Prerequisites: Python Imaging Library
This function scales a given image (provided as binary data in any format the PIL supports) to a specified size.
If the force parameter is True, the function makes sure that the resulting image is exactly the specified size, cropping and scaling it as necessary (but never distorting it) to make sure the whole image area is filled out.
If force is False, it simply uses the thumbnail function provided by the PIL, which preserves the image aspect ratio and does not increase the image dimensions beyond those of the original file, so you may not get an image that has the exact dimensions you specified.
The result image is returned as JPEG data.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | def rescale(data, width, height, force=True):
"""Rescale the given image, optionally cropping it to make sure the result image has the specified width and height."""
import Image as pil
from cStringIO import StringIO
max_width = width
max_height = height
input_file = StringIO(data)
img = pil.open(input_file)
if not force:
img.thumbnail((max_width, max_height), pil.ANTIALIAS)
else:
src_width, src_height = img.size
src_ratio = float(src_width) / float(src_height)
dst_width, dst_height = max_width, max_height
dst_ratio = float(dst_width) / float(dst_height)
if dst_ratio < src_ratio:
crop_height = src_height
crop_width = crop_height * dst_ratio
x_offset = float(src_width - crop_width) / 2
y_offset = 0
else:
crop_width = src_width
crop_height = crop_width / dst_ratio
x_offset = 0
y_offset = float(src_height - crop_height) / 3
img = img.crop((x_offset, y_offset, x_offset+int(crop_width), y_offset+int(crop_height)))
img = img.resize((dst_width, dst_height), pil.ANTIALIAS)
tmp = StringIO()
img.save(tmp, 'JPEG')
tmp.seek(0)
output_data = tmp.getvalue()
input_file.close()
tmp.close()
return output_data
|
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Comments
I didn't realize that "ANTIALIAS" was available under 'pil'. Or that 'pil' was lowercase... At any rate, I borrowed your scaling algorithm for my image resizer. Many thanks for writing code that "just works"!
It's flawlessly scaling nice little images.
While I understand that 'JPEG' is a nice normalization for file format, if I were to use this snippet in an unaltered form, I'd want it to have a switch for preserving the file type.
Never can please everyone :)
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Thanks for your example. While reading PIL docs I found out that you could drop lines 14 to 30 in favor of the following:
from PIL import ImageOps
img = ImageOps.fit(img, (max_width, max_height,), method=pil.ANTIALIAS)
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