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manipulation_classification.md

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Manipulation Classification

The manipulation classification workflow involves training a forensic analysis network (FAN) to identify subtle post-processing operations applied to the image. The model starts with the camera ISP and is followed by photo manipulations and a distribution channel. The FAN can access images after they have been degraded (e.g., down-sampled and compressed) by the channel. The model is shown below:

The main script for training the entire workflow is train_manipulation.py. The script accepts command line parameters to control the model. An example command is shown and explained below:

> python3 train_manipulation.py \
--epochs=2501                `# Run optimization for 2,500 epochs` \
--end 3                      `# Repeat the experiment 3 times` \
--patch 128                  `# The output from NIP should be 128x128 RGB image` \
--ds none                    `# Skip down-sampling in the channel` \
--jpeg 50                    `# Use JPEG with QF 50 as channel compression` \
--nip DNet                   `# Use DNet model for camera ISP` \
--cam D90                    `# Use Nikon D90 images` \
--manip sharpen:1,gaussian,jpeg:80,awgn:4,median `# List of included manipulations` \
--dir ./data/m/jpeg-nip+/50  `# Output directory` \
--train nip                  `# Models for optimization, here only NIP` \
--ln 0.1 --ln 0.05 --ln 0.01 `# Repeat training for these regularization strenghts`

The list of included manipulations is comma-separated and can include optional strength (after a colon). The results will be generated into:

data/m/{experiment label}/{quality level}/{camera}/{nip}/{regularization}/{run number}/
# Example 1: Experiments with learned compression on native camera output
data/m/7-raw/dcn+/32c/D90/DNet/fixed-nip/lc-0.0500/000
# Example 2: Experiment with ISP optimization with JPEG-50 and UNet NIP
data/m/7-raw/jpeg-nip+/50/D90/UNet/ln-0.1000/000/

The script generates:

  • training.json - JSON file with training progress and performance stats,
  • manip_validation_*.jpg - visual presentation of training progress (change of loss, PSNR, etc. over time)
  • nip_validation_*.jpg - current snapshot of patches developed by the NIP
  • models/{fan,...} - current snapshot of the models (FAN and other optimized models)

The results can be quickly visualized using the results.py script.

Batch Training

To simplify running experiments, the training script can be easily scripted (cf. train_manipulation_batch.sh).