Python / Pillow: How to scale an image

问题

Suppose I have an image which is 2322px x 4128px. How do I scale it so that both the width and height are both less than 1028px?

I won't be able to use Image.resize (https://pillow.readthedocs.io/en/latest/reference/Image.html#PIL.Image.Image.resize) since that requires me to give both the new width and height. What I plan to do is (pseudo code below):

if (image.width or image.height) > 1028:
    if image.width > image.height:
        tn_image = image.scale(make width of image 1028)
        # since the height is less than the width and I am scaling the image
        # and making the width less than 1028px, the height will surely be
        # less than 1028px
    else: #image's height is greater than it's width
        tn_image = image.scale(make height of image 1028)

I am guessing I need to use Image.thumbnail, but according to this example (http://pillow.readthedocs.org/en/latest/reference/Image.html#create-thumbnails) and this answer (How do I resize an image using PIL and maintain its aspect ratio?), both the width and the height are provided in order to create the thumbnail. Is there any function which takes either the new width or the new height (not both) and scales the entire image?

回答1:

Noo need to reinvent the wheel, there is the Image.thumbnail method available for this:

maxsize = (1028, 1028)
image.thumbnail(maxsize, PIL.Image.ANTIALIAS)

Ensures the resulting size is not bigger than the given bounds while maintains the aspect ratio.

Specifying PIL.Image.ANTIALIAS applies a high-quality downsampling filter for better resize result, you probably want that too.

回答2:

Use Image.resize, but calculate both width and height.

if image.width > 1028 or image.height > 1028:
    if image.height > image.width:
        factor = 1028 / image.height
    else:
        factor = 1028 / image.width
    tn_image = image.resize((int(image.width * factor), int(image.height * factor)))

来源：https://stackoverflow.com/questions/24745857/python-pillow-how-to-scale-an-image