Bengali.ai Handwritten Character Recognition Challenge: 100-ish solution(?)

My scripts for the Bengali.ai handwritten character Recognition challenge 2019. Although I could not submit the final trained models within the competition deadline, later I found out that it would get me a 100-ish private Leadeboard position.

I added customized 1 channel input seresext, densenet, efficientnet and ghostnet models in this repo.

My Method:

• Trained each model for around 100 epochs with OHEM cross-entropy loss.
• Trained the first 30 epochs with rate=1 for OHEM loss. Then gradually decreased the rate to 0.65 over the next 35 epochs. This approach significantly increased my Grapheme recall.
• Applied CutOut, CutMix and Mixup augmentations.
• Used heavy augmentations during training se-resnext101 model.

Things that works:

• SE-Resnext50
• CutMix + MixUp
• OHEM Loss
• Gem (Did not compare with AvgPool)
• Mish (Did not compare with ReLU)
• Training for longer epochs and no early stopping
• Rely on validation loss rather than recall score.

Things that may work:

• AugMix
• EfficientNet with customized last Convolutional Layer
• SE-Resnext101 (Teacher-Student model)
• Focal Loss with EfficientNet-B4

Important Discussions:

• Validation Data
• Focal Loss + OHEM: Note: Unstable
• Discussion on how to train with EfficientNet
• MaxBlurPool2D
• Augmix Implementation

Resources:

• Half Precision GeM:

def gem(x, p=3, eps=1e-6):
    x = x.double() # x=x.to(torch.float32) # comment this during inference
    x = F.avg_pool2d(x.clamp(min=eps).pow(p), (x.size(-2), x.size(-1))).pow(1./p)
    return x.half() # Comment this line in inference code use ## return x

class GeM(nn.Module):
    def init(self, p=3, eps=1e-6):
        super(GeM,self).init()
        # super().init()
        self.p = Parameter(torch.ones(1)*p)
        # print(self.p.dtype)
        self.eps = eps
    def forward(self, x):
        return gem(x, p=self.p, eps=self.eps)
    def repr(self):
        return self.class.name + '(' + 'p=' + '{:.4f}'.format(self.p.data.tolist()[0]) + ', ' + 'eps=' + str(self.eps) + ')'

How to run

• Run pip install -r requirements.txt
• Run train.py

Credits

Thanks to the kaggle community for sharing a lot of resources and making the tasks easier for us. Here is a list of discussions from where I've borrowed codes and/or became inspired to write codes:

• Augmix
• GridMask
• MixUp and CutMix
• OHEM Loss

More resources will be added soon.