how to use compareHist function opencv

问题

img = cv2.imread('mandrill.png')
histg = cv2.calcHist([img],[0],None,[256],[0,256])

if len (sys.argv) < 2:
    print >>sys.stderr, "Usage:", sys.argv[0], "<image>..."
    sys.exit (1)

for fn in sys.argv[1:]:
    im = cv2.imread (fn)

histr = cv2.calcHist([im],[0],None,[256],[0,256])
a = cv2.compareHist(histr,histg,cv2.cv.CV_COMP_CORREL)
print a

I am trying to use the code above to compare the correlation between histograms histr and histg when I run the code the I get the error

'module' object has no attribute 'cv'

It seems that CV3 the names of the various correlation functions have changed. What are the names of the various correlation functions?

回答1:

The opencv version you are using has cv2.cv.CV_COMP_CORREL renamed to cv2.HISTCMP_CORREL

The function name changes are as follows (left hand side shows the names for opencv2, right hand side shows the name for the latest version of opencv(opencv3)):

cv2.cv.CV_COMP_CORREL:: cv2.HISTCMP_CORREL
cv2.cv.CV_COMP_CHISQR :: cv2.HISTCMP_CHISQR/ cv2.HISTCMP_CHISQR_ALT
cv2.cv.CV_COMP_INTERSECT :: cv2.HISTCMP_INTERSECT
cv2.cv.CV_COMP_BHATTACHARYYA :: cv2.HISTCMP_BHATTACHARYYA

回答2:

As Zdar mentioned it looks like the constants have been renamed in opencv3.0 to:

cv2.HISTCMP_CORREL
cv2.HISTCMP_CHISQR
cv2.HISTCMP_INTERSECT 
cv2.HISTCMP_BHATTACHARYYA
a = cv2.compareHist(histr,histg,cv2.HISTCMP_CORREL) should work

回答3:

sample code for compare histogram in OpenCV 3.2

import cv2

path='location_of_images'
im1 = cv2.imread(path+'/'+'first.jpg',0)
hist1 = cv2.calcHist([im1],[0],None,[256],[0,256])

im2 = cv2.imread(path+'/'+'second.jpg',0)
hist2 = cv2.calcHist([im2],[0],None,[256],[0,256])

a=cv2.compareHist(hist1,hist2,cv2.HISTCMP_BHATTACHARYYA)

print a

return value show how close to your test image with compared one. example: cv2.HISTCMP_BHATTACHARYYA method gives zero(0.0) for the same image. other methods are cv2.HISTCMP_CHISQR,cv2.HISTCMP_CHISQR_ALT,cv2.HISTCMP_CORREL cv2.HISTCMP_HELLINGER,cv2.HISTCMP_INTERSECT,cv2.HISTCMP_KL_DIV.

来源：https://stackoverflow.com/questions/40451706/how-to-use-comparehist-function-opencv

标签

python

OpenCV

histogram