ultralytics/docs/en/models/yolov3.md

---
comments: true
description: Discover YOLOv3 and its variants YOLOv3-Ultralytics and YOLOv3u. Learn about their features, implementations, and support for object detection tasks.
keywords: YOLOv3, YOLOv3-Ultralytics, YOLOv3u, object detection, Ultralytics, computer vision, AI models, deep learning
---

# YOLOv3, YOLOv3-Ultralytics, and YOLOv3u

## Overview

This document presents an overview of three closely related object detection models, namely [YOLOv3](https://pjreddie.com/darknet/yolo/), [YOLOv3-Ultralytics](https://github.com/ultralytics/yolov3), and [YOLOv3u](https://github.com/ultralytics/ultralytics).

1. **YOLOv3:** This is the third version of the You Only Look Once (YOLO) object detection algorithm. Originally developed by Joseph Redmon, YOLOv3 improved on its predecessors by introducing features such as multiscale predictions and three different sizes of detection kernels.

2. **YOLOv3-Ultralytics:** This is Ultralytics' implementation of the YOLOv3 model. It reproduces the original YOLOv3 architecture and offers additional functionalities, such as support for more pre-trained models and easier customization options.

3. **YOLOv3u:** This is an updated version of YOLOv3-Ultralytics that incorporates the anchor-free, objectness-free split head used in YOLOv8 models. YOLOv3u maintains the same backbone and neck architecture as YOLOv3 but with the updated detection head from YOLOv8.

![Ultralytics YOLOv3](https://raw.githubusercontent.com/ultralytics/assets/main/yolov3/banner-yolov3.png)

## Key Features

- **YOLOv3:** Introduced the use of three different scales for detection, leveraging three different sizes of detection kernels: 13x13, 26x26, and 52x52. This significantly improved detection accuracy for objects of different sizes. Additionally, YOLOv3 added features such as multi-label predictions for each bounding box and a better feature extractor network.

- **YOLOv3-Ultralytics:** Ultralytics' implementation of YOLOv3 provides the same performance as the original model but comes with added support for more pre-trained models, additional training methods, and easier customization options. This makes it more versatile and user-friendly for practical applications.

- **YOLOv3u:** This updated model incorporates the anchor-free, objectness-free split head from YOLOv8. By eliminating the need for pre-defined anchor boxes and objectness scores, this detection head design can improve the model's ability to detect objects of varying sizes and shapes. This makes YOLOv3u more robust and accurate for object detection tasks.

## Supported Tasks and Modes

The YOLOv3 series, including YOLOv3, YOLOv3-Ultralytics, and YOLOv3u, are designed specifically for object detection tasks. These models are renowned for their effectiveness in various real-world scenarios, balancing accuracy and speed. Each variant offers unique features and optimizations, making them suitable for a range of applications.

All three models support a comprehensive set of modes, ensuring versatility in various stages of model deployment and development. These modes include [Inference](../modes/predict.md), [Validation](../modes/val.md), [Training](../modes/train.md), and [Export](../modes/export.md), providing users with a complete toolkit for effective object detection.

| Model Type         | Tasks Supported                        | Inference | Validation | Training | Export |
| ------------------ | -------------------------------------- | --------- | ---------- | -------- | ------ |
| YOLOv3             | [Object Detection](../tasks/detect.md) | ✅        | ✅         | ✅       | ✅     |
| YOLOv3-Ultralytics | [Object Detection](../tasks/detect.md) | ✅        | ✅         | ✅       | ✅     |
| YOLOv3u            | [Object Detection](../tasks/detect.md) | ✅        | ✅         | ✅       | ✅     |

This table provides an at-a-glance view of the capabilities of each YOLOv3 variant, highlighting their versatility and suitability for various tasks and operational modes in object detection workflows.

## Usage Examples

This example provides simple YOLOv3 training and inference examples. For full documentation on these and other [modes](../modes/index.md) see the [Predict](../modes/predict.md), [Train](../modes/train.md), [Val](../modes/val.md) and [Export](../modes/export.md) docs pages.

!!! Example

    === "Python"

        PyTorch pretrained `*.pt` models as well as configuration `*.yaml` files can be passed to the `YOLO()` class to create a model instance in python:

        ```python
        from ultralytics import YOLO

        # Load a COCO-pretrained YOLOv3n model
        model = YOLO("yolov3n.pt")

        # Display model information (optional)
        model.info()

        # Train the model on the COCO8 example dataset for 100 epochs
        results = model.train(data="coco8.yaml", epochs=100, imgsz=640)

        # Run inference with the YOLOv3n model on the 'bus.jpg' image
        results = model("path/to/bus.jpg")
        ```

    === "CLI"

        CLI commands are available to directly run the models:

        ```bash
        # Load a COCO-pretrained YOLOv3n model and train it on the COCO8 example dataset for 100 epochs
        yolo train model=yolov3n.pt data=coco8.yaml epochs=100 imgsz=640

        # Load a COCO-pretrained YOLOv3n model and run inference on the 'bus.jpg' image
        yolo predict model=yolov3n.pt source=path/to/bus.jpg
        ```

## Citations and Acknowledgements

If you use YOLOv3 in your research, please cite the original YOLO papers and the Ultralytics YOLOv3 repository:

!!! Quote ""

    === "BibTeX"

        ```bibtex
        @article{redmon2018yolov3,
          title={YOLOv3: An Incremental Improvement},
          author={Redmon, Joseph and Farhadi, Ali},
          journal={arXiv preprint arXiv:1804.02767},
          year={2018}
        }
        ```

Thank you to Joseph Redmon and Ali Farhadi for developing the original YOLOv3.

## FAQ

### What is YOLOv3, and how does it improve object detection?

YOLOv3 is the third iteration of the _You Only Look Once (YOLO)_ object detection algorithm. It enhances object detection accuracy by utilizing three different sizes of detection kernels: 13x13, 26x26, and 52x52. This allows the model to detect objects at multiple scales, improving accuracy for objects of varying sizes. YOLOv3 also supports multi-label predictions for bounding boxes and includes a superior feature extractor network.

### Why should I use Ultralytics' implementation of YOLOv3?

Ultralytics' implementation of YOLOv3, known as YOLOv3-Ultralytics, retains the original model's architecture but adds significant enhancements. It offers more pre-trained models, additional training methods, and customization options, making it user-friendly and versatile for practical applications. This implementation enhances the usability and flexibility of YOLOv3 in real-world object detection tasks.

### How does YOLOv3u differ from YOLOv3 and YOLOv3-Ultralytics?

YOLOv3u is an updated version of YOLOv3-Ultralytics that incorporates the anchor-free, objectness-free split head used in YOLOv8 models. This update eliminates the need for pre-defined anchor boxes and objectness scores, making YOLOv3u more robust and accurate in detecting objects of varying sizes and shapes, without altering the backbone and neck architecture of YOLOv3.

### Can I use YOLOv3 models for multiple prediction tasks?

Yes, the YOLOv3 series, including YOLOv3, YOLOv3-Ultralytics, and YOLOv3u, are designed for object detection tasks. They support several modes such as [Inference](../modes/predict.md), [Validation](../modes/val.md), [Training](../modes/train.md), and [Export](../modes/export.md). This versatility ensures they can be used effectively across different stages of model deployment and development in various applications.

### How can I train a YOLOv3 model using Ultralytics?

You can train a YOLOv3 model using Ultralytics by leveraging the Python code or CLI commands:

**Using Python:**

```python
from ultralytics import YOLO

# Load a COCO-pretrained YOLOv3n model
model = YOLO("yolov3n.pt")

# Display model information (optional)
model.info()

# Train the model on the COCO8 example dataset for 100 epochs
results = model.train(data="coco8.yaml", epochs=100, imgsz=640)

# Run inference with the YOLOv3n model on the 'bus.jpg' image
results = model("path/to/bus.jpg")
```

**Using CLI:**

```bash
# Load a COCO-pretrained YOLOv3n model and train it on the COCO8 example dataset for 100 epochs
yolo train model=yolov3n.pt data=coco8.yaml epochs=100 imgsz=640

# Load a COCO-pretrained YOLOv3n model and run inference on the 'bus.jpg' image
yolo predict model=yolov3n.pt source=path/to/bus.jpg
```

For more details, visit the [Train](../modes/train.md) and [Predict](../modes/predict.md) documentation pages.