README.md

Meta Transfer Learning for Few Shot Semantic Segmentation using U-Net

• Meta Transfer Learning for Few Shot Semantic Segmentation using U-Net
  • Requirements
  • Characteristics
    • Model and Technique
    • Datasets
    • Losses
  • Code structure
  • Running Experiments
  • Hyperparameters and Options
  • Training Plots
  • Results
  • Acknowledgement

Requirements

PyTorch and Torchvision needs to be installed before running the scripts, together with PIL for data-preprocessing and tqdm for showing the training progress.

To run this repository, kindly install python 3.5 and PyTorch 0.4.0 with Anaconda.

You may download Anaconda and read the installation instruction on their official website: https://www.anaconda.com/download/

Create a new environment and install PyTorch and torchvision on it:

conda create --name segfew python=3.5
conda activate segfew
conda install pytorch=0.4.0 
conda install torchvision -c pytorch

Clone this repository:

git clone https://github.com/ahirsharan/MTL_Segmentation.git

Characteristics:

Model and Technique

• (U-Net) Convolutional Networks for Biomedical Image Segmentation (2015): [Paper]
• (Meta Tranfer Learning) Meta-Transfer Learning for Few-Shot Learning: [Paper]

Datasets

• COCO Stuff: For COCO, there is two partitions, CocoStuff10k with only 10k that are used for training the evaluation, note that this dataset is outdated, can be used for small scale testing and training, and can be downloaded here. For the official dataset with all of the training 164k examples, it can be downloaded from the official website.

• Few-Shot: For Few Shot(FSS1000), there are 1000 object classes folder each with 10 images with ground truth mask for segmentation. This dataset can be used for few shot learning and can be downloaded here.

Losses

In addition to the Cross-Entropy loss:

• Dice-Loss, which measures of overlap between two samples and can be more reflective of the training objective (maximizing the mIoU), but is highly non-convexe and can be hard to optimize.
• CE Dice loss, the sum of the Dice loss and CE, CE gives smooth optimization while Dice loss is a good indicator of the quality of the segmentation results.
• Focal Loss, an alternative version of the CE, used to avoid class imbalance where the confident predictions are scaled down.
• Lovasz Softmax lends it self as a good alternative to the Dice loss, where we can directly optimization for the mean intersection-over-union based on the convex Lovász extension of submodular losses (for more details, check the paper: The Lovász-Softmax loss).

Code Structure

The code structure is based on MTL-template and Pytorch-Segmentation.

.
|
├── FewShotPreprocessing.py     # utility to organise the Few-shot data into train,test and val set
|
|  
├── dataloader              
|   ├── dataset_loader.py       # data loader for pre datasets
|   ├── mdataset_loader.py      # data loader for meta task dataset
|   └── samplers.py             # samplers for meta task dataset(Few-Shot) 
|
|
├── models                      
|   ├── mtl.py                  # meta-transfer class
|   ├── unet_mtl.py             # unet class
|   └── conv2d_mtl.py           # meta-transfer convolution class
|
├── trainer                     
|   ├── pre.py                  # pre-train trainer class
|   └── meta.py                 # meta-train trainer class
|
|
├── utils                       
|   ├── gpu_tools.py            # GPU tool functions
|   ├── metrics.py              # Metrics functions
|   ├── losses.py               # Loss functions
|   ├── lovasz_losses.py        # Lovasz Loss function
|   └── misc.py                 # miscellaneous tool functions
|
├── main.py                     # the python file with main function and parameter settings
├── run_pre.py                  # the script to run pre-train phase
└── run_meta.py                 # the script to run meta-train and meta-test phases

Running Experiments

Run pretrain phase:

python run_pre.py

Run meta-train and meta-test phase:

python run_meta.py

Hyperparameters and Options

Hyperparameters and options in main.py.

• model_type The network architecture
• dataset Meta dataset
• phase pre-train, meta-train or meta-eval
• seed Manual seed for PyTorch, "0" means using random seed
• gpu GPU id
• dataset_dir Directory for the images
• max_epoch Epoch number for meta-train phase
• num_batch The number for different tasks used for meta-train
• shot Shot number, how many samples for one class in a task
• teshot Test-Shot number, how many samples for one class in a meta test task
• way Way number, how many classes in a task
• train_query The number of training samples for each class in a task
• val_query The number of test samples for each class in a task
• meta_lr1 Learning rate for SS weights
• meta_lr2 Learning rate for Base learner weights (meta task)
• base_lr Learning rate for the inner loop
• update_step The number of updates for the inner loop
• step_size The number of epochs to reduce the meta learning rates
• gamma Gamma for the meta-train learning rate decay
• init_weights The pretained weights for meta-train phase
• pre_init_weights The pretained weights for pre-train phase
• eval_weights The meta-trained weights for meta-eval phase
• meta_label Additional label for meta-train
• pre_max_epoch Epoch number for pre-train psase
• pre_batch_size Batch size for pre-train phase
• pre_lr Learning rate for pre-train pahse
• pre_gamma Gamma for the preteain learning rate decay
• pre_step_size The number of epochs to reduce the pre-train learning rate
• pre_custom_weight_decay Weight decay for the optimizer during pre-train

Training Plots

Pre-Train Phase

Mean IoU	CE Loss

Meta-Train Phase

Mean IoU	CE Loss

Meta-Val Phase

Mean IoU	CE Loss

Results

• The Pre-trained weights for both Pre-Train and Meta Tasks can be found here pertaining to Max-IoU.

• Some of the best results for 3-shot learning 😄 :

|-----------Image--------------Ground Truth---------------Prediction---------|

Acknowledgement

• Pytorch-Segmentation
• Meta-Transfer Learning for Few-Shot Learning