PIL does not recognize dpi of some jpeg images #8632
Description
It seems that for some jpeg images Pillow does not report correct DPI.
For instance, I created with Gimp a PNG file of size 1x1 pixels with resolution of 123 dpi (test2.png) and then I converted it with imagemagick to test2.jpg. The command was:
$ convert --version
Version: ImageMagick 6.9.10-23 Q16 x86_64 20190101 https://imagemagick.org
Copyright: © 1999-2019 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP
Delegates (built-in): bzlib djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png tiff webp wmf x xml zlib
$ convert test2.png test2.jpg
I attach both files (zipped, as images.zip). When I use Pillow to read dpi of test2.jpg, this is what I get:
$ ipython3
In [1]: from PIL import Image
In [2]: print(Image.__version__)
10.4.0
In [3]: Image.open('test2.jpg').info
Out[3]: {'jfif': 257, 'jfif_version': (1, 1), 'jfif_unit': 2, 'jfif_density': (48, 48)}
I see that jfif_density and jfif_unit pair is correct (48 px/cm is 123 px/in), but I think that this info structure should also contain 'dpi' entry - and it does not contain it. For instance, when I create a similar jpeg file directly from Gimp (test3.jpg, also attached), it works as I want:
$ ipython3
/usr/lib/python3/dist-packages/IPython/core/interactiveshell.py:935: UserWarning: Attempting to work in a virtualenv. If you encounter problems, please install IPython inside the virtualenv.
warn("Attempting to work in a virtualenv. If you encounter problems, please "
Python 3.8.10 (default, Nov 7 2024, 13:10:47)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.13.0 -- An enhanced Interactive Python. Type '?' for help.
In [1]: from PIL import Image
In [2]: print(Image.__version__)
10.4.0
In [3]: Image.open('test3.jpg').info
Out[3]:
{'jfif': 257,
'jfif_version': (1, 1),
'dpi': (123, 123),
'jfif_unit': 1,
'jfif_density': (123, 123),
'exif': b'Exif\x00\x00II*\x00\x08\x00\x00\x00\x07\x00\x0e\x01\x02\x00\x12\x00\x00\x00b\x00\x00\x00\x1a\x01\x05\x00\x01\x00\x00\x00t\x00\x00\x00\x1b\x01\x05\x00\x01\x00\x00\x00|\x00\x00\x00(\x01\x03\x00\x01\x00\x00\x00\x02\x00\x00\x001\x01\x02\x00\r\x00\x00\x00\x84\x00\x00\x002\x01\x02\x00\x14\x00\x00\x00\x92\x00\x00\x00i\x87\x04\x00\x01\x00\x00\x00\xa6\x00\x00\x00\x00\x00\x00\x00Created with GIMP\x00{\x00\x00\x00\x01\x00\x00\x00{\x00\x00\x00\x01\x00\x00\x00GIMP 2.10.18\x00\x002024:12:28 07:13:34\x00\x02\x00\x86\x92\x07\x00\x19\x00\x00\x00\xc4\x00\x00\x00\x01\xa0\x03\x00\x01\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00Created with GIMP\x00',
'progressive': 1,
'progression': 1}