Add Chinese Modes and Tasks Docs (#6274)

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---
comments: true
description: Learn how to utilize callbacks in the Ultralytics framework during train, val, export, and predict modes for enhanced functionality.
keywords: Ultralytics, YOLO, callbacks guide, training callback, validation callback, export callback, prediction callback
---
## Callbacks
Ultralytics framework supports callbacks as entry points in strategic stages of train, val, export, and predict modes. Each callback accepts a `Trainer`, `Validator`, or `Predictor` object depending on the operation type. All properties of these objects can be found in Reference section of the docs.
## Examples
### Returning additional information with Prediction
In this example, we want to return the original frame with each result object. Here's how we can do that
```python
def on_predict_batch_end(predictor):
# Retrieve the batch data
_, im0s, _, _ = predictor.batch
# Ensure that im0s is a list
im0s = im0s if isinstance(im0s, list) else [im0s]
# Combine the prediction results with the corresponding frames
predictor.results = zip(predictor.results, im0s)
# Create a YOLO model instance
model = YOLO(f'yolov8n.pt')
# Add the custom callback to the model
model.add_callback("on_predict_batch_end", on_predict_batch_end)
# Iterate through the results and frames
for (result, frame) in model.track/predict():
pass
```
## All callbacks
Here are all supported callbacks. See callbacks [source code](https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/callbacks/base.py) for additional details.
### Trainer Callbacks
| Callback | Description |
|-----------------------------|---------------------------------------------------------|
| `on_pretrain_routine_start` | Triggered at the beginning of pre-training routine |
| `on_pretrain_routine_end` | Triggered at the end of pre-training routine |
| `on_train_start` | Triggered when the training starts |
| `on_train_epoch_start` | Triggered at the start of each training epoch |
| `on_train_batch_start` | Triggered at the start of each training batch |
| `optimizer_step` | Triggered during the optimizer step |
| `on_before_zero_grad` | Triggered before gradients are zeroed |
| `on_train_batch_end` | Triggered at the end of each training batch |
| `on_train_epoch_end` | Triggered at the end of each training epoch |
| `on_fit_epoch_end` | Triggered at the end of each fit epoch |
| `on_model_save` | Triggered when the model is saved |
| `on_train_end` | Triggered when the training process ends |
| `on_params_update` | Triggered when model parameters are updated |
| `teardown` | Triggered when the training process is being cleaned up |
### Validator Callbacks
| Callback | Description |
|----------------------|-------------------------------------------------|
| `on_val_start` | Triggered when the validation starts |
| `on_val_batch_start` | Triggered at the start of each validation batch |
| `on_val_batch_end` | Triggered at the end of each validation batch |
| `on_val_end` | Triggered when the validation ends |
### Predictor Callbacks
| Callback | Description |
|------------------------------|---------------------------------------------------|
| `on_predict_start` | Triggered when the prediction process starts |
| `on_predict_batch_start` | Triggered at the start of each prediction batch |
| `on_predict_postprocess_end` | Triggered at the end of prediction postprocessing |
| `on_predict_batch_end` | Triggered at the end of each prediction batch |
| `on_predict_end` | Triggered when the prediction process ends |
### Exporter Callbacks
| Callback | Description |
|-------------------|------------------------------------------|
| `on_export_start` | Triggered when the export process starts |
| `on_export_end` | Triggered when the export process ends |

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---
comments: true
description: Master YOLOv8 settings and hyperparameters for improved model performance. Learn to use YOLO CLI commands, adjust training settings, and optimize YOLO tasks & modes.
keywords: YOLOv8, settings, hyperparameters, YOLO CLI commands, YOLO tasks, YOLO modes, Ultralytics documentation, model optimization, YOLOv8 training
---
YOLO settings and hyperparameters play a critical role in the model's performance, speed, and accuracy. These settings and hyperparameters can affect the model's behavior at various stages of the model development process, including training, validation, and prediction.
YOLOv8 `yolo` CLI commands use the following syntax:
!!! example ""
=== "CLI"
```bash
yolo TASK MODE ARGS
```
=== "Python"
```python
from ultralytics import YOLO
# Load a YOLOv8 model from a pre-trained weights file
model = YOLO('yolov8n.pt')
# Run MODE mode using the custom arguments ARGS (guess TASK)
model.MODE(ARGS)
```
Where:
- `TASK` (optional) is one of `[detect, segment, classify, pose]`. If it is not passed explicitly YOLOv8 will try to guess the `TASK` from the model type.
- `MODE` (required) is one of `[train, val, predict, export, track, benchmark]`
- `ARGS` (optional) are any number of custom `arg=value` pairs like `imgsz=320` that override defaults.
For a full list of available `ARGS` see the [Configuration](cfg.md) page and `defaults.yaml` GitHub [source](https://github.com/ultralytics/ultralytics/blob/main/ultralytics/cfg/default.yaml).
#### Tasks
YOLO models can be used for a variety of tasks, including detection, segmentation, classification and pose. These tasks differ in the type of output they produce and the specific problem they are designed to solve.
**Detect**: For identifying and localizing objects or regions of interest in an image or video.
**Segment**: For dividing an image or video into regions or pixels that correspond to different objects or classes.
**Classify**: For predicting the class label of an input image.
**Pose**: For identifying objects and estimating their keypoints in an image or video.
| Key | Value | Description |
|--------|------------|-------------------------------------------------|
| `task` | `'detect'` | YOLO task, i.e. detect, segment, classify, pose |
[Tasks Guide](../tasks/index.md){ .md-button .md-button--primary}
#### Modes
YOLO models can be used in different modes depending on the specific problem you are trying to solve. These modes include:
**Train**: For training a YOLOv8 model on a custom dataset.
**Val**: For validating a YOLOv8 model after it has been trained.
**Predict**: For making predictions using a trained YOLOv8 model on new images or videos.
**Export**: For exporting a YOLOv8 model to a format that can be used for deployment.
**Track**: For tracking objects in real-time using a YOLOv8 model.
**Benchmark**: For benchmarking YOLOv8 exports (ONNX, TensorRT, etc.) speed and accuracy.
| Key | Value | Description |
|--------|-----------|---------------------------------------------------------------|
| `mode` | `'train'` | YOLO mode, i.e. train, val, predict, export, track, benchmark |
[Modes Guide](../modes/index.md){ .md-button .md-button--primary}
## Train
The training settings for YOLO models encompass various hyperparameters and configurations used during the training process. These settings influence the model's performance, speed, and accuracy. Key training settings include batch size, learning rate, momentum, and weight decay. Additionally, the choice of optimizer, loss function, and training dataset composition can impact the training process. Careful tuning and experimentation with these settings are crucial for optimizing performance.
| Key | Value | Description |
|-------------------|----------|------------------------------------------------------------------------------------------------|
| `model` | `None` | path to model file, i.e. yolov8n.pt, yolov8n.yaml |
| `data` | `None` | path to data file, i.e. coco128.yaml |
| `epochs` | `100` | number of epochs to train for |
| `patience` | `50` | epochs to wait for no observable improvement for early stopping of training |
| `batch` | `16` | number of images per batch (-1 for AutoBatch) |
| `imgsz` | `640` | size of input images as integer or w,h |
| `save` | `True` | save train checkpoints and predict results |
| `save_period` | `-1` | Save checkpoint every x epochs (disabled if < 1) |
| `cache` | `False` | True/ram, disk or False. Use cache for data loading |
| `device` | `None` | device to run on, i.e. cuda device=0 or device=0,1,2,3 or device=cpu |
| `workers` | `8` | number of worker threads for data loading (per RANK if DDP) |
| `project` | `None` | project name |
| `name` | `None` | experiment name |
| `exist_ok` | `False` | whether to overwrite existing experiment |
| `pretrained` | `True` | (bool or str) whether to use a pretrained model (bool) or a model to load weights from (str) |
| `optimizer` | `'auto'` | optimizer to use, choices=[SGD, Adam, Adamax, AdamW, NAdam, RAdam, RMSProp, auto] |
| `verbose` | `False` | whether to print verbose output |
| `seed` | `0` | random seed for reproducibility |
| `deterministic` | `True` | whether to enable deterministic mode |
| `single_cls` | `False` | train multi-class data as single-class |
| `rect` | `False` | rectangular training with each batch collated for minimum padding |
| `cos_lr` | `False` | use cosine learning rate scheduler |
| `close_mosaic` | `10` | (int) disable mosaic augmentation for final epochs (0 to disable) |
| `resume` | `False` | resume training from last checkpoint |
| `amp` | `True` | Automatic Mixed Precision (AMP) training, choices=[True, False] |
| `fraction` | `1.0` | dataset fraction to train on (default is 1.0, all images in train set) |
| `profile` | `False` | profile ONNX and TensorRT speeds during training for loggers |
| `freeze` | `None` | (int or list, optional) freeze first n layers, or freeze list of layer indices during training |
| `lr0` | `0.01` | initial learning rate (i.e. SGD=1E-2, Adam=1E-3) |
| `lrf` | `0.01` | final learning rate (lr0 * lrf) |
| `momentum` | `0.937` | SGD momentum/Adam beta1 |
| `weight_decay` | `0.0005` | optimizer weight decay 5e-4 |
| `warmup_epochs` | `3.0` | warmup epochs (fractions ok) |
| `warmup_momentum` | `0.8` | warmup initial momentum |
| `warmup_bias_lr` | `0.1` | warmup initial bias lr |
| `box` | `7.5` | box loss gain |
| `cls` | `0.5` | cls loss gain (scale with pixels) |
| `dfl` | `1.5` | dfl loss gain |
| `pose` | `12.0` | pose loss gain (pose-only) |
| `kobj` | `2.0` | keypoint obj loss gain (pose-only) |
| `label_smoothing` | `0.0` | label smoothing (fraction) |
| `nbs` | `64` | nominal batch size |
| `overlap_mask` | `True` | masks should overlap during training (segment train only) |
| `mask_ratio` | `4` | mask downsample ratio (segment train only) |
| `dropout` | `0.0` | use dropout regularization (classify train only) |
| `val` | `True` | validate/test during training |
[Train Guide](../modes/train.md){ .md-button .md-button--primary}
## Predict
The prediction settings for YOLO models encompass a range of hyperparameters and configurations that influence the model's performance, speed, and accuracy during inference on new data. Careful tuning and experimentation with these settings are essential to achieve optimal performance for a specific task. Key settings include the confidence threshold, Non-Maximum Suppression (NMS) threshold, and the number of classes considered. Additional factors affecting the prediction process are input data size and format, the presence of supplementary features such as masks or multiple labels per box, and the particular task the model is employed for.
| Key | Value | Description |
|-----------------|------------------------|--------------------------------------------------------------------------------|
| `source` | `'ultralytics/assets'` | source directory for images or videos |
| `conf` | `0.25` | object confidence threshold for detection |
| `iou` | `0.7` | intersection over union (IoU) threshold for NMS |
| `half` | `False` | use half precision (FP16) |
| `device` | `None` | device to run on, i.e. cuda device=0/1/2/3 or device=cpu |
| `show` | `False` | show results if possible |
| `save` | `False` | save images with results |
| `save_txt` | `False` | save results as .txt file |
| `save_conf` | `False` | save results with confidence scores |
| `save_crop` | `False` | save cropped images with results |
| `show_labels` | `True` | show object labels in plots |
| `show_conf` | `True` | show object confidence scores in plots |
| `max_det` | `300` | maximum number of detections per image |
| `vid_stride` | `False` | video frame-rate stride |
| `stream_buffer` | `bool` | buffer all streaming frames (True) or return the most recent frame (False) |
| `line_width` | `None` | The line width of the bounding boxes. If None, it is scaled to the image size. |
| `visualize` | `False` | visualize model features |
| `augment` | `False` | apply image augmentation to prediction sources |
| `agnostic_nms` | `False` | class-agnostic NMS |
| `retina_masks` | `False` | use high-resolution segmentation masks |
| `classes` | `None` | filter results by class, i.e. classes=0, or classes=[0,2,3] |
| `boxes` | `True` | Show boxes in segmentation predictions |
[Predict Guide](../modes/predict.md){ .md-button .md-button--primary}
## Val
The val (validation) settings for YOLO models involve various hyperparameters and configurations used to evaluate the model's performance on a validation dataset. These settings influence the model's performance, speed, and accuracy. Common YOLO validation settings include batch size, validation frequency during training, and performance evaluation metrics. Other factors affecting the validation process include the validation dataset's size and composition, as well as the specific task the model is employed for. Careful tuning and experimentation with these settings are crucial to ensure optimal performance on the validation dataset and detect and prevent overfitting.
| Key | Value | Description |
|---------------|---------|--------------------------------------------------------------------|
| `save_json` | `False` | save results to JSON file |
| `save_hybrid` | `False` | save hybrid version of labels (labels + additional predictions) |
| `conf` | `0.001` | object confidence threshold for detection |
| `iou` | `0.6` | intersection over union (IoU) threshold for NMS |
| `max_det` | `300` | maximum number of detections per image |
| `half` | `True` | use half precision (FP16) |
| `device` | `None` | device to run on, i.e. cuda device=0/1/2/3 or device=cpu |
| `dnn` | `False` | use OpenCV DNN for ONNX inference |
| `plots` | `False` | show plots during training |
| `rect` | `False` | rectangular val with each batch collated for minimum padding |
| `split` | `val` | dataset split to use for validation, i.e. 'val', 'test' or 'train' |
[Val Guide](../modes/val.md){ .md-button .md-button--primary}
## Export
Export settings for YOLO models encompass configurations and options related to saving or exporting the model for use in different environments or platforms. These settings can impact the model's performance, size, and compatibility with various systems. Key export settings include the exported model file format (e.g., ONNX, TensorFlow SavedModel), the target device (e.g., CPU, GPU), and additional features such as masks or multiple labels per box. The export process may also be affected by the model's specific task and the requirements or constraints of the destination environment or platform. It is crucial to thoughtfully configure these settings to ensure the exported model is optimized for the intended use case and functions effectively in the target environment.
| Key | Value | Description |
|-------------|-----------------|------------------------------------------------------|
| `format` | `'torchscript'` | format to export to |
| `imgsz` | `640` | image size as scalar or (h, w) list, i.e. (640, 480) |
| `keras` | `False` | use Keras for TF SavedModel export |
| `optimize` | `False` | TorchScript: optimize for mobile |
| `half` | `False` | FP16 quantization |
| `int8` | `False` | INT8 quantization |
| `dynamic` | `False` | ONNX/TF/TensorRT: dynamic axes |
| `simplify` | `False` | ONNX: simplify model |
| `opset` | `None` | ONNX: opset version (optional, defaults to latest) |
| `workspace` | `4` | TensorRT: workspace size (GB) |
| `nms` | `False` | CoreML: add NMS |
[Export Guide](../modes/export.md){ .md-button .md-button--primary}
## Augmentation
Augmentation settings for YOLO models refer to the various transformations and modifications applied to the training data to increase the diversity and size of the dataset. These settings can affect the model's performance, speed, and accuracy. Some common YOLO augmentation settings include the type and intensity of the transformations applied (e.g. random flips, rotations, cropping, color changes), the probability with which each transformation is applied, and the presence of additional features such as masks or multiple labels per box. Other factors that may affect the augmentation process include the size and composition of the original dataset and the specific task the model is being used for. It is important to carefully tune and experiment with these settings to ensure that the augmented dataset is diverse and representative enough to train a high-performing model.
| Key | Value | Description |
|---------------|---------|-------------------------------------------------|
| `hsv_h` | `0.015` | image HSV-Hue augmentation (fraction) |
| `hsv_s` | `0.7` | image HSV-Saturation augmentation (fraction) |
| `hsv_v` | `0.4` | image HSV-Value augmentation (fraction) |
| `degrees` | `0.0` | image rotation (+/- deg) |
| `translate` | `0.1` | image translation (+/- fraction) |
| `scale` | `0.5` | image scale (+/- gain) |
| `shear` | `0.0` | image shear (+/- deg) |
| `perspective` | `0.0` | image perspective (+/- fraction), range 0-0.001 |
| `flipud` | `0.0` | image flip up-down (probability) |
| `fliplr` | `0.5` | image flip left-right (probability) |
| `mosaic` | `1.0` | image mosaic (probability) |
| `mixup` | `0.0` | image mixup (probability) |
| `copy_paste` | `0.0` | segment copy-paste (probability) |
## Logging, checkpoints, plotting and file management
Logging, checkpoints, plotting, and file management are important considerations when training a YOLO model.
- Logging: It is often helpful to log various metrics and statistics during training to track the model's progress and diagnose any issues that may arise. This can be done using a logging library such as TensorBoard or by writing log messages to a file.
- Checkpoints: It is a good practice to save checkpoints of the model at regular intervals during training. This allows you to resume training from a previous point if the training process is interrupted or if you want to experiment with different training configurations.
- Plotting: Visualizing the model's performance and training progress can be helpful for understanding how the model is behaving and identifying potential issues. This can be done using a plotting library such as matplotlib or by generating plots using a logging library such as TensorBoard.
- File management: Managing the various files generated during the training process, such as model checkpoints, log files, and plots, can be challenging. It is important to have a clear and organized file structure to keep track of these files and make it easy to access and analyze them as needed.
Effective logging, checkpointing, plotting, and file management can help you keep track of the model's progress and make it easier to debug and optimize the training process.
| Key | Value | Description |
|------------|----------|------------------------------------------------------------------------------------------------|
| `project` | `'runs'` | project name |
| `name` | `'exp'` | experiment name. `exp` gets automatically incremented if not specified, i.e, `exp`, `exp2` ... |
| `exist_ok` | `False` | whether to overwrite existing experiment |
| `plots` | `False` | save plots during train/val |
| `save` | `False` | save train checkpoints and predict results |

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---
comments: true
description: 'Learn how to use Ultralytics YOLO through Command Line: train models, run predictions and exports models to different formats easily using terminal commands.'
keywords: Ultralytics, YOLO, CLI, train, validation, prediction, command line interface, YOLO CLI, YOLO terminal, model training, prediction, exporting
---
# Command Line Interface Usage
The YOLO command line interface (CLI) allows for simple single-line commands without the need for a Python environment. CLI requires no customization or Python code. You can simply run all tasks from the terminal with the `yolo` command.
<p align="center">
<br>
<iframe width="720" height="405" src="https://www.youtube.com/embed/GsXGnb-A4Kc"
title="YouTube video player" frameborder="0"
allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share"
allowfullscreen>
</iframe>
<br>
<strong>Watch:</strong> Mastering Ultralytics YOLOv8: CLI & Python Usage and Live Inference
</p>
!!! example
=== "Syntax"
Ultralytics `yolo` commands use the following syntax:
```bash
yolo TASK MODE ARGS
Where TASK (optional) is one of [detect, segment, classify]
MODE (required) is one of [train, val, predict, export, track]
ARGS (optional) are any number of custom 'arg=value' pairs like 'imgsz=320' that override defaults.
```
See all ARGS in the full [Configuration Guide](./cfg.md) or with `yolo cfg`
=== "Train"
Train a detection model for 10 epochs with an initial learning_rate of 0.01
```bash
yolo train data=coco128.yaml model=yolov8n.pt epochs=10 lr0=0.01
```
=== "Predict"
Predict a YouTube video using a pretrained segmentation model at image size 320:
```bash
yolo predict model=yolov8n-seg.pt source='https://youtu.be/LNwODJXcvt4' imgsz=320
```
=== "Val"
Val a pretrained detection model at batch-size 1 and image size 640:
```bash
yolo val model=yolov8n.pt data=coco128.yaml batch=1 imgsz=640
```
=== "Export"
Export a YOLOv8n classification model to ONNX format at image size 224 by 128 (no TASK required)
```bash
yolo export model=yolov8n-cls.pt format=onnx imgsz=224,128
```
=== "Special"
Run special commands to see version, view settings, run checks and more:
```bash
yolo help
yolo checks
yolo version
yolo settings
yolo copy-cfg
yolo cfg
```
Where:
- `TASK` (optional) is one of `[detect, segment, classify]`. If it is not passed explicitly YOLOv8 will try to guess the `TASK` from the model type.
- `MODE` (required) is one of `[train, val, predict, export, track]`
- `ARGS` (optional) are any number of custom `arg=value` pairs like `imgsz=320` that override defaults. For a full list of available `ARGS` see the [Configuration](cfg.md) page and `defaults.yaml`
GitHub [source](https://github.com/ultralytics/ultralytics/blob/main/ultralytics/cfg/default.yaml).
!!! warning "Warning"
Arguments must be passed as `arg=val` pairs, split by an equals `=` sign and delimited by spaces ` ` between pairs. Do not use `--` argument prefixes or commas `,` between arguments.
- `yolo predict model=yolov8n.pt imgsz=640 conf=0.25` &nbsp;
- `yolo predict model yolov8n.pt imgsz 640 conf 0.25` &nbsp;
- `yolo predict --model yolov8n.pt --imgsz 640 --conf 0.25` &nbsp;
## Train
Train YOLOv8n on the COCO128 dataset for 100 epochs at image size 640. For a full list of available arguments see the [Configuration](cfg.md) page.
!!! example "Example"
=== "Train"
Start training YOLOv8n on COCO128 for 100 epochs at image-size 640.
```bash
yolo detect train data=coco128.yaml model=yolov8n.pt epochs=100 imgsz=640
```
=== "Resume"
Resume an interrupted training.
```bash
yolo detect train resume model=last.pt
```
## Val
Validate trained YOLOv8n model accuracy on the COCO128 dataset. No argument need to passed as the `model` retains it's training `data` and arguments as model attributes.
!!! example "Example"
=== "Official"
Validate an official YOLOv8n model.
```bash
yolo detect val model=yolov8n.pt
```
=== "Custom"
Validate a custom-trained model.
```bash
yolo detect val model=path/to/best.pt
```
## Predict
Use a trained YOLOv8n model to run predictions on images.
!!! example "Example"
=== "Official"
Predict with an official YOLOv8n model.
```bash
yolo detect predict model=yolov8n.pt source='https://ultralytics.com/images/bus.jpg'
```
=== "Custom"
Predict with a custom model.
```bash
yolo detect predict model=path/to/best.pt source='https://ultralytics.com/images/bus.jpg'
```
## Export
Export a YOLOv8n model to a different format like ONNX, CoreML, etc.
!!! example "Example"
=== "Official"
Export an official YOLOv8n model to ONNX format.
```bash
yolo export model=yolov8n.pt format=onnx
```
=== "Custom"
Export a custom-trained model to ONNX format.
```bash
yolo export model=path/to/best.pt format=onnx
```
Available YOLOv8 export formats are in the table below. You can export to any format using the `format` argument, i.e. `format='onnx'` or `format='engine'`.
| Format | `format` Argument | Model | Metadata | Arguments |
|--------------------------------------------------------------------|-------------------|---------------------------|----------|-----------------------------------------------------|
| [PyTorch](https://pytorch.org/) | - | `yolov8n.pt` | ✅ | - |
| [TorchScript](https://pytorch.org/docs/stable/jit.html) | `torchscript` | `yolov8n.torchscript` | ✅ | `imgsz`, `optimize` |
| [ONNX](https://onnx.ai/) | `onnx` | `yolov8n.onnx` | ✅ | `imgsz`, `half`, `dynamic`, `simplify`, `opset` |
| [OpenVINO](https://docs.openvino.ai/latest/index.html) | `openvino` | `yolov8n_openvino_model/` | ✅ | `imgsz`, `half` |
| [TensorRT](https://developer.nvidia.com/tensorrt) | `engine` | `yolov8n.engine` | ✅ | `imgsz`, `half`, `dynamic`, `simplify`, `workspace` |
| [CoreML](https://github.com/apple/coremltools) | `coreml` | `yolov8n.mlpackage` | ✅ | `imgsz`, `half`, `int8`, `nms` |
| [TF SavedModel](https://www.tensorflow.org/guide/saved_model) | `saved_model` | `yolov8n_saved_model/` | ✅ | `imgsz`, `keras` |
| [TF GraphDef](https://www.tensorflow.org/api_docs/python/tf/Graph) | `pb` | `yolov8n.pb` | ❌ | `imgsz` |
| [TF Lite](https://www.tensorflow.org/lite) | `tflite` | `yolov8n.tflite` | ✅ | `imgsz`, `half`, `int8` |
| [TF Edge TPU](https://coral.ai/docs/edgetpu/models-intro/) | `edgetpu` | `yolov8n_edgetpu.tflite` | ✅ | `imgsz` |
| [TF.js](https://www.tensorflow.org/js) | `tfjs` | `yolov8n_web_model/` | ✅ | `imgsz` |
| [PaddlePaddle](https://github.com/PaddlePaddle) | `paddle` | `yolov8n_paddle_model/` | ✅ | `imgsz` |
| [ncnn](https://github.com/Tencent/ncnn) | `ncnn` | `yolov8n_ncnn_model/` | ✅ | `imgsz`, `half` |
## Overriding default arguments
Default arguments can be overridden by simply passing them as arguments in the CLI in `arg=value` pairs.
!!! tip ""
=== "Train"
Train a detection model for `10 epochs` with `learning_rate` of `0.01`
```bash
yolo detect train data=coco128.yaml model=yolov8n.pt epochs=10 lr0=0.01
```
=== "Predict"
Predict a YouTube video using a pretrained segmentation model at image size 320:
```bash
yolo segment predict model=yolov8n-seg.pt source='https://youtu.be/LNwODJXcvt4' imgsz=320
```
=== "Val"
Validate a pretrained detection model at batch-size 1 and image size 640:
```bash
yolo detect val model=yolov8n.pt data=coco128.yaml batch=1 imgsz=640
```
## Overriding default config file
You can override the `default.yaml` config file entirely by passing a new file with the `cfg` arguments, i.e. `cfg=custom.yaml`.
To do this first create a copy of `default.yaml` in your current working dir with the `yolo copy-cfg` command.
This will create `default_copy.yaml`, which you can then pass as `cfg=default_copy.yaml` along with any additional args, like `imgsz=320` in this example:
!!! example ""
=== "CLI"
```bash
yolo copy-cfg
yolo cfg=default_copy.yaml imgsz=320
```

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---
comments: true
description: Discover how to customize and extend base Ultralytics YOLO Trainer engines. Support your custom model and dataloader by overriding built-in functions.
keywords: Ultralytics, YOLO, trainer engines, BaseTrainer, DetectionTrainer, customizing trainers, extending trainers, custom model, custom dataloader
---
Both the Ultralytics YOLO command-line and Python interfaces are simply a high-level abstraction on the base engine executors. Let's take a look at the Trainer engine.
## BaseTrainer
BaseTrainer contains the generic boilerplate training routine. It can be customized for any task based over overriding the required functions or operations as long the as correct formats are followed. For example, you can support your own custom model and dataloader by just overriding these functions:
* `get_model(cfg, weights)` - The function that builds the model to be trained
* `get_dataloader()` - The function that builds the dataloader More details and source code can be found in [`BaseTrainer` Reference](../reference/engine/trainer.md)
## DetectionTrainer
Here's how you can use the YOLOv8 `DetectionTrainer` and customize it.
```python
from ultralytics.models.yolo.detect import DetectionTrainer
trainer = DetectionTrainer(overrides={...})
trainer.train()
trained_model = trainer.best # get best model
```
### Customizing the DetectionTrainer
Let's customize the trainer **to train a custom detection model** that is not supported directly. You can do this by simply overloading the existing the `get_model` functionality:
```python
from ultralytics.models.yolo.detect import DetectionTrainer
class CustomTrainer(DetectionTrainer):
def get_model(self, cfg, weights):
...
trainer = CustomTrainer(overrides={...})
trainer.train()
```
You now realize that you need to customize the trainer further to:
* Customize the `loss function`.
* Add `callback` that uploads model to your Google Drive after every 10 `epochs`
Here's how you can do it:
```python
from ultralytics.models.yolo.detect import DetectionTrainer
from ultralytics.nn.tasks import DetectionModel
class MyCustomModel(DetectionModel):
def init_criterion(self):
...
class CustomTrainer(DetectionTrainer):
def get_model(self, cfg, weights):
return MyCustomModel(...)
# callback to upload model weights
def log_model(trainer):
last_weight_path = trainer.last
...
trainer = CustomTrainer(overrides={...})
trainer.add_callback("on_train_epoch_end", log_model) # Adds to existing callback
trainer.train()
```
To know more about Callback triggering events and entry point, checkout our [Callbacks Guide](callbacks.md)
## Other engine components
There are other components that can be customized similarly like `Validators` and `Predictors`
See Reference section for more information on these.

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---
comments: true
description: Boost your Python projects with object detection, segmentation and classification using YOLOv8. Explore how to load, train, validate, predict, export, track and benchmark models with ease.
keywords: YOLOv8, Ultralytics, Python, object detection, segmentation, classification, model training, validation, prediction, model export, benchmark, real-time tracking
---
# Python Usage
Welcome to the YOLOv8 Python Usage documentation! This guide is designed to help you seamlessly integrate YOLOv8 into your Python projects for object detection, segmentation, and classification. Here, you'll learn how to load and use pretrained models, train new models, and perform predictions on images. The easy-to-use Python interface is a valuable resource for anyone looking to incorporate YOLOv8 into their Python projects, allowing you to quickly implement advanced object detection capabilities. Let's get started!
For example, users can load a model, train it, evaluate its performance on a validation set, and even export it to ONNX format with just a few lines of code.
!!! example "Python"
```python
from ultralytics import YOLO
# Create a new YOLO model from scratch
model = YOLO('yolov8n.yaml')
# Load a pretrained YOLO model (recommended for training)
model = YOLO('yolov8n.pt')
# Train the model using the 'coco128.yaml' dataset for 3 epochs
results = model.train(data='coco128.yaml', epochs=3)
# Evaluate the model's performance on the validation set
results = model.val()
# Perform object detection on an image using the model
results = model('https://ultralytics.com/images/bus.jpg')
# Export the model to ONNX format
success = model.export(format='onnx')
```
## [Train](../modes/train.md)
Train mode is used for training a YOLOv8 model on a custom dataset. In this mode, the model is trained using the specified dataset and hyperparameters. The training process involves optimizing the model's parameters so that it can accurately predict the classes and locations of objects in an image.
!!! example "Train"
=== "From pretrained(recommended)"
```python
from ultralytics import YOLO
model = YOLO('yolov8n.pt') # pass any model type
results = model.train(epochs=5)
```
=== "From scratch"
```python
from ultralytics import YOLO
model = YOLO('yolov8n.yaml')
results = model.train(data='coco128.yaml', epochs=5)
```
=== "Resume"
```python
model = YOLO("last.pt")
results = model.train(resume=True)
```
[Train Examples](../modes/train.md){ .md-button .md-button--primary}
## [Val](../modes/val.md)
Val mode is used for validating a YOLOv8 model after it has been trained. In this mode, the model is evaluated on a validation set to measure its accuracy and generalization performance. This mode can be used to tune the hyperparameters of the model to improve its performance.
!!! example "Val"
=== "Val after training"
```python
from ultralytics import YOLO
model = YOLO('yolov8n.yaml')
model.train(data='coco128.yaml', epochs=5)
model.val() # It'll automatically evaluate the data you trained.
```
=== "Val independently"
```python
from ultralytics import YOLO
model = YOLO("model.pt")
# It'll use the data YAML file in model.pt if you don't set data.
model.val()
# or you can set the data you want to val
model.val(data='coco128.yaml')
```
[Val Examples](../modes/val.md){ .md-button .md-button--primary}
## [Predict](../modes/predict.md)
Predict mode is used for making predictions using a trained YOLOv8 model on new images or videos. In this mode, the model is loaded from a checkpoint file, and the user can provide images or videos to perform inference. The model predicts the classes and locations of objects in the input images or videos.
!!! example "Predict"
=== "From source"
```python
from ultralytics import YOLO
from PIL import Image
import cv2
model = YOLO("model.pt")
# accepts all formats - image/dir/Path/URL/video/PIL/ndarray. 0 for webcam
results = model.predict(source="0")
results = model.predict(source="folder", show=True) # Display preds. Accepts all YOLO predict arguments
# from PIL
im1 = Image.open("bus.jpg")
results = model.predict(source=im1, save=True) # save plotted images
# from ndarray
im2 = cv2.imread("bus.jpg")
results = model.predict(source=im2, save=True, save_txt=True) # save predictions as labels
# from list of PIL/ndarray
results = model.predict(source=[im1, im2])
```
=== "Results usage"
```python
# results would be a list of Results object including all the predictions by default
# but be careful as it could occupy a lot memory when there're many images,
# especially the task is segmentation.
# 1. return as a list
results = model.predict(source="folder")
# results would be a generator which is more friendly to memory by setting stream=True
# 2. return as a generator
results = model.predict(source=0, stream=True)
for result in results:
# Detection
result.boxes.xyxy # box with xyxy format, (N, 4)
result.boxes.xywh # box with xywh format, (N, 4)
result.boxes.xyxyn # box with xyxy format but normalized, (N, 4)
result.boxes.xywhn # box with xywh format but normalized, (N, 4)
result.boxes.conf # confidence score, (N, 1)
result.boxes.cls # cls, (N, 1)
# Segmentation
result.masks.data # masks, (N, H, W)
result.masks.xy # x,y segments (pixels), List[segment] * N
result.masks.xyn # x,y segments (normalized), List[segment] * N
# Classification
result.probs # cls prob, (num_class, )
# Each result is composed of torch.Tensor by default,
# in which you can easily use following functionality:
result = result.cuda()
result = result.cpu()
result = result.to("cpu")
result = result.numpy()
```
[Predict Examples](../modes/predict.md){ .md-button .md-button--primary}
## [Export](../modes/export.md)
Export mode is used for exporting a YOLOv8 model to a format that can be used for deployment. In this mode, the model is converted to a format that can be used by other software applications or hardware devices. This mode is useful when deploying the model to production environments.
!!! example "Export"
=== "Export to ONNX"
Export an official YOLOv8n model to ONNX with dynamic batch-size and image-size.
```python
from ultralytics import YOLO
model = YOLO('yolov8n.pt')
model.export(format='onnx', dynamic=True)
```
=== "Export to TensorRT"
Export an official YOLOv8n model to TensorRT on `device=0` for acceleration on CUDA devices.
```python
from ultralytics import YOLO
model = YOLO('yolov8n.pt')
model.export(format='onnx', device=0)
```
[Export Examples](../modes/export.md){ .md-button .md-button--primary}
## [Track](../modes/track.md)
Track mode is used for tracking objects in real-time using a YOLOv8 model. In this mode, the model is loaded from a checkpoint file, and the user can provide a live video stream to perform real-time object tracking. This mode is useful for applications such as surveillance systems or self-driving cars.
!!! example "Track"
=== "Python"
```python
from ultralytics import YOLO
# Load a model
model = YOLO('yolov8n.pt') # load an official detection model
model = YOLO('yolov8n-seg.pt') # load an official segmentation model
model = YOLO('path/to/best.pt') # load a custom model
# Track with the model
results = model.track(source="https://youtu.be/LNwODJXcvt4", show=True)
results = model.track(source="https://youtu.be/LNwODJXcvt4", show=True, tracker="bytetrack.yaml")
```
[Track Examples](../modes/track.md){ .md-button .md-button--primary}
## [Benchmark](../modes/benchmark.md)
Benchmark mode is used to profile the speed and accuracy of various export formats for YOLOv8. The benchmarks provide information on the size of the exported format, its `mAP50-95` metrics (for object detection and segmentation)
or `accuracy_top5` metrics (for classification), and the inference time in milliseconds per image across various export formats like ONNX, OpenVINO, TensorRT and others. This information can help users choose the optimal export format for their specific use case based on their requirements for speed and accuracy.
!!! example "Benchmark"
=== "Python"
Benchmark an official YOLOv8n model across all export formats.
```python
from ultralytics.utils.benchmarks import benchmark
# Benchmark
benchmark(model='yolov8n.pt', data='coco8.yaml', imgsz=640, half=False, device=0)
```
[Benchmark Examples](../modes/benchmark.md){ .md-button .md-button--primary}
## Using Trainers
`YOLO` model class is a high-level wrapper on the Trainer classes. Each YOLO task has its own trainer that inherits from `BaseTrainer`.
!!! tip "Detection Trainer Example"
```python
from ultralytics.models.yolo import DetectionTrainer, DetectionValidator, DetectionPredictor
# trainer
trainer = DetectionTrainer(overrides={})
trainer.train()
trained_model = trainer.best
# Validator
val = DetectionValidator(args=...)
val(model=trained_model)
# predictor
pred = DetectionPredictor(overrides={})
pred(source=SOURCE, model=trained_model)
# resume from last weight
overrides["resume"] = trainer.last
trainer = detect.DetectionTrainer(overrides=overrides)
```
You can easily customize Trainers to support custom tasks or explore R&D ideas. Learn more about Customizing `Trainers`, `Validators` and `Predictors` to suit your project needs in the Customization Section.
[Customization tutorials](engine.md){ .md-button .md-button--primary}