Month: April 2024

When working with object detection using Ultralytics YOLO v8 in Python and attempting to add bounding boxes for classified objects to the camera image, it is possible to encounter a problem with the boxes field being undefined (equal to None).

The solution is to make sure you are using the yolov8n.pt model and not yolov8n-cls.pt: the latter does not seem to have this value set.

The -cls version of the model only returns text descriptions and not the bounding boxes.

In short the solution is to load the model using:

YOLO("yolov8n.pt")

instead of:

YOLO("yolov8n-cls.pt")

The following code shows a complete example of classifying objects using YOLO and adding bounding boxes.
Comments indicate where the problem with boxes being equal to None appears.

import cv2

from ultralytics import YOLO

captureObject = cv2.VideoCapture(0)
captureObject.set(3, 840)
captureObject.set(4, 780)

# Do not use yolov8n-cls.pt unless you do not need bounding boxes.
yoloModel = YOLO("yolov8n.pt")

# Get all class labels.
classLabels = list(yoloModel.names.values())

# Main loop.
while True:
  ret, img = captureObject.read()
  cv2.imshow("webcam", img)

  # Classify objects.
  results = yoloModel(img, stream=True)

  for r in results:
    boundingBoxes = r.boxes
    # The value of boxes is None if using yolov8n-cls.pt
    if boundingBoxes != None:
      for box in boundingBoxes:
        # Get coordinates.
        x1, y1, x2, y2 = box.xyxy[0]
        # Convert to integer types.
        x1, y1, x2, y2 = int(x1), int(y1), int(x2), int(y2)

        # Draw bounding box rectangle inside camera image.
        cv2.rectangle(img, 
          (x1, y1), 
          (x2, y2), 
          (255, 0, 255), 
          3)

        # Add classification label on top of bounding box.
        classIndex = int(box.cls[0])
        label = classLabels[classIndex]
        cv2.putText(img, 
          label, 
          [x1, y1], 
          cv2.FONT_HERSHEY_SIMPLEX, 
          1, 
          (255, 0, 0), 
          2)

  # Re-paint with overlay rectangles.
  cv2.imshow("webcam", img)

  # Exit with 'q' key.
  if cv2.waitKey(1) == ord("q"):
    break

captureObject.release()
cv2.destroyAllWindows()