阈值与平滑处理

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阈值处理是指剔除图像像素内像素值高于一定值或低于一定值的像素点。

OpenCV提供了函数cv2.threshold()和函数cv2.adaptiveThreshold(),用于实现阈值处理。

阈值处理
ret, dst = cv2.threshold(src, thresh, maxval, type)
src： 输入图，只能输入单通道图像，通常来说为灰度图
dst： 输出图
thresh： 阈值
maxval： 当像素值超过了阈值（或者小于阈值，根据type来决定），所赋予的值
type：二值化操作的类型，包含以下5种类型： cv2.THRESH_BINARY； cv2.THRESH_BINARY_INV；
cv2.THRESH_TRUNC； cv2.THRESH_TOZERO；cv2.THRESH_TOZERO_INV
cv2.THRESH_BINARY 超过阈值部分取maxval（最大值），否则取0
cv2.THRESH_BINARY_INV THRESH_BINARY的反转
cv2.THRESH_TRUNC 大于阈值部分设为阈值，否则不变
cv2.THRESH_TOZERO 大于阈值部分不改变，否则设为0
cv2.THRESH_TOZERO_INV THRESH_TOZERO的反转

eg:阈值运算（threshold）：二值化、反二值化、截断、超阈值零处理、低阈值零处理

 import cv2
import numpy as np
#from matplotlib import pyplot as plt

peppa = cv2.imread('peppa.jpg')
img=cv2.cvtColor(peppa,cv2.COLOR_BGR2GRAY)
cv2.imshow('Peppa',img)
ret,thresh1 = cv2.threshold(img,200,255,cv2.THRESH_BINARY)
ret,thresh2 = cv2.threshold(img,200,255,cv2.THRESH_BINARY_INV)
ret,thresh3 = cv2.threshold(img,200,255,cv2.THRESH_TRUNC)
ret,thresh4 = cv2.threshold(img,200,255,cv2.THRESH_TOZERO)
ret,thresh5 = cv2.threshold(img,200,255,cv2.THRESH_TOZERO_INV)
cv2.imshow('BINARY',thresh1)
cv2.imshow('BINARY_INV',thresh2)
# cv2.imshow('TRUNC',thresh3)
# cv2.imshow('TOZERO',thresh4)
# cv2.imshow('TOZERO_INV',thresh5)
peppa_body=cv2.bitwise_and(peppa,peppa,mask=thresh2)
cv2.imshow('peppa_body',peppa_body)
cv2.waitKey()
cv2.destroyAllWindows()

平滑处理与模糊处理

img = cv2.imread("peppa_gaussian.jpg")
blur = cv2.blur(img, (7, 7))
box = cv2.boxFilter(img,-1,(7,7), normalize=True)
gaussian = cv2.GaussianBlur(img, (7, 7), 10)
median = cv2.medianBlur(img, 7)
bilater=cv2.bilateralFilter(img,9,75,75)
kernel = np.array((
[-2, -1, 0],
[-1,1,1],
[0, 1, 2]), dtype="float32")
filter2D=cv2.filter2D(img,-1,kernel)
cv2.imshow('img',img)
cv2.imshow('blur',blur)
cv2.imshow('box',box)
cv2.imshow('gaussian',gaussian)
cv2.imshow('median',median)
cv2.imshow('bilater',bilater)
cv2.imshow('filter2D',filter2D)
cv2.waitKey()
cv2.destroyAllWindows()