DPI doesn't work for CMYK save

[007gzs]

What did you do?

save a jpeg image where param dpi

What did you expect to happen?

the new jpg image dpi same as the dpi param

What actually happened?

new file doesn't have dpi info

What are your OS, Python and Pillow versions?

• OS: window7/centos 7
• Python: 2.7.5/3.6.8
• Pillow: 6.1.0

    from PIL import Image
    img = Image.open("test1.jpg")
    print("test1.jpg", img.info.get('dpi'))
    other_img = Image.open("test2.jpg")
    print("test2.jpg", other_img.info.get('dpi'))
    img.paste(other_img.resize((200, 200), Image.LANCZOS), (0, 0))
    img.save("test3.jpg", dpi=(300, 300), quality="keep")
    new_img = Image.open("test3.jpg")
    print("test3.jpg", new_img.info.get('dpi'))

sample_file.zip

[radarhere]

Looks like this is because the image is in CMYK mode -

from PIL import Image
im = Image.new("CMYK", (100, 100))
im.save("out.jpg", dpi=(300, 300))

new_im = Image.open("out.jpg")
print("out.jpg", new_im.info.get('dpi'))  # out.jpg None

[radarhere]

You may or may not be interested in this as an immediate solution - remove the 'quality' argument, convert to RGB, and it works -

from PIL import Image
img = Image.open("test1.jpg")
print("test1.jpg", img.info.get('dpi'))
other_img = Image.open("test2.jpg")
print("test2.jpg", other_img.info.get('dpi'))
img.paste(other_img.resize((200, 200), Image.LANCZOS), (0, 0))
img.convert("RGB").save("test3.jpg", dpi=(300, 300))
new_img = Image.open("test3.jpg")
print("test3.jpg", new_img.info.get('dpi'))

[007gzs]

but I need to save it in CMYK format for my users to print.

[radarhere]

Is saving it as TIFF an option?

from PIL import Image
img = Image.open("test1.jpg")
print("test1.jpg", img.info.get('dpi'))
other_img = Image.open("test2.jpg")
print("test2.jpg", other_img.info.get('dpi'))
img.paste(other_img.resize((200, 200), Image.LANCZOS), (0, 0))
img.save("test3.tiff", dpi=(300, 300), quality="keep")
new_img = Image.open("test3.tiff")
print("test3.tiff", new_img.info.get('dpi'))

[radarhere]

Actually, I've realised that this is a duplicate of #1676