Opencv function usage details 1~10, including code examples

opencv Common methods 1

1.cv2.imread()

Read image （ Read image ; The first parameter is the image path ; The second is cv2.IMREAD_COLOR： Read in the color image ;cv2.IMREAD_GRAYSCALE: Read in grayscale image .）

img_bg=cv2.imread("C:/Users/Lenovo/PycharmProjects/pythonProject3/IMG_0228.JPG")
print(img_bgr)

If you print img_bgr, Will output its pixels

2.cv2.imshow()

Display images （image1 It's the window name ,img_bgr Is the image to display ）

cv2.imshow('image1', img_bgr)

3.cv2.waitKey()

For waiting for the key , When the user presses the keyboard , This statement will be executed , And get its return value delay > 0 when , Program at given delay Wait for the user's key to trigger within the time perhaps Waiting for one delay Time , Program continues . if delay = 0 when , It means that the user must click the keyboard to trigger the program to continue .

cv2.waitKey(5000) # 5000ms,5s  Program continues , Of course, you can click the keyboard to execute immediately 

4.cv2.destroyWindow()

Used to release or destroy the specified window ,winname It's the window name

None = cv2.destroyWindow(winname)

5.cv2.destroyAllWindows()

Used to release or destroy all windows

None = cv2.destroyAllWindows()

6.cv2.imwwrite()

Used to save images ,retval Is the return value . If saved successfully , Returns the logical value true （True）; If the save is unsuccessful , Returns the logical value false （False）

filename Is the path name of the target file to be saved , Include file extensions .img Is the name of the saved image .

params Is to save type parameters , It's optional .

 retval = cv2.imwwrite(filename,img[, params])

Runnable cases

import cv2 as cv
import numpy as np
img = np.ones([400, 400, 1], np.uint8)
img = img*0
# img[:, :, 0] = np.ones([400, 400])*127
cv.imshow("new image", img)
cv.waitKey(5000)  # 5000ms,5s  Program continues , Of course, you can click the keyboard to execute immediately 
cv.imwrite("D:/myImage.png", img)

7. Image classification

1. Binary image

Binary image （ Only black and white are included ）

White pixels are 1, Black pixels are 0

2. Grayscale image

Grayscale image （ Grayscale processing as 256 Gray scale （ It's exactly a byte ） Use numerical interval [0,255] Express ）,

among .[0] It means pure black ,[255] It means pure white

3. Color images

Color images Three primary colors （ red 、 green 、 blue ）

RGB In the color space , There is R the red channel 、G Green channel 、B Blue channel

After different combinations, common 256256256=16777216 Color

The channel order is R->G->B for example （205,89,68）

8. Pixel processing

# Generate a 8*8 Two dimensional array of , All values are 0,,, The data type is np.uint8,（ In fact, it can be seen as a black image .）
#img[0, 3] = 255  It will be the first 0 Xing di 3 The pixels of the column are set to 255
#img = np.zeros((8, 8), dtype=np.uint8)

import cv2
import numpy as np
img = np.zeros((8, 8), dtype=np.uint8)
print("img = \n", img)
cv2.imshow("one",img)
print(" Read pixels  img[0, 3]=", img[0, 3])
img[0, 3] = 255
print(" After modification  img = \n", img)
print(" Read the modified pixels  img [0, 3] = ",img[0, 3])
cv2.imshow("two", img)
cv2.waitKey()
cv2.destroyAllWindows()

9. Editing an image

（ Is to change a whole piece into a certain color ）

import cv2
img = cv2.imread("C:/Users/Lenovo/PycharmProjects/pythonProject3/IMG_0228.JPG", 0)
cv2.imshow("before", img)
for i in range(10, 100):
    for j in range(80, 100):
        img[i, j] = 255
cv2.imshow("after", img)
cv2.waitKey()
cv2.destroyAllWindows()

10. Create three monochrome pictures

among ！ The first two ： Represents the number of all lines of the selected picture , And number of columns ,1 On behalf of the 2 Channels （0 Represents the first channel ）.

If there is a picture img, be img[20：30, 60：70, 1] It means the... Of the selected picture 20 To 30 That's ok , The first 60 To 70 Column , And the first 2 Channels .

#[300（ Number of lines in the picture ）,300（ The number of columns in the picture ,3（ The number of channels in the picture ）]

import numpy as np
import cv2
# ---------------blue---------------
blue = np.zeros((300, 300, 3), dtype=np.uint8)
blue[:, :, 0] = 255
print("blue = \n", blue)
cv2.imshow("blue", blue)
# -------------green---------------
green = np.zeros((300, 300, 3), dtype=np.uint8)
green[:, :, 1] = 255
print("green = \n", green)
cv2.imshow("green", green)
# -------------red---------------
red = np.zeros((300, 300, 3), dtype=np.uint8)
red[:, :, 2] = 255
print("red = \n", red)
cv2.imshow("red", red)
# ------------- release window ---------------
cv2.waitKey()
cv2.destroyAllWindows()