Version 1 - December 2017 Automatic JPEG Grid Detection with Controlled False Alarms, and Its Image Forensic Applications
Version 2 - January 2020 Local JPEG Grid Detector via Blocking Artifacts
by Rafael Grompone von Gioi grompone@gmail.com and Tina Nikoukhah tinanikoukhah@gmail.com
This program implements a local a-contrario detector of the JPEG block origin.
The following libraries are required for image input/output:
- libpng
- LibTIFF
- libjpeg
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src/god.c: Main code.
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src/acontrario.c and src/acontrario.h: A contrario formulation.
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src/windows.c and src/windows.h: Functions used for the voting process.
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src/misc.c and src/misc.h: Useful functions.
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README.md: this file.
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LICENSE: GNU AFFERO GENERAL PUBLIC LICENSE Version 3.
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Makefile: Compilation instructions.
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src/iio.c and src/iio.h: iio code and header.
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*.png: Test images.
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create_svg.py: Creates final masks from txt files to svg files. A typical execution is as follows:
python create_svg.py luminance.png list_windows.txt > <output.svg>
The compiling instruction is
makeor if you want the code to be parallel
make openmpfrom the directory where the source codes and the Makefile are located.
To verify a correct compilation you can apply the algorithm to the test images 'pelican.png' and 'roma.png'. This can be done by executing:
make testThis should print the following message:
test on pelican.png
===================
./god pelican.png 128
image size: 512 x 512
window step size: 128
number of meaningful windows 32 of 36 (88 %)
number of windows (meaningful votes) for each JPEG grid origin:
0 0 0 0 0 0 32 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
best log(NFA) for each JPEG grid origin:
- - - - - - -91.5 -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
number of different meaningful grids: 1
most meaningful grid origin 6 0 with NFA: 10^-91.4726
most meaningful grid different from (0,0), the image may have been cropped!
test on roma.png
================
./god roma.png 128
image size: 512 x 512
window step size: 128
number of meaningful windows 0 of 36 (0 %)
number of windows (meaningful votes) for each JPEG grid origin:
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
best log(NFA) for each JPEG grid origin:
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
- - - - - - - -
number of different meaningful grids: 0
no meaningful grid found
no suspicious traces found in the image with the performed analysis.
The program is executed as:
god
(use ./god if the command is not included in the current path). That should print the following usage:
Error: use: god <image> <window_step>
The command takes an input image as argument. Any image file format handled by Enric Meinhardt-Llopis' IIO library can be used. This includes, for example, PNG, JPG, TIFF, PPM, PGM.
A typical execution is as follows:
./god pelican.png 128
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luminance.png: Luminance image.
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cross_diff.png: Cross-difference filter applied to the image.
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list_windows.txt: Attributes for each window. Each line is composed of eight numbers separated by spaces, that are: top left coordinate x of the window, top left coordinate y of the window, bottom right x coordinate of the window, bottom right y coordinate of the window, log NFA x, log NFA y, most significant grid x coordinate, most significant grid y coordinate. For example, the line:
1 1 200 200 -407.534 -330.733 0 0
means that the window starting at pixel (1,1) to (200,200) voted horizontally with a NFA at 10^-407.534 and vertically at 10^-330.733 for the grid origin (0,0).
Copyright (c) 2018-2019 Rafael Grompone von Gioi grompone@gmail.com Copyright (c) 2018-2019 Tina Nikoukhah tina.nikoukhah@gmail.com
GOD is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
GOD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License along with this program. If not, see https://www.gnu.org/licenses/.
We would be grateful to receive any comment, especially about errors, bugs, or strange results.