【OpenCV 入门到精通 04】视频入门与绘图交互：从摄像头到鼠标画笔

【OpenCV 入门到精通 04】视频入门与绘图交互：从摄像头到鼠标画笔

标签：OpenCV VideoCapture 绘图 鼠标事件 轨迹栏 难度：⭐ 入门 | 阅读时长：约 55 分钟 | 系列：第 04/12 集 前置：03 图像入门 | 下一集：05 核心操作

写在前面

图像处理不止静态照片——监控、直播、自动驾驶都涉及 视频流。本集覆盖视频读写、基本绘图、鼠标交互和轨迹栏，对应官方 2_2 视频入门 和 2_3~2_5 GUI 特性。

本集学习目标

• 使用 VideoCapture 读取摄像头和视频文件
• 使用 VideoWriter 保存视频
• 掌握 line、rectangle、circle 等绘图函数
• 实现鼠标画板和轨迹栏调色板

文章目录

• 【OpenCV 入门到精通 04】视频入门与绘图交互：从摄像头到鼠标画笔
• • 写在前面
  • 本集学习目标
  • 4.1 视频读取 VideoCapture
  • • 读取视频文件
    • 读取摄像头
  • 4.2 视频保存 VideoWriter
  • 4.3 绘图函数
  • • 绘图函数速查
  • 4.4 鼠标作为画笔
  • • 鼠标事件
  • 4.5 轨迹栏调色板
  • 4.6 踩坑指南
  • 4.7 本集小结

4.1 视频读取 VideoCapture

读取视频文件

import cv2

cap = cv2.VideoCapture("video.mp4")

while cap.isOpened():
ret, frame = cap.read() # ret=是否成功, frame=当前帧
if not ret:
break
cv2.imshow("Video", frame)
if cv2.waitKey(25) & 0xFF == ord('q'): # 约40fps
break

cap.release()
cv2.destroyAllWindows()

读取摄像头

cap = cv2.VideoCapture(0) # 0=默认摄像头，1=外接

# 获取属性
fps = cap.get(cv2.CAP_PROP_FPS)
w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
print(f"分辨率: {w}x{h}, FPS: {fps}")

4.2 视频保存 VideoWriter

cap = cv2.VideoCapture(0)
w = int(cap.get(3))
h = int(cap.get(4))
fps = 20.0

fourcc = cv2.VideoWriter_fourcc(*'mp4v')
out = cv2.VideoWriter('output.mp4', fourcc, fps, (w, h))

while cap.isOpened():
ret, frame = cap.read()
if not ret: break
out.write(frame)
cv2.imshow("Recording", frame)
if cv2.waitKey(1) & 0xFF == ord('q'): break

cap.release()
out.release()
cv2.destroyAllWindows()

4.3 绘图函数

import cv2
import numpy as np

img = np.zeros((400, 600, 3), dtype=np.uint8)

# 直线
cv2.line(img, (50,50), (200,200), (0,255,0), 2)

# 矩形
cv2.rectangle(img, (250,50), (400,150), (255,0,0), 2)
cv2.rectangle(img, (250,200), (400,300), (0,0,255), –1) # -1=填充

# 圆
cv2.circle(img, (500,100), 50, (0,255,255), –1)

# 椭圆
cv2.ellipse(img, (500,250), (80,40), 0, 0, 360, (255,255,0), 2)

# 多边形
pts = np.array([[100,300],[200,250],[300,300],[200,350]], np.int32)
cv2.polylines(img, [pts], True, (255,0,255), 2)

# 文字
cv2.putText(img, "OpenCV", (100,380), cv2.FONT_HERSHEY_SIMPLEX, 1, (255,255,255), 2)

cv2.imshow("Drawing", img)
cv2.waitKey(0)

绘图函数速查

4.4 鼠标作为画笔

import cv2
import numpy as np

drawing = False
color = (0, 0, 255)

def mouse_callback(event, x, y, flags, param):
global drawing, color
if event == cv2.EVENT_LBUTTONDOWN:
drawing = True
elif event == cv2.EVENT_MOUSEMOVE and drawing:
cv2.circle(img, (x, y), 5, color, –1)
elif event == cv2.EVENT_RBUTTONDOWN:
color = (np.random.randint(0,255), np.random.randint(0,255), np.random.randint(0,255))
elif event == cv2.EVENT_LBUTTONUP:
drawing = False

img = np.zeros((400, 600, 3), dtype=np.uint8)
cv2.namedWindow("Paint")
cv2.setMouseCallback("Paint", mouse_callback)

while True:
cv2.imshow("Paint", img)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cv2.destroyAllWindows()

鼠标事件

4.5 轨迹栏调色板

import cv2
import numpy as np

def nothing(x):
pass

img = np.zeros((300, 512, 3), np.uint8)
cv2.namedWindow("Palette")
cv2.createTrackbar("R", "Palette", 0, 255, nothing)
cv2.createTrackbar("G", "Palette", 0, 255, nothing)
cv2.createTrackbar("B", "Palette", 0, 255, nothing)

while True:
r = cv2.getTrackbarPos("R", "Palette")
g = cv2.getTrackbarPos("G", "Palette")
b = cv2.getTrackbarPos("B", "Palette")
img[:] = (b, g, r) # BGR
cv2.imshow("Palette", img)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cv2.destroyAllWindows()

4.6 踩坑指南

4.7 本集小结

参考：2_2 视频入门 | 2_3 绘图功能