5 Types of Image Annotation


The act of labelling a picture is known as an image annotation. One label for the whole image or several labels for each cluster of pixels might be used as examples. Giving human annotators access to animal photographs and asking them to annotate each image with the appropriate animal name is a straightforward illustration. 

Naturally, the labelling approach depends on the kinds of picture annotations employed for the project. These labelled photos would then be sent to a computer vision system known as “ground truth data.” The model would then be able to differentiate between animals in unannotated photos after receiving training. While the aforementioned illustration is relatively straightforward, more complex picture annotation is necessary to expand into more complex fields of computer vision, such as autonomous cars.

The Top 5 Types Of Image Annotations

Do you know which picture annotation will work best for your project? Five popular forms of picture annotations are shown below, along with some examples of their uses.

3D Cuboids

Similar to bounding boxes, 3D cuboid annotation requests annotators to outline certain portions of an image. Bounding boxes merely showed length and breadth, whereas 3D cuboids include labels for length, width, and a rough representation of depth.

Human image annotation services use 3D cuboid annotation to create a box around the item of interest and set anchor points at each of the object’s edges. The annotator makes an educated guess as to where the edge would be based on the size, height, and angle of the picture if one of the item’s edges is obscured or obstructed by another object in the image.

Enclosing Boxes

Bounding box annotation involves giving human annotators a picture and asking them to draw a box around specific elements in the image. Every item’s edge should be as near to the box as is practical. Typically, the job is completed on unique platforms that vary from business to business. Some businesses can modify their current platforms to meet your demands if your project has specific requirements.

One specific application for bounding boxes would be the creation of autonomous cars. Annotators would be given instructions to use bounding boxes to delineate vehicles, pedestrians, and bicycles in traffic images.

To enable the autonomous car to recognise these objects in real-time and steer clear of them, developers would input the bounding-box-annotated photos into a machine-learning model.

Semantic Segmentation

Semantic segmentation is significantly more detailed and specific than the preceding instances on this list, which focuses on defining an object’s bounds or outside edges. The semantic segmentation method involves assigning a tag to each pixel in a picture. Those who outsource data entry services often provide a set of predetermined tags for projects requiring semantic segmentation – and the service provider must tag every element on the page.

Annotators would use platforms akin to those used in polygonal annotation to draw lines around a group of pixels they want to tag. AI-assisted platforms can also be used for this. For example, the computer may be able to roughly segment the borders of an automobile but make a mistake and segment the shadows beneath the vehicle as well. Human annotators might choose a different method to remove undesirable pixels in a similar situation.

Medical imaging equipment is another industry in which semantic segmentation is frequently used. Annotators are given a photograph of a person and instructed to identify each body part with the appropriate term for anatomy and body part labelling. Additionally, extremely specific tasks like labelling brain lesions in CT scan pictures may be accomplished via semantic segmentation.

Splines And Lines

Although lines and splines have many uses, their principal function is to teach machines to identify lanes and limits. As their name implies, annotators simply draw lines around the limits you want your computer to understand.

Warehouse robots may be programmed to precisely put products on a conveyor belt or boxes in a row using lines and splines. Autonomous cars, however, are where lines and splines annotations are most frequently used. Autonomous cars may be programmed to recognise boundaries and stay in one lane without straying by marking road lanes and walkways.


Due to an object’s shape, size, or position inside the picture, a 3D cuboid or a bounding box may not always fit it adequately. Additionally, there are occasions when developers need more exact annotation for certain items in a picture, such as automobiles in traffic shots or landmarks and structures in aerial photographs. Developers could choose polygonal annotation in these circumstances.

When using polygons, annotators make lines by placing dots around the object’s outside border. The procedure resembles a game of connecting the dots while simultaneously inserting the dots. Then, a specified set of classes, such as automobiles, bicycles, or trucks, are used to annotate the space inside the circle encircled by the dots. A multi-class annotation is one where more than one class is given to annotate.


Regardless of the kind of image annotation, having a partner you can rely on to launch your next machine-learning project is quite valuable. AI annotation will be the future! To obtain the most accurate and the best readings of your image data, humans must still verify it. 

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