Thumbnail generation keeping the aspect ratio of the target width and height

thumbnails.py

# vim: set fileencoding: utf-8 :
#
import os

try:
    from PIL import Image
except ImportError:
    import Image

try:
    from cStringIO import StringIO as StringIO
except ImportError:
    from StringIO import StringIO



def get_thumbnail(img_filename, img_data, new_width, new_height, crop=True):
    """
    Create a thumbnailed version of the image.

    `img_filename` is used for detecting the image format using the filename
    extension. `img_data` is a `str` containing the bytes from the file.
    `size_x` and `size_y` denote the desired image format.

    If `crop`, then crop the image before calculating the thumbnail. Depending
    on the target size and the resulting ratio parts of the image will be
    removed either on the top/bottom or left/right parts.

    """
    img = Image.open(StringIO(img_data))
    ratio = float(new_height)/new_width

    if crop:
        # crop the image either on right and left or on top and bottom
        (width, height) = img.size
        ratio_orig = float(height)/width
        left, top, right, bottom = 0, 0, width, height

        if ratio_orig > ratio:
            # crop from the top and bottom of the original image
            top = int((height - (width * ratio)) / 2)
            bottom = height - top

        elif ratio_orig < ratio:
            # crop from the left and right of the original image
            left = int((width - (height / ratio)) / 2)
            right = width - left

        img = img.crop((left, top, right, bottom))

    img.thumbnail((new_width, new_height), Image.ANTIALIAS)
    thumbnail = StringIO()
    ext = os.path.splitext(img_filename)[1][1:].upper()
    img.save(thumbnail, ext.replace('JPG', 'JPEG'))
    return thumbnail.getvalue()