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目录

一、关键点预测

二、图像预处理

二、推理

三、后处理与可视化

3.1、后处理

3.2、特征点可视化

四、完整pytorch代码

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一、关键点预测

注：本篇只是阐述推理流程，tensorrt实现后续跟进。

yolov8-pose的tensorrt部署代码稍后更新，还是在仓库：GitHub - FeiYull/TensorRT-Alpha: 🔥🔥🔥TensorRT-Alpha supports YOLOv8、YOLOv7、YOLOv6、YOLOv5、YOLOv4、v3、YOLOX、YOLOR...🚀🚀🚀CUDA IS ALL YOU NEED.🍎🍎🍎It also supports end2end CUDA C acceleration and multi-batch inference.

也可以关注：TensorRT系列教程-CSDN博客

以下是官方预测代码：

from ultralytics import YOLO
model = YOLO(model='yolov8n-pose.pt')
model.predict(source="d:/Data/1.jpg", save=True)

推理过程无非是：图像预处理 -> 推理 -> 后处理 + 可视化，这三个关键步骤在文件大概247行：D:\CodePython\ultralytics\ultralytics\engine\predictor.py，代码如下：

# Preprocess
with profilers[0]:im = self.preprocess(im0s) # 图像预处理# Inference
with profilers[1]:preds = self.inference(im, *args, **kwargs) # 推理# Postprocess
with profilers[2]:self.results = self.postprocess(preds, im, im0s) # 后处理

二、图像预处理

通过debug，进入上述self.preprocess函数，看到代码实现如下。处理流程大概是：padding（满足矩形推理），图像通道转换，即：BGR装RGB，检查图像数据是否连续，存储顺序有HWC转为CHW，然后归一化。需要注意，原始pytorch框架图像预处理的时候，会将图像缩放+padding为HxW的图像，其中H、W为32倍数，而导出tensorrt的时候，为了高效推理，H、W 固定为640x640。

def preprocess(self, im):"""Prepares input image before inference.Args:im (torch.Tensor | List(np.ndarray)): BCHW for tensor, [(HWC) x B] for list."""not_tensor = not isinstance(im, torch.Tensor)if not_tensor:im = np.stack(self.pre_transform(im))im = im[..., ::-1].transpose((0, 3, 1, 2))  # BGR to RGB, BHWC to BCHW, (n, 3, h, w)im = np.ascontiguousarray(im)  # contiguousim = torch.from_numpy(im)img = im.to(self.device)img = img.half() if self.model.fp16 else img.float()  # uint8 to fp16/32if not_tensor:img /= 255  # 0 - 255 to 0.0 - 1.0return img

二、推理

图像预处理之后，直接推理就行了，这里是基于pytorch推理。

def inference(self, im, *args, **kwargs):visualize = increment_path(self.save_dir / Path(self.batch[0][0]).stem,mkdir=True) if self.args.visualize and (not self.source_type.tensor) else Falsereturn self.model(im, augment=self.args.augment, visualize=visualize)

三、后处理与可视化

3.1、后处理

网络推理输出特征图维度为：56x8400，其中：

• 8400表示候选目标数量，
• 56 = xywhc + points * 17，points的长度为3，分别为：xyc，即：特征点的坐标和置信度

尽管推理输出特征图中，每一行既有bbox，还有keypoints，但是NMS的时候，依然只作用于bbox，下面代码作了NMS之后，将筛选之后的目标中bbox、keypoints进行坐标值缩放（缩放到原图尺寸坐标系）。

def postprocess(self, preds, img, orig_imgs):"""Return detection results for a given input image or list of images."""preds = ops.non_max_suppression(preds,self.args.conf,self.args.iou,agnostic=self.args.agnostic_nms,max_det=self.args.max_det,classes=self.args.classes,nc=len(self.model.names))results = []for i, pred in enumerate(preds):orig_img = orig_imgs[i] if isinstance(orig_imgs, list) else orig_imgsshape = orig_img.shapepred[:, :4] = ops.scale_boxes(img.shape[2:], pred[:, :4], shape).round()pred_kpts = pred[:, 6:].view(len(pred), *self.model.kpt_shape) if len(pred) else pred[:, 6:]pred_kpts = ops.scale_coords(img.shape[2:], pred_kpts, shape)path = self.batch[0]img_path = path[i] if isinstance(path, list) else pathresults.append(Results(orig_img=orig_img,path=img_path,names=self.model.names,boxes=pred[:, :6],keypoints=pred_kpts))return results

3.2、特征点可视化

bbox可视化没什么好说的，说下17个特征点的可视化，在文件：D:\CodePython\ultralytics_fire_smoke\ultralytics\utils\plotting.py171行，绘制特征点需要注意，需要按照预定义的顺序绘制，其中特征点置信度需要足够大。

def kpts(self, kpts, shape=(640, 640), radius=5, kpt_line=True):"""Plot keypoints on the image.Args:kpts (tensor): Predicted keypoints with shape [17, 3]. Each keypoint has (x, y, confidence).shape (tuple): Image shape as a tuple (h, w), where h is the height and w is the width.radius (int, optional): Radius of the drawn keypoints. Default is 5.kpt_line (bool, optional): If True, the function will draw lines connecting keypointsfor human pose. Default is True.Note: `kpt_line=True` currently only supports human pose plotting."""if self.pil:# Convert to numpy firstself.im = np.asarray(self.im).copy()nkpt, ndim = kpts.shapeis_pose = nkpt == 17 and ndim == 3kpt_line &= is_pose  # `kpt_line=True` for now only supports human pose plotting# 绘制特征点for i, k in enumerate(kpts):color_k = [int(x) for x in self.kpt_color[i]] if is_pose else colors(i)x_coord, y_coord = k[0], k[1]if x_coord % shape[1] != 0 and y_coord % shape[0] != 0:if len(k) == 3:conf = k[2]if conf < 0.5:continuecv2.circle(self.im, (int(x_coord), int(y_coord)), radius, color_k, -1, lineType=cv2.LINE_AA)# 绘制线段if kpt_line:ndim = kpts.shape[-1]for i, sk in enumerate(self.skeleton):pos1 = (int(kpts[(sk[0] - 1), 0]), int(kpts[(sk[0] - 1), 1]))pos2 = (int(kpts[(sk[1] - 1), 0]), int(kpts[(sk[1] - 1), 1]))if ndim == 3:conf1 = kpts[(sk[0] - 1), 2]conf2 = kpts[(sk[1] - 1), 2]if conf1 < 0.5 or conf2 < 0.5:continueif pos1[0] % shape[1] == 0 or pos1[1] % shape[0] == 0 or pos1[0] < 0 or pos1[1] < 0:continueif pos2[0] % shape[1] == 0 or pos2[1] % shape[0] == 0 or pos2[0] < 0 or pos2[1] < 0:continuecv2.line(self.im, pos1, pos2, [int(x) for x in self.limb_color[i]], thickness=2, lineType=cv2.LINE_AA)if self.pil:# Convert im back to PIL and update drawself.fromarray(self.im)

这里给一张特征点顺序图：

四、完整pytorch代码

将以上流程合并起来，并加以修改，完整代码如下：

import torch
import cv2 as cv
import numpy as np
from ultralytics.data.augment import LetterBox
from ultralytics.utils import ops
from ultralytics.engine.results import Results
import copy# path = 'd:/Data/1.jpg'
path = 'd:/Data/6406402.jpg'
device = 'cuda:0'
conf = 0.25
iou = 0.7# preprocess
im = cv.imread(path)
# letterbox
im = [im]
orig_imgs = copy.deepcopy(im)
im = [LetterBox([640, 640], auto=True, stride=32)(image=x) for x in im]
im = im[0][None] # im = np.stack(im)
im = im[..., ::-1].transpose((0, 3, 1, 2))  # BGR to RGB, BHWC to BCHW, (n, 3, h, w)
im = np.ascontiguousarray(im)  # contiguous
im = torch.from_numpy(im)
img = im.to(device)
img = img.float()
img /= 255
# load model pt
ckpt = torch.load('yolov8n-pose.pt', map_location='cpu')
model = ckpt['model'].to(device).float()  # FP32 model
model.eval()# inference
preds = model(img)
prediction = ops.non_max_suppression(preds, conf, iou, agnostic=False, max_det=300, classes=None, nc=len(model.names))results = []
for i, pred in enumerate(prediction):orig_img = orig_imgs[i] if isinstance(orig_imgs, list) else orig_imgsshape = orig_img.shapepred[:, :4] = ops.scale_boxes(img.shape[2:], pred[:, :4], shape).round()pred_kpts = pred[:, 6:].view(len(pred), *model.kpt_shape) if len(pred) else pred[:, 6:]pred_kpts = ops.scale_coords(img.shape[2:], pred_kpts, shape)img_path = pathresults.append(Results(orig_img=orig_img,path=img_path,names=model.names,boxes=pred[:, :6],keypoints=pred_kpts))# show
plot_args = {'line_width': None,'boxes': True,'conf': True, 'labels': True}
plot_args['im_gpu'] = img[0]
result = results[0]
plotted_img = result.plot(**plot_args)
cv.imshow('plotted_img', plotted_img)
cv.waitKey(0)
cv.destroyAllWindows()
print()