Model Validation with Ultralytics YOLO

Introduction

Validation is a critical step in the machine learning pipeline, allowing you to assess the quality of your trained models. Val mode in Ultralytics YOLOv8 provides a robust suite of tools and metrics for evaluating the performance of your object detection models. This guide serves as a complete resource for understanding how to effectively use the Val mode to ensure that your models are both accurate and reliable.

Watch: Ultralytics Modes Tutorial: Validation

Why Validate with Ultralytics YOLO?

Here's why using YOLOv8's Val mode is advantageous:

Precision: Get accurate metrics like mAP50, mAP75, and mAP50-95 to comprehensively evaluate your model.
Convenience: Utilize built-in features that remember training settings, simplifying the validation process.
Flexibility: Validate your model with the same or different datasets and image sizes.
Hyperparameter Tuning: Use validation metrics to fine-tune your model for better performance.

Key Features of Val Mode

These are the notable functionalities offered by YOLOv8's Val mode:

Automated Settings: Models remember their training configurations for straightforward validation.
Multi-Metric Support: Evaluate your model based on a range of accuracy metrics.
CLI and Python API: Choose from command-line interface or Python API based on your preference for validation.
Data Compatibility: Works seamlessly with datasets used during the training phase as well as custom datasets.

Tip

YOLOv8 models automatically remember their training settings, so you can validate a model at the same image size and on the original dataset easily with just yolo val model=yolov8n.pt or model('yolov8n.pt').val()

Usage Examples

Validate trained YOLOv8n model accuracy on the COCO8 dataset. No argument need to passed as the model retains it's training data and arguments as model attributes. See Arguments section below for a full list of export arguments.

Example

PythonCLI

from ultralytics import YOLO

# Load a model
model = YOLO('yolov8n.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
metrics.box.map50  # map50
metrics.box.map75  # map75
metrics.box.maps   # a list contains map50-95 of each category

yolo detect val model=yolov8n.pt  # val official model
yolo detect val model=path/to/best.pt  # val custom model

Arguments for YOLO Model Validation

When validating YOLO models, several arguments can be fine-tuned to optimize the evaluation process. These arguments control aspects such as input image size, batch processing, and performance thresholds. Below is a detailed breakdown of each argument to help you customize your validation settings effectively.

Argument	Type	Default	Description
`data`	`str`	`None`	Specifies the path to the dataset configuration file (e.g., `coco8.yaml`). This file includes paths to validation data, class names, and number of classes.
`imgsz`	`int`	`640`	Defines the size of input images. All images are resized to this dimension before processing.
`batch`	`int`	`16`	Sets the number of images per batch. Use `-1` for AutoBatch, which automatically adjusts based on GPU memory availability.
`save_json`	`bool`	`False`	If `True`, saves the results to a JSON file for further analysis or integration with other tools.
`save_hybrid`	`bool`	`False`	If `True`, saves a hybrid version of labels that combines original annotations with additional model predictions.
`conf`	`float`	`0.001`	Sets the minimum confidence threshold for detections. Detections with confidence below this threshold are discarded.
`iou`	`float`	`0.6`	Sets the Intersection Over Union (IoU) threshold for Non-Maximum Suppression (NMS). Helps in reducing duplicate detections.
`max_det`	`int`	`300`	Limits the maximum number of detections per image. Useful in dense scenes to prevent excessive detections.
`half`	`bool`	`True`	Enables half-precision (FP16) computation, reducing memory usage and potentially increasing speed with minimal impact on accuracy.
`device`	`str`	`None`	Specifies the device for validation (`cpu`, `cuda:0`, etc.). Allows flexibility in utilizing CPU or GPU resources.
`dnn`	`bool`	`False`	If `True`, uses the OpenCV DNN module for ONNX model inference, offering an alternative to PyTorch inference methods.
`plots`	`bool`	`False`	When set to `True`, generates and saves plots of predictions versus ground truth for visual evaluation of the model's performance.
`rect`	`bool`	`False`	If `True`, uses rectangular inference for batching, reducing padding and potentially increasing speed and efficiency.
`split`	`str`	`val`	Determines the dataset split to use for validation (`val`, `test`, or `train`). Allows flexibility in choosing the data segment for performance evaluation.

Each of these settings plays a vital role in the validation process, allowing for a customizable and efficient evaluation of YOLO models. Adjusting these parameters according to your specific needs and resources can help achieve the best balance between accuracy and performance.

Example Validation with Arguments

The below examples showcase YOLO model validation with custom arguments in Python and CLI.