Textual Metadata Dataset Construction

Automatic Image Dataset Construction with Multiple Textual Metadata

Overview

This skill provides a framework for automatically collecting diverse, high-quality image datasets from the web using semantic query expansion and progressive CNN-based filtering. The methodology addresses key challenges:

1. Dataset Bias: Reduces bias by expanding queries semantically
2. Noise Reduction: Filters irrelevant images through clustering and CNNs
3. Cross-Dataset Generalization: Creates datasets that generalize well to unseen domains

Key Innovation: Uses Google Books Ngrams Corpora for query expansion to capture richer semantic descriptions, then progressively filters using CNNs.

When to Use This Skill

Use this skill when:

• Building training datasets that need to generalize across domains
• Current datasets suffer from selection bias
• Manual annotation budget is limited
• Need diverse image coverage for a concept
• Building datasets for image classification or object detection
• Comparing performance with established datasets (STL-10, CIFAR-10)

Core Workflow

Phase 1: Query Expansion

1. Initial Query Definition:

   initial_queries = ["dog", "car", "airplane"]
   

2. Semantic Expansion with N-gram Corpora:

   def expand_query_with_ngrams(query, ngram_data):
       """
       Expand query using Google Books Ngrams:
       - Find co-occurring terms
       - Add synonyms and related concepts
       - Include descriptive modifiers
       
       Example: "dog" → ["dog breed", "puppy", "canine", 
                         "dog playing", "dog running", ...]
       """
       expansions = []
       
       # Get bigrams containing the query
       bigrams = get_ngrams(query, n=2, ngram_data=ngram_data)
       
       # Get trigrams for context
       trigrams = get_ngrams(query, n=3, ngram_data=ngram_data)
       
       # Combine and rank by frequency
       expansions = rank_by_relevance(bigrams + trigrams)
       
       return expansions
   

3. Visual Saliency Filtering:

   def filter_expansions(expansions, visual_model):
       """
       Remove expansions that are:
       - Visually non-salient (abstract concepts)
       - Less relevant to visual domain
       - Too generic or too specific
       
       Use pre-trained visual model to score saliency
       """
       filtered = []
       for exp in expansions:
           # Check if expansion corresponds to visually identifiable concept
           saliency_score = visual_model.predict_saliency(exp)
           if saliency_score > threshold:
               filtered.append(exp)
       return filtered
   

Phase 2: Web Image Retrieval

1. Multi-Query Image Collection:

   def collect_images(expanded_queries, images_per_query=500):
       """
       Retrieve images using expanded queries:
       - Use multiple search engines
       - Collect metadata (source URL, query used)
       - Diversify sources to reduce bias
       """
       all_images = []
       
       for query in expanded_queries:
           images = search_engine.image_search(
               query, 
               num_results=images_per_query
           )
           for img in images:
               img['source_query'] = query
           all_images.extend(images)
       
       return all_images
   

2. Initial Preprocessing:

   def preprocess_images(images):
       """
       - Remove duplicates (perceptual hash)
       - Validate image format
       - Resize to standard dimensions
       - Remove corrupted files
       """
       pass
   

Phase 3: Clustering-Based Noise Filtering

1. Feature Extraction:

   def extract_features(images, cnn_model):
       """
       Extract deep features using pre-trained CNN
       (e.g., VGG, ResNet features from penultimate layer)
       """
       features = []
       for img in images:
           feat = cnn_model.extract_features(img)
           features.append(feat)
       return np.array(features)
   

2. Cluster Analysis:

   from sklearn.cluster import KMeans
   
   def cluster_and_filter(features, images, n_clusters=10):
       """
       Cluster images by visual similarity:
       - Identify core clusters (likely relevant)
       - Remove outlier clusters (likely noise)
       - Keep images from dense, coherent clusters
       """
       kmeans = KMeans(n_clusters=n_clusters)
       clusters = kmeans.fit_predict(features)
       
       # Analyze cluster statistics
       cluster_stats = analyze_clusters(clusters, features)
       
       # Remove outlier clusters (low density, high variance)
       valid_clusters = [
           c for c in cluster_stats 
           if c['density'] > threshold and c['coherence'] > min_coherence
       ]
       
       filtered_images = [
           img for img, c in zip(images, clusters)
           if c in valid_clusters
       ]
       
       return filtered_images
   

Phase 4: Progressive CNN Filtering

1. Initial CNN Training:

   def train_initial_classifier(clustered_images, num_classes):
       """
       Train initial CNN classifier on clustered data:
       - Use cluster assignments as pseudo-labels
       - Fine-tune pre-trained model
       """
       model = load_pretrained_cnn()
       model = fine_tune(model, clustered_images)
       return model
   

2. Progressive Refinement:

   def progressive_filtering(images, model, iterations=3):
       """
       Iteratively refine dataset:
       1. Classify all images with current model
       2. Remove low-confidence predictions
       3. Retrain model on refined set
       4. Repeat
       """
       for i in range(iterations):
           # Predict on all images
           predictions = model.predict(images)
           
           # Filter by confidence
           confident_samples = [
               (img, pred) for img, pred in zip(images, predictions)
               if pred['confidence'] > confidence_threshold(i)
           ]
           
           # Retrain on refined set
           model = train_classifier(confident_samples)
           
           images = [s[0] for s in confident_samples]
       
       return images, model
   

Phase 5: Dataset Finalization

1. Quality Verification:

   def verify_dataset_quality(dataset, test_set):
       """
       Evaluate dataset quality:
       - Cross-dataset generalization (test on STL-10, CIFAR-10)
       - Class balance analysis
       - Diversity metrics
       """
       # Train classifier on generated dataset
       model = train_classifier(dataset)
       
       # Test on external datasets
       stl10_accuracy = evaluate(model, stl10_test)
       cifar10_accuracy = evaluate(model, cifar10_test)
       
       return {
           'cross_dataset_acc': (stl10_accuracy + cifar10_accuracy) / 2,
           'class_balance': compute_balance(dataset),
           'diversity': compute_diversity(dataset)
       }
   

2. Export Dataset:

   dataset/
   ├── train/
   │   ├── class_1/
   │   ├── class_2/
   │   └── ...
   ├── val/
   ├── test/
   ├── metadata.json
   └── dataset_stats.md
   

Key Techniques

Query Expansion Strategy

• Use Google Books Ngrams (n=2,3,4) for semantic expansion
• Filter by visual saliency to remove abstract terms
• Balance specificity vs. diversity in expansions

Progressive Filtering

• Start with loose confidence threshold (~0.5)
• Increase threshold each iteration (~0.6, 0.7, 0.8)
• Allows gradual refinement without losing good samples early

Reducing Dataset Bias

• Use multiple search engines
• Diversify query expansions
• Cluster analysis ensures visual diversity
• Cross-domain validation confirms generalization

Best Practices

1. Query Expansion:

   • Start with 5-10 core concepts per category
   • Generate 20-50 expansions per core concept
   • Filter to top 10-20 based on visual saliency

2. Clustering:

   • Use k-means with k = 10-20 clusters per category
   • Validate cluster coherence manually on samples
   • Remove clusters with < 5% of total images

3. Progressive Filtering:

   • Use 3-5 iterations
   • Start confidence threshold: 0.5
   • Increase by 0.1 per iteration
   • Stop when dataset size stabilizes

4. Validation:

   • Always test on external datasets
   • Compare with CIFAR-10, STL-10 baselines
   • Report cross-dataset accuracy

Expected Results

Based on original research:

• Generates datasets larger than manually labeled alternatives
• Achieves comparable generalization to STL-10, CIFAR-10
• Significant performance gains on:
  • Image classification
  • Cross-dataset generalization
  • Object detection

Dependencies

# Deep learning
pip install torch torchvision  # or tensorflow

# Clustering
pip install scikit-learn

# Image processing
pip install pillow opencv-python

# N-gram data
# Download Google Books Ngrams: https://storage.googleapis.com/books/ngrams/books/datasetsv3.html

Integration with Other Skills

• pytorch: Train classifiers during filtering
• scikit-learn: Clustering and evaluation
• matplotlib: Visualize cluster distributions
• exploratory-data-analysis: Dataset statistics

References

• "Automatic Image Dataset Construction with Multiple Textual Metadata" (IEEE ICME 2016)
• Google Books Ngram Viewer: https://books.google.com/ngrams