        im = Image.open(os.path.join(album.path,image))
        im.thumbnail(size, Image.ANTIALIAS)
        thumb_path = os.path.join(album.path, 'thumbs', file + ".thumb" + ".jpeg")
        im.save(thumb_path)

Although this works, I end up with different sizes images (some are portrait and some are landscape), but I want all of the images to have an exact size. Maybe a sensible cropping?

UPDATE:

I don't mind cropping a small portion of the image. When I said sensible cropping I mean something like this algorythm:

if image is portrait:
    make width 80px
    crop the height (will be more than 80px)
else if image is landscape:
    make height 80px
    crop the width to 80px (will be more than 80px)

回答1:

Here is my take on doing a padded fit for an image:

#!/usr/bin/env python

from PIL import Image, ImageChops

F_IN = "/path/to/image_in.jpg"
F_OUT = "/path/to/image_out.jpg"

size = (80,80)

image = Image.open(F_IN)
image.thumbnail(size, Image.ANTIALIAS)
image_size = image.size

thumb = image.crop( (0, 0, size[0], size[1]) )

offset_x = max( (size[0] - image_size[0]) / 2, 0 )
offset_y = max( (size[1] - image_size[1]) / 2, 0 )

thumb = ImageChops.offset(thumb, offset_x, offset_y)
thumb.save(F_OUT)

It first uses the thumbnail operation to bring the image down to within your original bounds and preserving the aspect. Then it crops it back out to actually fill the size of your bounds (since unless the original image was square, it will be smaller now), and we find the proper offset to center the image. The image is offset to the center, so you end up with black padding but no image cropping.

Unless you can make a really sensible guess at a proper center crop without losing possible important image data on the edges, a padded fit approach will work better.

Update

Here is a version that can do either center crop or pad fit.

#!/usr/bin/env python

from PIL import Image, ImageChops, ImageOps

def makeThumb(f_in, f_out, size=(80,80), pad=False):

    image = Image.open(f_in)
    image.thumbnail(size, Image.ANTIALIAS)
    image_size = image.size

    if pad:
        thumb = image.crop( (0, 0, size[0], size[1]) )

        offset_x = max( (size[0] - image_size[0]) / 2, 0 )
        offset_y = max( (size[1] - image_size[1]) / 2, 0 )

        thumb = ImageChops.offset(thumb, offset_x, offset_y)

    else:
        thumb = ImageOps.fit(image, size, Image.ANTIALIAS, (0.5, 0.5))

    thumb.save(f_out)


source = "/path/to/source/image.JPG"

makeThumb(source, "/path/to/source/image_padded.JPG", pad=True)
makeThumb(source, "/path/to/source/image_centerCropped.JPG", pad=False)

回答2:

Obviously, you would need to crop or pad the images. You could do something like below to get a maximal centered crop according to the aspect ratio of the thumbnails (untested):

aspect = lambda size: float(size[0]) / float(size[1])
sa = aspect(size)
if aspect(im.size) > sa:
    width = int(sa * im.size[1])
    left = (im.size[0] - width) / 2
    im = im.crop((left, 0, left + width, im.size[1]))
else:
    height = int(im.size[0] / sa)
    top = (im.size[1] - height) / 2
    im = im.crop((0, top, im.size[0], top + height))
im.thumbnail(size, Image.ANTIALIAS)

回答3:

If you use easy-thumbnails you'll need to set crop to True and upscale to True to always fill-up the space (have the exact same dimensions).

Ex: makes image_2 fits in image_1 dimensions:

    thumbnailer = get_thumbnailer(image_2)
    thumbnail = thumbnailer.generate_thumbnail(thumbnail_options={
        'crop': True,
        'upscale': True,
        'size': image_1.size
    })
    image_2 = thumbnail.image

来源：https://stackoverflow.com/questions/9103257/resize-image-maintaining-aspect-ratio-and-making-portrait-and-landscape-images-e