openCV python语言入门

2021-07-05 15:07:23

准备

2.openCV python文档，清华源的cv库最新版本是4.5.5

图片常识

openCV 中的默认颜色格式通常称为 RGB，但实际上是 BGR（字节反转）。因此，标准（24 位）彩色图像中的第一个字节将是 8 位蓝色分量，第二个字节将是绿色，第三个字节将是红色。然后第四、第五和第六个字节将是第二个像素（蓝色，然后是绿色，然后是红色），依此类推。

RGB图在cv中的顺序是BGR，(0,0,0)表示黑色，(255,255,255)表示白色

灰度图中0表示纯黑色，255表示纯白

openCV中的灰度图(GRAY)以uint8存储，RGB３通道彩色图也是uint８，范围就是0~255

BGR->GRAY转换

基本函数

1.显示和编辑图像

import cv2 as cv
import sys
img = cv.imread("a.jpg")
if img is None:
    sys.exit("Could not read the image.")
eye = img[52:66,70:84]#取出图片中人物的眼睛
img[20:34,48:62] = eye
cv.imshow("Display window", img)
k = cv.waitKey(0)#无限制地等待用户按键
if k == ord("s"):
    cv.imwrite("a.png", img)#图像另存为

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a.jpg a.png

2.拆分和合并颜色通道

import cv2 as cv
import sys
img = cv.imread("a.jpg")
if img is None:
    sys.exit("Could not read the image.")
b,g,r = cv.split (img)#拆分蓝 绿 红颜色通道
img = cv.merge ((b,g,r))
print(img.shape)
cv.imshow("Display window", img)
img[:,:,2] = 0#红色像素设置为0
cv.imshow("Display window", img)
k = cv.waitKey(0)#无限制地等待用户按键

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3.添加边框并使用matplot展示多张图片

import cv2 as cv
import numpy as np
from matplotlib import pyplot as plt
BLUE = [255,0,0]
img1 = cv.imread('a.jpg')

b,g,r = cv.split(img1)
img1 = cv.merge((r,g,b))

replicate = cv.copyMakeBorder(img1,10,10,10,10,cv.BORDER_REPLICATE)
reflect = cv.copyMakeBorder(img1,10,10,10,10,cv.BORDER_REFLECT)
reflect101 = cv.copyMakeBorder(img1,10,10,10,10,cv.BORDER_REFLECT_101)
wrap = cv.copyMakeBorder(img1,10,10,10,10,cv.BORDER_WRAP)
constant= cv.copyMakeBorder(img1,10,10,10,10,cv.BORDER_CONSTANT,value=BLUE)

plt.subplot(231),plt.imshow(img1),plt.title('ORIGINAL')
plt.subplot(232),plt.imshow(replicate,'gray'),plt.title('REPLICATE')
plt.subplot(233),plt.imshow(reflect,'gray'),plt.title('REFLECT')
plt.subplot(234),plt.imshow(reflect101,'gray'),plt.title('REFLECT_101')
plt.subplot(235),plt.imshow(wrap,'gray'),plt.title('WRAP')
plt.subplot(236),plt.imshow(constant,'gray'),plt.title('CONSTANT')

#图片是用matplotlib展示的，plt和cv的红蓝通道被交换了
plt.show()

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Figure_1.png

subplot介绍

4.与或操作与掩码的应用

例子所展示的场景：将一张白底的logo图片的logo抠出放置到另一张图片上

import cv2 as cv
import numpy as np
img1 = cv.imread('b.jpg')
img2 = cv.imread('opencv-logo-white.png')
# I want to put logo on top-left corner, So I create a ROI
rows,cols,channels = img2.shape
roi = img1[0:rows, 0:cols]
# Now create a mask of logo and create its inverse mask also
img2gray = cv.cvtColor(img2,cv.COLOR_BGR2GRAY)

ret, mask = cv.threshold(img2gray, 10, 255, cv.THRESH_BINARY)
#ret 为预设的thresh阈值
mask_inv = cv.bitwise_not(mask)
# Now black-out the area of logo in ROI
img1_bg = cv.bitwise_and(roi,roi,mask = mask_inv)#mask参数 对应点值不为0则相与，为0则相应点各通道置0 呈黑色
cv.imshow('img1bg',img1_bg)
cv.waitKey(0)

# Take only region of logo from logo image.
img2_fg = cv.bitwise_and(img2,img2,mask = mask)
cv.imshow('img2fg',img2_fg)
cv.waitKey(0)

# Put logo in ROI and modify the main image
dst = cv.add(img1_bg,img2_fg)
img1[0:rows, 0:cols ] = dst
cv.imshow('res',img1)
cv.waitKey(0)
cv.destroyAllWindows()

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思路介绍：

　　1.先将3通道图转为灰度图

　　img2gray = cv.cvtColor(img2,cv.COLOR_BGR2GRAY)

　　灰度图的纯白区域灰度值为255，纯黑为0