Yolo Pose Estimation and Skeleton
Introduction
Make a pose estimator and use it to make a moving skeleton.
Use Yolo from Ultralytics.
- Python 3.7+
- Yolo v11
- A CUDA-enabled GPU (optional but recommended for faster inference).
pip install ultralytics opencv-python numpy
Yolo
There are 17 keypoints. YOLOv11’s pose model outputs:
- (x, y) coordinates for each keypoint and
- confidence scores indicating the model’s certainty in each keypoint’s position.
Image detection
-
AN image before and after the code.
from ultralytics import YOLO
import matplotlib.pyplot as plt
import cv2
#from PIL import Image
model = YOLO("yolo11n-pose.pt") # n, s, m, l, x versions available
results = model.predict(source="sample_image.jpg")
plt.figure(figsize=(10, 10))
plt.title('YOLOv11 Pose Results')
plt.axis('off')
plt.imshow(cv2.cvtColor(results[0].plot(), cv2.COLOR_BGR2RGB))
The results list includes results[0].keypoints.xy, results[0].keypoints.xyn and results[0].keypoints.conf data. Printing that gives some general information about what is found and how fast, and a tensor vector which includes the position data.
image 1/1 /home/mol/Documents/python/skeletor/people2.jpg: 512x640 5 persons, 26.0ms
Speed: 1.4ms preprocess, 26.0ms inference, 38.0ms postprocess per image at shape (1, 3, 512, 640)
tensor([[[1608.5103, 516.1241],
[1600.1213, 497.7412],
[1613.1257, 497.1426],
[1568.5618, 506.6950],
[1648.6650, 505.3312],
[1556.0571, 614.9849],
[1692.7899, 615.2242],
[1540.9780, 763.7505],
[1755.1765, 773.1780],
[1548.3131, 886.3889],
[1795.6322, 892.2405],
[1588.8513, 896.8289],
[1680.1824, 896.3278],
[1574.6792, 1117.8225],
[1675.2017, 1118.2271],
[1589.6167, 1317.0865],
[1671.6086, 1320.7114]],
[[1097.3536, 432.4247],
[1086.8494, 405.5817],
[1092.0603, 402.9798],
[ 987.7101, 409.1143],
[1076.7693, 412.7003],
[ 924.9458, 531.9528],
[1117.5946, 533.4085],
[ 875.2901, 720.3015],
[1186.5740, 715.3069],
[ 862.7459, 861.0502],
[1189.9052, 849.3643],
[ 957.1283, 837.9849],
[1090.0930, 841.1834],
[ 920.7561, 1110.6389],
[1099.1434, 1116.8433],
[ 925.5239, 1367.9281],
[1102.7339, 1381.9753]],
To print the coordinates of keypoints, use
for r in results[0].keypoints.xy:
print(r)
Use cv2 to plot the image. This cv2 plotting will be used in the next part.
image = cv2.imread(filename)
cv2.namedWindow("image", cv2.WINDOW_KEEPRATIO)
cv2.imshow("image", image)
cv2.resizeWindow("image", 600, 600)
cv2.waitKey(0)
cv2.destroyAllWindows()
CUDA:0 problem
A CUDA:0 tensor is a tensor that is stored on a GPU, and thus isn't accessible to the CPU. To have it in Numpy, use:
- Copy the data from the GPU to the CPU: `torch.cuda.to_cpu()`.
- Reorder the data (from a column-major format to a row-major): `numpy.transpose()`. Not needed in this simple 1d example.
- Convert the data to NumPy: `numpy.asarray()`, and convert to integer.
xy_hip =results[0].keypoints.xy[0][12]
cpu_xyhip = np.asarray( xy_hip.cpu() ).astype(np.int64) #Copy and convert;
Pose to skeleton
The keypoint coordinates need to be converted to bones; as an example, femur is located between
- 12 (left hip) and 14 (left knee) or
- 13 (right hip) and 15 (right knee)
