How to perform JPEG compression in Python without writing/reading

Question

I'd like to work directly with compressed JPEG images. I know that with PIL/Pillow I can compress an image when I save it, and then read back the compressed image - e.g.

from PIL import Image
im1 = Image.open(IMAGE_FILE)
IMAGE_10 = os.path.join('./images/dog10.jpeg')
im1.save(IMAGE_10,"JPEG", quality=10)
im10 = Image.open(IMAGE_10)

but, I'd like a way to do this without the extraneous write and read. Is there some Python package with a function that will take an image and quality number as inputs and return a jpeg version of that image with the given quality?

https://gist.github.com/rigoneri/4716919 – Ajay Jun 11 '15 at 04:38 — Ajay, Jun 11 '15 at 04:38
You can write to StringIO instead of a file. – swstephe Jun 11 '15 at 04:42 — swstephe, Jun 11 '15 at 04:42

score 19 · Accepted Answer · edited Aug 27 '19 at 07:50

19

For in-memory file-like stuff, you can use StringIO. Take a look:

from io import StringIO # "import StringIO" directly in python2
from PIL import Image
im1 = Image.open(IMAGE_FILE)

# here, we create an empty string buffer    
buffer = StringIO.StringIO()
im1.save(buffer, "JPEG", quality=10)

# ... do something else ...

# write the buffer to a file to make sure it worked
with open("./photo-quality10.jpg", "w") as handle:
    handle.write(buffer.contents())

If you check the photo-quality10.jpg file, it should be the same image, but with 10% quality as the JPEG compression setting.

edited Aug 27 '19 at 07:50

M.T

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answered Jun 11 '15 at 04:45

Sam Gammon

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Doesn't work for me with Python 3.5. I changed `buffer = StringIO.String()` to `buffer = StringIO()` and imported `from io import StringIO`, but when I try to do `im1.save()` it crashes with `TypeError: string argument expected, got 'bytes'` – Groosha Nov 16 '16 at 16:39
1

I think it's supposed to be: `buffer=StringIO.StringIO()` – Mark Walker Jun 11 '17 at 06:15
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Now you have to use BytesIO insted of StringIO eg `from io import BytesIO` ; `buffer = BytesIO()` – Andrea993 Oct 28 '20 at 11:26
@Andrea993 I followed your update but got this error: `handle.write(buffer.contents()) … AttributeError: '_io.BytesIO' object has no attribute 'contents'` – Madamadam Sep 09 '21 at 22:40
I had to change: `with open("./photo-quality10.jpg", "wb") as handle: handle.write(buffer.getbuffer())` – DavidBu Sep 27 '21 at 15:53

score 11 · Answer 2 · edited May 23 '17 at 12:25

11

Using BytesIO

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

def generate(self, image, format='jpeg'):
    im = self.generate_image(image)
    out = BytesIO()
    im.save(out, format=format,quality=75)
    out.seek(0)
    return out

StringIO is missing in Python3.0, ref to : StringIO in python3

edited May 23 '17 at 12:25

Community

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answered Jan 24 '17 at 01:39

Super Engine

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How to perform JPEG compression in Python without writing/reading

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