devanagari-character-recognition

DHCD – Devanagari Handwritten Character Recognition

This repository contains a custom Convolutional Neural Network (CNN) trained from scratch to recognize 46 classes of handwritten Devanagari characters and digits. The model is implemented in PyTorch and achieves approximately 98.42% test accuracy on the Devanagari Handwritten Character Dataset (DHCD).

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Model Overview

• Model Type: Custom CNN (Model A)
• Task: Image Classification (OCR – handwritten characters)
• Input: 32×32 grayscale images (white foreground on black background)
• Output: 46-class softmax probabilities
• Framework: PyTorch

The architecture is intentionally designed for small fixed-size inputs, aggressively reducing spatial dimensions to 1×1 before classification to enforce global feature learning.

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Architecture

Layer progression:

1. Input: 32×32×1
2. Conv(64, 5×5) → LRN → ReLU → MaxPool
3. Conv(128, 5×5) → LRN → ReLU → MaxPool
4. Conv(256, 5×5) → LRN → ReLU → (1×1×256)
5. Flatten → Dropout(0.5) → Linear(256 → 46)

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Dataset

• Dataset: Devanagari Handwritten Character Dataset (DHCD)

• Total Images: ~92,000

• Classes: 46

  • Digits: 0–9 (10)
  • Consonants: 36 basic Devanagari characters

• Image Size: 32×32 pixels

• Color Space: Grayscale

• Writers: Multiple native writers

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Dataset Split

The dataset was split in a class-balanced manner:

• Training: ~80%
• Validation: ~10%
• Test: ~10%

Each split preserves an approximately equal number of samples per class. The validation set was used for convergence monitoring and hyperparameter tuning, while the test set was held out entirely for final evaluation.

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Training Details

• Optimizer: SGD with Momentum
• Epochs: 20
• Loss Function: Cross-Entropy Loss
• Regularization: Dropout (p = 0.5)
• Normalization: Local Response Normalization (LRN)

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Performance

• Test Accuracy: ~98.42%

The model performs consistently well across most characters, with minor confusion only between visually similar glyphs.

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Usage

⚠️ Important: Because this is a custom architecture, the model class must be defined exactly as used during training before loading the weights.

Quickstart

import torch
import torch.nn as nn
import torch.nn.functional as F
import torchvision.transforms as transforms
from PIL import Image

class ModelA(nn.Module):
    def __init__(self, num_classes=46):
        super().__init__()
        self.conv1 = nn.Conv2d(1, 64, 5)
        self.lrn1 = nn.LocalResponseNorm(5)
        self.pool1 = nn.MaxPool2d(2)

        self.conv2 = nn.Conv2d(64, 128, 5)
        self.lrn2 = nn.LocalResponseNorm(5)
        self.pool2 = nn.MaxPool2d(2)

        self.conv3 = nn.Conv2d(128, 256, 5)
        self.lrn3 = nn.LocalResponseNorm(5)

        self.dropout = nn.Dropout(0.5)
        self.fc = nn.Linear(256, num_classes)

    def forward(self, x):
        x = self.pool1(F.relu(self.lrn1(self.conv1(x))))
        x = self.pool2(F.relu(self.lrn2(self.conv2(x))))
        x = F.relu(self.lrn3(self.conv3(x)))
        x = x.view(x.size(0), -1)
        x = self.dropout(x)
        return self.fc(x)

device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
model = ModelA().to(device)
model.load_state_dict(torch.load("dhcd-model.pth", map_location=device))
model.eval()

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Limitations

• Requires exact 32×32 input resolution
• Sensitive to color inversion
• Cannot process multi-character images
• Performance may degrade on unseen handwriting styles

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Ethical Considerations

• Trained only on handwritten Devanagari characters
• No personal or sensitive data used
• Not intended for critical decision-making systems

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Reproducibility

To reproduce results:

1. Use the provided dhcd.ipynb notebook
2. Apply identical preprocessing
3. Match the architecture definition exactly

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Citation

Devanagari Handwritten Character Recognition using a Custom CNN,
Arpit Gaur, 2025

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License

Released under the MIT License.