背景的分离

适用范围

双峰直方图的图片。彩色图像直方图的双荷花RGB直方图也有比较明显的双峰0-10和100-200.改成灰度直方图也是这样吗？

灰度直方图

灰度直方图

代码

import cv2 
import numpy as np
import matplotlib.pyplot as plt

#计算灰度直方图
def calcGrayHist(grayimage):
    #灰度图像矩阵的高，宽
    rows, cols = grayimage.shape
    print(grayimage.shape)
    #存储灰度直方图
    grayHist = np.zeros([256],np.uint64)
    for r in range(rows):
        for c in range(cols):
            grayHist[grayimage[r][c]] += 1
    plt.plot(grayHist)
    plt.show() 
    return grayHist


#阈值分割：直方图阈值法 
def threshTwoPeaks(image):
    if len(image.shape) == 2:
        gray = image
    else:
        gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    #计算灰度直方图
    histogram = calcGrayHist(gray)
    #寻找灰度直方图的最大峰值对应的灰度值
    maxLoc = np.where(histogram==np.max(histogram))
    firstPeak = maxLoc[0][0]
    #寻找灰度直方图的第二个峰值对应的灰度值
    measureDists = np.zeros([256],np.float32)
    for k in range(256):
        measureDists[k] = pow(k-firstPeak,2)*histogram[k]
    maxLoc2 = np.where(measureDists==np.max(measureDists))
    secondPeak = maxLoc2[0][0]

    #找到两个峰值之间的最小值对应的灰度值，作为阈值
    thresh = 0
    if firstPeak > secondPeak:#第一个峰值再第二个峰值的右侧
        temp = histogram[int(secondPeak):int(firstPeak)]
        minloc = np.where(temp == np.min(temp))
        thresh = secondPeak + minloc[0][0] + 1
    else:#第一个峰值再第二个峰值的左侧
        temp = histogram[int(firstPeak):int(secondPeak)]
        minloc = np.where(temp == np.min(temp))
        thresh =firstPeak + minloc[0][0] + 1

    #找到阈值之后进行阈值处理，得到二值图
    threshImage_out = gray.copy()
    #大于阈值的都设置为255
    threshImage_out[threshImage_out > thresh] = 255
    threshImage_out[threshImage_out <= thresh] = 0
    return thresh, threshImage_out

if __name__ == "__main__":
    img = cv2.imread('./sucai6/hua.jpg')
    #img = cv2.resize(img,(300,400))
    thresh,threshImage_out = threshTwoPeaks(img)
    print(thresh)
    cv2.imshow('src',img) 
    cv2.imshow('threshImage_out',threshImage_out) 
    re=cv2.bitwise_and(img,img,mask=threshImage_out)
    cv2.imshow('re',re) 
    cv2.waitKey(0)
    cv2.destroyAllWindows()

验证

荷花前景

荷花正下方的一块前景是枯败的莲蓬或荷叶，不失为一个亮点。查看原图在以荷花为中心镜像的正上方有支嫩绿的莲蓬，相得益彰真是好看。

总结

一张图的RGB三通道直方图跟转成的灰度图的直方图是相似的。