import  numpy as np
import cv2 as cv

#1.OPENCV读取图像显示图像
image =cv.imread("lena.jpg")
cv.imshow("image", image)

#2.显示图像的长宽高
h,w,c = image.shape
print(h,w,c)
#3.通道转换为从Bgr 转RGB
rgb=cv.cvtColor(image,cv.COLOR_BGR2RGB)
cv.imshow("rgb", rgb)

#4.np 创建掩膜
blank = np.zeros_like(image)
blank[:,:]=(127,127,127)
dst=cv.subtract(image,blank)
cv.imshow("dst", dst)

# 5.cv.resize修改图像大小
image2=cv.resize(image,(256,256))
cv.imshow("image2", image2)


#6.利用np创建roi
blob=np.float32(image)/255.0  #注意需要进行归一化后才可显示
print(blob.shape, blob.dtype)
cv.imshow("blob", blob)

roi=blob[200:350,200:350]
cv.imshow("roi", roi)

cv.waitKey(0)
cv.destroyAllWindows()

# 7.cv 视频显示
cap=cv.VideoCapture("example_dsh.mp4")
while True:
    ret,frame=cap.read()
    if not ret:
        break
    cv.imshow("frame", frame)
    #等待1ms
    c=cv.waitKey(1)
    #按ESC按键退出
    if c==27:
        break


cv.destroyAllWindows()