Define Classes & Tags
This article explains how to create and manage classes and tags for data annotation in the Labeling Tool to ensure structured and consistent labeling within a project.
Last updated
Was this helpful?
This article explains how to create and manage classes and tags for data annotation in the Labeling Tool to ensure structured and consistent labeling within a project.
Last updated
Was this helpful?
Definitions are a centralized place where all classes and tags used for data annotation are managed. A class defines an object category and specifies the type of geometry that will represent this class in annotations, such as bounding boxes, masks, polygons, etc. Tags describe not only the annotations themselves but can also apply to frames, images, and more. Properly defined classes and tags ensure consistent and structured annotations throughout the entire project
The Definitions tab, available both in the Project and in the Labeling Tool, is divided into two main categories:
Classes - for managing object classes.
Tags - for managing tags used in data annotation.
Adding a new classes and tags: you can create a new class or tag by clicking the + NEW CLASS or + NEW TAG button and filling in the required fields.
Editing: each class and tag can be edited by changing its parameters such as name, color, scope and value type.
Archiving: if a class or tag is not needed temporarily, it can be archived so that it is not displayed in the list of active elements but remains in the project. Archived classes and tags can be restored at any time.
Sorting: Sort classes and tags to quickly find the elements you need.
Newest (default) — displays the most recently created items first.
Oldest — displays the oldest items first.
Name (A-Z) and Name (Z-A) — sorts items alphabetically in ascending or descending order.
Shape (A-Z) and Shape (Z-A) — (for classes only) sorts items by shape type in ascending or descending order.
Although both tags and classes are used to identify objects, they serve distinct purposes:
Classes: Represent clear categories that an object belongs to, such as "car", "truck", or "bus" for vehicles.
Tags: Provide specific information about objects or images, such as context or properties. Tags are more flexible and can include details not tied to formal classifications. For example, the tag "Traffic Density" can have values "High" or "Low" indicating the level of traffic density, and the tag "Action" can signify the actions of an object (e.g. "Stopped" or "Moves").
An image or an object can have multiple tags assigned, while each object usually belongs to a single class, i.e. classes are used to explicitly categorize objects. Tags can be more personalized and focused on specific characteristics and attributes. Tags typically add context and descriptive attributes not necessarily related to the formal classification of an object.
Classes are object categories used to annotate images and video by creating shapes on objects. Each class represents an object type, and each annotated object in an image or video frame has exactly one class associated with it.
TITLE — the name of the class. The name should be unique and clearly describe the object, for example, "Person," "Car," or "Tree."
COLOR — the color assigned to the class, displayed on the screen to visually differentiate the annotation.
HOTKEY — a shortcut key assigned to the class for quick annotation during labeling.
Click on the + NEW CLASS button to start creating a new class.
Set a unique title for the class to clearly identify it.
Add a description (optional) and assign a for quick selection during labeling.
Choose the Shape for the class (e.g., Bounding Box to label an object with rectangular frame).
Generate or choose a color for the class to visually differentiate it from other classes.
Tags serve as data annotation and classification tool. These attributes, assigned to images/videos or labeled objects, make it simple to sort things and give important information about what's in an image.
TITLE — the name of the tag. Like classes, tags should have unique names, for example, "Highway", "Traffic Density", "Action".
APPLICABLE TO — the scope of the tag's application (e.g., video only, objects only, videos and objects).
Image Tags: Apply to images and provide information like category, properties (resolution), geographic details, and content.
Object Tags: Apply to objects within images, detailing characteristics (e.g., "broken" equipment), state (e.g., "ripe" fruit), and localization (e.g., "anterior" placenta).
Some tags can be applied to both images and objects. Such Tags may describe both image characteristics and individual objects at the same time, providing comprehensive labeling.
SCOPE (for videos project) — the tag’s range of application:
Global — the tag applies to the entire video or object.
Frame-based — the tag applies only to specific frames in the video.
Global and Frame-based — allows you to use a tag for the entire video or object as well as for individual frames at the same time. This means that you can set a global tag for the entire video or object, denoting a permanent property, and apply it to individual frames to label temporary changes or events.
TAG VALUE TYPE — the type of value associated with the tag:
None (Tag without Value): Used to flag specific properties. For example, a tag "train" might mark data for neural network training.
Text Tag: Contains textual descriptions or comments about the object or image.
Number Tag: Represents numeric properties, useful for regression tasks (e.g., size, weight).
One of: Indicates that the value must be one of a predefined set, such as colors (Red, Blue, Green).
COLOR — the color displayed on the screen to make the tag easily identifiable.
Click on the + NEW TAG button to start creating a new tag.
Set a unique title for the tag to clearly identify it.
Assign a hotkey (optional) for quick selection during labeling.
Choose or generate a color for the tag to visually distinguish it from other tags.
Select "Applicable to" to define whether the tag will be used for:
Images and objects
Images only
Objects only
Define the tag’s value type:
None: a tag without a value.
Text: allows adding a text description or comments.
Number: represents numerical properties.
Single choice (One of): select one option from a predefined set.
Additional Scope option for video projects:
Global and Frame-based: tag can be applied globally or to specific frames.
Frame-based: tag is applied only to specific frames.
Global: tag applies to the entire video or object as a whole.
Click Save to complete the creation of the new tag.
To apply the same tag multiple times:
From the Project: Go to Settings > Tags and find Multiple Tags Mode.
From the Image Labeling Toolbox: Click on the Tag icon, hover over 🔁, and click the blue link Setting to enable Multiple Tags Mode.
Classes and Tags created manually by an annotator inside the Labeling Tool (during the annotation process) are automatically added to the project’s Definitions on the Projects page.
These classes and tags immediately become available to all team members — they appear in the Labeling Tool for other annotators as well.
This behavior enables the following:
Dynamic expansion of the project structure, even if the Definitions were not configured in advance.
Consistency across the team, by maintaining a single, shared list of classes and tags.
Avoiding duplication, since new items are added directly to the central schema.
The locations where classes and tags can be defined directly in the Labeling Tool vary depending on the type of data being annotated. This is expected, since the interface of the Labeling Tool also slightly differs based on the data type in use.
Let’s go through each case one by one.
When working with images, the Definitions panel is located on the left side of the Labeling Tool.
To add a new class or tag:
click the plus + on the panel, then choose whether you want to add a class or a tag.
In the modal window that appears, configure the class or tag parameters, then click Create to save it.
The newly created class or tag will immediately appear in the Definitions panel for all annotators and become available for annotation.
To create a new Class and simultaneously reassign it to an existing object in the project:
In the Objects panel (located on the right side of the Labeling Tool), select an object and click ⌄ next to its current class name. And in the dropdown menu, select Create class.
In the modal window that appears, configure the new class parameters, then click Create to save it.
The new class will immediately appear in the Definitions panel on the left and will be automatically assigned to the selected object in the Objects panel.
When working with videos, the Definitions panel is located on the right side of the Labeling Tool.
To add a new class or tag:
click the plus + on the panel, then choose whether you want to add a class or a tag.
In the modal window that appears, configure the class or tag parameters, then click Create to save it.
The newly created class or tag will immediately appear in the Definitions panel for all annotators and become available for annotation.
The locations where classes and tags can be defined in the Labeling Tool are the same for Dicom Volume and Point Cloud.
Let’s walk through the process using Dicom Volume as an example.
So you can create a new class directly from the Objects panel and simultaneously reassign it to an existing object in the project.
To do this:
In the Objects panel (located on the right side of the Labeling Tool), select an object and click ⌄ next to its current class name. And in the dropdown menu, select Create class.
In the modal window that appears, configure the new class parameters, then click Create to save it.
Creating a New Tag from the Objects Panel
You can also create a new Tag directly from the Objects panel while annotating an object:
In the Objects panel, select an object.
In the Tags Available section, click the Add project tags definitions icon.
In the modal window that appears, configure the new tag parameters, then click Create to save it.
The newly created tag will immediately appear in the Objects panel for all annotators and become available for annotation.
SHAPE — the annotation shape for the class. Available options include , , , , , , Cuboid 2D, Alpha Mask, and Any Shape.
To learn more about the practical uses of tags and explore advanced tools, check out our in-depth blog post: . This guide provides valuable insights and real-world examples to help you maximize the potential of tagging in your projects.
