How to Label Images for Machine Learning


Image labeling gives the benefit of tagging and detecting particular details or objects inside the image. In computer vision, the process of image labeling includes assigning particular tags to unprocessed data. The unprocessed data can be images and videos. Every tag denotes a particular object class that is related to the data. Labels are used by supervised machine learning (ML) models to train them to recognize a specific object type in unorganized data. Supervised ML models can assign a particular meaning to unprocessed data with the aid of labels.

In this article we will guide you how to label images for machine learning efficiently in your dataset.

What is Image Labeling?

The term image labeling is one of the data labeling kinds. The benefit of image labeling is that it recognizes and perfectly entitles the specific features inside the picture. These labels are very beneficial for the algorithms of computer vision for identifying specific objects. A simple example of this image labeling is that skyscrapers are easily detectable among other buildings. So, in this way, these labels are helpful for the model to understand the difference between skyscrapers and other buildings.

However, to build datasets containing various objects for computer vision models, image annotation is employed. Then these datasets are divided into two significant sets. First is the training set, which is utilized for primary model training. The second set is the validation set which is utilized to analyze the model’s efficiency.

The superior dataset can be built with the help of this image labeling technique which, as a result, can assist the model inefficiently learning the capability to recognize the objects. Machine learning scientists are constantly modifying and enhancing the dynamic process of label images for machine learning.

Why is Image Labeling Important for AI and Machine Learning?

A significant step that is utilized in creating supervised models having computer vision capabilities is image labeling. This technique of image labeling for machine learning models is very beneficial as it trains the models to label the complete image or recognize groups of objects inside the image. There are various methods in which this technique is helpful. Some of them are:

1. Creating beneficial models for artificial intelligence (AI)

Tools and methods for image labeling assist in highlighting or capturing particular objects inside an image. Thus, the images, with the help of these labels, become very easily readable by machines. Also, the images which are highlighted with the help of these labels are utilized in the training of datasets of AI as well as machine learning models.

2. Enhancing Computer Vision

Image labeling is a very helpful tool that enables object detection, which as a result, enhances the precision of computer vision. These labels are very helpful for training machine learning and Artificial Intelligence, which as a result, assist these models in recognizing the patterns as long as they can detect objects by themselves.

Types of Image Labeling

1. Image Classification

The data can be annotated to the image with the help of adding a label for the purpose of image classification. A database’s number of distinct labels corresponds to the number of classes it may categorize.

There are three important kinds of classification, and these are mentioned below:

  • Multi-label classification: More than one label can be present in every image
  • Binary class classification: Only 2 labels are present
  • Multiclass classification: Various labels are present

2. Image Segmentation

Image segmentation is the process of separating objects from the background as well as from other objects. This process utilizes computer vision models to do it. Image segmentation typically utilizes a pixel map that has the same size as the image. In this map, the 1 number denotes the presence of the object, and the 0 number denotes the absence of any annotations.

If multiple objects inside the object need to be segmented, then the segmentation process involves concatenating pixel maps for every object channel-wise. Also, it utilizes the maps as the model’s ground truth.

Image Segmentation

Figure: Image Segmentation Source

3. Object Detection

In the Object Detection process, various objects along with their accurate objects are detected with the help of computer vision. In contrast to image classification, object detection process utilizes the process of annotation of every object by utilizing bounding boxes.

The bounding box is the tiny rectangle section that has the object inside it. Tags are frequently used in conjunction with bounding box annotations to give every bounding box a label inside the image.

4. Pose Estimation

Distinct from every other type, Pose Estimation utilizes models of computer vision which helps to calculate the pose of the person inside the image. This process involves the detection of key points in the people’s body. Then these key points are compared with body points to calculate the pose. In explanation, the key points are used as based values for the pose estimation process.

In addition, pose estimation utilizes the process of labeling the easy coordinates with tags. So, every coordinate serves as a location of a particular key point. Further, these key points are recognized by the tags inside the image. Below figure shows the post estimation in computer vision.

Pose Estimation

Figure: Pose Estimation Source


Steps to Label Images for Machine Learning

Effective image labeling for computer vision includes the following steps:

1. In each image, identify all objects of interest

Computer vision models are developed to identify the pixel pattern of the object. During the model training, it is important to label each object inside the images. The false negative term is applied to the model if the labeling of the objects is not performed.

2. Entirety of an Object is Label

The bounding box that is utilized to label the object must include an object of interest in its entirety. When an object is only partially labeled, our model becomes confused about what a full object is.

3. Occluded Objects are Labeled

Occlusion occurs when an object inside an image is partially hidden from view because something prevents it. Even Occluded things should be labelled if possible. Furthermore, it is often recommended to identify the Occluded object as if it remained completely viewable instead of creating a bounding box for the partially visible object.

4. Building Precise Bounding Boxes

A precise bounding box means it should be tight or close to the area of interest. Tight or precise bounding boxes enable the model to learn more efficiently because a tight bounding box includes the most relevant object pixels rather than the irrelevant portion.

5. Name Your Labels with Specific Term

When multiple kinds of objects exist in the dataset, then it is preferable to assign each object to its specific class or term.

Name the labels with Specific Term

Figure: Name the labels with Specific Term Source