Image Segmentation | Techniques & Types

Image Segmentation | Techniques & Types

Sun Jul 09 2023

In today's digital age, images are critical in everything from healthcare and autonomous driving to social media and e-commerce. But to extract meaningful features from images, we need to understand their content and structure. This is where image segmentation comes in. In this blog post, we will explore the fascinating world of image segmentation, how it works, annotation techniques, different types, popular segmentation techniques, and its wide range of applications.

What is image segmentation?

Image segmentation is a computer vision technique that divides an image into multiple distinct regions or segments based on specific characteristics such as color, texture, or shape. Image segmentation aims to simplify an image's representation, making it easier to analyze and extract valuable information from different parts of the image. Technically, segmentation is how we can identify objects, people, or other important elements in the image using pixels.

How Does Image Segmentation Work?

Image segmentation algorithms use various mathematical models, machine learning algorithms, or deep neural networks to classify pixels or groups of pixels within an image. These algorithms analyze the visual features of the image and assign each pixel to a specific segment or region. Several high-level image features can be useful for image segmentation. Some of these features are:

  • Color: Pixels with similar color values can be grouped.
  • Intensity: Pixels with similar brightness values can be grouped.
  • Texture: Pixels with similar patterns or textures can be grouped.
  • Edge: Pixels that form an edge or a boundary can be detected and separated from other pixels.
  • Shape: Pixels that form a specific shape or contour can be detected and separated from other pixels.

How Does Image Segmentation Work?

Annotation for Image Segmentation

Annotation is the process of adding labels or metadata to images to make them suitable for training machine learning models. Annotation for image segmentation involves creating masks or matrices that specify the labels for each pixel in the image.

Annotation for image segmentation can be done manually by experts or automatically by software tools. Manual annotation can ensure high quality and accuracy but can be time-consuming and costly. Automatic annotation can speed up the process but may introduce errors or inconsistencies.

Some of the common tools for annotation for image segmentation are:

  • Boundary annotation: Boundary annotation marks or annotates the boundaries or edges of objects or regions within an image or dataset. This annotation technique outlines the boundaries of objects to provide detailed information about their shape and location. In boundary annotation, annotators manually trace the contours or perimeters of objects using specialized annotation tools or software. Annotators typically draw lines or curves along the edges of objects, closely following their shape.
  • VGG Image Annotator (VIA): This is an online tool that allows users to draw shapes, such as polygons, circles, ellipses, etc., around objects and assign labels to them. It supports various formats such as JPEG, PNG, BMP, TIFF, etc.
  • Labelbox: This is another online platform that provides various tools for annotation for different tasks such as classification, segmentation, object detection, etc.
  • CVAT: This is an open-source tool that allows users to annotate images and videos for different kinds of tasks.
Annotation for Image Segmentation

Types of Image Segmentation

Image segmentation can be categorized into several types, including:

  • Thresholding Segmentation: This technique involves setting a threshold value to separate pixels based on their intensity or color.
  • Edge-based Segmentation: It identifies object boundaries by detecting edges or gradients within the image.
  • Region-based Segmentation: This approach groups pixels based on their visual features, color, or texture similarity.
  • Semantic segmentation: Semantic segmentation is the process of assigning a class label to each pixel in the image so that pixels with the same label belong to the same object or category.
  • Clustering-based Segmentation: It utilizes clustering algorithms to group pixels with similar attributes.
  • Instance segmentation is the process of assigning a class label and an instance label to each pixel in the image, such that pixels with the same class label and instance label belong to the same object or instance.
Types of Image Segmentation

Image Segmentation Techniques

There are many techniques for image segmentation, each with its own advantages and disadvantages. Some of the popular techniques are:

  • Convolutional Neural Networks (CNN): Deep learning-based approaches, such as U-Net and Mask R-CNN, have remarkably performed in image segmentation tasks.
  • Graph-based Segmentation: It represents an image as a graph and uses graph theory algorithms to partition it.
  • U-Net: This CNN-based technique consists of an encoder-decoder architecture with skip connections. The encoder extracts features from the input image and reduces its spatial resolution.
  • DeepLab: This technique consists of three main components: atrous convolution, atrous spatial pyramid pooling (ASPP), and fully connected conditional random field (CRF). Atrous convolution allows the network to capture multi-scale information without reducing the resolution. ASPP applies atrous convolution at different rates to capture context information at different scales. CRF refines the output mask by enforcing consistency and smoothness.

What Is Image Segmentation Used For?

Image segmentation finds applications in various domains, including:

  • Medical Imaging: Segmentation aids in identifying tumors, organs, or anatomical structures, assisting in diagnosis, treatment planning, and surgical guidance.
  • Object Recognition and Tracking: Segmentation facilitates object detection, tracking, and recognition tasks in computer vision applications.
  • Image Editing and Forensics: Segmenting images allows for selective editing, background removal, and image manipulation.
  • Autonomous Driving: Accurate segmentation enables object detection, lane detection, and scene understanding, contributing to safe and efficient autonomous vehicles.
  • Fingerprint recognition: Image segmentation can help extract fingerprints from images and enable biometric authentication, criminal identification, forensic analysis, etc.

These are just some of the examples of image segmentation applications. Image segmentation can be useful and beneficial in many more domains and scenarios.

What Is Image Segmentation Used For?


Image segmentation is a powerful technique that unlocks the potential of visual analysis. By dividing images into meaningful segments, we can understand their content, extract valuable information, and build intelligent systems in various fields. From medical imaging to autonomous driving, image segmentation applications are vast and growing.

If you are interested in learning more about image segmentation or other topics like computer vision applications, you can check out our website for more resources.

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