系列文章目录

当我们想比较两张图片相似度的时候，可以使用这一节提到的技术

• 直方图对比

• 反向投影

关于这两种技术的原理可以参考我上面贴的链接，下面是示例的代码：

0x01. 绘制直方图

import cv2.cv as cv

def drawGraph(ar,im, size): #Draw the histogram on the image
    minV, maxV, minloc, maxloc = cv.MinMaxLoc(ar) #Get the min and max value
    hpt = 0.9 * histsize
    for i in range(size):
        intensity = ar[i] * hpt / maxV #Calculate the intensity to make enter in the image
        cv.Line(im, (i,size), (i,int(size-intensity)),cv.Scalar(255,255,255)) #Draw the line
        i += 1

#---- Gray image
orig = cv.LoadImage(\"img/lena.jpg\", cv.CV_8U)

histsize = 256 #Because we are working on grayscale pictures which values within 0-255

hist = cv.CreateHist([histsize], cv.CV_HIST_ARRAY, [[0,histsize]], 1)

cv.CalcHist([orig], hist) #Calculate histogram for the given grayscale picture

histImg = cv.CreateMat(histsize, histsize, cv.CV_8U) #Image that will contain the graph of the repartition of values
drawGraph(hist.bins, histImg, histsize)

cv.ShowImage(\"Original Image\", orig)
cv.ShowImage(\"Original Histogram\", histImg)
#---------------------

#---- Equalized image
imEq = cv.CloneImage(orig)
cv.EqualizeHist(imEq, imEq) #Equlize the original image

histEq = cv.CreateHist([histsize], cv.CV_HIST_ARRAY, [[0,histsize]], 1)
cv.CalcHist([imEq], histEq) #Calculate histogram for the given grayscale picture
eqImg = cv.CreateMat(histsize, histsize, cv.CV_8U) #Image that will contain the graph of the repartition of values
drawGraph(histEq.bins, eqImg, histsize)

cv.ShowImage(\"Image Equalized\", imEq)
cv.ShowImage(\"Equalized HIstogram\", eqImg)
#--------------------------------

cv.WaitKey(0)

0x02. 反向投影

import cv2.cv as cv

im = cv.LoadImage(\"img/lena.jpg\", cv.CV_8U)

cv.SetImageROI(im, (1, 1,30,30))

histsize = 256 #Because we are working on grayscale pictures
hist = cv.CreateHist([histsize], cv.CV_HIST_ARRAY, [[0,histsize]], 1)
cv.CalcHist([im], hist)


cv.NormalizeHist(hist,1) # The factor rescale values by multiplying values by the factor
_,max_value,_,_ = cv.GetMinMaxHistValue(hist)

if max_value == 0:
    max_value = 1.0
cv.NormalizeHist(hist,256/max_value)

cv.ResetImageROI(im)

res = cv.CreateMat(im.height, im.width, cv.CV_8U)
cv.CalcBackProject([im], res, hist)

cv.Rectangle(im, (1,1), (30,30), (0,0,255), 2, cv.CV_FILLED)
cv.ShowImage(\"Original Image\", im)
cv.ShowImage(\"BackProjected\", res)
cv.WaitKey(0)