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?

Answer 1

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.