The command line tool djpeg can be used to dump the JPEG quantization tables. These tables affect the resulting quality of the image. Low values result in a better image quality with less artifacts and higher values result in lower image quality with more visible artifacts. For further information please refer to https://en.wikipedia.org/wiki/JPEG.
To check, if a poor image quality is caused by a high compression due to high quantization table values is can be useful to dump these tables and analyzing them.
Ready to use Docker image is available on DockerHub. https://hub.docker.com/repository/docker/ai2ys/djpeg-dump-qtables
To dump the quantization tables of a JPEG file run the following command.
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Local JPEG file
cat <jpeg file path> | docker run --rm -i ai2ys/djpeg-dump-qtables
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JPEG file from URL
curl -fsSL "<jpeg file url>" | docker run --rm -i ai2ys/djpeg-dump-qtables
Tested on Linux and Windows (with WSL2).
sudo apt-get update
sudo apt-get install -y libjpeg-progsUsing the command line tool djpeg locally the quantization tables of a file can be dumped using the following command.
djpeg -verbose -verbose -fast -outfile /dev/null <jpeg file path or url>This Docker image is based on "alpine" and therefore is small in size.
The batch script described below uses docker-compose for running the Docker container, which will also automatically build/pull the image, if not already available.
For batch processing multiple files at once use the bash script ./dump_jpeg_tables.sh as described below. As the bash script uses docker-compose having installed docker-compose is a prerequisite.
# processing single or multiple files
./dump_jpeg_tables <file paths or pattern, e.g. *.jpg>Example usage & output, dumping the tables for a single file.
$ ./dump_jpep_tables.sh img2.jpg
input file: 'img2.jpg'
libjpeg-turbo version 2.0.6 (build 20210314)
Copyright (C) 2009-2020 D. R. Commander
Copyright (C) 2015, 2020 Google, Inc.
Copyright (C) 2019 Arm Limited
Copyright (C) 2015-2016, 2018 Matthieu Darbois
Copyright (C) 2011-2016 Siarhei Siamashka
Copyright (C) 2015 Intel Corporation
Copyright (C) 2013-2014 Linaro Limited
Copyright (C) 2013-2014 MIPS Technologies, Inc.
Copyright (C) 2009, 2012 Pierre Ossman for Cendio AB
Copyright (C) 2009-2011 Nokia Corporation and/or its subsidiary(-ies)
Copyright (C) 1999-2006 MIYASAKA Masaru
Copyright (C) 1991-2017 Thomas G. Lane, Guido Vollbeding
Emulating The Independent JPEG Group's software, version 6b 27-Mar-1998
Start of Image
JFIF APP0 marker: version 1.02, density 1x1 0
Define Quantization Table 0 precision 0
5 3 3 5 7 12 15 18
4 4 4 6 8 17 18 16
4 4 5 7 12 17 21 17
4 5 7 9 15 26 24 19
5 7 11 17 20 33 31 23
7 10 16 19 24 31 34 28
15 19 23 26 31 36 36 30
22 28 28 29 34 30 31 30
Define Quantization Table 1 precision 0
5 5 7 14 30 30 30 30
5 6 8 20 30 30 30 30
7 8 17 30 30 30 30 30
14 20 30 30 30 30 30 30
30 30 30 30 30 30 30 30
30 30 30 30 30 30 30 30
30 30 30 30 30 30 30 30
30 30 30 30 30 30 30 30
Start Of Frame 0xc0: width=30, height=20, components=3
Component 1: 2hx2v q=0
Component 2: 1hx1v q=1
Component 3: 1hx1v q=1
Define Huffman Table 0x00
0 1 5 1 1 1 1 1
1 0 0 0 0 0 0 0
Define Huffman Table 0x10
0 2 1 3 3 2 4 3
5 5 4 4 0 0 1 125
Define Huffman Table 0x01
0 3 1 1 1 1 1 1
1 1 1 0 0 0 0 0
Define Huffman Table 0x11
0 2 1 2 4 4 3 4
7 5 4 4 0 1 2 119
Start Of Scan: 3 components
Component 1: dc=0 ac=0
Component 2: dc=1 ac=1
Component 3: dc=1 ac=1
Ss=0, Se=63, Ah=0, Al=0
End Of Image