Annotating with Polygons: Best Practices

Polygon annotation is a cornerstone of computer vision (CV), used for marking objects with precise boundaries. This technique enables machine learning (ML) models to process and interpret data accurately, especially when dealing with irregularly shaped objects.

Whether you're a seasoned data scientist or new to the field, this guide walks you through everything you need to know about polygon annotation—from its tools and techniques to its applications and future trends. 

Glossary for Beginners

Understanding polygon annotation requires familiarity with some foundational terms. Here’s a quick glossary:

TermDefinition
AnnotationThe process of labeling data (images, videos, text) to make it usable for training machine learning models.
PolygonA multi-point geometric shape used to outline objects in an image for precise annotation.
Bounding BoxA rectangular shape used for simpler object annotation; less precise than polygons.
SegmentationDividing an image into parts, often for identifying specific objects or regions.
CVATComputer Vision Annotation Tool, a popular open-source platform for creating annotations.
Hybrid AnnotationA mix of manual and automated annotation methods, combining the accuracy of humans with AI efficiency.
Ground Truth DataHigh-quality labeled data used as a benchmark for model evaluation and training.

What is Polygon Annotation?

Polygon annotation is a data labeling technique where multi-point polygons are drawn around objects in images. Each point defines a segment of the object's boundary, enabling precise, pixel-level annotation. Unlike bounding boxes, which define objects with rectangular shapes, polygons accommodate complex object outlines, such as road signs, animal contours, or anatomical structures. 

Polygon Annotation
Bounding Box Annotation
Polygon Annotation
Bounding Box Annotation

Why It Matters

  • Precision: Ideal for intricate shapes, where bounding boxes or ellipses fall short.
  • Data Richness: Offers detailed input for models, leading to improved predictions.
  • Adaptability: Widely used across industries from healthcare to autonomous driving. 

Why Should You Use Polygon Annotation?

Polygon annotation isn’t just about precision—it’s about unlocking the full potential of your dataset. Here are some compelling reasons to choose polygons:

1. Precision for Complex Shapes

Capturing irregular shapes like tree canopies, human silhouettes, or tumors requires the flexibility of polygons. This precision directly impacts model performance.

Fact: A 2023 study showed that models trained with polygon-annotated datasets achieved 18% higher accuracy in object segmentation tasks compared to bounding box-based datasets.

2. Enhanced Data Utilization

Polygon annotations maximize the value of each image by focusing on specific areas of interest, reducing noise in datasets.

3. Versatility Across Use Cases

From facial recognition to wildlife monitoring, polygons offer unmatched adaptability, making them suitable for both generic and specialized tasks. 

Tools for Polygon Annotation

Selecting the right annotation tool is essential for productivity and accuracy. Here’s a comparison of leading options:

ToolKey StrengthsKey Drawback
CVATOpen-source, supports video annotation, highly customizable, integrates with ML frameworks like TensorFlow and CUDA.Can be complex for beginners, steep learning curve.
SuperviselyCollaboration-friendly, AI-assisted labeling, offers a full suite for both annotation and dataset management.More expensive than other options, requires a commercial license for full features.
LabelMeSimple, easy to use, open-source, great for educational and research purposes.Limited advanced features, not ideal for large-scale commercial projects.
RoboflowAutomation capabilities, supports multiple annotation formats, integrates seamlessly with machine learning pipelines.Can become costly for large-scale projects, especially for premium features.

Manual, Automated, and Hybrid Approaches

Annotation workflows vary depending on resources, timelines, and dataset complexity. Here’s a breakdown of the three main approaches:

1. Manual Annotation

  • How it works: Human annotators draw polygons for every object in a dataset.
  • Pros: High accuracy, ideal for small datasets.
  • Cons: Labor-intensive and time-consuming.

2. Automated Annotation

  • How it works: Algorithms automatically detect and annotate objects.
  • Pros: Faster for large datasets.
  • Cons: Requires manual validation to ensure accuracy.

3. Hybrid Approach

  • How it works: Combines automated pre-labeling with manual refinement.
  • Best for: Large, complex datasets requiring high accuracy. 

Steps of Manual Annotation in CVAT

Here’s a step-by-step guide for annotating polygons manually in CVAT:

  1. Upload Your Dataset
    Import images or videos and organize them into tasks.
  2. Define Object Classes
    Standardize names to avoid ambiguity.
  3. Draw Polygons
    Use the polygon tool to mark object boundaries.
  4. Review and Refine
    Peer-review annotations for consistency.
  5. Export the Results
    Save annotations in formats like COCO, Pascal VOC, or YOLO. 

Techniques and Best Practices in Annotating with Polygons 

Consistency in Polygon Placement

One of the most important aspects of polygon annotation is maintaining consistency across the dataset. The precision with which polygons are drawn directly impacts the accuracy of the AI model during training.

When annotating objects, it's crucial to follow a standard process, whether that means adhering to a fixed number of points for similar objects or ensuring the vertices closely follow the object's edges. By standardizing the annotation approach, you minimize the risk of errors and ensure that your model learns the nuances of object boundaries effectively.

Leveraging AI-Assisted Tools

To streamline the annotation process, many teams now use AI-assisted tools that automatically suggest polygon shapes based on pre-trained models. These tools can be particularly helpful when dealing with large datasets, as they significantly reduce the amount of manual work required. 

However, while AI tools can handle the bulk of the annotation, human oversight is still necessary. An experienced annotator must review and adjust the suggested polygons to ensure they accurately match the boundaries of the objects. 

Challenges and Solutions

ChallengeSolution
Time-Consuming ProcessUse hybrid annotation for efficiency, implement keyboard shortcuts and macros. 
Inconsistent AnnotationsIntroduce peer reviews. .
Ambiguous Object EdgesLeverage edge-snapping and AI suggestions. 

Applications

Polygon annotation is widely used across industries:

1. Healthcare

Polygon annotation plays a transformative role in medical imaging, particularly in tumor segmentation. By outlining the exact boundaries of tumors in radiological scans, machine learning models trained on annotated data can significantly improve diagnostic accuracy and speed.

Tumor Segmentation
Consider radiologists examining MRI or CT scans. Tumor boundaries often appear irregular, making polygon annotation the ideal method for delineating them. Additionally, polygon annotation helps in other critical areas like vascular structure analysis or organ segmentation, expanding its role in precision healthcare. 

2. Retail

Retailers use annotated images from shelf cameras to track product positioning, ensuring shelves are organized and well-stocked. This precise annotation technique helps detect misplaced or empty spaces, reducing inventory mismanagement. 

For example, computer vision systems trained on polygon-annotated images can identify and notify staff about products that need restocking, streamlining the inventory management process and improving the shopping experience. 

3. Satellite Imagery

Geospatial analysis heavily relies on polygon annotation to interpret satellite imagery. By delineating features like buildings, forests, roads, and water bodies, it aids in urban planning and environmental monitoring. 

4. Agriculture: Monitoring Crop Health 

In agriculture, polygon annotation is a valuable tool for assessing plant health. 

Farmers and agronomists use annotated aerial images of vineyards or fields to detect early signs of diseases like leaf blight or fungal infections. By drawing precise polygon boundaries around affected areas, these systems provide actionable insights, allowing targeted interventions and reducing yield losses. 

Future Trends and Innovations

1. AI-Driven Annotation

AI tools are rapidly improving polygon annotation, automating the process and ensuring high accuracy. This innovation helps reduce manual effort while speeding up the dataset creation process.

2. Domain-Specific Annotation

Industry-specific platforms are enhancing workflows by offering tailored tools for sectors like healthcare and automotive. These solutions increase efficiency and accuracy for specialized applications like medical image analysis or self-driving car data.

3. Crowdsourced Annotation

Crowdsourcing is being leveraged to build large, diverse datasets by involving global annotators on platforms such as Toloka.ai. This approach helps cover more varied scenarios but requires effective quality control to ensure consistent, accurate labels.

4. AR and VR Integration

Polygon annotation is becoming essential for AR and VR applications, where precise object segmentation is needed for realistic simulations. This trend is driving innovation in industries such as gaming, education, and healthcare.

Conclusion

Polygon annotation is integral to creating high-quality datasets for machine learning. With evolving tools, expanded applications, and a growing focus on industry-specific customization, its role in shaping the future of AI is undeniable.

Insights into the Digital World

What is iBeta certification?

iBeta Certification Definition Imagine a world where your face, voice, or fingerprint unlocks everything from your phone to your bank […]

Annotating with Polygons: Best Practices

Polygon annotation is a cornerstone of computer vision (CV), used for marking objects with precise boundaries. This technique enables machine […]

What Is Named Entity Recognition in NLP?

Introduction to Named Entity Recognition (NER) Named Entity Recognition (NER) is a fundamental task in Natural Language Processing (NLP) that […]

What is anti-spoofing? A Complete Guide

Anti spoofing is an essential technology for defending against cyber threats like IP spoofing, email phishing, and DNS attacks. This […]

Annotating With Bounding Boxes – Best Practices

Introduction to Bounding Box Annotation Bounding box annotation is foundational to computer vision projects that rely on accurately identifying and […]

Image Classification in Machine Learning: A Complete Guide

In our increasingly digital world, image classification stands out as a foundational technology that enables machines to understand and interpret […]

What is Semantic Segmentation?

Image segmentation is a core task in computer vision that involves dividing an image into multiple segments or regions, typically […]

Semantic vs Instance Segmentation: All the Differences

In the rapidly advancing field of computer vision, image segmentation plays a pivotal role in enabling machines to understand and […]

What is Instance Segmentation?

Introduction What is Segmentation in Computer Vision? Segmentation is a core task in computer vision that involves dividing an image […]

What is Training Data? – A Complete Guide 2024

Why is Training Data Important? Training data is the foundation of Machine Learning (ML) models. Without good-quality training data, even […]

employer

Ready to work with us?