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https://github.com/bloodaxe/pytorch-toolbelt

PyTorch extensions for fast R&D prototyping and Kaggle farming
https://github.com/bloodaxe/pytorch-toolbelt

augmentation deep-learning focal-loss image-classification image-processing image-segmentation jaccard-loss kaggle machine-learning object-detection pipeline python pytorch segmentation test-time-augmentation tta

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PyTorch extensions for fast R&D prototyping and Kaggle farming

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README 

        
# Important Update



![ukraine-flag](docs/480px-Flag_of_Ukraine.jpg)



On February 24th, 2022, Russia declared war and invaded peaceful Ukraine. 

After the annexation of Crimea and the occupation of the Donbas region, Putin's regime decided to destroy Ukrainian nationality.

Ukrainians show fierce resistance and demonstrate to the entire world what it's like to fight for the nation's independence.



Ukraine's government launched a website to help russian mothers, wives & sisters find their beloved ones killed or captured in Ukraine - https://200rf.com & https://t.me/rf200_now (Telegram channel).

Our goal is to inform those still in Russia & Belarus, so they refuse to assault Ukraine. 



Help us get maximum exposure to what is happening in Ukraine, violence, and inhuman acts of terror that the "Russian World" has brought to Ukraine. 

This is a comprehensive Wiki on how you can help end this war: https://how-to-help-ukraine-now.super.site/ 



Official channels

* [Official account of the Parliament of Ukraine](https://t.me/verkhovnaradaofukraine)

* [Ministry of Defence](https://www.facebook.com/MinistryofDefence.UA)

* [Office of the president](https://www.facebook.com/president.gov.ua)

* [Cabinet of Ministers of Ukraine](https://www.facebook.com/KabminUA)

* [Center of strategic communications](https://www.facebook.com/StratcomCentreUA)

* [Minister of Foreign Affairs of Ukraine](https://twitter.com/DmytroKuleba)



Glory to Ukraine!



# Pytorch-toolbelt



A `pytorch-toolbelt` is a Python library with a set of bells and whistles for PyTorch for fast R&D prototyping and Kaggle farming:



## What's inside



* Easy model building using flexible encoder-decoder architecture.

* Modules: CoordConv, SCSE, Hypercolumn, Depthwise separable convolution and more.

* GPU-friendly test-time augmentation TTA for segmentation and classification

* GPU-friendly inference on huge (5000x5000) images

* Every-day common routines (fix/restore random seed, filesystem utils, metrics)

* Losses: BinaryFocalLoss, Focal, ReducedFocal, Lovasz, Jaccard and Dice losses, Wing Loss and more.

* Extras for [Catalyst](https://github.com/catalyst-team/catalyst) library (Visualization of batch predictions, additional metrics) 



Showcase: [Catalyst, Albumentations, Pytorch Toolbelt example: Semantic Segmentation @ CamVid](https://colab.research.google.com/drive/1OUPJYU7TzH5Vz1si6FBkooackuIlzaGr#scrollTo=GUWuiO5K3aUm)



# Why



Honest answer is "I needed a convenient way to re-use code for my Kaggle career". 

During 2018 I achieved a [Kaggle Master](https://www.kaggle.com/bloodaxe) badge and this been a long path. 

Very often I found myself re-using most of the old pipelines over and over again. 

At some point it crystallized into this repository. 



This lib is not meant to replace catalyst / ignite / fast.ai high-level frameworks. Instead it's designed to complement them.



# Installation



`pip install pytorch_toolbelt`



# How do I ... 



## Model creation



### Create Encoder-Decoder U-Net model



Below a code snippet that creates vanilla U-Net model for binary segmentation. 

By design, both encoder and decoder produces a list of tensors, from fine (high-resolution, indexed `0`) to coarse (low-resolution) feature maps. 

Access to all intermediate feature maps is beneficial if you want to apply deep supervision losses on them or encoder-decoder of object detection task, 

where access to intermediate feature maps is necessary.

 

```python

from torch import nn

from pytorch_toolbelt.modules import encoders as E

from pytorch_toolbelt.modules import decoders as D



class UNet(nn.Module):

    def __init__(self, input_channels, num_classes):

        super().__init__()

        self.encoder = E.UnetEncoder(in_channels=input_channels, out_channels=32, growth_factor=2)

        self.decoder = D.UNetDecoder(self.encoder.channels, decoder_features=32)

        self.logits = nn.Conv2d(self.decoder.channels[0], num_classes, kernel_size=1)



    def forward(self, x):

        x = self.encoder(x)

        x = self.decoder(x)

        return self.logits(x[0])

```



### Create Encoder-Decoder FPN model with pretrained encoder



Similarly to previous example, you can change decoder to FPN with contatenation. 



 ```python

from torch import nn

from pytorch_toolbelt.modules import encoders as E

from pytorch_toolbelt.modules import decoders as D



class SEResNeXt50FPN(nn.Module):

    def __init__(self, num_classes, fpn_channels):

        super().__init__()

        self.encoder = E.SEResNeXt50Encoder()

        self.decoder = D.FPNCatDecoder(self.encoder.channels, fpn_channels)

        self.logits = nn.Conv2d(self.decoder.channels[0], num_classes, kernel_size=1)



    def forward(self, x):

        x = self.encoder(x)

        x = self.decoder(x)

        return self.logits(x[0])

```



### Change number of input channels for the Encoder



All encoders from `pytorch_toolbelt` supports changing number of input channels. Simply call `encoder.change_input_channels(num_channels)` and first convolution layer will be changed.

Whenever possible, existing weights of convolutional layer will be re-used (in case new number of channels is greater than default, new weight tensor will be padded with randomly-initialized weigths).

Class method returns `self`, so this call can be chained.



```python

from pytorch_toolbelt.modules import encoders as E



encoder = E.SEResnet101Encoder()

encoder = encoder.change_input_channels(6)

```



## Misc



## Count number of parameters in encoder/decoder and other modules



When designing a model and optimizing number of features in neural network, I found it's quite useful to print number of parameters in high-level blocks (like `encoder` and `decoder`).

Here is how to do it with `pytorch_toolbelt`:



```python

from torch import nn

from pytorch_toolbelt.modules import encoders as E

from pytorch_toolbelt.modules import decoders as D

from pytorch_toolbelt.utils import count_parameters



class SEResNeXt50FPN(nn.Module):

    def __init__(self, num_classes, fpn_channels):

        super().__init__()

        self.encoder = E.SEResNeXt50Encoder()

        self.decoder = D.FPNCatDecoder(self.encoder.channels, fpn_channels)

        self.logits = nn.Conv2d(self.decoder.channels[0], num_classes, kernel_size=1)



    def forward(self, x):

        x = self.encoder(x)

        x = self.decoder(x)

        return self.logits(x[0])



net = SEResNeXt50FPN(1, 128)

print(count_parameters(net))

# Prints {'total': 34232561, 'trainable': 34232561, 'encoder': 25510896, 'decoder': 8721536, 'logits': 129}



```



### Compose multiple losses



There are multiple ways to combine multiple losses, and high-level DL frameworks like Catalyst offers way more flexible way to achieve this, but here's 100%-pure PyTorch implementation of mine:



```python

from pytorch_toolbelt import losses as L



# Creates a loss function that is a weighted sum of focal loss 

# and lovasz loss with weigths 1.0 and 0.5 accordingly.

loss = L.JointLoss(L.FocalLoss(), L.LovaszLoss(), 1.0, 0.5)

```



## TTA / Inferencing



### Apply Test-time augmentation (TTA) for the model



Test-time augmetnation (TTA) can be used in both training and testing phases. 



```python

from pytorch_toolbelt.inference import tta



model = UNet()



# Truly functional TTA for image classification using horizontal flips:

logits = tta.fliplr_image2label(model, input)



# Truly functional TTA for image segmentation using D4 augmentation:

logits = tta.d4_image2mask(model, input)



```



### Inference on huge images:



Quite often, there is a need to perform image segmentation for enormously big image (5000px and more). There are a few problems with such a big pixel arrays:

 1. There are size limitations on maximum size of CUDA tensors (Concrete numbers depends on driver and GPU version)

 2. Heavy CNNs architectures may eat up all available GPU memory with ease when inferencing relatively small 1024x1024 images, leaving no room to bigger image resolution.

  

One of the solutions is to slice input image into tiles (optionally overlapping) and feed each through model and concatenate the results back. 

In this way you can guarantee upper limit of GPU ram usage, while keeping ability to process arbitrary-sized images on GPU.

  



```python

import numpy as np

from torch.utils.data import DataLoader

import cv2



from pytorch_toolbelt.inference.tiles import ImageSlicer, CudaTileMerger

from pytorch_toolbelt.utils.torch_utils import tensor_from_rgb_image, to_numpy



image = cv2.imread('really_huge_image.jpg')

model = get_model(...)



# Cut large image into overlapping tiles

tiler = ImageSlicer(image.shape, tile_size=(512, 512), tile_step=(256, 256))



# HCW -> CHW. Optionally, do normalization here

tiles = [tensor_from_rgb_image(tile) for tile in tiler.split(image)]



# Allocate a CUDA buffer for holding entire mask

merger = CudaTileMerger(tiler.target_shape, 1, tiler.weight)



# Run predictions for tiles and accumulate them

for tiles_batch, coords_batch in DataLoader(list(zip(tiles, tiler.crops)), batch_size=8, pin_memory=True):

    tiles_batch = tiles_batch.float().cuda()

    pred_batch = model(tiles_batch)



    merger.integrate_batch(pred_batch, coords_batch)



# Normalize accumulated mask and convert back to numpy

merged_mask = np.moveaxis(to_numpy(merger.merge()), 0, -1).astype(np.uint8)

merged_mask = tiler.crop_to_orignal_size(merged_mask)

```



## Advanced examples



1. [Inria Sattelite Segmentation](https://github.com/BloodAxe/Catalyst-Inria-Segmentation-Example)

1. [CamVid Semantic Segmentation](https://github.com/BloodAxe/Catalyst-CamVid-Segmentation-Example)



## Citation



```

@misc{Khvedchenya_Eugene_2019_PyTorch_Toolbelt,

  author = {Khvedchenya, Eugene},

  title = {PyTorch Toolbelt},

  year = {2019},

  publisher = {GitHub},

  journal = {GitHub repository},

  howpublished = {\url{https://github.com/BloodAxe/pytorch-toolbelt}},

  commit = {cc5e9973cdb0dcbf1c6b6e1401bf44b9c69e13f3}

}

```