How to remove small object in image with Python

Question

i have a problem with my python code. I want to make image processing with chest X-rays in order to obtain a lung pattern. but my code results still have little stains. how to get rid of these small objects

and this is my code

import cv2
import numpy as np
from skimage import morphology

im = cv2.imread('image.jpg')
ret, thresh = cv2.threshold(im, 150, 255, cv2.THRESH_BINARY)
kernel = np.ones((5, 5), np.uint8)
opening = cv2.morphologyEx(thresh, cv2.MORPH_OPEN, kernel)
cleaned = morphology.remove_small_objects(opening, min_size=62, connectivity=2)
cv2.imshow("cleaned", cleaned)
cv2.waitKey(0)

P.S : when i try with the matlab code, the small object can be removed with this code

K=bwareaopen(~K,1500); %Remove small object (area) pixels less than 1500 pixels

and that code can remove small object well:

Answer 1

You can filter using contour area then apply morpholgical closing to fill the small holes in the image. Here's the result:

import cv2

# Load image, convert to grayscale, Gaussian blur, Otsu's threshold
image = cv2.imread('1.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray, (3,3), 0)
thresh = cv2.threshold(blur, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)[1]

# Filter using contour area and remove small noise
cnts = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
for c in cnts:
    area = cv2.contourArea(c)
    if area < 5500:
        cv2.drawContours(thresh, [c], -1, (0,0,0), -1)

# Morph close and invert image
kernel = cv2.getStructuringElement(cv2.MORPH_RECT, (5,5))
close = 255 - cv2.morphologyEx(thresh, cv2.MORPH_CLOSE, kernel, iterations=2)

cv2.imshow('thresh', thresh)
cv2.imshow('close', close)
cv2.waitKey()