Question

Scrapy framework has the built-in capability to generate thumbnails. Is there any way to set a desired size for only one side in IMAGES_THUMBS to keep the original image proportion though?

Answer 1

Had a look at Image.py in PIL module and it actually preserves the proportions automatically. The problem though that you can’t generate thumbnails of certain width or certain height – PIL will pick up either width or height depending on the original image and there’s no way to change that. Here’s the code that does the calculations.

    # preserve aspect ratio
    x, y = self.size
    if x > size[0]: y = max(y * size[0] / x, 1); x = size[0]
    if y > size[1]: x = max(x * size[1] / y, 1); y = size[1]
    size = x, y

The hacky way to do that is to set a really big value for the side you don’t care about, then the other side will always be used to generate the thumbnails.
So this does the trick for me:

 IMAGES_THUMBS = {
    'thumbs': (80, 100000),
 }

Definitely not the best way, and it may stop working with the future versions of PIL but it’s good enough for now.
Still interested in a better way to achieve the same thing.