ultralytics/docs/tasks/segment.md

comments	description
true	Learn what Instance segmentation is. Get pretrained YOLOv8 segment models, and how to train and export them to segments masks. Check the preformance metrics!

Instance segmentation goes a step further than object detection and involves identifying individual objects in an image and segmenting them from the rest of the image.

The output of an instance segmentation model is a set of masks or contours that outline each object in the image, along with class labels and confidence scores for each object. Instance segmentation is useful when you need to know not only where objects are in an image, but also what their exact shape is.

!!! tip "Tip"

YOLOv8 Segment models use the `-seg` suffix, i.e. `yolov8n-seg.pt` and are pretrained on [COCO](https://github.com/ultralytics/ultralytics/blob/main/ultralytics/datasets/coco.yaml).

Models

YOLOv8 pretrained Segment models are shown here. Detect, Segment and Pose models are pretrained on the COCO dataset, while Classify models are pretrained on the ImageNet dataset.

Models download automatically from the latest Ultralytics release on first use.

Model	size (pixels)	mAPbox 50-95	mAPmask 50-95	Speed CPU ONNX (ms)	Speed A100 TensorRT (ms)	params (M)	FLOPs (B)
YOLOv8n-seg	640	36.7	30.5	96.1	1.21	3.4	12.6
YOLOv8s-seg	640	44.6	36.8	155.7	1.47	11.8	42.6
YOLOv8m-seg	640	49.9	40.8	317.0	2.18	27.3	110.2
YOLOv8l-seg	640	52.3	42.6	572.4	2.79	46.0	220.5
YOLOv8x-seg	640	53.4	43.4	712.1	4.02	71.8	344.1

• mAP^val values are for single-model single-scale on COCO val2017 dataset.
  Reproduce by yolo val segment data=coco.yaml device=0
• Speed averaged over COCO val images using an Amazon EC2 P4d instance.
  Reproduce by yolo val segment data=coco128-seg.yaml batch=1 device=0|cpu

Train

Train YOLOv8n-seg on the COCO128-seg dataset for 100 epochs at image size 640. For a full list of available arguments see the Configuration page.

!!! example ""

=== "Python"

    ```python
    from ultralytics import YOLO
    
    # Load a model
    model = YOLO('yolov8n-seg.yaml')  # build a new model from YAML
    model = YOLO('yolov8n-seg.pt')  # load a pretrained model (recommended for training)
    model = YOLO('yolov8n-seg.yaml').load('yolov8n.pt')  # build from YAML and transfer weights
    
    # Train the model
    model.train(data='coco128-seg.yaml', epochs=100, imgsz=640)
    ```
=== "CLI"

    ```bash
    # Build a new model from YAML and start training from scratch
    yolo segment train data=coco128-seg.yaml model=yolov8n-seg.yaml epochs=100 imgsz=640

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

    # Build a new model from YAML, transfer pretrained weights to it and start training
    yolo segment train data=coco128-seg.yaml model=yolov8n-seg.yaml pretrained=yolov8n-seg.pt epochs=100 imgsz=640
    ```

Dataset format

YOLO segmentation dataset format can be found in detail in the Dataset Guide. To convert your existing dataset from other formats( like COCO etc.) to YOLO format, please use json2yolo tool by Ultralytics.

Val

Validate trained YOLOv8n-seg model accuracy on the COCO128-seg dataset. No argument need to passed as the model retains it's training data and arguments as model attributes.

!!! example ""

=== "Python"

    ```python
    from ultralytics import YOLO
    
    # Load a model
    model = YOLO('yolov8n-seg.pt')  # load an official model
    model = YOLO('path/to/best.pt')  # load a custom model
    
    # Validate the model
    metrics = model.val()  # no arguments needed, dataset and settings remembered
    metrics.box.map    # map50-95(B)
    metrics.box.map50  # map50(B)
    metrics.box.map75  # map75(B)
    metrics.box.maps   # a list contains map50-95(B) of each category
    metrics.seg.map    # map50-95(M)
    metrics.seg.map50  # map50(M)
    metrics.seg.map75  # map75(M)
    metrics.seg.maps   # a list contains map50-95(M) of each category
    ```
=== "CLI"

    ```bash
    yolo segment val model=yolov8n-seg.pt  # val official model
    yolo segment val model=path/to/best.pt  # val custom model
    ```

Predict

Use a trained YOLOv8n-seg model to run predictions on images.

!!! example ""

=== "Python"

    ```python
    from ultralytics import YOLO
    
    # Load a model
    model = YOLO('yolov8n-seg.pt')  # load an official model
    model = YOLO('path/to/best.pt')  # load a custom model
    
    # Predict with the model
    results = model('https://ultralytics.com/images/bus.jpg')  # predict on an image
    ```
=== "CLI"

    ```bash
    yolo segment predict model=yolov8n-seg.pt source='https://ultralytics.com/images/bus.jpg'  # predict with official model
    yolo segment predict model=path/to/best.pt source='https://ultralytics.com/images/bus.jpg'  # predict with custom model
    ```

See full predict mode details in the Predict page.

Export

Export a YOLOv8n-seg model to a different format like ONNX, CoreML, etc.

!!! example ""

=== "Python"

    ```python
    from ultralytics import YOLO
    
    # Load a model
    model = YOLO('yolov8n-seg.pt')  # load an official model
    model = YOLO('path/to/best.pt')  # load a custom trained
    
    # Export the model
    model.export(format='onnx')
    ```
=== "CLI"

    ```bash
    yolo export model=yolov8n-seg.pt format=onnx  # export official model
    yolo export model=path/to/best.pt format=onnx  # export custom trained model
    ```

Available YOLOv8-seg export formats are in the table below. You can predict or validate directly on exported models, i.e. yolo predict model=yolov8n-seg.onnx. Usage examples are shown for your model after export completes.

Format	format Argument	Model	Metadata	Arguments
PyTorch	-	yolov8n-seg.pt	✅	-
TorchScript	torchscript	yolov8n-seg.torchscript	✅	imgsz, optimize
ONNX	onnx	yolov8n-seg.onnx	✅	imgsz, half, dynamic, simplify, opset
OpenVINO	openvino	yolov8n-seg_openvino_model/	✅	imgsz, half
TensorRT	engine	yolov8n-seg.engine	✅	imgsz, half, dynamic, simplify, workspace
CoreML	coreml	yolov8n-seg.mlmodel	✅	imgsz, half, int8, nms
TF SavedModel	saved_model	yolov8n-seg_saved_model/	✅	imgsz, keras
TF GraphDef	pb	yolov8n-seg.pb	❌	imgsz
TF Lite	tflite	yolov8n-seg.tflite	✅	imgsz, half, int8
TF Edge TPU	edgetpu	yolov8n-seg_edgetpu.tflite	✅	imgsz
TF.js	tfjs	yolov8n-seg_web_model/	✅	imgsz
PaddlePaddle	paddle	yolov8n-seg_paddle_model/	✅	imgsz

See full export details in the Export page.