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How to annotate an image and what are the existing tools to annotate images?

May 27, 2022

What is image annotation?

Image annotation is the technology that lets the computer gain a deep understanding by labeling an image using text or annotation tools to show data features the user wants it to recognize on its own.

How are images annotated?

Choose any open-source software, which could be web-based. 

Prepare your image datasets

Identify and specify the labels to be applied, it may vary depending on the use case.

In each image, draw a box throughout the object you want to mark.

Select the category tag for every box you drew

Export the image annotation in the right format

Types of Image Annotation

Image annotation is mostly used with a variety of  image annotation methods like:

Image classification

This type of model requires images to have one label to decide the entire image.

It aims at identifying the presence of the same objects in images throughout a whole dataset. It’s a perfect way to gather abstract information and screen images that don’t fit the qualifications.

It is considered the fastest and easiest way to perform image annotation.

Also, it can be used to teach a machine to identify an object in an unlabeled image that looks like an object in different labeled images that were used to train the machine.

Object recognition/ Detection

Used to determine the location, presence, and number of one or more objects in an image, which can also be used to spot a single object. Using this model, the image annotation process needs boundaries to be defined around every detected object in an image.

Image Segmentation

Divides an image into definite components. Image segmentation is used to evaluate the visual content in images and find objects and boundaries, such as lines and curves, to know how objects within an image are the same or different. Projects that require higher accuracy in classifying inputs use this type of image annotation.

Classes of image recognition

Semantic segmentation draws boundaries between the same objects and is used to get the objects’ shape, location, number, size, and shape within an image.

Instance segmentation checks the number, location, presence, and size or shape of the objects within an image.

Pan optic segmentation provides data labels for the background and the object within an image. It uses both instance and semantic segmentation.

Boundary recognition

Determine objects’ boundaries within an image, it includes the edges of a specific object or regions of topography present in the image. Boundary recognition is an essential factor in the safe operation of autonomous vehicles or self-driving cars. Also, it can be used to teach an AI model to find the foreground from the background in an image or exclusion zones.

How can you easily annotate your image

Look for tools for annotating your image.

Load all your images to the website to annotate them.

Upload the image by selecting the preferred image to annotate, do not upload the .zip files.

Make sure you confirm if the annotation website you are using can be able to save your annotation instead do not refresh your tab if you are having annotation in progress since you will have to start from the beginning.

Hover on the object in the chosen image, click and drag to generate a rectangular box of the intended size.

Export the image annotation in the right format.

Image Annotation Methods

Bounding Boxes

These are rectangular boxes used to identify the object’s location within an image and draw a box around the target object, especially symmetrical objects. Bounding boxes can be two or three dimensional.

Landmarking

Used to determine basic points of interest within an image, annotate body position and adjustment using pose-point annotations, as well as plot characteristics in the data, such as with facial recognition.

Masking

A pixel-level annotation used to reveal areas of interest and hide other areas in an image.

Polygons

Polygons are also used to annotate asymmetrical objects within an image, such as vegetation, and houses.

Polyline

They are utilized when working with open shapes, such as sidewalks and road lane markers.

Tracking

Used to label the movement of an object across different frames of video.

Transcription

It is utilized to categorize text in images or videos if there is multimodal information in the data.

How do companies do image annotations?

Companies use both software, people and processes to collect, clean and annotate images. People can be employees who have a contract, or freelancers.

Best labeling image tools

Free

  • Isahit lab
  • Labelme.
  • CVAT

Paid

  • labelImg.
  • SuperAnnotate
  • V7

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