how to use compareHist function opencv

Question

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?

Answer 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