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true	Learn about the Ultralytics YOLO dataset format for segmentation models. Use YAML to train Detection Models. Convert COCO to YOLO format using Python.

Instance Segmentation Datasets Overview

Supported Dataset Formats

Ultralytics YOLO format

** Label Format **

The dataset format used for training YOLO segmentation models is as follows:

One text file per image: Each image in the dataset has a corresponding text file with the same name as the image file and the ".txt" extension.
One row per object: Each row in the text file corresponds to one object instance in the image.
Object information per row: Each row contains the following information about the object instance:
- Object class index: An integer representing the class of the object (e.g., 0 for person, 1 for car, etc.).
- Object bounding coordinates: The bounding coordinates around the mask area, normalized to be between 0 and 1.

The format for a single row in the segmentation dataset file is as follows:

<class-index> <x1> <y1> <x2> <y2> ... <xn> <yn>

In this format, <class-index> is the index of the class for the object, and <x1> <y1> <x2> <y2> ... <xn> <yn> are the bounding coordinates of the object's segmentation mask. The coordinates are separated by spaces.

Here is an example of the YOLO dataset format for a single image with two object instances:

0 0.6812 0.48541 0.67 0.4875 0.67656 0.487 0.675 0.489 0.66
1 0.5046 0.0 0.5015 0.004 0.4984 0.00416 0.4937 0.010 0.492 0.0104

Note: The length of each row does not have to be equal.

** Dataset file format **

The Ultralytics framework uses a YAML file format to define the dataset and model configuration for training Detection Models. Here is an example of the YAML format used for defining a detection dataset:

train: <path-to-training-images>
val: <path-to-validation-images>

nc: <number-of-classes>
names: [<class-1>, <class-2>, ..., <class-n>]

The train and val fields specify the paths to the directories containing the training and validation images, respectively.

The nc field specifies the number of object classes in the dataset.

The names field is a list of the names of the object classes. The order of the names should match the order of the object class indices in the YOLO dataset files.

NOTE: Either nc or names must be defined. Defining both are not mandatory.

Alternatively, you can directly define class names like this:

names:
  0: person
  1: bicycle

** Example **

train: data/train/
val: data/val/

nc: 2
names: ['person', 'car']

Usage

!!! example ""

=== "Python"

    ```python
    from ultralytics import YOLO
    
    # Load a model
    model = YOLO('yolov8n-seg.pt')  # load a pretrained model (recommended for training)

    # Train the model
    model.train(data='coco128-seg.yaml', epochs=100, imgsz=640)
    ```
=== "CLI"

    ```bash
    # Start training from a pretrained *.pt model
    yolo detect train data=coco128-seg.yaml model=yolov8n-seg.pt epochs=100 imgsz=640
    ```

Supported Datasets

Port or Convert label formats

COCO dataset format to YOLO format

from ultralytics.yolo.data.converter import convert_coco

convert_coco(labels_dir='../coco/annotations/', use_segments=True)

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