How to count objects in image using python?

Question

I am trying to count the number of drops in this image and the coverage percentage of the area covered by those drops. I tried to convert this image into black and white, bu

Answer 1

The idea is to isolate the background form the inside of the drops that look like the background. Therefore i found the connected components for the background and the inside drops took the largest connected component and change its value to be like the foreground value which left me with an image which he inside drops as a different value than the background. Than i used this image to fill in the original threshold image. In the end using the filled image i calculated the relevant values

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

# Read image
I = cv2.imread('drops.jpg',0);

# Threshold
IThresh = (I>=118).astype(np.uint8)*255

# Remove from the image the biggest conneced componnet

# Find the area of each connected component
connectedComponentProps = cv2.connectedComponentsWithStats(IThresh, 8, cv2.CV_32S)

IThreshOnlyInsideDrops = np.zeros_like(connectedComponentProps[1])
IThreshOnlyInsideDrops = connectedComponentProps[1]
stat = connectedComponentProps[2]
maxArea = 0
for label in range(connectedComponentProps[0]):
    cc = stat[label,:]
    if cc[cv2.CC_STAT_AREA] > maxArea:
        maxArea = cc[cv2.CC_STAT_AREA]
        maxIndex = label


# Convert the background value to the foreground value
for label in range(connectedComponentProps[0]):
    cc = stat[label,:]
    if cc[cv2.CC_STAT_AREA] == maxArea:
        IThreshOnlyInsideDrops[IThreshOnlyInsideDrops==label] = 0
    else:
        IThreshOnlyInsideDrops[IThreshOnlyInsideDrops == label] = 255

# Fill in all the IThreshOnlyInsideDrops as 0 in original IThresh
IThreshFill = IThresh
IThreshFill[IThreshOnlyInsideDrops==255] = 0
IThreshFill = np.logical_not(IThreshFill/255).astype(np.uint8)*255
plt.imshow(IThreshFill)

# Get numberof drops and cover precntage
connectedComponentPropsFinal = cv2.connectedComponentsWithStats(IThreshFill, 8, cv2.CV_32S)
NumberOfDrops = connectedComponentPropsFinal[0]
CoverPresntage = float(np.count_nonzero(IThreshFill==0)/float(IThreshFill.size))

# Print
print "Number of drops = " + str(NumberOfDrops)
print "Cover precntage = " + str(CoverPresntage)