影象分析之閾值與平滑處理
阿新 • • 發佈:2020-11-16
1.影象閾值
#### ret, dst = cv2.threshold(src, thresh, maxval, type)
- src: 輸入圖,只能輸入單通道影象,通常來說為灰度圖
- dst: 輸出圖
- thresh: 閾值
- maxval: 當畫素值超過了閾值(或者小於閾值,根據type來決定),所賦予的值
- type:二值化操作的型別,包含以下5種類型: cv2.THRESH_BINARY; cv2.THRESH_BINARY_INV; cv2.THRESH_TRUNC; cv2.THRESH_TOZERO;cv2.THRESH_TOZERO_INV
- cv2.THRESH_BINARY 超過閾值部分取maxval(最大值),否則取0
- cv2.THRESH_BINARY_INV THRESH_BINARY的反轉
- cv2.THRESH_TRUNC 大於閾值部分設為閾值,否則不變
- cv2.THRESH_TOZERO 大於閾值部分不改變,否則設為0
- cv2.THRESH_TOZERO_INV THRESH_TOZERO的反轉
import cv2 #opencv讀取的格式是BGR import numpy as np import matplotlib.pyplot as plt#Matplotlib是RGB img=cv2.imread('cat.jpg') img_gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY) ret, thresh1 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_BINARY) ret, thresh2 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_BINARY_INV) ret, thresh3= cv2.threshold(img_gray, 127, 255, cv2.THRESH_TRUNC) ret, thresh4 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_TOZERO) ret, thresh5 = cv2.threshold(img_gray, 127, 255, cv2.THRESH_TOZERO_INV) titles = ['Original Image', 'BINARY', 'BINARY_INV', 'TRUNC', 'TOZERO', 'TOZERO_INV'] images = [img, thresh1, thresh2, thresh3, thresh4, thresh5]for i in range(6): plt.subplot(2, 3, i + 1), plt.imshow(images[i], 'gray') plt.title(titles[i]) plt.xticks([]), plt.yticks([]) plt.show()
2.平滑處理
1)均值濾波
# 均值濾波 # 簡單的平均卷積操作 img = cv2.imread('lena.jpg') blur = cv2.blur(img, (3, 3)) cv2.imshow('img', img) cv2.imshow('blur', blur) cv2.waitKey(0) cv2.destroyAllWindows()
2)
# 方框濾波,normalize為TRUE時就和均值濾波一樣 # 基本和均值一樣,可以選擇歸一化,容易越界 box = cv2.boxFilter(img, -1, (3, 3), normalize=False) cv2.imshow('box', box)
3)
# 高斯濾波 # 高斯模糊的卷積核裡的數值是滿足高斯分佈,相當於更重視中間的 aussian = cv2.GaussianBlur(img, (5, 5), 1) cv2.imshow('aussian', aussian)
4)
# 中值濾波 # 相當於用中值代替 median = cv2.medianBlur(img, 5) # 中值濾波 cv2.imshow('median', median)
3.一次性拼接展示多個圖片
# 展示所有的 res = np.hstack((blur, aussian, median)) res2 = np.vstack((blur, aussian, median)) cv2.imshow('median vs average', res) cv2.imshow('median vs average', res2)