def part4():

    f, axarr = plt.subplots(2, 3)
    frostfogSrc = cv.imread("a2images/frostfog.png", 0)

    frostfogEH=cv.equalizeHist(frostfogSrc)
    axarr[0,0].set_title("equalizeHist")
    axarr[0, 0].imshow(frostfogEH,cmap='gray')
    histN, b, l = axarr[0,1].hist(frostfogEH.ravel(), histSize, histRange, True,  label="normal",color='blue')
    histC = axarr[0, 2].hist(frostfogEH.ravel(), histSize, histRange, True, None, True, label="cumulative",color='green')
    axarr[0, 1].bar(b[:-1], histN * (1/max(histN)), np.diff(b),color='b')

    mn,mx,mmnl,mxl=cv.minMaxLoc(frostfogSrc)
    print(mn,mx,mmnl,mxl)

    x,y=frostfogSrc.shape
    frostfogCS=frostfogSrc.copy()
    for i in range(0,x):
        for j in range(0,y):
            frostfogCS[i,j]= ((frostfogCS[i,j]-mn)/(mx-mn))*255

    axarr[1, 0].set_title("constant stretching")
    axarr[1, 0].imshow(frostfogCS, cmap='gray')

    histN, b, l = axarr[1, 1].hist(frostfogCS.ravel(), histSize, histRange, True, label="normal", color='blue')
    histC = axarr[1, 2].hist(frostfogCS.ravel(), histSize, histRange, True, None, True, label="cumulative",
                             color='green')
    axarr[1, 1].bar(b[:-1], histN * (1 / max(histN)), np.diff(b), color='b')


    plt.show()