How to change the dpi or density when saving images using PIL

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I'm trying to compress a jpg file using PIL (to be more specific, Pillow)

I know images can be compressed by doing this: 

from PIL import Image
im = Image.open(img_path)
im = im.resize(new_size, Image.ANTIALIAS)
im.save(output_path, optimize=True, quality=50)

But I want to go further by tweaking more params, like this: 

im.save(output_path, optimize=True, quality=50, jfif_unit=1, dpi=(72,72), jfif_density=(72,72))

Unfortunately, it does not change dpi or density at all. How am I suppose to achieve that?

python-imaging-library python-3.x
1 Answers

With a little help from some articles here and there I came up with the below:

def set_image_dpi_resize(image):
    """
    Rescaling image to 300dpi while resizing
    :param image: An image
    :return: A rescaled image
    """
    length_x, width_y = image.size
    factor = min(1, float(1024.0 / length_x))
    size = int(factor * length_x), int(factor * width_y)
    image_resize = image.resize(size, Image.ANTIALIAS)
    temp_file = tempfile.NamedTemporaryFile(delete=False, suffix='1.png')
    temp_filename = temp_file.name
    image_resize.save(temp_filename, dpi=(300, 300))
    return temp_filename

The above changes the dpi (to 300) and resizes the image. It saves all the results to a temporary image.

Though you may not want to change the size sometimes but only the dpi, therefore you can use the below:

def set_image_dpi(image):
    """
    Rescaling image to 300dpi without resizing
    :param image: An image
    :return: A rescaled image
    """
    image_resize = image
    temp_file = tempfile.NamedTemporaryFile(delete=False, suffix='.png')
    temp_filename = temp_file.name
    image_resize.save(temp_filename, dpi=(300, 300))
    return temp_filename

For all the above you will need two imports:

from PIL import Image
import tempfile

I understand that if you run a code to check many images in batch (e.g. I am looping through thousands of photos, doing this operation for each one of them) you do not want your App Data temp folder to be full with temps. Therefore I also have a delete close method (to close the file) and a delete method (to delete it from my temp). Please note that you cannot delete it without closing it:

def close_image(image):
    """
    Closes opened image
    :param image: An image
    :return: None
    """
    image.close()


def removing_file(path):
    """
    Removing file by path
    :param path: The path of a file
    :return: None
    """
    # Try/except library import
    try:
        import os  # Miscellaneous OS library
    except ImportError as ImportException:
        raise ImportError("Cannot import needed libraries. Please contact administrator and give the code FN0001")
    os.remove(path)

Hope it helps.

user_128416090
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