Python PIL, preserve quality when resizing and saving

Question

I have a large image, which I resize in PIL so that it is 250 pixels wide. This is the width that it will be shown on my website.

However, the resolution is really bad. I see that it has changed the dpi from 180 to 96. If I resize the image in a program like Windows Paint then it maintains the 180 dpi. This Paint-resized image looks a lot better on my website. (The paint-resized image is 40kb while the PIL resized image is 16kb)

How do I maintain the dpi (or set it to some max that looks good on websites)

I resize this using PIL:

image = image.resize((new_width, new_height), Image.ANTIALIAS)
image.save(filepath)

I have tried:

dpi = image.info['dpi']  # (180, 180)
image.save(filepath, dpi = dpi)

but it makes no difference. The dpi is 180, but the resolution is still bad. I'm guessing that the dpi needs to be set during resizing?

EDIT:

The issue seems to be the saving, not the resizing. Even if I start with the Paint-resized image (and therefore do not resize the image in PIL), it still saves it as the crappy quality 96 dpi (16kb) intead of keeping it as it is.

Paint just ignores the DPI. But so do web browsers, unless you're specifically doing Retina-specific (or non-Apple-equivalent) CSS. If it's 250 pixels wide, and lay it out in a 250-pixel `img` tag, the DPI is irrelevant. — abarnert, Oct 15 '13 at 18:21
Something is different because the 40kb image looks way better than the 16kb image even though both are 250px wide. — user984003, Oct 15 '13 at 18:22
@user984003: What format are you saving the file in? Is it JPG or something else lossy? — abarnert, Oct 15 '13 at 18:23
@user984003: Then that's almost certainly your problem, not the DPI. — abarnert, Oct 15 '13 at 18:26

score 13 · Accepted Answer · edited May 23 '17 at 12:34

13

Thanks to the discussion with abarnert, I (he) realized that the issue was the saving, not the resizing.

And then I was able to find this, which solved the issue:

image_fullsize.save(filepath+name_fullsize, quality=95)

from here: How to adjust the quality of a resized image in Python Imaging Library?

edited May 23 '17 at 12:34

Community

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answered Oct 15 '13 at 18:58

user984003

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quality was the answer to me. – Vadim Aug 08 '19 at 09:18
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worked perfectly! – sdasara Feb 03 '21 at 21:43
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img.save('test.jpg', quality=100, subsampling=0) https://jdhao.github.io/2019/07/20/pil_jpeg_image_quality/ – Atendra Gautam Jul 21 '22 at 04:57

Python PIL, preserve quality when resizing and saving

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